Patent Publication Number: US-2019175974-A1

Title: Anchored resistance exercise device with sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application No. 62/162,653 filed on May 15, 2015, the teachings of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to exercise equipment, and more particularly to resistance exercise equipment. 
     BACKGROUND 
     Exercise systems that incorporate an anchor and one or more extendible tethers coupled to the anchor to provide exercise resistance have been known for quite some time. For example, U.S. Pat. No. 1,432,013 to Herbert, U.S. Pat. No. 5,362,295 to Nurge and U.S. Patent Application Publication No. 2010/0041528 in the name of Todd disclose arrangements in which elastic cords are attached to a belt so that a user can use the cords to provide exercise resistance to arm movements. However, these arrangements do not gather data about exercise performance. 
     U.S. Patent Application Publication No. 2014/0142864 in the name of Spears et al. describes an exercise system comprising a belt and two resistive deformable elements connecting the belt to two handles. Although this document does describe collection of exercise data, it proposes a complicated sensor arrangement for achieving this purpose. 
     SUMMARY 
     Broadly speaking, exercise systems according to aspects of the present disclosure comprise an anchor, one or more extendible tethers coupled to the anchor, one or more two-element sensors for detecting movement of a respective tether, and one or more sensor alignment arms for maintaining alignment between the two elements of a respective sensor. 
     In one aspect, an exercise system comprises an anchor and at least one extendible tether coupled to the anchor and extending from a mooring on the anchor to a grip end having a grip element. Each extendible tether is longitudinally movable between an extended configuration and a retracted configuration. The exercise system further comprises at least one sensor alignment arm movably coupled to the anchor and at least one sensor. Each sensor is associated with a respective sensor alignment arm and extendible tether, and each sensor comprises a first sensor element and a second sensor element. The first sensor element is carried by the sensor alignment arm and the second sensor element is carried by the extendible tether. Each sensor alignment arm is movably coupled to a respective one of the at least one extendible tether so that the extendible tether is longitudinally movable relative to the sensor alignment arm and angular movement of the extendible tether relative to the anchor moves the sensor alignment arm relative to the anchor to maintain longitudinal alignment between the sensor alignment arm and the extendible tether and thereby maintain longitudinal alignment between the first sensor element and the second sensor element. Each sensor is configured or adapted to detect movement of the second sensor element past the first sensor element in at least a first longitudinal direction as the extendible tether moves between the extended configuration and the retracted configuration. 
     In some embodiments, the exercise system has two opposed extendible tethers, two opposed sensor alignment arms and two sensors. 
     In some embodiments, the anchor is a belt, and each extendible tether may comprise a resistance band. The exercise system may further comprise anchor points on the belt for receiving additional resistance bands. 
     In some embodiments, the sensor(s) may be coupled to an external computing device. The external computing device may be releasably carried by the anchor. In other embodiments, the sensor(s) may be coupled to a wireless transmitter, which may be carried by the anchor. 
     In one particular embodiment, the anchor is a belt and two extendible tethers in the form of resistance bands are secured to the belt so that the resistance bands extend from the user&#39;s hips or waist when the belt is worn. Such an embodiment has particular application to boxing and mixed-martial-art (MMA) training, although it is not limited to such applications and can be used in support of a wide variety of training activities. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features will become more apparent from the following description in which reference is made to the appended drawings wherein: 
         FIG. 1  is a perspective view of a first exemplary exercise system according to an aspect of the present disclosure; 
         FIG. 1A  is a perspective view of the exercise system of  FIG. 1 , showing additional resistance bands and mixed martial arts gloves releasably received thereon; 
         FIG. 1B  is a perspective view of the exercise system of  FIG. 1 , showing additional resistance bands and weightlifting gloves releasably received thereon; 
         FIG. 2  is a plan view of the exercise system of  FIG. 1 ; 
         FIG. 3A  shows a portion of the exercise system of  FIG. 1  with an extendible tether and associated sensor alignment arm in a first angular position with the extendible tether in a retracted configuration; 
         FIG. 3B  shows a portion of the exercise system of  FIG. 1  with the extendible tether and associated sensor alignment arm in the first angular position with the extendible tether moving between the retracted configuration and an extended configuration; 
         FIG. 3C  shows a portion of the exercise system of  FIG. 1  with the extendible tether and associated sensor alignment arm in the first angular position with the extendible tether in the extended configuration; 
         FIG. 4A  shows a portion of the exercise system of  FIG. 1  with the extendible tether and associated sensor alignment arm in a second angular position with the extendible tether in the retracted configuration; 
         FIG. 4B  shows a portion of the exercise system of  FIG. 1  with the extendible tether and associated sensor alignment arm in the second angular position with the extendible tether moving between the retracted configuration and the extended configuration; 
         FIG. 4C  shows a portion of the exercise system of  FIG. 1  with the extendible tether and associated sensor alignment arm in the second angular position with the extendible tether in the extended configuration. 
