Abstract:
An activity monitor such as a wrist-worn device has an accelerometer which continuously detects motion of the user. The activity monitor also has an on-demand heart rate monitor which is activated by the user touching it from time to time. A calorie expenditure based on the motion of the user can be modified based on a heart rate measurement. Further, a determination can be made as to whether the user has made repetitive motions for a period of time. If the repetitive motions are detected, a calorie expenditure based on the heart rate is determined and compared to the calorie expenditure based on the user motion, and the higher value prevails. A situation is avoided in which the activity monitor underestimates the calories expended, such as when the user is exercising strenuously but the accelerometer indicates relatively little motion, e.g., during strength training.

Description:
BACKGROUND 
       [0001]    Activity monitors have become popular as a tool for promoting exercise and a healthy lifestyle. An activity monitor can include an accelerometer which can measure motions such as steps taken while walking or running, and estimate an amount of calories used. Moreover, user-specific information such as age, gender, height and weight can be used to tailor the estimate to the user. Such monitors can be worn on the wrist, belt or arm, for instance, or carried in the pocket. The monitor can be worn during an intended workout period or as a general, all day, free living monitor, where the user may perform specific exercises at some times while going about their daily activities at other times, e.g., including sitting, standing and sleeping. 
         [0002]    An activity monitor can include a heart rate monitor. Heart rate monitors are also used to monitor individuals, typically during an exercise session in which the user tries to maintain a target heart rate. Some ECG-based monitors are worn on a chest strap, where the electrodes of the monitor are constantly in contact with the body and can therefore continuously determine heart rate. Heart rate data can be transmitted from the chest strap to a display such as on a wrist worn device for easy viewing by the user. Other monitors are wrist-worn, for example, and only determine the heart rate on demand, when the user touches electrodes on the monitor or provides another manual control input. The electrodes can be buttons on part of the watch case, for instance. In one approach, an additional ECG electrode contacts the user on the back of the watch. Other monitors use electrodes attached to gloves, on armbands or on small devices the user touches. 
       SUMMARY 
       [0003]    As described herein, an activity monitor is provided for detecting an amount of energy, e.g., calories, burned by a user over a period of time. The activity monitor includes an accelerometer and an on-demand heart rate monitor. A calorie expenditure is computed based on the motion of the user as determined by the accelerometer, and this calorie expenditure can be modified from time to time when the on-demand heart rate monitor is activated. The monitor can increase the calorie expenditure when the heart rate monitor indicates the user is exercising strenuously but the accelerometer indicates relatively little motion by the user such as during strength training exercises. A situation is avoided in which the activity monitor underestimates the calories expended. 
         [0004]    In one approach, an activity monitor includes an accelerometer, an on-demand heart rate monitor and a processor. The accelerometer is adapted to measure activity of a user. The on-demand heart rate monitor is adapted to measure a heart rate of the user in response to the user touching the heart rate monitor. The processor is in communication with the accelerometer and the on-demand heart rate monitor. The processor determines an activity-based energy expenditure based on the activity and a heart rate-based energy expenditure based on the heart rate and provides an output energy expenditure based on a comparison of the heart rate-based energy expenditure with the activity-based energy expenditure. 
         [0005]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    In the drawings, like-numbered elements correspond to one another. 
           [0007]      FIG. 1A  depicts a front view of an example activity monitor. 
           [0008]      FIG. 1B  depicts a rear view of the activity monitor of  FIG. 1A . 
           [0009]      FIG. 1C  depicts an example block diagram of the activity monitor of  FIG. 1A . 
           [0010]      FIG. 2A  depicts example accelerometer readings during vigorous exercise such as running, showing a relatively high amount of activity, where a repetitive pattern is detected. 
           [0011]      FIG. 2B  depicts example accelerometer readings during strength training exercises, showing a relatively low amount of activity, where a repetitive pattern is detected. 
           [0012]      FIG. 2C  depicts example heart rate values  220  corresponding to the high activity of  FIG. 2A , and a plot  221  of example heart rate values corresponding to the low activity of  FIG. 2B . 
           [0013]      FIG. 2D  depicts a plot  230  of example calorie burn rates corresponding to the high activity of  FIG. 2A , and a plot  231  of example calorie burn rates corresponding to the low activity of  FIG. 2B . 
