Patent Publication Number: US-2023148908-A1

Title: Action state estimation apparatus, action state estimation method, action state learning apparatus, and action state learning method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT Application No. PCT/JP2021/027254, filed Jul. 21, 2021, which claims priority to Japanese Patent Application No. 2020-129387, filed Jul. 30, 2020, and Japanese Patent Application No. 2020-129388, filed Jul. 30, 2020, the entire contents of each of which are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a system and method for estimating an action state including a loaded state of a muscle from a detection result of a tremor and a system and method (e.g., an action state learning technology) of generating an action state model for such an estimation technology. 
     BACKGROUND 
     Japanese Patent Application Publication No. 2011-182824 (hereinafter “Patent Literature 1”) discloses an action state estimation apparatus that converts a measurement signal of a displacement detection sensor into a frequency component. The action state estimation apparatus disclosed in Patent Literature 1 estimates an action state from a component of a predetermined frequency band. 
     However, conventional apparatus and method that are shown in Patent Literature 1 need to convert a measurement signal of a sensor into a frequency component. Therefore, a processing load to generate the estimation signal increases. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to provide an action state estimation system and method that significantly reduces a processing load while achieving a desired estimation accuracy. 
     In an exemplary aspect, an action state estimation apparatus is provided that includes a first sampling portion, a first statistic calculation portion, an action state model storage, and an estimation calculation portion. The first sampling portion samples a displacement measurement signal of a test subject within a predetermined time and generates displacement measurement data. Moreover, the first statistic calculation portion calculates a first statistic of the displacement measurement data. The action state model storage stores an action state model modeled by associating the first statistic with a loaded state of a desired muscle. The estimation calculation portion estimates the loaded state by setting the first statistic as an input vector and using the action state model. 
     In this configuration, the loaded state is estimated by directly using the displacement measurement data. As a result, the processing load is significantly reduced while the desired estimation accuracy is achieved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a functional block diagram of an action state estimation apparatus according to a first exemplary embodiment. 
         FIG.  2    is a table showing an example of a setting of a level of importance according to the first exemplary embodiment. 
         FIG.  3    is a flow chart showing a main process of an action state estimation method according to the first exemplary embodiment. 
         FIG.  4    is a functional block diagram of an action state learning apparatus according to the first exemplary embodiment. 
         FIG.  5    is a flow chart showing a main process of an action state learning method according to the first exemplary embodiment. 
         FIG.  6 A  shows an example of time variation of signal strength,  FIG.  6 B  shows signal strength distribution, and  FIG.  6 C  shows strength block data. 
         FIG.  7    is a table showing an example of a setting of a level of importance according to a second exemplary embodiment. 
         FIG.  8 A  shows an example of time variation of signal strength,  FIG.  8 B  shows strength block data (an average value), and  FIG.  8 C  is a view showing strength block data (an integrated value). 
         FIG.  9    is a functional block diagram of an action state estimation apparatus according to a third exemplary embodiment. 
         FIG.  10 A  and  FIG.  10 B  are tables showing an example of a setting of a level of importance according to the third exemplary embodiment. 
         FIG.  11    is a flow chart showing a main process of an action state estimation method according to the third exemplary embodiment. 
         FIG.  12    is a functional block diagram of an action state learning apparatus according to the third exemplary embodiment. 
         FIG.  13    is a flow chart showing a main process of an action state learning method according to the third exemplary embodiment. 
         FIG.  14 A  and  FIG.  14 B  are tables showing an example of a setting of a level of importance according to a fourth exemplary embodiment. 
         FIG.  15    is a flow chart showing a main process of an action state learning method according to a fifth exemplary embodiment. 
         FIG.  16    shows a concept of synchronization. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     (First Exemplary Embodiment) 
     An action state estimation technology and an action state model generation technology according to a first exemplary embodiment will be described with reference to the drawings. 
     (Configuration and Processing of Action State Estimation Apparatus) 
       FIG.  1    is a functional block diagram of an action state estimation apparatus according to the first exemplary embodiment. As shown in  FIG.  1   , the action state estimation apparatus  10  includes a sampling portion  11 , a statistic calculation portion  12 , an estimation calculation portion  14 , and an action state model storage  13 . Each functional portion configuring the action state estimation apparatus  10  can be implemented as an electronic circuit, an IC, a storage medium storing a program that, when executed by a calculation processing device, is configured to perform a function of each function portion, where the calculation processing device (e.g., a CPU) is configured to execute the program. 
     In operation, the sampling portion  11  receives an input of a displacement measurement signal from a displacement detection sensor  101 . The sampling portion  11  generates displacement measurement data by sampling the displacement measurement signal by a predetermined sampling frequency (100 Hz, for example). In other words, the sampling portion  11  generates the displacement measurement data without converting the displacement measurement signal into a frequency component. Moreover, the sampling portion  11  outputs the displacement measurement data to the statistic calculation portion  12 . 
     It is noted that the displacement detection sensor  101  can be implemented as a piezoelectric sensor, an acceleration sensor, or the like. The displacement detection sensor  101  does not need to be disposed at a position of a muscle of which the loaded state is estimated, and may be disposed at a position at which a tremor to be produced by the muscle to be estimated is able to be measured. In addition, the displacement detection sensor  101  may be one sensor disposed at one location or can be two or more sensors disposed at two or more locations. The displacement detection sensor  101  generates and outputs a displacement measurement signal. The displacement measurement signal is a signal obtained by converting displacement on a skin surface due to tremor and deformation into the voltage. 
     For purposes of this disclosure, the tremor can be considered an involuntary movement that shows rhythmical muscle activity, for example. In other words, the tremor is fine and fast postural tremor seen in normal people, is called a physiological tremor, and is a frequency from 8 Hz to 12 Hz, for example. It is noted that shaking seen in an ill individual, such as a Parkinson&#39;s patient, is a pathologic tremor, is a frequency from 4 Hz to 7 Hz, for example, and is not considered as an object of the tremor in the present invention. The use of a tremor provides the following various types of advantages over myoelectric potential. For example, detection (measurement) of a tremor can be performed without a direct attachment to a surface (e.g., a skin or the like) of a body, such as a human body, to be detected. The detection of a tremor can also detect muscle contraction and expansion. The detection of a tremor can further detect a variation associated with muscle fatigue. 
     The statistic calculation portion  12  calculates a statistic from the displacement measurement data. In particular, the statistic calculation portion  12  calculates statistics from a plurality of displacement measurement data within a predetermined period (for 1 second, for example). 