         FIG. 5A  shows a portion of a second exemplary exercise system according to an aspect of the present disclosure with an extendible tether and associated sensor alignment arm in a first angular position with the extendible tether in a retracted configuration; 
         FIG. 5B  shows a portion of the exercise system of  FIG. 5A  with the extendible tether and associated sensor alignment arm in the first angular position with the extendible tether moving between the retracted configuration and an extended configuration; 
         FIG. 5C  shows a portion of the exercise system of  FIG. 5A  with the extendible tether and associated sensor alignment arm in the first angular position with the extendible tether in the extended configuration; 
         FIG. 6A  shows a portion of the exercise system of  FIG. 5A  with the extendible tether and associated sensor alignment arm in a second angular position with the extendible tether moving between the retracted configuration and the extended configuration; 
         FIG. 6B  shows a portion of the exercise system of  FIG. 5A  with the extendible tether and associated sensor alignment arm in the second angular position with the extendible tether in the extended configuration; 
         FIG. 7A  is a bottom plan view showing a portion of the exercise system of  FIG. 5A  with an extendible tether and associated sensor alignment arm in the first angular position with the extendible tether in a retracted configuration; 
         FIG. 7B  is a bottom plan view showing a portion of the exercise system of  FIG. 5A  with the extendible tether and associated sensor alignment arm in the first angular position with the extendible tether moving between the retracted configuration and an extended configuration; and 
         FIG. 7C  is a bottom plan view showing a portion of the exercise system of  FIG. 5A  with the extendible tether and associated sensor alignment arm in the first angular position with the extendible tether in the extended configuration. 
     
    
    
     DETAILED DESCRIPTION 
     Reference is now made to  FIG. 1 , which shows a first exemplary exercise system  100  according to an aspect of the present disclosure. In the exemplary exercise system  100  shown in  FIG. 1 , the anchor takes the form of a belt  102 , which may be, for example, a suitably modified weightlifter&#39;s belt, which may be fastened around a user&#39;s waist in known manner, for example by way of a buckle or hook-and-loop fasteners such as those offered under the trademark “Velcro”. 
     Two opposed extendible tethers  104  are coupled to the belt  102 . In the illustrated embodiment, each of the extendible tethers  104  comprises a resilient cylindrical elastomeric resistance band which has been doubled over onto itself. Each of the extendible tethers  104  extends from a mooring  106  on the belt  102 . In the illustrated embodiment, each of the extendible tethers  104  is anchored to the belt  102  inside a sleeve  108  having reinforced terminal cuffs  110  at each end, and thus the openings of the sleeves  108  form the moorings  106  in that the sleeve openings define the locations where the respective extendible tethers  104  are free to make substantial angular movements relative to the belt  102 . Thus, in the illustrated embodiment, the extendible tethers  104  are not anchored to the belt  102  at the moorings  106  but can move longitudinally in and out of the openings of the sleeves  108 . In other embodiments, the moorings may be locations where the extendible tethers are anchored. For example, in an embodiment where the sleeve is omitted from the belt, the mooring for each extendible tether may be the outermost position where that extendible tether is anchored to the belt. In the illustrated embodiment, each of the extendible tethers  104  comprises an individual resistance band, that is, there are two resistance bands: one for each of the extendible tethers  104 . In other embodiments, a single resistance band may provide both of the extendible tethers, with each end of the single resistance band forming one of the extendible tethers; in such an embodiment the single resistance band may be doubled over as well. In still further embodiments, multiple resistance bands may be used to form each extendible tether. Each extendible tether may be anchored to the belt at a single point or at multiple points. 