           [0014]      FIG. 2E  depicts a plot  240  of cumulative calories burned based on the high calorie burn rate  230  of  FIG. 2D , and a plot  242  of cumulative calories burned based on the plot  231  of lower calorie burn rate of  FIG. 2D . 
           [0015]      FIG. 2F  depicts example accelerometer readings during strength training exercises, showing little or no activity, where a repetitive pattern is not detected. 
           [0016]      FIG. 2G  depicts example heart rate values  220  corresponding to the high activity of  FIG. 2A , and example heart rate values  261  corresponding to  FIG. 2F . 
           [0017]      FIG. 2H  depicts the plot  230  of example calorie burn rates corresponding to the high activity of  FIG. 2A , and example plots  271  and  273  of calorie burn rates corresponding to  FIG. 2F . 
           [0018]      FIG. 2I  depicts the plot  240  of cumulative calories burned based on the plot  230  of high calorie burn rate of  FIG. 2D , and plots  280  and  282  of cumulative calories burned based on the plots  271  and  273  of calorie burn rates of  FIG. 2H . 
           [0019]      FIG. 3A  depicts a setup process for the activity monitor of  FIG. 1A . 
           [0020]      FIG. 3B  depicts a relationship between activity type and calorie burn rate in accordance with step  304  of  FIG. 3A . 
           [0021]      FIG. 3C  depicts a relationship between calorie burn rate and heart rate in accordance with step  306  of  FIG. 3A . 
           [0022]      FIG. 3D  depicts an operational mode for the activity monitor of  FIG. 1A . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    An activity monitor is provided for detecting an amount of energy, e.g., calories, burned by a user over a period of time. 
         [0024]      FIG. 1A  depicts a front view of an example activity monitor. The activity monitor  100  can be a wristwatch type device comprising a watch face and a strap for wearing around the wrist in this example, but other implementations are possible. For example, such monitors can be worn on the belt, head, chest, arm or carried in the pocket. A monitor could also include multiple components which are attached to different parts of the body. For example, the different components can include accelerometers which are attached to different parts of the body, e.g., the arm and leg, to gain a more complete understanding of the user&#39;s activity. The activity monitor  100  includes a case  101 , a crown  104 , a mode select button  105  and electrodes  102  and  103 . A display device  109  includes a region  106  which depicts a heart rate (HR) (e.g., 110 beats per minutes or bpm), a region  107  which depicts an amount of calories (e.g., 400 calories) consumed in a monitoring session, and a region  108  which depicts a time of day (e.g., 1:25:00 pm). The mode select button  105  may allow the user to activate different operational modes and to input user-specific information such as age, gender, height, weight or body mass index. 
         [0025]    The activity monitor can include an on-demand heart rate monitor which determines the heart rate only in response to a specific manual user action. For example, an ECG-based monitor can be provided in which the heart rate is determined when the user touches the electrodes  102  and  103 . An additional electrode  110  on the back of the activity monitor also contacts the user&#39;s skin to complete the ECG circuit as depicted in  FIG. 1B . As another example, ultrasonic based monitors determine the heart rate when the user activates a button. Optical sensors can also be used to determine heart rate. These types of monitors are popular since they do not require an electrode-carrying chest strap. They allow the user to check his heart rate from time to time rather than continuously. 
         [0026]      FIG. 1C  depicts an example block diagram of the activity monitor of  FIG. 1A . In this example, the circuitry  120  includes a processor  121 , a memory  122 , a display  123 , electrodes  124 , user controls  125 , a heart rate monitor  126  and an accelerometer  127 , such as a three-axis accelerometer. The processor and memory  122  can be part of a micro-processor controller. The diagram is meant to provide a high level understanding of the activity monitor. Specific implementations can take many forms. For example, heart rate signals can be subject to analog signal processing, analog to digital conversion, time domain processing, conversion to the frequency domain such using a Fast Fourier Transform and frequency domain processing. Accelerometer signals can be similarly processed. 