     Types of statistics include, for example, an average value, a maximum value, a minimum value, a median value, a 1% value, a 5% value, a 25% value, a 75% value, a 95% value, a 99% value, a variance value, a skewness value, a kurtosis value, and an integrated value. It is noted that the types of statistics are not limited to these examples, and may be others as long as a value is obtained from time-series displacement measurement data. The statistic calculation portion  12  calculates a plurality of types of statistics out of these values. It is also noted that an x % value refers to a value located at x % counted in ascending order from the minimum value, among the plurality of displacement measurement data within a period. 
     The statistic calculation portion  12  then outputs the plurality of types of statistics that have been calculated, to the estimation calculation portion  14 . 
     The action state model storage  13  stores an action state model. The action state model includes a relationship between various types of statistics of displacement measurement data and a loaded state of a muscle to be estimated. In an exemplary aspect, the action state model can previously generated by an action state learning apparatus  20  to be described below, for example, and is stored in the action state model storage  13 . 
     The estimation calculation portion  14  estimates the loaded state of a muscle to be estimated by using the action state model stored in the action state model storage  13  and setting a plurality of statistics as an input vector. In such a case, the estimation calculation portion  14  sets a level of importance of the statistics used for estimation, according to the muscle to be estimated. This level of importance is set to the action state model, for example. 
       FIG.  2    is a table showing an example of a setting of a level of importance according to the first exemplary embodiment. A muscle M1, a muscle M2, a muscle M3, and a muscle M4 show a type of muscle of which the loaded state is able to be estimated by measured displacement. For example, in a case in which the displacement detection sensor 101 is disposed at a place at which tendons of an ankle are gathered, more specifically, in front of the ankle and in back of the ankle, the muscle M1, the muscle M2, the muscle M3, and the muscle M4 are able to set a soleus muscle, a gastrocnemius muscle, a tibialis anterior muscle, a quadriceps femoris muscle, a hamstring muscle, or the like. In addition, each of the statistics A1 to A15 is set to any of the above various types of statistics (e.g., the average value, the maximum value, the minimum value, the median value, the 1% value, the 5% value, the 25% value, the 75% value, the 95% value, the 99% value, the variance value, the skewness value, the kurtosis value, the integrated value, or the like). 
     For example, in the case of  FIG.  2   , with respect to the muscle M1, the level of importance to the estimation is set to an order of the statistic A1, the statistic A2, the statistic A8, the statistic A12, and the statistic A7 in order of the first place, the second place, the third place, the fourth place, and the fifth place. In addition, with respect to the muscle M2, the level of importance to the estimation is set to the order of the statistic A3, the statistic A5, the statistic A2, the statistic A14, and the statistic A15 in order of the first place, the second place, the third place, the fourth place, and the fifth place. Hereinafter, with respect to the muscle M3 and the muscle M4 as well, as shown in  FIG.  2   , the level of importance is set to the statistic. 
     The estimation calculation portion  14 , when setting the muscle to be estimated, is configured to estimate a loaded state (e.g., a muscle potential value) of the muscle from the plurality of statistics, by using the level of importance that is set according to the muscle. It is noted that the loaded state of the muscle is not limited to the muscle potential value and may be any other data that is expressed as a value. 
     More specifically, for example, the estimation calculation portion  14  calculates an estimation result of the loaded state for each statistic that is estimated from each of the statistics ranked from the first place to the fifth place in the level of importance and the action state model. Then, the estimation calculation portion  14  weights each estimation result according to the level of importance, and calculates an estimation result of a final loaded state by performing addition averaging or the like, for example. It is also noted that the number of statistics the estimation calculation portion  14  uses for estimation is not limited to this example. For example, estimation calculation may be performed from the statistics ranked from the first place to the tenth place in the level of importance. 
     The estimation calculation portion  14 , when the number of types of the muscle to be estimated is one, estimates a loaded state by using the statistic and the level of importance according to the muscle. On the other hand, the estimation calculation portion  14 , when the number of types of the muscle to be estimated is two or more, sets a statistic and a level of importance for each muscle and estimates a loaded state with respect to each muscle. 
     With such a configuration, the action state estimation apparatus  10  is configured to estimate the loaded state of a muscle without performing processing to convert measurement data into a frequency component. As a result, the action state estimation apparatus  10  significantly reduces a processing load while achieving a desired estimation accuracy. 
     Furthermore, with such a configuration, the action state estimation apparatus  10 , for each muscle to be estimated, individually sets the type of statistic used for estimation, and the level of importance. As a result, the action state estimation apparatus  10  is able to estimate the loaded state of a muscle with a higher accuracy. 
     In addition, with such a configuration, the action state estimation apparatus  10 , even when the position of the displacement detection sensor  101  is not at a position of a muscle to be estimated, is configured to estimate the loaded state of the muscle. As a result, the action state estimation apparatus  10  is also configured to estimate the loaded state with respect to a muscle that is not appeared on a body surface or a muscle (e.g., a muscle away from a position in which the displacement detection sensor  101  is disposed, as an example) for which the muscle potential is not able to be directly measured. The displacement detection sensor  101  is disposed on an ankle, so that the action state estimation apparatus  10  is able to estimate the loaded state of a quadriceps femoris muscle, a hamstring muscle (a biceps femoris muscle, a semimembranosus muscle, a semitendinosus muscle, an adductor magnus muscle), a tibialis anterior muscle, a gastrocnemius muscle, a soleus muscle, and a gluteus maximus muscle. In addition, the action state estimation apparatus  10  is configured to estimate a linked state of a plurality of muscles. 
     Moreover, an effect due to an error in the position in which the displacement detection sensor  101  is disposed is able to be significantly reduced. Therefore, the disposition of the displacement detection sensor  101  is facilitated, and an operation for estimation of a loaded state is facilitated. 
     In addition, with such a configuration, the loaded state of a plurality of muscles can be estimated, using the displacement measurement signal of the displacement detection sensor  101  in common, so that an action state estimation system including a sensor and the action state estimation apparatus can be reduced in size. 
     Moreover, in such a configuration, the statistic to be used and the level of importance are individually set for each muscle to be estimated. Therefore, the action state estimation apparatus  10  is configured able to estimate the loaded state of a plurality of muscles with a high accuracy by using the displacement measurement signal of the displacement detection sensor  101  in common. 
     In addition, with such a configuration, a loaded state can be estimated not as a class, but as a value. In this manner, a loaded state is estimated with a value, so that the action state estimation apparatus  10  is configured to present and manage a more accurate loaded state, and is configured to provide more appropriate notification or the like, to a test subject. 