     Each of the extendible tethers  104  extends from a respective one of the moorings  106  on the belt  102  to a grip end  112  having a grip element. In the illustrated embodiment shown in  FIG. 1 , the grip elements take the form of flexible padded cylindrical handgrips  114 . In other embodiments, the grip elements may be gloves, such as a mixed martial art (MMA) style gloves  114 A as shown in  FIG. 1A  or weightlifter&#39;s gloves  114 B as shown in  FIG. 1B , or boxing gloves. In yet further embodiments, the grip elements may take other forms, such as balls, wrist straps, handles or grips of various types or even simple loops knotted into the extendible tethers  104 . Each extendible tether  104  is longitudinally movable between an extended configuration and a retracted configuration. In the illustrated embodiment, since the extendible tethers  104  are formed by resilient resistance bands, the extended configuration is a stretched configuration and the retracted configuration is an unstretched or “rest” configuration. 
     In the illustrated embodiment, each of the moorings  106  is located at a position on the belt  102  that will be proximal to the user&#39;s hips or waist when the belt  102  is fastened about the user&#39;s waist. In this embodiment, the extendible tethers  104  will be positioned to provide exercise resistance to various arm movements when a user grasps the handgrips  114  or wears the gloves  114 A,  114 B. For example, a user may perform arm movements such as punches used in boxing or punches and other strikes used in MMA, pressing or extension movements such as push-ups or lateral raises, with the extendible tethers  104  providing resistance to those movements. 
     Continuing to refer to  FIGS. 1, 1A, 1B and 2 , two sensor alignment arms  120  are movably coupled to the belt  102  adjacent to respective ones of the moorings  106 . Thus, each sensor alignment arm  120  is associated with a respective one of the extendible tethers  104 . In the illustrated embodiment, each sensor alignment arm  120  is coupled to the belt  102  by a rotatable coupling  122  (see  FIGS. 2 and 4A to 4C ) so that it can rotate relative to the belt  102 , and is also able to flex toward and away from the belt  102  and to twist in response to force applied to the sensor alignment arm  120  by the respective extendible tether  104 . In the illustrated embodiment, the sensor alignment arms  120  are formed from a suitable flexible, resilient plastic to provide the desired flexibility; in other embodiments the sensor alignment arms may be substantially rigid and incorporate a flexible portion. In still further embodiments, the sensor alignment arms may be coupled to the belt by a ball joint or other coupling providing the required freedom of movement relative to the belt, and may be flexible, substantially rigid, or a combination thereof. 
     In addition, the exercise system  100  further comprises two sensors  124 , with each sensor  124  associated with a respective sensor alignment arm  120  and extendible tether  104 . Thus, in the illustrated embodiment the exercise system has two opposed extendible tethers  104 , two opposed sensor alignment arms  120  and two sensors  124 , arranged as two associated groups, each group comprising one extendible tether  104 , one sensor alignment arm  120  and one sensor  124 . Each of the sensors  124  comprises a first sensor element carried by the respective sensor alignment arm  120  and a second sensor element carried by the respective extendible tether  104 . The sensor  124  is adapted to detect movement of the second sensor element past the first sensor element in at least a first longitudinal direction. In the illustrated embodiment, each of the sensors  124  comprises a paired reed switch  126  and magnet  128 , with the reed switch  126  being fixed to the respective sensor alignment arm  120  and the magnet  128  being fixed to the respective extendible tether  104 .  FIG. 2  shows the mounting for the reed switches  126 , which are located under respective protective shrouds  130  ( FIG. 1 ) on the sensor alignment arms  120 ; the reed switches  126  are shown in dashed lines in other Figures. Similarly, the magnets  128  are positioned inside mountings  129  secured to the extendible tethers  104  and are shown in dashed lines in the Figures. Thus, in this embodiment the reed switches  126  are the first sensor elements and the magnets  128  are the second sensor elements. 
