Patent Publication Number: US-2021177336-A1

Title: Muscle Activity Monitoring

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 15/560,476, filed Sep. 21, 2017, now pending, which application is a U.S. National Stage of International Application No. PCT/AU2016/050203, filed Mar. 22, 2016, which claims the benefit of and priority to Australian Patent Application No. 2015901026, filed Mar. 23, 2015, the contents of each of which are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a system and method for monitoring the muscle activity of a subject, and in particular to a system for monitoring muscle activity of a subject using at least one garment worn by the subject in use. 
     DESCRIPTION OF THE PRIOR ART 
     The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates. 
     Whilst it is known to provide devices for monitoring activity, these are generally limited to detecting movement through the use of movement sensors, which does not accurately track muscle activity. Measuring muscle activity by recording electrical signals from muscles, in a process commonly referred to as EMG (Electromyography) is known, this generally uses needle electrodes inserted into the muscles of the subject, which is therefore restrictive and therefore only used in limited situations. 
     SUMMARY OF THE PRESENT INVENTION 
     In one broad form the invention seeks to provide a system for monitoring muscle activity of a biological subject, the system including: 
     a) at least one garment including a number of arrays of electrodes positioned on the garment so that when the garment is worn by a subject in use, the electrodes contact skin of the subject and generate electrical signals indicative of electrical potentials within respective muscles of the subject; and,
         b) at least one electronic processing device that:       

     i) processes signals from the electrodes in each electrode array to determine a muscle activation for parts of the respective muscles; and, 
     ii) uses the muscle activation to determine at least one muscle indicator indicative of muscle activity of the subject. 
     In another broad form the invention seeks to provide a method for monitoring muscle activity of a biological subject, the method including:
         a) providing the subject with at least one garment including a number of arrays of electrodes positioned on the garment so that when the garment is worn by the subject, the electrodes contact skin of the subject and generate electrical signals indicative of electrical potentials within respective muscles of the subject; and,   b) in at least one electronic processing device:
           i) processing signals from the electrodes in each electrode array to determine a muscle activation for parts of the respective muscles; and,   ii) using the muscle activation to determine at least one muscle indicator indicative of muscle activity of the subject.   
               

     In another broad form the invention seeks to provide a garment for use in monitoring muscle activity of a biological subject, the garment including a number of arrays of electrodes positioned on the garment so that when the garment is worn by a subject in use, the electrodes contact skin of the subject and generate electrical signals indicative of electrical potentials within respective muscles of the subject. 
     Typically the muscle activation is indicative of at least one of a magnitude and frequency of muscle activation. 
     Typically the muscle indicator includes at least one of:
         a) an intramuscular indicator indicative of muscle activation within a muscle;   b) an intermuscular indicator indicative of a relative muscle activation of contralateral muscles on contralateral limbs;   c) an efficiency indicator indicative of the relative efficiency of muscle activation of muscles; and,   d) a muscle fatigue indicator indicative of a muscle fatigue.       

     Typically the at least one processing device, for each muscle:
         a) determines an average muscle activation;   b) compares the muscle activation of parts of the muscle to the average muscle activation; and,   c) determines an intramuscular indicator at least in part using results of the comparison.       

     Typically the at least one processing device, for each pair of contralateral muscles:
         a) compares the muscle activation of each muscle in the pair; and,   b) determines an intermuscular indicator at least in part using results of the comparison.       

     Typically the at least one processing device:
         a) determines a muscle activation pattern indicative of the muscle activation of each of a number of muscles;   b) compares the muscle activation pattern to a reference muscle activation pattern; and,   c) determines an efficiency indicator at least in part using the results of the comparison.       

     Typically the at least one processing device:
         a) determines an activity being performed by the subject; and,   b) selects one of a number of predefined reference activation patterns at least partially in accordance with the determined activity.       

     Typically the at least one processing device determines the activity being performed at least one of:
         a) by analysing muscle activation patterns; and,   b) in accordance with user input commands.       

     Typically the at least one processing device selects one of a number of predefined reference activation patterns in accordance with subject parameters including at least one of:
         a) a subject age;   b) a subject sex;   c) a subject weight;   d) a subject height; and,   e) a subject fitness level.       

     Typically the predefined reference activation patterns include a previous recorded activation pattern for the subject. 
     Typically the at least one processing device:
         a) determines a current muscle activation pattern indicative of the muscle activation of each of a number of muscles;   b) determines previous muscle activation patterns;   c) identifies a historical activation based on at least one of a mean and maximum of the previous muscle activation patterns;   d) compares the current muscle activation pattern to the historical activation pattern; and,   e) determines a fatigue indicator at least in part using the results of the comparison.       

     Typically the at least one processing device:
         a) generates a representation at least partially based on the at least one muscle indicator; and,   b) causes the representation to be displayed to a user.       

     Typically the representation includes at least one of:
         a) an alphanumeric indication of the at least one muscle indicator;   b) a graphical representation of a muscle activation pattern for at least one muscle; and,   c) a graphical representation of results of a comparison of a muscle activation pattern to a reference muscle activation pattern.       

     Typically the electrodes are at least one of:
         a) conductive fabric electrodes woven into the garment; and,   b) dry electrodes provided in the garment.       

     Typically the electrodes are at least one of:
         a) silver plated nylon electrodes; and,   b) silver plated nanowire electrodes.       

     Typically each array of electrodes includes a plurality of electrodes arranged in a grid. 
     Typically each electrode has a surface area that is at least one of:
         a) between 0.5 cm 2  and 3.0 cm 2 ;   b) between 0.75 cm 2  and 1.5 cm 2 ;   c) about 0.75±0.25 cm 2 ;   d) about 1.0±0.25 cm 2 ;   e) about 1.25±0.25 cm 2 ;   j) about 1.5±0.25 cm 2 ;   g) about 1.75±0.25 cm 2 ;   h) about 2.0±0.25 cm 2 ;   i) about 2.5±0.5 cm 2 ; and,   j) about 1 cm 2 .       

     Typically electrodes in the array are spaced by at least one of:
         a) between 0.5 cm and 2.0 cm;   b) between 0.75 cm and 1.75 cm;   c) between 1.0 cm and 1.5 cm;   d) about 0.75±0.25 cm;   e) about 1.0±0.25 cm;   f) about 1.25±0.25 cm; and,   g) about 1.5±0.25 cm.       