     (Action State Estimation Method) 
       FIG.  3    is a flow chart showing a main process of an action state estimation method according to the first exemplary embodiment of the present invention. It is noted that, since the specific content of each processing is described by the above configurations, the following will be schematically described below. 
     The action state estimation apparatus  10  inputs a displacement measurement signal (S 11 ). The action state estimation apparatus  10  executes sampling to the displacement measurement signal, and generates displacement measurement data (S 12 ). The action state estimation apparatus  10  calculates a statistic from the displacement measurement data (S 13 ). 
     The action state estimation apparatus  10  obtains an action state model (S 14 ). The action state estimation apparatus  10  estimates a loaded state by using the action state model and setting the statistic as an input vector (S 15 ). 
     It is also noted that the above processing may be programmed and stored in a storage medium or the like, and may be executed by an arithmetic processing apparatus such as a CPU. 
     (Configuration and Processing of Action State Learning Apparatus) 
     The above action state model is generated, for example, as shown below.  FIG.  4    is a functional block diagram of the action state learning apparatus according to the first exemplary embodiment of the present invention. 
     As shown in  FIG.  4   , the action state learning apparatus  20  includes a sampling portion  11 , a statistic calculation portion  12 , an action state model storage  13 , a sampling portion  21 , a modeling reference value calculation portion  22 , and a learning calculation portion  24 . The sampling portion  11 , the statistic calculation portion  12 , and the action state model storage  13  are as described above, and thus the description will be omitted. 
     In operation, the sampling portion  21  receives an input of a muscle activity measurement signal (e.g., a muscle potential signal, for example) from the muscle activity detection sensor  102 . The sampling portion  21  generates muscle activity measurement data by sampling the muscle activity measurement signal by a predetermined sampling frequency (100 Hz, for example). The sampling portion  21  then outputs the muscle activity measurement data to the modeling reference value calculation portion  22 . 
     It is noted that the muscle activity detection sensor  102  is a sensor configured for measuring muscle activity, for example, is a myoelectric sensor (e.g., an electromyograph). The muscle activity detection sensor  102  is disposed at a position of a muscle of which the loaded state is to be estimated. More specifically, the muscle activity detection sensor  102  is disposed at a position of a muscle that is a source of muscle activity that produces a tremor to be measured by the muscle activity detection sensor  102 . The muscle activity detection sensor  102  detects muscle activity, and generates and outputs a muscle activity measurement signal. In an exemplary aspect, the muscle activity detection sensor  102  can be a single sensor disposed with respect to one type of muscles or can be two or more sensors disposed according to a muscle with respect to a plurality of types of muscles. 
     The modeling reference value calculation portion  22  calculates a modeling reference value from the muscle activity measurement data. For example, the modeling reference value calculation portion  22  calculates an absolute average value of the muscle activity measurement data within a predetermined period as the modeling reference value. The absolute average value refers to an average value of an absolute value of the measurement data. 
     It is noted that the modeling reference value is not limited to the absolute average value and may use a regressionable value such as, for example, an average value, a maximum value, a minimum value, a median value, a 1% value, a 5% value, a 25% value, a 75% value, a 95% value, a 99% value, a variance value, a skewness value, or a kurtosis value. Furthermore, the modeling reference value is able to represent a class of a load, such as large, medium, or small, that is able to be classified from the muscle activity measurement data. 
     The modeling reference value calculation portion  22  outputs the modeling reference value to the learning calculation portion  24 . 
     The learning calculation portion  24  performs learning by using the statistic and the modeling reference value, and generates an action state model. More specifically, for example, the learning calculation portion  24  performs learning by setting the statistic as an explanatory variable and the modeling reference value as an objective variable and using a gradient boosting method that utilizes a decision tree algorithm. The learning calculation portion  24  repeats the learning, and, when obtaining a predetermined inference accuracy, generates an action state model by using such a result. It is noted that a method of learning is not limited to the gradient boosting method, and may also use a method such as boosting represented by a similar AdaBoost method. In addition, other methods of learning may use an SVM, a GMM, an HMM, a neural network, a learning Bayesian network, or the like. Furthermore, by use of a plurality of learning devices as the learning calculation portion  24 , an ensemble method that weights a result of the plurality of learning devices and then performs majority voting may be used. 
     With the configuration and processing, the action state learning apparatus  20  is configured to properly set the action state model. 
     (Method of Generating Action State Model) 
       FIG.  5    is a flow chart showing a main process of an action state learning method according to the first exemplary embodiment of the present invention. It is noted that, since the specific content of each processing is described by the above configurations, the following will be schematically described below. 
     The action state learning apparatus  20  inputs a displacement measurement signal (S 21 ). The action state learning apparatus  20  executes sampling to the displacement measurement signal, and generates displacement measurement data (S 22 ). The action state learning apparatus  20  calculates a statistic from the displacement measurement data (S 23 ). 
     The action state learning apparatus  20  inputs a muscle activity measurement signal (S 31 ). The action state learning apparatus  20  executes sampling to the muscle activity measurement signal, and generates muscle activity measurement data (S 32 ). The action state learning apparatus  20  calculates a modeling reference value from the muscle activity measurement data (S 33 ). 
     The action state learning apparatus  20  executes learning using the statistic and the modeling reference value, and generates an action state model (S 41 ). 
     It is noted that the above processing may be programmed and stored in a storage medium or the like, and may be executed by an arithmetic processing apparatus such as a CPU, as described above. 
     In addition, as seen from the configurations of the action state estimation apparatus  10  and the action state learning apparatus  20  according to the present exemplary embodiment, by use of the configuration according to the present exemplary embodiment, during learning, a highly accurate action state model can be generated although it is necessary to use a relatively large-scale muscle potential measurement means such as an electromyograph, whereas, during actual use (when the action state estimation apparatus  10  is in use), it is unnecessary to use a relatively large-scale muscle potential measurement means such as an electromyograph. In other words, during actual use, with a simple configuration, a loaded state is able to be estimated (measured) with a little burden on a test subject. 
     (Second Exemplary Embodiment) 
     An action state estimation technology and an action state model generation technology according to a second exemplary embodiment will be described with reference to the drawings. The action state estimation technology according to the second exemplary embodiment is different in a method of calculating a statistic from the action state estimation technology shown in the first exemplary embodiment.  FIG.  6 A  shows an example of time variation of signal strength,  FIG.  6 B  shows signal strength distribution, and  FIG.  6 C  shows strength block data. 