     Reference is now made to  FIGS. 3A to 4C . Each sensor alignment arm  120  is movably coupled to the respective extendible tether  104  so that the extendible tether  104  is longitudinally movable relative to the sensor alignment arm  120  through the guide aperture  132 . In the illustrated embodiment, each sensor alignment arm  120  has a guide aperture  132 , and the respective extendible tether  104  passes through the guide aperture  132 . The guide aperture  132  is large enough so that the extendible tether  104  is longitudinally movable relative to the sensor alignment arm  120  through the guide aperture  132 . The edges of the guide aperture  132  are smoothly beveled to reduce resistance to longitudinal motion of the extendible tether  104  through the guide aperture  132 . Optionally, a suitable bushing or bearing (not shown) may be positioned in the guide aperture  132  to facilitate sliding movement of the respective extendible tether  104 ; the second exemplary exercise system  200  described further below includes such a bearing. The guide aperture  132  is further sized so that when the extendible tether  104  moves angularly relative to the belt  102 , the respective extendible tether  104  will engage the inner surface of the guide aperture  132  to pull the sensor alignment arm  120  in a corresponding angular movement relative to the belt  102 . Thus, angular movement of each extendible tether  104  and its associated sensor alignment arm  120  relative to the belt  102  will be substantially in unison (i.e. subject to any play between the extendible tether  104  and the guide aperture  132 ). Any play between the extendible tether  104  and the guide aperture  132  should be small enough to keep the reed switch  126  and magnet  128  in longitudinal alignment. Accordingly, angular movement of the extendible tether  104  relative to the belt  102  also moves the sensor alignment arm  120  relative to the belt to maintain longitudinal alignment between the sensor alignment arm  120  and the extendible tether  104 . This in turn maintains longitudinal alignment between the reed switch  126  and the magnet  128 . Therefore, when the extendible tether  104  moves between the extended configuration and the retracted configuration, the magnet  128  is constrained to move past the reed switch  126  and open the reed switch  126 . Optionally, other embodiments may have circuit configurations where movement of the magnet  128  past the reed switch  126  closes the reed switch  126 . 
       FIGS. 3A to 3C  show an extendible tether  104  and the associated sensor alignment arm  120  in a first angular position relative to the belt  102  and  FIGS. 4A to 4C  show an extendible tether  104  and the associated sensor alignment arm  120  in a second angular position relative to the belt  102 .  FIGS. 3A and 4A  show the extendible tether  104  in the retracted (unstretched) configuration, with the magnet  128  disposed inwardly of the reed switch  126 , relative to the belt  102 .  FIGS. 3B and 4B  show the extendible tether  104  moving between the retracted configuration and the extended (stretched) configuration, with the magnet  128  moving across the reed switch  126  to activate the reed switch  126 . FIGS.  3 C and  4 C show the extendible tether  104  in the extended configuration, with the magnet  128  disposed outwardly of the reed switch  126 , relative to the belt  102 . 
     Opening or closing (i.e. activating) the reed switch  126  provides an electrical signal that the associated extendible tether  104  has moved between the extended configuration and the retracted configuration. Such electrical signals can be used to gather data about the manner in which the exercise system  100  is being used. For example, the electrical signals may be used to count the number of repetitions (e.g. exercises or strikes), measure the duration of each repetition or strike, and the time between repetitions or strikes. For boxing or MMA training, the duration of a strike (the time between consecutive paired actuations of the same reed switch  126 ) can be used to calculate a strike velocity value. The gathered data can in turn be used for further calculations, such as estimating the number of calories burned during a given period. To facilitate this data gathering, the reed switches  126  may be coupled to an external computing device. In the illustrated embodiment, the reed switches  126  are coupled by wires  134  ( FIGS. 1, 1A, 1B ) to a wireless transmitter  136 , which, when a reed switch  126  is activated, transmits wireless signals to an external computing device in the form of a wireless cyclocomputer console  140  that uses the wireless signals to determine and display performance data, such as calories burned, number of repetitions (e.g. exercises or strikes), duration of each repetition or strike, time between repetitions or strikes and strike velocity values. The wireless transmitter  136  is carried by the belt  102 ; in particular, the wireless transmitter  136  is secured to the sleeve  108  and covered by a protective pad  144 . The wires  134  pass through the sleeve  108  and emerge from an aperture therein to reach the wireless transmitter  136 ; the portions of the wires  134  extending between the terminal cuffs  110  and the reed switches  126  are covered by flexible protective sheaths  148 . The cyclocomputer console  140  is also carried by the belt  102 ; in the illustrated embodiment the cyclocomputer console  140  is releasably mounted to the belt  102  by hook-and-loop fasteners such as those offered under the trademark “Velcro”. 