         [0027]    The processor may be in communication with each of the other components and transmit signals to them and/or receive signals from them. The memory can store code which is executed by the processor to perform the functionality described herein. The memory is an example of a computer-readable storage apparatus having computer-readable software embodied thereon for programming a processor to perform a method. For example, non-volatile memory can be used. Volatile memory such as a working memory of the processor can also be used. The display  123  can represent circuitry used to provide the display device  109  of  FIG. 1A , for instance. The electrodes  124  can represent circuitry used to provide the electrodes  102  and  103  of  FIG. 1A , for instance. The heart rate monitor determines an instantaneous heart rate of a user who is touching the electrodes. The accelerometer takes acceleration readings at a prescribed rate such as multiple times per second. 
         [0028]      FIG. 2A  depicts example accelerometer readings during vigorous exercise such as running, showing a relatively high amount of activity, where a repetitive pattern is detected. An accelerometer has the ability to measure acceleration in one, two or three directions, such as along the x, y and z axes of a Cartesian coordinate system. The magnitude of acceleration can be determined as well. In some cases, the acceleration is not recorded unless it exceeds threshold. A movement of a user is represented by acceleration readings, e.g., along the x, y and z axes. In one approach, each movement results in an activity count. Generally, the level of activity of a user over time can be determined based on the acceleration readings. For example, amplitude, frequency and zero-crossings of the acceleration can be used to determine a level of activity. Higher amplitudes, frequencies and zero-crossings are associated with a higher activity level. 
         [0029]    In the example provided, time extends on the horizontal axis and amplitude is on the vertical axis. The amplitude could represent a component (Ax, Ay, Az) along one of the x, y and z axes of an amplitude vector, or the amplitude could represent the magnitude of an amplitude vector, e.g., the square root of Ax̂2+Aŷ2+Aẑ3. The amplitude extends generally between A 4  and A 3 . Acceleration readings  201  and  205  indicate small movements. Subsequent acceleration readings such as  202  and  204 , with a zero crossing  203  between them, indicate larger, relatively high frequency movements. For example, the user may be running. The larger, relatively high frequency movements extend from t 1   a  to t 9 . 
         [0030]    In some cases, the type of exercise that a user is performing can be detected based on characteristics of the accelerometer readings. For example, a training process may be performed in which the user performs specified exercises and the resulting accelerometer readings are recorded. Accelerometer readings from a subsequent exercise period can be compared to the recorded accelerometer readings (signatures) to identify the exercise being performed, as well as a pace of the exercise based on the frequency of movement. For example, it may be determined that a user is running at 3 miles per hour. The type of exercise which is performed and the pace of the exercise can further be correlated with a rate of calories burned by the user based on scientific studies which have been published. The rate of calories burned can be tailored to a particular user based on factors such as age, gender, height and weight. This information can all be encompassed within control logic of the processor  121  using appropriate formulas and tables. 
         [0031]    A time point t 10  is an example time at which a user obtains a heart rate. In an example scenario, the user obtains a heart rate shortly after completing an intense exercise session. 
         [0032]      FIG. 2B  depicts example accelerometer readings during strength training exercises, showing a relatively low amount of activity, where a repetitive pattern is detected. The amplitude and time scales are the same as in  FIG. 2A . The amplitude extends generally between A 1  and A 2 . Acceleration readings  211  and  215  indicate small movements. Subsequent acceleration readings such as  212  and  214 , with a zero crossing  213  between them, indicate low-moderate amplitude and frequency movements which extend from t 1   a  to t 9 . The acceleration peaks are at t 1 -t 8 . A period of repetitive activity TPrp extends from t 1   a -t 9 . Remaining periods in which repetitive activity is not detected include TP 1  (t 0 -t 1   a ) and TP 2  (t 9 -t 10 ). 
         [0033]    This acceleration profile may occur when the user is performing strength training. For example, strength training can involve lifting weights or performing calisthenics such as as pushups or chin ups. These types of exercises can result in relatively low acceleration readings since the activity monitor may move very little or not at all. For example, a wrist worn activity monitor would not move very much during pushups or chin ups. However, the user is performing strenuous exercise using the large muscles of the body, so the heart rate will increase significantly. A calorie measuring technique which relied only on the acceleration readings would significantly underestimate the calorie consumption, leading to incorrect information for the user. 