     The statistic calculation portion  12  calculates signal strength distribution from displacement measurement data within a predetermined period. The signal strength distribution refers to the displacement measurement data within a predetermined period that are arranged in order of increasing signal strength. For example, the statistic calculation portion  12 , as shown in  FIG.  6 A , when obtaining the signal strength of time t1 to time t100 set by a predetermined sampling period (e.g., a sampling frequency), as shown in  FIG.  6 B , sets a rank R1 to a rank R100 in order of increasing signal strength and arranges ranks in order from the rank R1 to the rank R100. 
     The statistic calculation portion  12  generates strength block data from the signal strength distribution, and outputs the strength block data as a statistic. More specifically, the statistic calculation portion  12  sets a strength block (e.g., a signal strength block) for each predetermined number in order of increasing signal strength against the signal strength distribution. The statistic calculation portion  12  calculates an integrated value for each strength block, and generates the strength block data. For example, in the case of  FIG.  6 C , the statistic calculation portion  12  divides the measurement data into blocks of 10 pieces each. In one example, the statistic calculation portion  12  sets the signal strength from the rank R1 to the rank R10 as a strength block B1, and calculates an integrated value of the signal strength from the rank R1 to the rank R10. The statistic calculation portion  12  performs such processing from the strength block B1 to a strength block B10, and outputs a result as a statistic. 
     The estimation calculation portion  14  then estimates an action state by using the statistic based on the signal strength distribution. In such a case, the estimation calculation portion  14  estimates an action state by using the level of importance. 
       FIG.  7    is a table showing an example of a setting of the level of importance according to the second exemplary embodiment. As shown in  FIG.  7   , in the second exemplary embodiment, the level of importance is set for each muscle, to the strength block of the signal strength distribution. 
     For example, in the case of  FIG.  7   , with respect to the muscle M1, the level of importance to the estimation is set to an order of the strength block B10, the strength block B9, the strength block B6, the strength block B3, and the strength block B5 in order of the first place, the second place, the third place, the fourth place, and the fifth place. In addition, with respect to the muscle M2, the level of importance to the estimation is set to an order of the strength block B10, the strength block B8, the strength block B9, the strength block B7, and the strength block B1 in order of the first place, the second place, the third place, the fourth place, and the fifth place. Hereinafter, with respect to the muscle M3 and the muscle M4 as well, as shown in  FIG.  7   , the level of importance is set to the statistic (e.g., the strength block). 
     The estimation calculation portion  14 , when setting a muscle to be estimated, estimates a loaded state of the muscle from a plurality of statistics (e.g., values of the strength block), by using the level of importance that is set according to the muscle. 
     With this configuration, the action state estimation apparatus according to the second exemplary embodiment, as with the action state estimation apparatus  10  according to the first exemplary embodiment, is configured to estimate a loaded state of the muscle without performing processing to convert the measurement data into a frequency component. As a result, the action state estimation apparatus significantly reduces a processing load while achieving a necessary estimation accuracy. 
     It is noted that, in the above description (see  FIG.  6 A ,  FIG.  6 B , and  FIG.  6 C ), the plurality of measurement data are arranged in order of strength, the plurality of strength blocks are set, and an integrated value is calculated for each of the plurality of strength blocks and used as a statistic. However, in such a case, the integrated value can be replaced with an average value. 
     Furthermore, in an aspect to be described below with reference to  FIG.  8 A ,  FIG.  8 B , and  FIG.  8 C , a plurality of blocks (e.g., time blocks) are set to the plurality of measurement data in a time range, and an average value or an integrated value is calculated for each of the plurality of time blocks and used as a statistic. 
     When using an average value, the statistic calculation portion  12  divides the plurality of measurement data within time for statistic calculation into a time-series block (e.g., a time block), and calculates an average value for each time block. When using an integrated value, the statistic calculation portion  12  divides the plurality of measurement data within time for statistic calculation into a time-series block (e.g., a time block), and calculates an integrated value for each time block. The statistic calculation portion  12  then sets the average value or the integrated value as a value (e.g., a statistic) of the time block. 
       FIG.  8 A  shows an example of time variation of signal strength,  FIG.  8 B  shows time block data (e.g., an average value), and  FIG.  8 C  is a view showing time block data (e.g., an integrated value). 
     For example, when the measurement data as shown in  FIG.  8 A  is obtained, time blocks B1t to B10t arranged over time are set with respect to the signal strength from the time t1 to the time t100. The time block B1t corresponds to time t1 to t10, and the time block B2t corresponds to the time t11 to the time t20. Similarly, the time blocks B3t to B9t are set, and the time block B10t corresponds to the time t91 to the time t100. 
     When using an average value, for the time block B1t, the statistic calculation portion  12  calculates an average value of the signal strength of the time t1 to the time t10, and sets the average value as a statistic of the time block B1t. Similarly, the statistic calculation portion 12 calculates an average value of the time blocks B2t to B9t, and sets the average value as each statistical value. Then, the statistic calculation portion  12 , for the time block B10t, calculates an average value of the signal strength of the time t91 to the time t100, and sets the average value as a statistic of the time block B10t. 
     When using an integrated value, for the time block B1t, the statistic calculation portion  12  calculates an integrated value of the signal strength of the time t1 to the time t10, and sets the integrated value as a statistic of the time block B1t. Similarly, the statistic calculation portion  12  calculates an integrated value of the time blocks B2t to B9t, and sets the integrated value as each statistical value. Then, the statistic calculation portion  12 , for the time block B10t, calculates an integrated value of the signal strength of the time t91 to the time t100, and sets the integrated value as a statistic of the time block B10t. 
     (Third Exemplary Embodiment) 
     An action state estimation technology and an action state model generation technology according to a third exemplary embodiment will be described with reference to the drawings. 
     (Configuration and Processing of Action State Estimation Apparatus) 
       FIG.  9    is a functional block diagram of an action state estimation apparatus according to the third exemplary embodiment. As shown in  FIG.  9   , an action state estimation apparatus  10 A is different from the action state estimation apparatus  10  according to the first exemplary embodiment in that a sampling portion  31 , a statistic calculation portion  32 , an action state model storage  13 A, and an estimation calculation portion  14 A are provided. Other configurations of the action state estimation apparatus  10 A are the same as or similar to the configurations of the action state estimation apparatus  10 , and a description of the same or similar configurations will be omitted. 
     As illustrated, the action state estimation apparatus  10 A includes a sampling portion  11 , a statistic calculation portion  12 , an estimation calculation portion  14 A, an action state model storage  13 A, a sampling portion  31 , and a statistic calculation portion  32 . Each function portion configuring the action state estimation apparatus  10 A can be implemented by an electronic circuit, an IC, a storage medium storing a program to execute a function of each function portion, and a calculation processing device (such as a CPU) that executes the program as similarly described above with respect to the first exemplary embodiment. 