     Although in the illustrated embodiment the external computing device is a cyclocomputer console  140 , in other embodiments the sensors may communicate with more sophisticated external computing devices, such as a smartphone, tablet, laptop, desktop or other type of computer executing appropriate software, or other suitable types of processing hardware. For example, a smartphone or tablet may be provided with an application configured to run on the iOS or Android operating systems, or a desktop or laptop computer can be provided with appropriate software configured for Windows or Mac OS operating systems. Any suitable type of wireless transmission may be used, for example known protocols such as Wi-Fi, FM radio or Bluetooth may be used. Moreover, while in the illustrated embodiment the sensors are coupled to a wireless transmitter, in other embodiments they may be coupled directly by wire to a suitable computing device or other suitable types of processing hardware. 
     Reference is now made to  FIGS. 5A to 7C , which show a portion of a second exemplary exercise system  200  according to the present disclosure. The second exemplary exercise system  200  shown in  FIGS. 5A to 7C  is similar to the first exemplary exercise system  100  shown in  FIGS. 1 to 4C , with like reference numerals denoting corresponding features except with the prefix “2” instead of “1”. Hence, in the second exemplary exercise system  200 , the belt is denoted by reference  202 , the extendible tethers are denoted by reference  204 , and so on. 
     The second exemplary exercise system  200  shown in  FIGS. 5A to 7C  differs from the first exemplary exercise system  100  shown in  FIGS. 1 to 4C  in the structure and arrangement of the alignment arms  220  and in the manner in which the sensors  224  are carried. As with the first exemplary exercise system  100 , the sensors  224  of the second exemplary exercise system  200  may communicate with a cyclocomputer, or with more sophisticated external computing devices, such as a smartphone, tablet, laptop, desktop or other type of computer executing appropriate software, or other suitable types of processing hardware. 
     As noted above, the second exemplary exercise system  200  incorporates a rotatable bearing  258  in each of the guide apertures  232 ; the bearings  258  may each be, for example, a coil spring that can be threaded onto the outer edge of the respective alignment arm  220  at the distal end  268  thereof as shown. 
     In addition, in the second exemplary exercise system  200  each of the first sensor elements, that is, the magnets  228 , are mounted on respective sensor carriers  260  that are in turn carried by the respective extendible tethers  204 . The sensor carriers  260  are curved, with the magnets  228  disposed in the outwardly facing concavity so as to be positioned between the sensor carriers  260  and the extendible tethers  204 ; the magnets  228  are secured in an enclosure  262 . The sensor alignment arms  220  are formed from a suitable flexible, resilient plastic, with the distal portions (the portions furthest from the sleeve end cuffs  220 ) being reinforced so as to be more rigid (e.g. a 2:1 ratio) than the proximal portions (the portions closest to the sleeve end cuffs  220 ). As best seen in  FIGS. 7A to 7C , the shrouds  230  which protect the reed switches  226  take the form of sloped or curved guide ramps which can serve as travel surfaces for the sensor carriers  260  when the sensor alignment arms  220  are flexed outwardly away from the belt  202 . In the second exemplary exercise system  200 , the sensor alignment arms  220  each incorporate a guide tube  263  and a divider post  264  (shown in  FIGS. 6A and 6B ) extends into each guide tube  263  to enforce separation between the doubled-over strands of the resistance bands that form the extendible tether  204 . The divider post  264  may be an extension of part of the rotatable coupling that rotatably secures the sensor alignment arms  220  to the belt  202 . 