         [0034]      FIG. 2C  depicts a plot  220  of example heart rate values corresponding to the high activity of  FIG. 2A , and a plot  221  of example heart rate values corresponding to the low activity of  FIG. 2B . These plots are not known by the activity monitor, in one approach, but are provided for understanding. As mentioned, some form of repetitive activity is detected in a time period of t 1   a -t 9 . Plot  221  represents a heart rate which yields the same calorie consumption as determines based on the activity. In this case, the heart rate is initially at HR 1  then peaks at HR 2 . Plot  220  represents an actual heart rate of the user. The user obtains a heart rate reading of HR 3  (e.g., 110 bpm) at t 10 . In this case, the heart rate is initially at HR 1  then peaks at HR 4 . The heart rate decreases gradually when the strenuous exercise stops at t 9  and reaches HR 3  at t 10 . The rate of decrease in the heart rate for an individual user after the user stops an activity can be determined. Thus, knowing that the heart rate is HR 3  at t 10 , and knowing that the activity stopped at t 9 , the amount of decay D in the heart rate can be determined. From, HR 4  can be determined from HR 3 +D. 
         [0035]      FIG. 2D  depicts a plot  230  of example calorie burn rates corresponding to the high activity of  FIG. 2A , and a plot  231  of example calorie burn rates corresponding to the low activity of  FIG. 2B . The calorie burn rate can be a function of time. The plot  231  may be recorded by the activity monitor while the plot  230  is not known to the activity monitor, in one approach, but is provided for understanding. 
         [0036]    Plot  230  indicates that a burn rate of BR 1  applies from t 0 -t 1   a , a burn rate of BR 4  applies from t 2   a -t 9 , and a burn rate of BR 3  applies at t 10 . For example, the data of  FIG. 3C  can be referenced to determine that BR 3  correlates with HR 3 , the heart rate reading. A burn rate based on the measured heart rate BR(HR) is set to BR 3 . A burn rate based on the activity BR(A) is BR 1  from t 0 -t 1   a , increases to BR 2  from t 1   a -t 2   a,  is at BR 2  from t 2   a -t 9 , decreases to BR 1  after t 9  and is at BR 1  until t 10 . Line  232  represents BR(HR). The heavy lines indicate the burn rate which is used to determine calories consumption. Essentially, BR(HR) is substituted for BR(A) during TPrp and BR(A) is used at other times (e.g., TP 1  and TP 2 ), in one approach. It is assumed that BR(HR) provides a more accurate representation of the burn rate than BR(A) during the period of repetitive activity.  FIG. 2E  depicts a plot  240  of cumulative calories burned based on the plot  230  of high calorie burn rate of  FIG. 2D , and a plot  242  of cumulative calories burned based on the plot  231  of lower calorie burn rate of  FIG. 2D . The cumulative calories burned is obtained by integrating the burn rate over time. CMP(HR) represents the calories burned based on the heart rate measurement at t 10 . Specifically, assuming BR 3  applies over the time period t 10 -t 0 , the cumulative calories burned at t 10  is BR 3 ×(t 10 -t 0 )=CMP 7 . CMP(A) represents the calories burned based on the activity level. It starts at 0, reaches a value CMP 1  at t 1   a , reaches a value CMP 3  at t 9  and reaches a value CMP 4  at t 10 . In this example, CMP(HR)&gt;CMP(A) (e.g., CMP 7 &gt;CMP 4 ) at t 10 . A heavy line  241  represents a cumulative calories burned which is obtained by applying the burn rate BR(HR) in place of the burn rate BR(A) during TPrp. As can be seen, the slope of the plot  241  matches that of the plot  240  during TPrp. In contrast, the slope of the plot  242  is lower than that of the plot  240  during TP 1  and TP 2 . After TPrp, in TP 2 , the slope of the plot  241  matches that of the plot  242 . CMP 6  is the cumulative amount of calories burned (e.g., 400 calories) which is output to the user. Essentially, CMP(A) receives a boost based on the heart rate to provide a more realistic result. If the heart rate was not considered, a lower CMP of CMP 4  would be output instead. 