     In operation, the statistic calculation portion  12  calculates the statistic shown in the first exemplary embodiment as a displacement statistic, and outputs the statistic to the estimation calculation portion  14 A. 
     The sampling portion  31  receives an input of a motion measurement signal from a motion detection sensor  300 . The sampling portion  31  generates motion measurement data by sampling the motion measurement signal by a predetermined sampling frequency (100 Hz, for example). In other words, the sampling portion  31  generates the motion measurement data without converting the motion measurement signal into a frequency component. The sampling portion  31  outputs the motion measurement data to the statistic calculation portion  32 . 
     It is noted that the motion detection sensor  300  is used by using an acceleration sensor, an angular velocity sensor, or the like. The motion detection sensor  300  does not need to be disposed at a position of a muscle of which the loaded state is estimated, and may be disposed at a position at which a motion of a test subject to occur by the muscle to be estimated is able to be measured. In addition, the motion detection sensor  300  may be one sensor disposed at one location place or may be two or more sensors disposed at two or more locations. The motion detection sensor  300  is configured to detect the motion of a test subject, and generates and outputs a motion measurement signal. 
     The statistic calculation portion  32  calculates a motion statistic from the motion measurement data arranged in time series. In particular, the statistic calculation portion  32  calculates a motion statistic from a plurality of motion measurement data within a predetermined period (for 1 second, for example). 
     Types of motion statistics include, for example, an average value, a maximum value, a minimum value, a median value, a 1% value, a 5% value, a 25% value, a 75% value, a 95% value, a 99% value, a variance value, a skewness value, a kurtosis value, and an integrated value. It is to be noted that the types of motion statistics are not limited to these examples, and may be others as long as a value is obtained from time-series motion measurement data. The statistic calculation portion  32  calculates a plurality of types of motion statistics out of these values. It is to be noted that an x % value refers to a value that corresponds to the top x % of the maximum value 100% of the plurality of motion measurement data within a period. 
     The statistic calculation portion  32  outputs the plurality of types of motion statistics that have been calculated, to the estimation calculation portion  14 A. 
     The action state model storage  13 A stores an action state model that includes a relationship between various types of displacement statistics and various types of motion statistics, and a loaded state of a muscle to be estimated. The action state model is previously generated by an action state learning apparatus  20 A to be described below, for example, and is stored (e.g., contained) in the action state model storage  13 A in an exemplary aspect. 
     The estimation calculation portion  14 A estimates the loaded state of a muscle to be estimated by using the action state model stored in the action state model storage  13 A and setting a displacement statistic and a motion statistic as an input vector. In such a case, the estimation calculation portion  14 A sets a level of importance of the displacement statistic and a level of importance of the motion statistic that are used for estimation, according to the muscle to be estimated. The levels of importance are set to the action state model, for example. 
       FIG.  10 A  and  FIG.  10 B  are tables showing an example of a setting of the level of importance according to the third exemplary embodiment.  FIG.  10 A  shows the level of importance of the displacement statistic, and  FIG.  10 B  shows the level of importance of the motion statistic. In addition, in  FIG.  10 A  and  FIG.  10 B , a muscle M1, a muscle M2, a muscle M3, and a muscle M4 show a type of muscles of which the loaded state is able to be estimated by measured displacement. For example, in a case in which the displacement detection sensor  101  is disposed at a place at which tendons of an ankle are gathered, more specifically, in front of the ankle and in back of the ankle, the muscle M1, the muscle M2, the muscle M3, and the muscle M4 are able to set a soleus muscle, a gastrocnemius muscle, a tibialis anterior muscle, a quadriceps femoris muscle, a hamstring muscle, or the like. Each of the displacement statistics Ar1 to Ar15 is set to any one of the above various types of displacement statistics, and each of the motion statistics Aa1 to Aa15 is set to any one of the above various types of motion statistics. 
     For example, in the case of  FIG.  10 A , with respect to the muscle M1, the level of importance to the estimation is set to an order of the displacement statistic Ar1, the displacement statistic Ar2, the displacement statistic Ar8, the displacement statistic Ar12, and the displacement statistic Ar7 in order of the first place, the second place, the third place, the fourth place, and the fifth place. In addition, with respect to the muscle M2, the level of importance to the estimation is set to the order of the displacement statistic Ar3, the displacement statistic Ar5, the displacement statistic Ar2, the displacement statistic Ar14, and the displacement statistic Ar15 in order of the first place, the second place, the third place, the fourth place, and the fifth place. Hereinafter, with respect to the muscle M3 and the muscle M4 as well, as shown in  FIG.  10 A , the level of importance is set to the displacement statistic. 
     Furthermore, in the case of  FIG.  10 B , for example, with respect to the muscle M1, the level of importance to the estimation is set to an order of the motion statistic Aa1, the motion statistic Aa2, the motion statistic Aa8, the motion statistic Aa12, and the motion statistic Aa7 in order of the first place, the second place, the third place, the fourth place, and the fifth place. In addition, with respect to the muscle M2, the level of importance to the estimation is set to the order of the motion statistic Aa3, the motion statistic Aa5, the motion statistic Aa2, the motion statistic Aa14, and the motion statistic Aa15 in order of the first place, the second place, the third place, the fourth place, and the fifth place. Hereinafter, with respect to the muscle M3 and the muscle M4 as well, as shown in  FIG.  10 B , the level of importance is set to the motion statistic. 
     It is noted that the level of importance of the displacement statistic and the level of importance of the motion statistic with respect to one type of muscles may be set by a common level of importance or may be set individually according to various exemplary aspects. For example, in a case in which an index (e.g., a number) of the displacement statistic and an index (e.g., a number) of the motion statistic that are shown in  FIG.  10 A  and  FIG.  10 B  show the same type of a statistic, the level of importance of the displacement statistic and the level of importance of the motion statistic shown in  FIG.  10 A  and  FIG.  10 B  are able to be set by the common level of importance. 
     On the other hand, when the index (e.g., the number) of the displacement statistic shown in  FIG.  10 A  is set according to the type of the displacement statistic and the index (e.g., the number) of the motion statistic shown in  FIG.  10 B  is set according to the type of the motion statistic, the setting of the level of importance of the displacement statistic and the level of importance of the motion statistic are set individually. 