     Typically each electrode in the electrode array is electrically connected to a connector, the connector being for coupling the electrodes to the at least one processing device. 
     Typically at least one processing device is mounted in a pocket provided on the garment, the connector being provided at least partially within the pocket. 
     Typically each electrode in the electrode array is electrically connected to the connector via nanowires woven into the garment. 
     Typically the garment includes at least one of:
         a) pants for covering at least the groin and upper legs of the user; and,   b) a shirt for covering at least the torso of the user.       

     Typically the garment includes elasticated material to thereby urge the electrodes against the subject&#39;s skin. 
     Typically the garment is made of at least one of:
         a) polyamides;   b) polyester; and,   c) elastane.       

     Typically each array of electrodes is aligned with a respective muscle or muscle group. 
     Typically the muscle or muscle groups include at least one of:
         a) trapezius;   b) rhomboids;   c) latissimus dorsi;   d) erector spinae;   e) rotator cuff muscles (including supraspinatus, infraspinatus, subscapularis, teres minor/major); f) forearm extensors/flexors;   g) tibialis anterior/posterior;   h) thoracic paraspinals;   i) lumbar paraspinals;   j) biceps;   k) triceps;   l) quadriceps;   m) hamstrings;   n) adductors;   o) gluteals;   p) calves;   q) abdominals;   r) deltoids; and,   s) pectorals.       

     Typically system includes a measuring device, the measuring device including:
         a) a voltage sensor coupled to the electrodes for sensing electrical potentials between pairs of electrodes; and,   b) at least one processing device coupled to the voltage sensor for receiving signals indicative of the sensed voltages.       

     Typically the voltage sensor includes:
         a) a differential amplifier for amplifying analogue electrical signals obtained from a pair of electrodes; and,   b) an A/D convertor for converting an amplified differential voltage into a digital voltage signal, the digital voltage signal being provided to the at least one processing device for processing.       

     Typically the measuring device includes a filter for filtering electrical signals. 
     Typically the measuring device includes a switching device for selectively coupling the voltage sensor to respective pairs of electrodes in each array. 
     Typically the switching device is controlled at least in part by the at least one processing device. 
     Typically the system includes:
         a) a first electronic processing device attached to or worn by the subject that:
           i) acquires signals from the sensors;   ii) at least partially processes the signals; and,   
           b) a second processing device that wirelessly communicates with the first processing device and displays a representation at least partially based on the at least one muscle indicator.       

     Typically the system includes an ECG sensor for sensing cardiac activity of the subject and wherein the at least one electronic processing device:
         a) acquires signals from the ECG sensor; and,   b) determines a cardiac indicator indicative of cardiac activity of the subject.       

     Typically the system includes a respiratory sensor for sensing respiratory activity of the subject and wherein the at least one electronic processing device:
         a) acquires signals from the respiratory sensor; and,   b) determines a respiratory indicator indicative of respiratory activity of the subject.       

     Typically the at least one electronic processing device determines an activity indicator indicative of an overall activity of the subject using:
         a) the at least one muscle indicator; and,   b) at least one of:
           i) a cardiac indicator indicative of cardiac activity of the subject; and,   ii) a respiratory indicator indicative of respiratory activity of the subject.   
               