         [0037]    A line  243  provides another example of CMP(HR), where CMP(HR)&lt;CMP(A) (e.g., CMP 7   a &lt;CMP 4 ) at t 10 . For example, if the user has performed a repetitive activity which is not very strenuous, such as waving the arms back and forth, the heart rate reading will be relatively low, resulting in a lower burn rate and cumulative calories burned. Also, if the user performs a strenuous repetitive activity but waits a relatively long time to take the heart rate reading, it will be relatively low. 
         [0038]      FIG. 2F  depicts example accelerometer readings during strength training exercises, showing little or no activity, where a repetitive pattern is not detected. In this example, accelerometer readings  250 - 253  indicate little or no activity. However, the user may still be exercising strenuously. For example, little or no activity may be sensed by the accelerometer during various strength training exercises or during other exercise, e.g., riding a stationary bicycle, in which the activity monitor is essentially not moving. When the heart rate is measured at t 10  and is relatively high, it can be concluded that the user has in fact been exercising vigorously, so that the calorie expenditure which is determined by the accelerometer readings alone would underestimate the calorie expenditure. However, the specific period of the vigorous exercise may not be known since the period of exercise may not be detectable within a longer monitoring period. In this situation, a reasonable compromise is to assume that a calorie burn rate based on the heart rate applies over a predetermined period (TP) immediately before the heart rate measurement at t 10 . As an example, ten minutes can be used. Another approach is for the activity monitor to prompt the user with a message such as: Your heart rate is 100 bpm. How long have you been exercising? The user can then enter a time period, e.g., 20 minutes, and a calorie burn rate based on the heart rate is applied over the entered time period. 
         [0039]      FIG. 2G  depicts a plot  220  of example the heart rate values corresponding to the high activity of  FIG. 2A , and a plot  261  of example heart rate values corresponding to  FIG. 2F . Here, the activity measurements indicate essentially no activity, corresponding to a fixed heart rate at HR 1  (plot  261 ). Plot  220  is the same as discussed previously, as an assumption. As before, these plots are not known by the activity monitor, in one approach, but are provided for understanding. 
         [0040]      FIG. 2H  depicts the plot  230  of example calorie burn rates corresponding to the high activity of  FIG. 2A , and example plots  271  and  273  of calorie burn rates corresponding to  FIG. 2F . Plot  230  is the same as discussed previously. The heavy lines indicate the applicable burn rate. Plot  271  represents a burn rate BR(A)=BR 1  which applies during TP 3 , a remainder of the monitoring period. Line  272  represents a burn rate BR(HR)=BR 3  which applies during TP 4 . 
         [0041]      FIG. 2I  depicts the plot  240  of cumulative calories burned based on the plot  230  of high calorie burn rate of  FIG. 2D , and plots  280  and  282  of cumulative calories burned based on the plots  271  and  273  of calorie burn rates of  FIG. 2H . Plot  240  is the same as discussed previously. CMP(HR) represents the calories burned based on the heart rate measurement at t 10 . CMP(A) represents the calories burned based on the activity level. It starts at 0, reaches a value CMP 1  at t 1   a , reaches a value CMP 2   a  at t 9   a  and reaches a value CMP 3   a  at t 10 . The slope is fixed. A heavy line  241  represents a cumulative calories burned which is obtained by applying the burn rate BR(HR) in place of the burn rate BR(A) during TP 4 . The burn rate BR(A) applies during TP 3 . 
         [0042]    As can be seen, the slope of the plot  281  matches that of the plot  240  during TPrp. In contrast, the slope of the line  280  is lower than that of the plot  240  during TP 3  and is based on the burn rate of plot  272 . CMP 4   a  is the cumulative amount of calories burned which is output to the user. Essentially, CMP(A) receives a boost to provide a more realistic result. If the heart rate was not considered, a lower CMP of CMP 3   a  would be output instead. 