     According to an exemplary aspect, the level of importance of the displacement statistic and the level of importance of the motion statistic are set by the common level of importance, which makes it possible to simplify the setting of the level of importance and also simplify the estimation processing of an action state. On the other hand, the level of importance of the displacement statistic and the level of importance of the motion statistic are set individually, which makes it possible to set more various conditions to estimate an action state and estimate an action state with a further higher accuracy. 
     The estimation calculation portion  14 A, when setting the muscle to be estimated, estimates a loaded state (e.g., a muscle potential value) of the muscle from a plurality of displacement statistics and a plurality of motion statistics, by using the level of importance that is set according to the muscle. It is noted that the loaded state of the muscle is not limited to the muscle potential value and may be any other data that can be expressed as a value. 
     More specifically, for example, the estimation calculation portion  14 A calculates an estimation result of a loaded state from a pair of the displacement statistic of the motion statistic of the same rank in the level of importance and the action state model. The estimation calculation portion  14 A calculates the estimation result of a loaded state for each pair of the same rank in the level of importance. Then, the estimation calculation portion  14 A weights each estimation result according to the level of importance, and calculates the estimation result of a final loaded state by performing addition averaging or the like, for example. 
     It is noted that the estimation calculation portion  14 A is configured to individually calculate an estimation result of a loaded state from the displacement statistic and the action state model, and an estimation result of a loaded state from the motion statistic and the action state model, and is also configured to calculate an estimation result of a final loaded state from the estimation results. The number of displacement statistics and motion statistics that are used by the estimation calculation portion  14 A for estimation is not limited to this example and is able to be set properly. For example, estimation calculation may be performed from the statistics ranked from the first place to the tenth place in the level of importance. 
     The estimation calculation portion  14 A, when the number of types of the muscle to be estimated is one, estimates a loaded state by using the displacement statistic and the motion statistic and the level of importance according to the muscle. On the other hand, the estimation calculation portion  14 A, when the number of types of the muscle to be estimated is two or more, for each muscle, sets the displacement statistic and the motion statistic and the level of importance in each case and estimates a loaded state with respect to each muscle. 
     With this configuration, the action state estimation apparatus  10 A is configured to estimate a loaded state of a muscle by using a detection result of not only displacement including a tremor, but also a motion such as acceleration, angular velocity, or the like. The detection result of the motion such as sampled acceleration, angular velocity, or the like is strongly influenced by the motion of a test subject, and is highly correlated to muscle activity of the test subject. Then, since the action state estimation apparatus  10 A, since estimating an action state from microscopic tremor measurement data and macroscopic motion measurement data, estimates the loaded state of a muscle with a high accuracy. 
     Furthermore, in this configuration, the displacement measurement data are also sampled measurement data. Therefore, the action state estimation apparatus  10 A significantly reduces lack of information on a tremor associated with frequency conversion, and is configured to estimate the loaded state of a muscle with higher accuracy. 
     Furthermore, in such a configuration, the action state estimation apparatus  10 A, for each muscle to be estimated, individually sets the type of displacement statistic and the motion statistic that are used for estimation, and the level of importance. As a result, the action state estimation apparatus  10 A is configured to estimate the loaded state of a muscle with a much higher accuracy. 
     In addition, with such a configuration, the action state estimation apparatus  10 A, even when the position of the displacement detection sensor  101  and a position of the motion detection sensor  300  are not at a position of a muscle to be estimated, is configured to estimate the loaded state of the muscle. As a result, the action state estimation apparatus  10 A is also configured to estimate the loaded state with respect to a muscle that is not appeared on a body surface or a muscle (e.g., a muscle away from a position in which the displacement detection sensor  101  or the motion detection sensor  300  is disposed) for which the muscle potential is not able to be directly measured. The displacement detection sensor  101  and the motion detection sensor  300  are disposed on an ankle, so that the action state estimation apparatus  10 A is able to estimate the loaded state of a quadriceps femoris muscle, a hamstring muscle (e.g., a biceps femoris muscle, a semimembranosus muscle, a semitendinosus muscle, an adductor magnus muscle), a tibialis anterior muscle, a gastrocnemius muscle, a soleus muscle, and a gluteus maximus muscle. In addition, the action state estimation apparatus  10 A is configured to estimate a linked state of a plurality of muscles. 
     Moreover, an effect due to an error in the position in which the displacement detection sensor  101  is disposed is significantly reduced. Therefore, the disposition of the displacement detection sensor  101  and the motion detection sensor  300  is facilitated, and an operation for estimation of a loaded state is facilitated. 
     In addition, with such a configuration, the loaded state of a plurality of muscles can be estimated, using the displacement measurement signal of the displacement detection sensor  101  and the motion measurement signal of the motion detection sensor  300  in common, so that an action state estimation system including a sensor and the action state estimation apparatus can be reduced in size. 
     Moreover, in such a configuration, the displacement statistic and the motion statistic that are used and the level of importance are individually set for each muscle to be estimated. Therefore, the action state estimation apparatus  10 A is configured to estimate the loaded state of a plurality of muscles with a high accuracy by using a measurement signal of the displacement detection sensor  101  and a measurement signal of the motion detection sensor  300  in common. 
     In addition, with such a configuration, a loaded state can be estimated not as a class but as a value. In this manner, a loaded state is estimated with a value, so that the action state estimation apparatus  10 A is configured to present and manage a more accurate loaded state, and is configured to provide more appropriate notification or the like, to a test subject. 
     (Action State Estimation Method) 
       FIG.  11    is a flow chart showing a main process of an action state estimation method according to the third exemplary embodiment. It is noted that, since the specific content of each processing is described by the above configurations, the following will be schematically described below. 
     The action state estimation apparatus  10 A inputs a displacement measurement signal (S 11 A). The action state estimation apparatus  10 A executes sampling to the displacement measurement signal, and generates displacement measurement data (S 12 A). The action state estimation apparatus  10 A calculates a displacement statistic from the displacement measurement data (S 13 A). 
     The action state estimation apparatus  10 A inputs a motion measurement signal (S 21 A). The action state estimation apparatus  10 A executes sampling to the motion measurement signal, and generates motion measurement data (S 22 A). The action state estimation apparatus  10 A calculates a motion statistic from the motion measurement data (S 23 A). 
     The action state estimation apparatus  10 A obtains an action state model (S 14 A). The action state estimation apparatus  10 A estimates a loaded state by using the action state model and setting the displacement statistic and the motion statistic as an input vector (S 15 A). 
     It is noted that the above processing may be programmed and stored in a storage medium or the like, and may be executed by an arithmetic processing apparatus such as a CPU, as described above, for example. 