     It will be appreciated that the broad forms of the invention and their respective features can be used in conjunction, interchangeably and/or independently, and reference to separate broad forms is not intended to be limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An example of the present invention will now be described with reference to the accompanying drawings, in which:— 
         FIG. 1A  is schematic diagram of a first garment for use in monitoring muscle activity of a biological subject; 
         FIG. 1B  is schematic diagram of a second garment for use in monitoring muscle activity of a biological subject; 
         FIG. 2  is a flow chart of an example of a method for monitoring muscle activity of a biological subject; 
         FIG. 3A  is a schematic diagram of a first example of a system for use in monitoring muscle activity of a biological subject; 
         FIG. 3B  is a schematic diagram of a second example of a system for use in monitoring muscle activity of a biological subject; 
         FIG. 4  is a flow chart of an example of a method for preparing the system to monitor muscle activity of a biological subject; 
         FIGS. 5A and 5B  are a flow chart of a specific example of a method for monitoring muscle activity of a biological subject using the system of  FIG. 3 ; 
         FIG. 6  is a flow chart of an example of a method for determining an intramuscular indicator; 
         FIG. 7  is a flow chart of an example of a method for determining an intermuscular indicator; 
         FIG. 8  is a flow chart of an example of a method for determining an efficiency indicator; and, 
         FIG. 9  is a flow chart of an example of a method for determining a fatigue indicator. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Examples of garments for use in monitoring muscle activity of a subject are shown in  FIGS. 1A and 1B . 
     The garments  110 ,  120  each include a number of arrays of electrodes  111 ,  121  positioned on the garment  110 ,  120  so that when the garment is worn by a subject in use, the electrodes contact skin of the subject and generate electrical signals indicative of electrical potentials within respective muscles of the subject. In this example, the garments are in the form of a shirt  110  for covering at least the torso and parts of the arms of the user and pants  120  for covering at least the groin and upper legs of the user, although other suitable arrangements can be used as will be described in more detail below. 
     In use, the electrodes  111 ,  121  are electrically connected to at least one processing device that operates to process signals and determine at least one muscle activity indicator. The at least one processing device could be of any suitable form, and could include a wearable custom or off the shelf processing device and/or a suitably programmed general purpose processing system, such as a computer system, smart phone, smartwatch, tablet or the like. 
     An example of a method of use of the system will now be described with reference to  FIG. 2 . 
     In this example, at step  200 , the subject wears the garment(s) and performs activities at step  210 . The activities could be of any suitable form depending on the preferred implementation or use. For example, if the subject is an athlete or sports person, the activities could include exercises, participating in a sporting event, training or the like. Alternatively, the subject may be undergoing monitoring as part of a medical assessment, for example to assess muscle strength and movement patterns in individuals having muscular or neurological conditions such as myolysis, myasthenia gravis, muscular dystrophy, or the like, in which case the activities could include day-to-day activities, defined sequences of movements, exercises or the like. 
     At step  220 , the electrodes  111 ,  121  generate electrical signals based on electrical activity within the subject&#39;s muscles, with the processing device processing these signals at step  230  to determine a muscle activation for parts of the respective muscles. The muscle activation is indicative of the degree of electrical activity within the respective parts of the muscle and in particular at least one of the frequency and/or magnitude of activation, and therefore corresponds broadly to the amount of work being performed by the respective part of the muscle. Thus, signals from different pairs of electrodes within each array are used to determine a degree of muscle activation for different parts of muscles within each muscle or muscle group. 
     At step  240 , the processing device uses the muscle activation to determine at least one muscle indicator indicative of muscle activity of the subject, with the indicator being optionally displayed at step  250 . 
     The indicator can be of any suitable form, and can include a number of different indicators examining different aspects of muscle activity. For example, the system can be used to determine any one or more of an intramuscular indicator indicative of muscle activation within a muscle, an intermuscular indicator indicative of a relative muscle activation of contralateral muscles on contralateral limbs, an efficiency indicator indicative of the relative efficiency of muscle activation of muscles when performing a task, and a muscle fatigue indicator indicative of a muscle fatigue. However, these examples are not intended to be limiting and additional and/or alternative indicators could be used depending on the preferred implementation. Specific example indicators and techniques for their derivation will be described in more detail below. 
     The above described steps can be performed periodically or continuously as a subject performs exercise. For example, the system could continuously monitor muscle activity, and display indicators in real time, allowing an individual to use these as feedback while performing activity. Additionally and/or alternatively, indicators and raw data could be stored, allowing these to be subsequently reviewed after the activity has been performed. 
     In any event, it will be appreciated that the indicators can be used to assess a wide range of different aspects of muscle activity, including for example whether the subject is using their muscles effectively, whether the muscles are functioning as expected/required, whether the subject is fatigued, whether the muscles are injured and/or at risk of injury, or the like. 
     Accordingly, the above described system and process allows a subject&#39;s muscle activation to be monitored, whilst the subject performs different activities, in turn allowing a muscle activity indicator to be determined. By allowing this to be performed using garments incorporating arrays of electrodes, this allows monitoring to be performed during a range of different activities, including sport, exercise and/or day-to-day activities, without impeding the subject. Additionally, through suitable arrangement of the electrodes, this allows information regarding the activation of different parts of different muscles to be monitored, allowing a range of different indicators to be derived, which can in turn be used to assess muscle function. This can be used for medical purposes, for example as part of the diagnosis and/or treatment of medical conditions, as well as for activity monitoring, for example to examine muscle activity of a participant in a sporting event to ensure the participant is functioning optimally. 
     As part of this, it will be appreciated that the indicator could be further used as part of general fitness tracking, for example by monitoring total muscle activity during a workout, which in turn can allow a more accurate assessment of calories burned to be made. 
     A number of further features will now be described. 
     The electrodes are typically integrally formed within the garment, and could include any suitable conductive dry electrodes, which may for example be woven into the garment as conductive fabric electrodes. In one particular example the electrodes are silver plated nylon electrodes, or the like, examples of which are described in WO2014/080403. However, it will be appreciated that any conductive or metal coated fabric or nanowire could be used. For example, the electrodes could be silver plated nanowire electrodes provided on an elastomeric substrate, such as polydimethylsiloxane (PDMS), similar to those described in “Wearable silver nanowire dry electrodes for electrophysiological sensing” by Amanda C. Myers, He Huang and Yong Zhu in RSC Adv., 2015, 5, 11627-11632|11627. This allows the electrodes to remain as part of the garment whilst the garment is washed, making the system readily useable in a variety of situations. Alternatively, electrodes could be screen printed or applied using any other suitable technique and could include using a stretchable resin base material with a conductive paste to provide a flexible electrode. 
     The garment is typically made of an elasticated material, which helps urge the electrodes against the subject&#39;s skin, avoiding the need for any adhesive, conductive gel, or the like, whilst ensuring good electrical contact between the electrodes and the subject&#39;s tissue, which is in turn important in ensuring accurate measurements are collected. The garment can be made of any suitable material, but is typically made of a mixture of polyamides and elastane, in the form of an elasticated compressive garment, similar to those marketed under the trade name Skins™. This is particularly beneficial as this allows the subject to simply wear the garment as though it were part of their normal sporting attire, whilst also providing the benefit of such garments. However, it will be appreciated that other materials could be used such as polyester, or the like. 
     Each array of electrodes typically includes at least two electrodes, and more typically a plurality of electrodes arranged in a grid. The electrodes typically have a surface area that is between 0.5 cm 2  and 3.0 cm 2 , between 0.75 cm 2  and 1.5 cm 2 , about 0.75±0.25 cm 2 , about 1.0±0.25 cm 2 , about 1.25±0.25 cm 2 , about 1.5±0.25 cm 2 , about 1.75±0.25 cm 2 , about 2.0±0.25 cm 2 , about 2.5±0.5 cm 2 , and more typically about 1 cm 2 . The electrodes can be of any shape and could include circular electrodes having a diameter of between 0.5 cm and 1.5 cm, and more typically about 1 cm. The electrodes are typically separated by between 0.5 cm and 2.0 cm, between 0.75 cm and 1.75 cm and between 1.0 cm and 1.5 cm, about 0.75±0.25 cm, about 1.0±0.25 cm, about 1.25±0.25 cm, about 1.5±0.25 cm, or approximately 2 cm between centres of adjacent electrodes, although alternative spacings could be used depending on the required resolution of the measurements. In this regard, it will be appreciated that different electrode sizes and/or spacings could be used to vary the resolution of the measurements, allowing measurements to be performed up to and include of muscle fibres connected to a single neural pathway ending. This allows the firing of individual neural muscle connections to be monitored. Further issues regarding electrode sizing and spacing can be found in “The Effects of Electrode Size and Orientation on the Sensitivity of Myoelectric Pattern Recognition Systems to Electrode Shift” by Aaron J. Young published in IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 58, NO. 9, September 2011. 