     Each of the sensor carriers  260  has two pairs of side-by-side tether openings  266  arranged in opposed relation to one another at the ends of the sensor carriers  260 . As with the first exemplary exercise system  100 , in the second exemplary exercise system  200 , each of the extendible tethers  204  comprises a resilient cylindrical elastomeric resistance band which has been doubled over onto itself; the strands of each of the resistance bands pass through the tether openings  266  in each of respective the sensor carriers  266 . The outer diameter of the strands of each of the resistance bands will be larger when the respective extendible tether  204  is in the retracted, unstretched configuration than when the respective extendible tether  204  is in the extended, stretched configuration. The tether openings  266  are sized, relative to the variable outer diameter of the resistance band, so that as the extendible tether  204  moves between the retracted/unstretched (rest) configuration and the extended/stretched configuration, the outer diameter of the resistance band is reduced from a size that forms an interference fit with the tether openings  266  to a size that can slide within the tether openings  266 . Thus, during an initial portion of the outward stroke from the retracted/unstretched configuration to the extended/stretched configuration, each sensor carrier  260  will be fixed to and carried by the respective extendible tether  204  due to the interference fit, and during a final portion of the outward stroke from the retracted/unstretched (rest) configuration to the extended/stretched configuration, each sensor carrier  260  and its respective extendible tether  204  can move independently of one another. Conversely, during an initial portion of the return stroke from the extended/stretched configuration to the retracted/unstretched (rest) configuration, each sensor carrier  260  and its respective extendible tether  204  can move independently of one another, and during a final portion of the return stroke from the extended/stretched configuration to the retracted/unstretched (rest) configuration, each sensor carrier  260  will be fixed to and carried by the respective extendible tether  204  due to the interference fit. This brings the first sensor element (magnet  228 ) affixed to the sensor carrier  260  back to its initial rest or retracted position, coupling with the second sensor element (reed switch  226 ). 
     Reference is now made to  FIGS. 5A to 5C  and  FIGS. 7A to 7C .  FIGS. 5A to 5B and 7A to 7B  show the initial portion of the outward stroke, during which the sensor carrier  260  is carried outwardly by the extendible tether  204  due to the interference fit.  FIGS. 5A and 7A  show the extendible tether  204  in the retracted (unstretched) configuration, with the magnet  228  disposed inwardly of the reed switch  226 , relative to the belt  202 .  FIGS. 5B and 7B  show the extendible tether  204  moving between the retracted configuration and the extended (stretched) configuration, with the magnet  228  moving across the reed switch  226  to activate the reed switch  226 .  FIGS. 5C and 7C  show completion of the initial portion of the outward stroke, with the magnet  228  disposed outwardly of the reed switch  226 , relative to the belt  202 . At completion of the initial portion of the outward stroke, the outer diameter of the strands of the resistance band will have been reduced to a size that can slide within the tether openings  266 , allowing the extendible tether  204  to continue to move toward the extended configuration during the final portion of the outward stroke even though further outward movement of the sensor carrier  260  is obstructed by the curved distal end  268  of the sensor alignment arm  220 . Conversely, during the initial portion of the return stroke, the strands of the resistance band can slide within the tether openings  266  with little or no movement of the sensor carrier  260 , and during the final portion of the return stroke the strands of the resistance band will engage the tether openings  266  in an interference fit so that the sensor carrier  260  is fixed to and carried by the extendible tethers  204  to return to its original position, as shown in  FIGS. 5A and 7A . Thus, the sensor carrier  260  is trapped between the curved distal end  268  of the sensor alignment arm  220  and the crest  270  of the shroud  230  (or the guide tube  263 ), and reciprocates therebetween as the extendible tether  204  reciprocates between the retracted configuration and the extended configuration. This facilitates movement of the magnet  228  across the reed switch  226  with each stroke even if the strokes are not of precisely the same length each time. 
     Although not shown in  FIGS. 5A to 7C , the reed switches  226  may be coupled by wires to a wireless transmitter which, when a reed switch  226  is activated, transmits wireless signals to an external computing device, or may be coupled directly by wire to a suitable computing device or other suitable types of processing hardware. For example, in one implantation of the second exemplary exercise system  200  the reed switches  226  are coupled to a Bluetooth/Arduino wireless transmitter which conveys the user&#39;s activity to a smartphone executing an application that computes, displays and stores that activity. 
     In the illustrated embodiments, the magnets  128 ,  228  are carried by the extendible tethers  104 ,  204  and the reed switches  126 ,  226  are carried by the sensor alignment arms  120 ,  220 ; this is one preferred configuration because it simplifies connection of the reed switch  126 ,  226  to the wireless transmitter (e.g. wireless transmitter  136 ). However, this configuration may be reversed, with the reed switch carried by the extendible tether and the magnet carried by the sensor alignment arm. Furthermore, while in the illustrated embodiments the sensors associated with each respective sensor alignment arm  120 ,  220  and extendible tether  104 ,  204  each comprise a paired reed switch  126 ,  226  and magnet  128 ,  228 , this is merely one exemplary type of sensor. Any two-element sensor may be used as long as it is adapted to detect movement of the second sensor element past the first sensor element in at least a first longitudinal direction as the extendible tether moves between the extended configuration and the retracted configuration. For example, in some alternative embodiments an optical sensor comprising an optical detector such as a CMOS or CCD camera and a visible detection element such as a specialized marking may be used. Other alternative embodiments may employ magnetic switches, mini magnetic switches, reed relays, micro switches, conventional switches, proximity switches, electronic relays, momentary contact actuators, or limit switches. 