         [0043]      FIG. 3A  depicts a setup process for the activity monitor of  FIG. 1A . At step  300 , the setup process begins. For example, the user may use the mode select button  105  to enter information such as by scrolling through menus. At step  302 , the user enters personal information (e.g., age, gender, height and weight). In another approach, the activity monitor can communicate with a host computing device which provides a user interface. At step  304 , the processor selects a function to relate calorie burn rate to activity for user. For example, see  FIG. 3B  which depicts a relationship between activity type and calorie burn rate. In a simplified example, different activities, e.g., Activity  1  or  2 , and different intensities, e.g.,  1 ,  2  and  3  can be associated with calorie burn rates (CBR). Calorie burn rates can be provided for repetitive activities such as certain exercises and non-repetitive activities such as sleeping and sitting. At step  306 , the processor selects a function to relate calorie burn rate to heart rate for user. For example, see  FIG. 3C  which depicts a relationship between calorie burn rate and heart rate. For instance, the heart rate HR 3  discussed previously corresponds to a burn rate BR 3 . 
         [0044]      FIG. 3D  depicts an operational mode for the activity monitor of  FIG. 1A . A monitoring session can be a relatively long period such as hours or days in which data is gathered. A monitoring period can be a shorter period which is a time between heart rate measurements. A monitoring session can have multiple monitoring periods. For example, a user may choose to obtain a heart rate reading every few minutes during an exercise session and less frequently during other activates. The steps include: start a monitoring session,  310 ; set CMS, calories burned in a monitoring session=0,  312 ; start a monitoring period in the monitoring session,  314 ; set CMP, calories burned in a monitoring period=0,  316 ; accelerometer obtains readings,  318 ; process accelerometer readings to detect activity,  320 ; and determine BR(A), calorie burn rate based on activity,  322 . 
         [0045]    Decision step  324  determines if a heart rate reading has been requested by the user. If decision step  324  is false, step  318  is repeated. If decision step  324  is true, additional steps include: determine and output heart rate HR,  326 ; determine CMP(A), amount of calories burned in monitoring period based on activity (activity-based energy expenditure),  328 ; determine BR(HR), calorie burn rate based on HR,  330 ; and determine CMP(HR), amount of calories burned in monitoring period based on HR (activity-based energy expenditure),  332 . 
         [0046]    Decision step  334  determines if CMP(HR)&gt;CMP(A). If decision step  334  is false, step  336  sets CMP=CMP(A). If decision step  334  is true, step  338  processes the accelerometer readings to determine if there is a repetitive pattern. 
         [0047]    Decision step  340  determines if there is a repetitive pattern. If decision step  340  is false, step  346  sets CMP based on BR(HR) for a predetermined time period (TP 4 ), and based on BR(A) for a remainder (TP 3 ) of the monitoring period. If decision step  340  is true, step  342  determines a time period TPrp of the repetitive pattern (t 1   a -t 9 ), a time period TP 2  between the end of pattern (t 9 ) and a time of the HR measurement (t 10 ) and time period TP 1  between the start of the monitoring period (t 0 ) and the start of pattern (t 1   a ). Step  344  sets CMP based on BR(HR) during TPrp, and based on BR(A) during TP 1  and TP 2 . Step  346  is then reached as discussed. Step  348  sets and outputs, e.g., via the display, CMS=CMS+CMP. The is the amount of calories burned in the monitoring session. For example, a cumulative total of calories burned can be provided over the course of hours or days. In one approach, the cumulative total of calories can be repeatedly updated, e.g., once every few seconds. When a heart rate reading is taken and this results in a boost to the cumulative total, the cumulative total can be updated in a step increase, e.g., from 400 to 450 calories. The activity monitor could provide a message or other notification to the user to inform him that the cumulative total has been boosted. This notification could continue for several minutes, for example. A record of such notifications could also be recalled by the user. 
         [0048]    Decision step  350  determines if there is a next monitoring period. Typically, this is true unless the user enters a command to end the monitoring session at step  352 . Step  314  follows if decision step  350  is true. 
         [0049]    Generally, data regarding calorie expenditures can be viewed on the display and/or uploaded to an online service for viewing and further analysis. Energy expenditure can be expressed in terms of calories, Joules or other measure. Energy expenditure can represent a burn rate and/or cumulative amount of calories. 
         [0050]    The foregoing detailed description of the technology herein has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the technology to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The described embodiments were chosen to best explain the principles of the technology and its practical application to thereby enable others skilled in the art to best utilize the technology in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the technology be defined by the claims appended hereto.