     Each electrode in the electrode array is electrically connected to a connector, for example via a respective conductive path running from the electrode to the connector. The conductive path can be formed of any appropriate conductive material, but in one example is made of conductive nanowires woven into the fabric. Such nanowires, typically made of coated nano tubes, are particularly advantageous as they are thin and flexible, allowing the garment to maintain its wearable characteristics, whilst being strong, resulting in a greater lifespan. 
     The connector is used for electrically connecting the electrodes to the at least one processing device. In this regard, the at least one processing device can be mounted in a pocket  112 ,  122  provided on the garment, with the connector being provided at least partially within the pocket. This allows the processing device to be easily connected/disconnected to the electrodes and hence removed from the garment as required, for example to allow the garment to be washed. This could be achieved using a “clip-in” arrangement, so that the processing device connects to the connector upon insertion into the pocket, although any suitable arrangement could be used. 
     As shown in  FIGS. 1A and 1B , the garment can include pants  120  for covering at least the groin and upper legs of the user or a shirt  110  for covering at least the torso of the user. It will be appreciated that other suitable arrangements could be used, such as fully body torso or leggings. 
     Each array of electrodes is typically aligned with a respective muscle or muscle group, including but not limited to any one or more of trapezius, rhomboids, latissimus dorsi, erector spinae, rotator cuff, forearm extensors/flexors, tibialis anterior/posterior, thoracic paraspinals, lumbar paraspinals, biceps, triceps, quadriceps, hamstrings, adductors, gluteals, calves, abdominals, deltoids and pectorals. It will be appreciated that the particular configuration used may depend on the intended application, and in particular which muscles are of interest from the perspective of monitoring. 
     The muscle activation can be determined from the signals generated by the electrodes in any suitable manner. For example, the muscle activation can be indicative of at least one of a magnitude and frequency of the signals, and can be determined using appropriate signals processing techniques, such as Fourier analysis or the like. It will be appreciated from this that the signals are Electromyography (EMG) signals, and accordingly appropriate signal processing techniques used for EMG could be employed. 
     Having determined the muscle activation, additional processing is performed in order to determine the indicators. The nature of the processing will depend on the type of indicator being derived. 
     For example, to determine an intramuscular indicator the processing device typically determines an average muscle activation, compares the muscle activation of parts of the muscle to the average muscle activation and determines an intramuscular indicator at least in part using results of the comparison. Thus, this will identify if activation is relatively constant across the entire muscle, or whether some distinct parts of the muscle are undergoing greater or lesser activation, which can be useful in identifying potential injuries and/or muscle damage. 
     To determine an intermuscular indicator, the processing device compares the muscle activation of each muscle in a pair of contralateral muscles and then determines the intermuscular indicator at least in part using results of the comparison. Thus, this examines whether contralateral muscles, such as the hamstrings in each leg, are activating to a similar degree, or whether one muscle is being favoured over the other, which can in turn be indicative of injury, or an imbalance in muscle use. 
     To determine an efficiency indicator, the processing device can determine a muscle activation pattern indicative of the muscle activation of each of a number of muscles, compare the muscle activation pattern to a reference muscle activation pattern and, determine an efficiency indicator at least in part using the results of the comparison. Thus, this can use predefined muscle activation patterns to assess whether the subject&#39;s muscles are activating in an optimum pattern. The predefined muscle activations are typically defined based on a range of factors, such as the activities being performed, and characteristics of the subject. 
     Thus, the processing device typically determines an activity being performed by the subject and selects one of a number of predefined reference activation patterns at least partially in accordance with the determined activity. In this regard, it will be appreciated that a different activation pattern would be expected if the subject is performing squats, as opposed to running or jumping. Accordingly, by determining the activity being performed, this allows the processing device to select the most appropriate reference activation pattern. The processing device can determine the activity being performed using any suitable approach, such as analysing muscle activation patterns and/or in accordance with user input commands, or the like. Thus, the processing device can monitor the muscle activation patterns to automatically determine the particular activity being performed, without requiring input from the user. This would typically be performed by comparing measured muscle activity patterns to defined patterns representing different activities. 
     Additionally, the reference muscle activation pattern can be selected based on subject parameters, defining characteristics of the subject, such as a subject age, a subject sex, a subject weight, a subject height and a subject fitness level. Thus, different reference patterns could be established for different groups of individuals, allowing the muscle activation pattern of the subject to be compared to patterns of similar individuals performing similar activities. Thus, the activity pattern recorded for other individuals can be used to establish an idealised baseline as the reference activity pattern, with the subject&#39;s activity being compared to this to identify deviation from the baseline. 
     Additionally and/or alternatively the reference activation pattern can include a previous recorded activation pattern for the subject. This can be useful, for example, to monitor improvement and/or worsening of muscle activation during certain activities. This can be used to identify improvements as a result of training, medical intervention or rehabilitation, or problems arising, for example due to progression of muscle related disorders. Such prior activation patterns could be stored as part of a user profile, stored either locally on the processing device, or remotely, for example in a cloud or network based store. 
     The processing device can determine a fatigue indicator by determining a current muscle activation pattern indicative of the muscle activation of each of a number of muscles, determining previous muscle activation patterns, identifying a historical activation based on at least one of a mean and maximum of the previous muscle activation patterns, comparing the current muscle activation pattern to the historical activation pattern and determining a fatigue indicator at least in part using the results of the comparison. Thus, this allows changes in muscle activation over time to be used to determine a level of a fatigue. In one example, this process is performed at least partially based on the frequency of muscle activation, which is a known indicator of muscle fatigue, as will be described in more detail below. 
     It will be appreciated form the above that the system can use a wide range of different analysis techniques in order to analyse the muscle activation signals and determine one or more muscle indicators. This could include pattern recognition, in which muscle activation patterns are compared to reference or previously measured activation patterns. Alternatively, this could involve performing component analysis, such as principle component analysis (PCA) in order to identify components of the muscle activation signals, and hence derive the indicators therefrom. For example, this could involve analysing signal amplitude, frequency, gradients, or the like, and using these to determine the muscle indicators. 
     Typically the processing device generates a representation at least partially based on the indicator and causes the representation to be displayed to a user. This allows the one or more indicators to be displayed to a user, allowing the user to view the current muscle activation of the subject. In this regard, it will be appreciated that the subject could be the user, although this is not essential and alternatively the user could be a third party that is monitoring or observing the subject. For example, the user could be a medical practitioner reviewing monitoring the muscle health or activity levels of a patient. Alternatively, the user could be a coach or trainer monitoring the muscle activity of a trainee, such as an athlete or the like. 
     The representation could be of any suitable form but typically includes an alphanumeric indication of the indicator, a graphical representation of a muscle activation pattern for at least one muscle and/or a graphical representation of results of a comparison of a muscle activation pattern to a reference muscle activation pattern. Different representations could be used for different indicators, and typically the user would have the ability to select a desired representation type. 