     For example, in one embodiment employing a physical switching arrangement, each sensor alignment arm may include a guide slot, and a guide pin may be secured to the extendible tether, with the guide pin sliding along the guide slot as the extendible tether moves between the extended configuration and the retracted configuration. A physical switch can be positioned so that the guide pin will actuate the switch as the guide pin slides along the guide slot. Thus, in this alternate embodiment, the physical switches are the first sensor elements and the guide pins are the second sensor elements. In such an embodiment, the physical switch may be, for example, a Z15G1744 micro switch. Because the guide pin will slide along the guide slot as the extendible tether moves between the extended configuration and the retracted configuration, the extendible tether will be longitudinally movable relative to the sensor alignment arm through the guide aperture. When the extendible tether moves angularly, it will pull the guide pin into engagement with the longitudinal edge of the guide slot so as to move the sensor alignment arm and maintain longitudinal alignment between the sensor alignment arm and the extendible tether. This will in turn maintain longitudinal alignment between the switch (first sensor element) carried by the sensor alignment arm and the guide pin (second sensor element) carried by the extendible tether. 
     In the illustrated embodiments, the belts  102 ,  202  are also provided with anchor points in the form of rigid hooks  150 ,  250  secured to the belts  102 ,  202  for receiving additional resistance bands. As shown in  FIGS. 1A and 1B , additional resistance bands  152  may be coupled to the grip elements, such as the gloves  114 A,  114 B and extend between the grip elements and the hooks  150  to supplement the resistance provided by the extendible tethers  104 . As also shown in  FIGS. 1A and 1B , additional resistance bands  154  may extend from the hooks  150  to separate, discrete grip elements  156 , for example to provide for leg exercises. Other types of anchor points may be used instead of hooks, for example loops or carabiners. Each hook  150 ,  250  is rotatable so that its orientation is adjustable to accommodate the additional resistance bands (e.g. resistance bands  152 ,  154 ). 
     In the exemplary embodiments, the anchor takes the form of a belt  102 ,  202 ; this is merely one exemplary type of anchor. In other embodiments, the anchor may be, for example, a chest strap, a vest, or a wall anchor, chair anchor or door anchor. Similarly, while resistance bands have been used to provide the extendible tethers  104 ,  204  in the exemplary embodiments, in other embodiments other types of extendible tethers may be used. For example, the extendible tether may be a retractable cable on a resistance flywheel, in which case the extended configuration is one in which the cable is extended from the flywheel and the retracted configuration is one in which the cable is wound about the flywheel. 
     Moreover, while the exemplary embodiments described herein have included two extendible tethers  104 ,  204  with respective associated sensors  124 ,  224 , it is contemplated that in other embodiments there may be only a single extensible tether and associated sensor, or more than two extendible tethers with respective associated sensors. For example, alternate embodiments may include four extendible tethers with respective associated sensors, with two extendible tethers being for the arms and two being for the legs. 
     Moreover, an exercise system according to an aspect of the present disclosure may incorporate additional sensors, which may also be coupled to an external computing device. For example, a heart rate monitor may be coupled to an external computing device, or additional sensors such as accelerometers may be placed in or on the alignment arms and/or grip elements and coupled to an external computing device. Exercise systems according to aspects of the present disclosure can accommodate one or more sensors and/or a combination of sensor types such as but not limited to accelerometers, gyroscopes, and position sensors to measure expenditure of energy in calories and distinguish between types of movement and activity, for example to distinguish among various motions and strikes, including punches such as upper cuts, crosses, hooks, and kicks such as round house, side kick, front kick, and exercises such as presses, lateral raises, curls and so forth. 
     Thus, several embodiments have been described by way of example. It will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the claims.