     (Configuration and Processing of Action State Learning Apparatus) 
     The above action state model is generated, for example, as shown below.  FIG.  12    is a functional block diagram of an action state learning apparatus according to the third exemplary embodiment. 
     As shown in  FIG.  12   , the action state learning apparatus  20 A includes a sampling portion  11 , a statistic calculation portion  12 , an action state model storage  13 A, a sampling portion  21 , a modeling reference value calculation portion  22 , a learning calculation portion  24 A, a sampling portion  31 , and a statistic calculation portion  32 . The sampling portion  11 , the statistic calculation portion  12 , the action state model storage  13 A, the sampling portion  31 , and the statistic calculation portion  32  are as described above, and thus the description will be omitted. 
     In operation, the sampling portion  21  receives an input of a muscle activity measurement signal (e.g., a muscle potential signal) from the muscle activity detection sensor  102 . The sampling portion  21  generates muscle activity measurement data by sampling the muscle activity measurement signal by a predetermined sampling frequency (100 Hz, for example). The sampling portion  21  outputs the muscle activity measurement data to the modeling reference value calculation portion  22 . 
     It is noted that the muscle activity detection sensor  102  is a sensor configured to measure muscle activity, for example, is a myoelectric sensor (e.g., an electromyograph). The muscle activity detection sensor  102  is disposed at a position of a muscle of which the loaded state is to be estimated. More specifically, the muscle activity detection sensor  102  is disposed at a position of a muscle that is a source of muscle activity that produces a tremor to be measured by the muscle activity detection sensor  102 . The muscle activity detection sensor  102  detects muscle activity, and generates and outputs a muscle activity measurement signal. The muscle activity detection sensor  102  can be a single sensor disposed with respect to one type of muscles or can be two or more sensors disposed according to a muscle with respect to a plurality of types of muscles. 
     The modeling reference value calculation portion  22  calculates a modeling reference value from the muscle activity measurement data. For example, the modeling reference value calculation portion  22  calculates an absolute average value of the muscle activity measurement data within a predetermined period as the modeling reference value. The absolute average value refers to an average value of an absolute value of the measurement data. 
     It is noted that the modeling reference value is not limited to the absolute average value and may use a regressionable value such as, for example, an average value, a maximum value, a minimum value, a median value, a 1% value, a 5% value, a 25% value, a 75% value, a 95% value, a 99% value, a variance value, a skewness value, or a kurtosis value. Furthermore, the modeling reference value is able to represent a class of a load, such as large, medium, or small, that is able to be classified from the muscle activity measurement data. 
     The modeling reference value calculation portion  22  outputs the modeling reference value to the learning calculation portion  24 A. 
     The learning calculation portion  24 A is configured to perform learning by using the displacement statistic and the motion statistic, and the modeling reference value, and generates an action state model. More specifically, for example, the learning calculation portion  24 A performs learning by setting the displacement statistic and the motion statistic as an explanatory variable and the modeling reference value as an objective variable and using a gradient boosting method that utilizes a decision tree algorithm. The learning calculation portion  24 A repeats the learning, and, when obtaining a predetermined inference accuracy, generates an action state model by using such a result. 
     It is noted that a method of learning is not limited to the gradient boosting method, and may also use a method such as boosting represented by a similar AdaBoost method according to alternative exemplary aspects. In addition, other methods of learning may use an SVM, a GMM, an HMM, a neural network, a learning Bayesian network, or the like. 
     Furthermore, by use of a plurality of learning devices as the learning calculation portion  24 A, an ensemble method that weights a result of the plurality of learning devices and then performs majority voting may be used. 
     With the configuration and processing, the action state learning apparatus  20 A is able to properly set the action state model. 
     (Action State Learning Method) 
       FIG.  13    is a flow chart showing a main process of an action state learning method according to the third exemplary embodiment. 
     In operation, the action state learning apparatus  20 A inputs a displacement measurement signal and a motion measurement signal (S 41 A). The action state learning apparatus  20 A executes sampling to the displacement measurement signal, generates displacement measurement data, executes sampling to a motion measurement signal, and generates motion measurement data (S 42 A). The action state learning apparatus  20 A calculates a displacement statistic from the displacement measurement data, and calculates a motion statistic from the motion measurement data (S 43 A). 
     The action state learning apparatus  20 A inputs a muscle activity measurement signal (S 51 A). The action state learning apparatus  20 A executes sampling to the muscle activity measurement signal, and generates muscle activity measurement data (S 52 A). The action state learning apparatus  20 A calculates a modeling reference value from the muscle activity measurement data (S 53 A). 
     The action state learning apparatus  20 A executes learning using the displacement statistic and the motion statistic, and the modeling reference value, and generates an action state model (S 61 A). 
     It is noted that the above processing may be programmed and stored in a storage medium or the like, and may be executed by an arithmetic processing apparatus such as a CPU, as described above, for example. 
     (Fourth Exemplary Embodiment) 
     An action state estimation technology and an action state model generation technology according to a fourth exemplary embodiment will be described. The action state estimation technology according to the fourth exemplary embodiment is different from the action state estimation technology shown in the third exemplary embodiment in that strength block data of the displacement statistic and the motion statistic is used. A method of generating the strength block data of the motion statistic is the same as or similar to the method of generating the strength block data of the displacement statistic according to the third exemplary embodiment, and thus the description using a specific example will be omitted. 
     The statistic calculation portion  12  generates strength block data (e.g., displacement strength block data) of displacement measurement data from signal strength distribution of the displacement measurement data, and outputs the strength block data as a displacement statistic. More specifically, the statistic calculation portion  12  sets a strength block (e.g., a signal strength block) for each predetermined number in order of increasing signal strength against the signal strength distribution. The statistic calculation portion  12  calculates an integrated value for each strength block, and generates the displacement strength block data. 
     It is noted that the statistic calculation portion  32  has the same or similar configuration as the statistic calculation portion  12 , and performs the same processing as the statistic calculation portion  12 , to the motion measurement data. As a result, the statistic calculation portion  32  calculates and outputs a motion statistic including the strength block data (e.g., motion strength block data) of the motion measurement data. 
     The estimation calculation portion  14 A estimates an action state by using the displacement statistic and the motion statistic based on the signal strength distribution. In such a case, the estimation calculation portion  14 A estimates an action state by using the level of importance. 
       FIG.  14 A  and  FIG.  14 B  are tables showing an example of a setting of the level of importance according to the fourth exemplary embodiment.  FIG.  14 A  shows the level of importance of the displacement statistic, and  FIG.  14 B  shows the level of importance of the motion statistic. As shown in  FIG.  14 A  and  FIG.  14 B , in the fourth exemplary embodiment, the level of importance is set for each muscle, to the strength block of the signal strength distribution. 