     Whilst the system can use a single processing device, such as a single worn processing system, more typically functionality is distributed between multiple processing devices. In this case, the system typically includes a first electronic processing device attached to or worn by the subject that acquires signals from the sensors and at least partially processes the signals and a second processing device that wirelessly communicates with the first processing device and displays a representation at least partially based on the indicator. This allows monitoring of the subject to be performed remotely, without impeding the subject. This also allows more computationally expensive operations to be handled remotely to the subject, minimising the hardware requirements of the device worn by the user. 
     In one particular example, the first processing device is part of a measuring device including a voltage sensor coupled to the electrodes for sensing electrical potentials between pairs of electrodes and at least one processing device coupled to the voltage sensor for receiving signals indicative of the sensed voltages, and at least partially processing these, for example to determine signal parameters. The measuring device is typically mounted within the pocket, and is adapted to communicate with a separate remote second processing device, for example forming part of a host device, such as a smart phone, tablet or the like, allowing representations of the indicator to be viewed thereon. 
     From this it will be appreciated that the measuring device can be a lightweight portable battery operated unit that is worn by the subject during activity, with the host device being provided remotely allowing the muscle activity of the subject to be monitored. 
     The voltage sensor typically includes a differential amplifier for amplifying analogue electrical signals obtained from a pair of electrodes and an A/D convertor for converting an amplified differential voltage into a digital voltage signal, the digital voltage signal being provided to the at least one processing device for processing. The measuring device can also include a filter for filtering electrical signals, for example using an analogue anti-aliasing front end filter, or a bandpass filter in the digital domain to remove extraneous noise or other signal components. The measuring device can include a switching device for selectively coupling a single voltage sensor to respective pairs of electrodes in each array, or alternatively, multiple voltage sensors could be provided, with each being adapted to measure signals from a respective pair of electrodes. This allows readings to be obtained from different pairs of electrodes within each array, with this being controlled by the processing device within the measuring device. 
     The system can also include additional sensors to determine other physiological parameters. For example, the system can include an ECG sensor for sensing cardiac activity of the subject, with the processing device acquiring signals from the ECG sensor and determining a cardiac indicator indicative of cardiac activity of the subject. Similarly, the system can include a respiratory sensor for sensing respiratory activity of the subject, in which case the processing device typically acquires signals from the respiratory sensor and determines a respiratory indicator indicative of respiratory activity of the subject. 
     When cardiac and/or respiratory indicators are determined, the processing device can determine an activity indicator indicative of an overall activity of the subject using the at least one muscle indicator one or more of the cardiac indicator and respiratory indicator. 
     A specific example of the electronic components of the system will now be described in more detail with reference to  FIG. 3A . 
     In this example, as previously described the system  300  includes a measuring device  310 , which is adapted to be coupled to the garment and worn by the user, and a host device  320 , which is in communication with the measuring device, to allow indicators to be displayed thereon. 
     In this example, the measuring device  310  includes a microprocessor  311 , coupled to a memory  312  and an external interface  313 , such as a wireless communications interface for communicating with the host device  320 . 
     The measuring device  310  includes a switching device  314 , such as a dual band multiplexer, which is coupled to respective electrode arrays  331 ,  332 ,  333 , via a port  316  and corresponding connector  330  provided on the garment. Although three electrode arrays are shown, this is for the purpose of illustration only, and in practice any number of electrode arrays maybe provided, depending on the preferred implementation. 
     The switching device  314  is also coupled to a voltage sensor  315 , allowing signals from respective pairs of electrodes within the arrays to be provided thereto. The voltage sensor typically includes a differential amplifier  315 . 1 , for amplifying a potential difference across the pair of electrodes and an analogue-to-digital convertor (ADC)  315 . 2  for digitising the resulting potential difference signal. An optional filter (not shown) is also provided for filtering the signals for example using a bandpass filter, to remove any signal components from other sources, such as noise in the leads, or other biological signals, such as ECG signals or the like. Accordingly, in use, the voltage sensor  315  amplifies the potential difference between the electrodes in the respective pair, and generates an analogue voltage signal, which is then filtered and digitised before being provided to the processor  311  for analysis. 
     In use, the processor  311  controls the switching device  314  to connect the differential amplifier to respective pairs of electrodes within a given electrode array  331 ,  332 ,  333 , based on a defined measurement protocol. The measurement protocol typically defines a sequence of pairs of electrodes from which measurements should be taken, and may be stored in the memory  312  and selected depending on the desired outcome, as will be described in more detail below. 
     An alternative configuration is shown in  FIG. 3B , in which multiple voltage sensors  315  are provided, with each being coupled to a respective pair of electrodes. In practice this configuration could be provided using a sequence of daisy chained ADCs  315 . 2 , although any suitable configuration could be used. It will be appreciated that this configuration allows muscle activation signals to be measured from multiple pairs of electrodes in parallel, allowing measurements for multiple muscles and parts of muscles to be performed substantially simultaneously. This reduces overall measurement time, allowing repeated measurements to be performed at a higher rate, whilst also assisting with analysis of the signals, by allowing signals captured at an identical time to be analysed. 
     In each case, the measuring device  310  may also include a cardiac signal sensor  342  coupled to ECG electrodes  341 , via the connector  330  and port  316 . The cardiac signal sensor  342  typically includes an amplifier  342 . 1  and an analogue-to-digital convertor (ADC)  342 . 2 , as well as an optional filter (not shown). Similarly the measuring device can include a respiratory signal sensor  352  coupled to a respiratory sensor  351  via the port  316  and connector  330 . The nature of the respiratory sensor will vary depending on the preferred implementation and could include a sensor for measuring tension in an elastic belt extending round the chest or abdomen of the subject, or an inductance sensor that includes a conductive loop of wire attached to the subject. Example commercial inductance sensors include Philips Respironics zRIP inductive respiratory effort sensors. In either case, the respiratory signal sensor  352  typically includes an amplifier  352 . 1  and an analogue-to-digital convertor (ADC)  352 . 2 , as well as an optional filter (not shown). 
     It will be appreciated that the cardiac and respiratory signal sensors  342 ,  352  are not essential, and in particular would only be required when used in conjunction with a garment, such as the shirt garment  110  including respective ECG electrodes  341  or respiratory sensor  351 . Typically however standard measuring devices would be used in conjunction with the pants and shirt garments  120 ,  110 , with the cardiac and respiratory signal sensors  342 ,  352  being unused if not required, thereby allowing common componentry to be used for the pant and shirt based measuring devices. 
     In use, the microprocessor  311  executes instructions in the form of applications software stored in the memory  312  to allow communication with the host device  320 , as well as to control operation of the switching device  314 , and at least partially process signals from the voltage sensor  315 , the cardiac signal sensor  342  or respiratory signal sensor  352 , providing an output based on the processed signals to the host device. 
     It will be appreciated from the above, that the measuring device  310  can include any suitable electronic processing device such as a microprocessor, microchip processor, logic gate configuration, firmware optionally associated with implementing logic such as an FPGA (Field Programmable Gate Array), or any other electronic device, system or arrangement. 
     The measuring device  310  can also include other ancillary sensor systems, such as a GPS (Global Position System), accelerometers, gyroscopes or the like, allowing additional parameters, such as movement of the subject to be sensed and used in determining indicators and/or monitoring activity. 
     The host device  320  typically includes a microprocessor  321 , a memory  322 , an input/output device  323 , such as a keyboard and/or display, and an external interface  324 , interconnected via a bus  325  as shown. In this example the external interface  324  can be utilised for connecting the host device  320  to peripheral devices, such as the measuring device  310 , as well as other devices, such as communications networks, databases, other storage devices, or the like. Although a single external interface  325  is shown, this is for the purpose of example only, and in practice multiple interfaces using various methods (eg. Ethernet, serial, USB, wireless or the like) may be provided. 
     In use, the microprocessor  321  executes instructions in the form of applications software stored in the memory  322  to allow communication with the measuring device  310 , for example to control operation of the measuring device  320 , to receive outputs therefrom, and to at least partially process outputs to create and display representations of one or more indicators. 
     Accordingly, it will be appreciated that the host devices  320  may be formed from any suitable processing system, such as a suitably programmed PC, Internet terminal, lap-top, or hand-held PC, and in one preferred example is either a tablet, or smart phone, or the like. However, it will also be understood that the host device  320  can be any electronic processing device such as a microprocessor, microchip processor, logic gate configuration, firmware optionally associated with implementing logic such as an FPGA (Field Programmable Gate Array), or any other electronic device, system or arrangement. 
     Examples of the processes for monitoring muscle activity will now be described in further detail. For the purpose of these examples it is assumed that the host device  320  is a smart phone, tablet, smartwatch or other similar computing device that executes a software application that allows for communication with one or more measuring devices  310 , each of which is associated with a respective garment. 
     However, it will be appreciated that the above described configuration assumed for the purpose of the following examples is not essential, and numerous other configurations may be used. It will also be appreciated that the partitioning of functionality between the host devices  320 , and the measuring devices  310  may vary. For example, the operation of the measuring device  310  could be controlled by a user via a user interface displayed on the measuring device, allowing the measurement process to be performed, with data indicative of measured signals being pushed to the host device, thereby allowing measurements to be performed without requiring the host device. It will also be appreciated that the host device could be connected to one or more other processing systems, such as part of a cloud or other distributed architecture. 
     An example of a process for configuring the system for performing muscle measurement will now be described with reference to  FIG. 4 . 
     Initially, at step  400  the subject wears one or more garment(s), with respective measuring device(s) being connected to each garment at step  405 . Thus, the connector  330  of each garment would be plugged into the port  316  of the respective measuring device  310 , with this then being secured in the pocket of the garment. 
     At step  410 , the measuring device(s) are connected to the host device  320 . Thus can be achieved using any suitable technique, such as using a wireless communications protocol, such as Bluetooth™, or the like. Accordingly, the measuring device  310  can be turned on, and a software application on the host device launched, with the host device  320  being controlled by the application to cause the host device  320  to detect and connect to any active measuring devices  310  within range. It will be appreciated that as part of this a pairing procedure may be required to ensure the host device  320  is connecting to the correct measuring device(s)  310 . As such pairing procedures are known in the art, this will not be described in any detail. 
     At step  415 , the host device checks the connection with each measuring device  310 , reconnecting at step  410  in the event that the connection is not operating successfully. This can be repeated until a successful connection is established, allowing the remaining procedures to be performed. 
     At step  420 , the host device  320  can be used to assign a respective measuring device  310  to a particular subject. This is typically achieved by creating an association between a unique identifier of each measuring device  310 , and an identifier associated with each subject, such as a name, or other suitable identifier. This allows a single host device to be used with measuring devices  310  associated with multiple subjects, so that a number of different subjects can be monitored using a single host device. This is particularly useful for scenarios such as team sports, where a coach or trainer could use a single host device to monitor the muscle activity of each team member. Alternatively, a medical practitioner could monitor many patients at once such as in a rehab or hospital environment. 
     Accordingly, the host device  320  can be used to present the user with a list of connected measuring devices  310 , allowing the user to allocate these to respective individuals. Information regarding the association is then typically stored in a store, such as the memory  322 , a remote database, or the like. 
     This process can also be used to ensure subject specific data is used during the analysis process. For example, a profile of each subject can be established, specifying subject characteristics, such as age, sex, weight, height, details of injuries, medical conditions and/or interventions, or the like. This information can be used when analysing recorded measurements, as will be described in more detail below. 
     At step  425 , the user can optionally select an activity to be performed, allowing this information to be used in controlling the monitoring and/or analysis of muscle activity. The activities are generally predefined, for example by a supplier of the system and/or a user or medical practitioner or the like, and may be stored in a reference database, or the like, allowing the host device  320  to display a list of predefined activities. Alternatively, the user can custom define activities, for example specifying the type of activity and any requirements associated with the monitoring and/or analysis process to be used. 
     In the case of the monitoring process, the defined activity can be used to control the relative degree of monitoring of different muscle groups. For example, when performing squats, the primary muscles used are leg muscles. Thus, monitoring can be controlled to increase the sample rate for the leg muscles, whilst decreasing the sampling rate for lesser used muscles, such as arm muscles. This can be used to maximise the resolution of data collection for the primary muscles used in the specified activity. 
     In terms of analysing results, knowledge of the activity performed can be used to select a specific reference muscle activity pattern, which can be used when determining the indicators. For example, this allows the muscle activity of the subject collected whilst performing squats to be compared to an idealised muscle activity pattern for an individual with similar physical characteristics. This also allows signals to be analysed using appropriate techniques, such as magnitude and/or frequency analysis, depending on the indicator to be determined. 
     At step  430 , the measurement process is triggered, for example by having the user select a “record now” option presented on the host device. At this point, the host device  320  communicates with the measuring device  310 , causing the measuring device  310  to commence measurement of muscle activity. As part of this process, the host device  320  can transfer instructions to the measuring device  310 , to control the measurement process, for example, instructing the measuring device to perform a particular measurement protocol. Once measurement has commenced, an indication of this can be provided, for example via the host device  320 , or through a visual or audible indication on the measuring device  310 , allowing the subject to be notified that activity can be commenced at step  435 . 
     It will be appreciated however that connecting the measuring device to the host device as set out in steps  410  to  425  could be performed after an activity has been recorded. In this instance, the user could simply activate the measuring device, for example using a suitable input button provided on the device, causing measurements to be performed. In this case, connection to the host device may only occur after the measurements have been recorded, or could be performed automatically during the activity, and reference to connection of the measuring and host devices prior to commencing activity is not intended to be limiting. 
     The process of monitoring muscle activity after commencing activity will now be described with reference to  FIGS. 5A and 5B . 
     In this example, at step  500 , the measuring device  310  determines the measurement protocol to be used for the sequence of measurements. The measurement protocol is typically retrieved from memory  312  based on instructions provided by the host device  320 , as described above with respect to  FIG. 4 , although alternatively may be received directly from the host device  320 , depending on the preferred implementation. Alternatively, the measurement protocol could be a standard protocol implemented when the measuring device is activated, or could be selected from protocols stored locally in the memory  312  based on manual input commands, for example in the event the measurement process is triggered without using the host device  320 . 
     At step  505 , the processor  311  selects a next pair of electrodes from which a measurement is to be taken, and controls the switching device  314  accordingly at step  510 , to thereby couple the respective pair of electrodes to the voltage sensor  315 . It will be appreciated that these steps are not required in the event that the apparatus of  FIG. 3B  is used, in which case measurements are performed for each pair of electrodes simultaneously. 
     The potential difference between the electrodes is amplified by the amplifier  315 . 1  at step  515 , before being filtered and digitised at step  520 . It will be appreciated that the measurement is typically performed over a predetermined time period, such as a few milliseconds, allowing the frequency and magnitude of the potential difference to be captured. The exact time period used will depend on the preferred implementation, and/or measurement protocol, as will be appreciated by persons skilled in the art. 
     The digitised voltage signals are provided to the processor  311 , which typically at least partially analyses the signals to determine signal parameters, which are then stored in the memory  312  at step  525 . It will be appreciated that the signals themselves can also be stored, although this is not necessary and hence will typically depend on storage availability. 