     The setting of the level of importance shown in  FIG.  14 A  is the same as or similar to the setting of the level of importance shown in  FIG.  10 A  except that the displacement statistic is a value of a strength block. The setting of the level of importance shown in  FIG.  14 B  is the same as or similar to the setting of the level of importance shown in  FIG.  10 B  except that the motion statistic is a value of a strength block. Therefore, the detailed description will be omitted. 
     The estimation calculation portion  14 A, when setting a muscle to be estimated, estimates a loaded state of the muscle from a plurality of displacement statistics (e.g., values of the strength block) and a plurality of motion statistics (e.g., values of the strength block), by using the level of importance that is set according to the muscle. 
     With this configuration, the action state estimation apparatus according to the fourth exemplary embodiment, as with the action state estimation apparatus  10 A according to the third exemplary embodiment, is configured to estimate the loaded state of the muscle with a high accuracy. 
     (Fifth Exemplary Embodiment) 
     An action state estimation technology and an action state model generation technology according to a fifth exemplary embodiment will be described with reference to the drawings. It is noted that the action state estimation technology according to the fifth exemplary embodiment is different from the action state estimation technology shown in the first exemplary embodiment in that a displacement measurement signal and a muscle activity measurement signal during learning are synchronized. Other methods of the action state estimation technology according to the fifth exemplary embodiment are the same as or similar to the methods of the action state estimation technology according to the first exemplary embodiment, and the description of the same or similar portions will be omitted. 
       FIG.  15    is a flow chart showing a main process of an action state learning method according to the fifth exemplary embodiment. As shown in  FIG.  15   , the action state learning method according to the fifth exemplary embodiment is different from the action state learning method according to the first exemplary embodiment in that synchronization processing is added. Other processing of the action state learning method according to the fifth exemplary embodiment is the same as or similar to the processing of the action state learning method according to the first exemplary embodiment, and the description of the same or similar processing will be omitted. 
     The action state learning apparatus  20  calculates a statistic and a modeling reference value, and then synchronizes the statistic with the modeling reference value (S 40 ).  FIG.  16    shows a concept of synchronization. As shown in  FIG.  16   , according to a difference in reaction between the displacement detection sensor  101  and the muscle activity detection sensor  102 , a time difference Δt occurs between reference time tot of a displacement measurement signal and reference time t0m of a muscle activity measurement signal. 
     Therefore, the learning calculation portion  24  detects the reference time t0t of a displacement measurement signal and the reference time t0m of a muscle activity measurement signal, and detects a time difference Δt by calculating the difference between the reference time t0t and the reference time t0m. The learning calculation portion  24  synchronizes the statistic with the modeling reference value by using the time difference Δt. 
     The learning calculation portion  24  performs learning by using the statistic and the modeling reference value that have been synchronized, and generates an action state model (S 41 ). 
     By performing such processing, the action state estimation apparatus  10  is configured to estimate the loaded state of a muscle with higher accuracy. 
     It is also noted that, when the learning is performed by use of a displacement measurement signal and a motion measurement signal, and a muscle activity measurement signal, the displacement measurement signal and the motion measurement signal may be synchronized with the muscle activity measurement signal to perform the learning. 
     In general, it is noted that the configuration and processing of each of the above exemplary embodiments are able to be combined. Then, the use of such a combination enables the action state estimation apparatus and the action state estimation method to achieve a higher estimation accuracy. For example, two statistics of the statistic obtained by sampling and the statistic obtained by calculating signal strength distribution are used in combination (i.e., both statistics can be used). 
     In addition, the above description shows an aspect in which a myoelectric sensor (e.g., an electromyograph) is used as the muscle activity detection sensor  102 . However, the muscle activity detection sensor  102  may be another sensor capable of measuring muscle activity such as MRI. 
     Moreover, the above description shows an aspect in which an inertia sensor such as an acceleration sensor or an angular velocity sensor is used as the motion detection sensor  300 . However, the motion detection sensor  300  may also use a motion sensor, an imaging sensor, or the like, for example. 
     In addition, the above description shows an aspect in which the displacement measurement signal is sampled. However, when the motion measurement signal is sampled, it is also possible to frequency-sample the displacement measurement signal. However, as described above, by sampling the displacement measurement signal, the action state estimation apparatus is configured to estimate the loaded state of a muscle with higher accuracy. 
     In view of the foregoing, the displacement detection sensor  101  is preferably a piezoelectric sensor. In other words, while another sensor such as an acceleration sensor improves accuracy by extracting a frequency component, the use of the piezoelectric sensor enables accurate estimation even without such an extraction of a frequency component. 
     Moreover, the above configuration and processing show an aspect in which the loaded state of a muscle is estimated as an action state. However, other action states of a test subject who has relevance to the loaded state of the muscle are able to be estimated. 
     In addition, the above configuration and processing show an aspect in which an action state is estimated by use of the displacement statistic and the motion statistic that are obtained by sampling and by adding no change or by use of the displacement statistic and the motion statistic that are obtained by calculating signal strength distribution. However, the action state estimation apparatus and the action state estimation method are also able to use a difference value (e.g., a change amount) or a rate of change of each statistic. Specifically, the action state estimation apparatus and the action state estimation method calculate a difference value (e.g., a change amount) or a rate of change of adjacent statistics in a plurality of statistics, and use a calculated value. Accordingly, the action state estimation apparatus and the action state estimation method are also able to estimate variation in the action state. 
     In addition, in estimation of a loaded state using the above action state model, the following items related to biological information may be added as an input vector. For example, at least one of the following items: BMI, height, weight, body fat percentage, muscle mass, grip strength (left, right, the first time, the second time), lower thigh minimum circumference, age (20s, 30s, 40s, 50s, 60s), and gender (female, male) of a person to be measured, may be added. As a result, the loaded state of a muscle can be estimated with a higher accuracy. 
     REFERENCE SIGNS LIST 
       10 ,  10 A: action state estimation apparatus 
       11 : sampling portion 
       12 : statistic calculation portion 
       13 ,  13 A: action state model storage 
       14 ,  14 A: estimation calculation portion 
       20 ,  20 A: action state learning apparatus 
       21 : sampling portion 
       22 : modeling reference value calculation portion 
       24 ,  24 A: learning calculation portion 
       31 : sampling portion 
       32 : statistic calculation portion 
       101 : displacement detection sensor 
       102 : muscle activity detection sensor 
       300 : motion detection sensor