     The nature of the processing performed by the processor  311  will vary depending on the preferred implementation, and can include for example performing a Fourier analysis to determine the magnitude of the voltage between electrodes for different frequency components within the measured signal. In this regard, the measurement protocol can define the processing to be performed and in particular any signal parameters that are to be determined, such as frequency components of interest and examples of types of analysis that can be performed are described in “ Techniques of MG signal analysis: detection, processing, classification and applications ” by M. B. I. Raez, M. S. Hussain, 1 and F. Mohd-Yasin in Biol Proced Online. 2006; 8: 11-35. 
     In any event, at step  530  the processor  311  determines if all required measurements have been completed, and if not returns to step  510  to control the switching device and record measurements for the next pair of electrodes. Again it will be appreciated that this is not required in the event that measurements are performed on all pairs of electrodes simultaneously. 
     At steps  535  and  540  the processor  311  will optionally record ECG and respiratory signals from the cardiac and respiratory sensors in a similar manner. It will be appreciated that in practice this is typically performed in parallel with the process described in steps  510  to  530 , so that cardiac and respiratory signals are recorded concurrently with collection of muscle activity signals. 
     Once muscle activity and optionally ECG and respiratory signals have been recorded, these can be used to determine indicators. This process can be performed in a variety of manners, and could include calculating the indicators in the processor  311 . More typically however, the signal parameters determined at step  525  are uploaded to the host device for analysis at step  545 . This allows processing to be distributed between the measuring device  310  and host device  320  and also avoids the need for references and calculation techniques to be stored on the measuring device. However, this is not essential and any suitable distribution of processing can be used. 
     Whilst upload of information can be performed once the measurement process has been concluded, more typically this is performed whilst collection of data continues, with the processor  311  returning to step  505  to select a next electrode pair, allowing indicators to be calculated and displayed dynamically as activities are ongoing. This is particularly useful in monitoring the ongoing effect of the activities being performed on muscle activity. In particular, this allows real-time feedback to be provided to the subject as the activities are performed. 
     At step  550 , the host device  320  determines various indicators, depending for example on the measurement protocol being performed, and examples of the derivation of specific indicators will be described in more detail below. 
     Once indicators have been determined, at step  555 , the host device  320  generates a representation of the indicators, allowing this to be displayed to a user. The nature of the representation will vary depending on the preferred implementation, user settings and the nature of the indicator. 
     In one example, the representation can include a simple alphanumeric indicator, indicative of a measured activity for one or more muscles and/or muscle groups. However, more typically the representation includes a graphical representation of a human body, illustrating one or more muscle groups, and showing visual indications of the indicators thereon. This could include colour coding of parts of individual muscles, or muscle groups to illustrate a level of activity relative to a baseline or other reference, showing a graph indicative of the level of ability, or the like. It will be appreciated that by having indicators indicative of muscle activity measured and displayed in real time can help provide useful feedback to the subject performing the activity, in particular allowing the individual to assess whether the activity is being performed effectively, and potentially to identify the onset of fatigue and/or the potential for injury. 
     An example of the process for determining an intramuscular indicator will now be described with reference to  FIG. 6 . 
     In this example, at step  600  a next muscle or muscle group is selected, with an average activation for the respective muscle or muscle group being determined at step  605 . In this example, the activation is typically based on the magnitude of the potential difference between pairs of electrodes, averaged for each pair of electrodes for the given muscle or muscle group. It will be appreciated that averaging could be performed in any appropriate manner, and in one example this could be achieved based on an average derived from measurements made between end points, and between end and mid points of the muscle. This reduces the number of measurements required to determine an average, whilst still allowing a reasonable accurate average to be determined. 
     At step  610 , the muscle activation for each part of the muscle or muscle group, as determined based on the magnitude of the potential difference between a pair of electrodes, is compared to the average activation. The results of the comparison are used to determine the intramuscular indicator at step  615 , specifically by identifying parts of the muscle or muscle group that are demonstrating an activation beyond one or more standard deviations of the average cell-cell muscle activation. At step  620 , it is determined if all muscles are complete, and if not the process returns to step  600 , otherwise the process ends at step  625 . 
     The intramuscular indicator can be of any form and is generally used to identify parts of the muscle or muscle group which are demonstrating above or below average activation, which is in turn used to identify potential muscle damage. For example, in the event that part of the muscle is damaged, this could be under activating, whilst over activating parts of a muscle could indicate the potential for injury. 
     In one example, the indicator is used to generate a representation in the form of a map of the respective muscle, with the location of over or under active parts of the muscle being identified thereon. For example, this could include colour coding to indicate the degree of under or over activation, as compared to the average activation. 
     An example of the process for determining an intermuscular indicator will now be described with reference to  FIG. 7 . 
     In this example, at step  700  a next contralateral muscle pair is selected. In this regard, the contralateral muscle pair is a pair of muscles or muscle groups positioned on contralateral parts and typically limbs, of the subject&#39;s body. 
     At step  705  an average activation for each muscle in the pair is determined, with this again being performed by averaging the magnitude of the potential difference for each pair of electrodes for the respective muscle or muscle group. 
     At step  710 , the average activation for each muscle is compared, with a difference being used to determine the intermuscular indicator at step  715 . At step  720 , it is determined if each pair is complete, and if not the process returns to step  700 . Otherwise, the process ends at step  720 . 
     In this instance, the intermuscular indication is indicative of any disparate average activation between contralateral muscles, and is used to identify any imbalance in muscle activation in the subject. It will be appreciated that this indicator is generally only determined when the user is performing an activity that places symmetrical loads on the muscles. 
     An example of the process for determining an efficiency indicator will now be described with reference to  FIG. 8 . 
     In this example, at step  800  a muscle activation for each muscle or muscle group is determined. Again this is typically performed by averaging the magnitude of the potential difference for each pair of electrodes for the respective muscle or muscle group. 
     At step  805 , a muscle activation pattern is determined, with this typically representing a proportion of the overall muscle activity attributable to each muscle. 
     At step  810 , a reference activation pattern is selected. The reference activation pattern can be determined based on a study of individuals in a sample population when the individuals are performing the same activity as the subject. The individuals are typically selected to have similar physical characteristics, such as sex, ethnicity, age, weight, height, body mass index, or the like, and are typically assessed as healthy individuals. Thus, it will be appreciated that the reference activation pattern represents an idealised activation pattern for the subject when performing the given activity. 
     However, additionally and/or alternatively, the reference muscle activation pattern could be defined by a user. For example, if the user is a practitioner, such as a physiotherapist, doctor, trainer, or the like, they may wish to define a reference activation pattern for a subject to achieve an end goal. This could be part of a treatment program, for example to assist in recovery from injury, or with a view to improving strength or movement. In this instance, it will be appreciated that the practitioner might be better able to determine a desired activation pattern based on an understanding of the requirements for the subject, which is therefore more appropriate than a fixed defined pattern. However, to assist in avoiding injury, the reference patterns could be tailored within defined limits, allowing some variation between subject goals or requirements to be accommodated, whilst ensuring the patterns that could be adverse to the subject are avoided. 
     As part of this, the system can allow different reference activation patterns to be shared, so for example, if a practitioner develops a pattern that is particularly effective at treating a particular injury or condition, or achieving a particular training goal, this can be shared with other users. 
     However, it will be appreciated that the use of “standard” defined reference patterns can also assist in ensuring consistency in assessment or treatment of subjects. This can ensure that biases inherent when different individuals monitor or treat a subject, are overcome or obviated, maximising the chance of issues being appropriately identified and addressed. 
     An example muscle activation pattern when performing squats is shown in Table 1 below, with the numbers representing a relative level of activity, defined to sum to 1. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Muscle 
                 Left 
                 Right 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Gluteals 
                 0.4 
                 0.4 
               
               
                   
                 Quadriceps 
                 0.175 
                 0.175 
               
               
                   
                 Hamstrings 
                 0.225 
                 0.225 
               
               
                   
                 Adductors 
                 0.1 
                 0.1 
               
               
                   
                 Calf 
                 0.1 
                 0.1 
               
               
                   
                   
               
            
           
         
       
     
     At step  815 , the measured activation pattern is compared to the reference activation pattern, with this being used to determine an efficiency indicator at step  820 . The efficiency indicator could be used to identify muscles or muscle groups that are over or under activating compared to the reference activation pattern, which in turn can identify issues either with the subject muscles, and/or the technique the subject is using when performing the respective activity. Thus, this can be used to identify if the subject is performing the activity in the most efficient manner. 
     An example of the process for determining a fatigue indicator will now be described with reference to  FIG. 9 . 
     In this example, at step  900  a current muscle activation pattern is determined for the subject. In this example, the activation pattern is typically based on the frequency of muscle firing and/or the wave complex analogous to the QRS complex of an ECG signal. 
     At step  905 , previous historical activation patterns recorded for the subject, when performing the same activity, are determined, for example by retrieving these from a store, such as a memory, a database, or the like. 
     At step  910 , the previous activation patterns are analysed to identify a maximum and/or average historical activation pattern at step  915 . The current activation pattern being compared to the historical maximum and/or average activation pattern at step  920 , with deviations from the average and/or maximum being used to determine a fatigue indicator at step  925 . Thus, this allows the changes in activation, and in particular changes in the frequency of activation over time to be monitored as a subject repeatedly performs a given activity, thereby allowing muscle fatigue to be assessed. 
     The fatigue indicator could also take into account additional factors, such absolute or relative changes in heart and/or respiratory rate, distance travelled or other movements, as determined from appropriate ones of the sensors. 
     It will also be appreciated that indicators indicative of a total activity for a defined period, such as a day, week, or specific workout period, could be determined, and used as part of a fitness monitoring program. This could include using muscle activity together with overall indicators of movement, heart rate and respiration, to calculate calories burned during an exercise program, with this being used as part of a broader fitness monitoring program, as will be appreciated by persons skilled in the art. 
     Accordingly, the above described system allows measurements of muscle activity to be performed through the use of wearable garments incorporating arrays of electrodes, which allow EMG signals indicative of muscle activation to be monitored. This in turn allows muscle activity to be measured whilst performing activities, including but not limited to sporting activities, exercises, and/or day-to-day activities. Data collected can be analysed allowing a number of different indicators to be derived, which can in turn provide insights into the muscle function and execution of the activities by the subject. This can include, but is not limited to identifying damage to muscles, imbalance in use of muscles, optimising the efficiency of muscle usage during defined activities, and detection of fatigue. The indicators can be displayed in real time as activities are performed and/or can be recorded and subsequently reviewed to allow for longitudinal study of muscle activity. 
     It will therefore be appreciated that the above described system can be used in a wide range of circumstances, including but not limited to training of subjects for sporting activities, monitoring subject during activities to identify the potential for or onset of injuries, and studying subjects in a medical context to identify muscle related conditions, such as muscle wastage, or the like. 
     Throughout this specification and claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers. 
     Persons skilled in the art will appreciate that numerous variations and modifications will become apparent. All such variations and modifications which become apparent to persons skilled in the art, should be considered to fall within the spirit and scope that the invention broadly appearing before described.