these include the 
 intrinsic flexor pollicis brevis , flexor pollicis longus , lumbricalis , flexor brevis , and 
 flexor longus muscles1 . toe - gripping 
 strength is measured in the sitting position with the trunk vertical , the hip and knee 
 joints at 90 , and the ankle joint in the neutral position1,2,3 . low toe - gripping strength is a risk factor of falls for the 
 elderly , and several studies have reported that toe - gripping strength is lower in subjects 
 with a history of falls than in those with no history of falls1,2,3,4 . furthermore , toe - gripping 
 strength can be increased by training5 , 
 which can decrease the risk of falls1 . souma et al.6 studied the % iemg of 
 several crural muscles ( the soleus muscle , medial head of the gastrocnemius muscle , and 
 tibialis anterior ) during toe - gripping in 3 different ankle joint positions10 of plantar 
 flexion and 0 and 10 of dorsiflexion  and reported that the crural muscles help the ankle 
 joint by co - contracting during toe - gripping . in another study , nakae et al.7 calculated the % iemg of the same muscles 
 during toe - gripping with subjects seated on the edge of a seat or standing , and reported 
 that the % iemg of the medial gastrocnemius muscle was significantly lower when subjects were 
 seated than when they were standing . however , as both studies focused on the activity of the 
 crural muscles , the activity of the femoral muscles during toe - gripping remains unclear . we 
 believe it is important to elucidate the contribution of femoral muscles to toe - gripping 
 strength . in the present study , we investigated femoral muscle activity during toe - gripping to 
 examine the role of the femoral muscles in toe - gripping strength . their 
 average ( mean  sd ) age , height , and body weight were 20.6  1.0  years , 159.4  6.3  cm , and 
 51.8  5.8  kg , respectively . this study was approved by the ethics committee for human 
 research of tohoku fukushi university , and written informed consent was received from all of 
 the subjects after the purpose of the study had been explained to them . toe - gripping strength of the dominant toe and emg activity of the ipsilateral thigh were 
 synchronously recorded to assess the activity of the rectus femoris and biceps femoris 
 muscles . toe - gripping strength was measured using a toe - gripping dynamometer ( t.k.k.3360 ; 
 takei co , ltd , niigata , japan ) . as described by uritani8 , the subjects were instructed to sit with their trunk in the 
 vertical position , hip and knee joints at 90 , and ankle joints in the neutral position . after a sufficient 
 number of training trials and adequate rest , toe - gripping strength was measured twice and 
 the maximal force was used in the analysis . for all subjects , the right toe was dominant 
 ( defined as the toe used to kick a ball ) . to measure the maximum voluntary contraction ( mvc ) activity of the rectus femoris muscles , 
 as described by kai9 , each subject was 
 instructed to sit on a chair with the hip and knee joints at 90 , and to exert maximal 
 isometric force of knee extension while resisting an opposing force applied by the examiner . the emg was recorded for 3 seconds while each subject exerted maximal force of knee 
 extension . to measure the mvc of the biceps femoris muscle , each subject was instructed to 
 generate maximal isometric force of knee flexion while resisting an opposing force applied 
 by the examiner . the emg was recorded for 3 seconds while each subject exerted maximal force 
 of knee flexion . after confirmation of adequate skin preparation ( skin resistance of less 
 than 5 k ) , three bipolar lead electrodes ( de-2.1 , delsys , inc . , boston , usa ) were attached 
 to the skin over the rectus femoris and the long head of the biceps femoris , as described by 
 peroto10 . for measurement of the rectus femoris muscle , the electrode was attached at the midpoint between the superior edge of the 
 patella and the anterior superior iliac spine . for measurement of the long head of the 
 biceps femoris , the electrode was attached at the midpoint between the head of the fibula 
 and ischial tuberosity . the emg signal was collected using ml846 power lab 4/26 ( sample : 1,000  hz ; ad instruments 
 co. , ltd . ) and transferred to a personal computer . the bandwidth was 20500  hz . the emg 
 signal segment selected and integrated ( integrated electromyogram : iemg ) for analysis was 
 the middle 1  s of the entire 3-s duration of continuous maximal toe - gripping strength . the iemg was analyzed using lab chart pro v7.3.5 ( ad instruments co. , ltd . ) and normalized 
 to the iemg of each muscle s mvc . repeated mann - whitney u tests were used to compare the % iemg of the 
 rectus and biceps femoris muscles . relationships between the % iemg of the rectus and biceps 
 femoris muscles were statistically analyzed using spearman s correlation coefficient . the average ( mean  sd ) toe - gripping strength was 20.9  3.6  kg . the average ( mean  sd ) 
 % iemg values of the rectus and biceps femoris muscles were 7.0%  6.2% and 25.6%  15.9% , 
 respectively . the % iemg of the biceps femoris was significantly higher than that of the 
 rectus femoris ( p < 0.01 , table 1table 1.comparison of the % iemg values of the rectus femoris and biceps femoris muscles 
 during toe - gripping actionrectus femorisbiceps femorismedian ( range :  min  max)median ( range :  min  max)%iemg4.8 * ( 1.521.1)27.2 ( 3.068.1)mann - whitney u test * : p < 0.05 ) . mann - whitney u test * : p < 0.05 using spearman s correlation coefficient analysis , a significant positive correlation was 
 found between the % iemg of the rectus femoris and that of the biceps femoris ( r = 0.548 , p in the present study , we found that the % iemg of the biceps femoris was significantly 
 higher than that of the rectus femoris . moreover , a significant positive correlation was 
 found between the % iemg of these two muscles . these results suggest that femoral muscles 
 co - contract during toe - gripping action , and thus possibly contribute to knee joint 
 stability . we found that toe - gripping action stimulates femoral muscle activity and that the % iemg of 
 the biceps femoris was significantly higher than that of the rectus femoris . sato et 
 al.11 reported that during 
 toe - gripping , the tibialis anterior and soleus muscles are activated first , followed by the 
 gradual activation of the medial head of the gastrocnemius muscle . the biceps femoris 
 initiates knee flexion , and the medial head of the gastrocnemius is a synergist for knee 
 flexion . additionally , active tension of the biceps femoris decreases during toe - gripping in 
 knee flexion . this may be because the length of the biceps femoris is shorter during active 
 tension than during resting tension . we think that the activation of the biceps femoris 
 during toe - gripping was caused by increasing motor unit recruitment and synchronization of 
 the impulse to compensate for decreasing activity of the biceps femoris . in the present study , we found a significant positive correlation between the % iemg of the 
 rectus femoris and that of the biceps femoris . this suggests that the % iemg of the rectus 
 femoris increases with increases in the % iemg of the biceps femoris . toe - gripping strength was measured using a closed kinetic chain movement , and therefore , 
 the likelihood of movement in the directions of flexion or extension of the knee joint is 
 less . however , because the gastrocnemius also acts on knee joint flexion during exertion of 
 toe - gripping strength , the knee joint is readily displaced in the direction of flexion . to 
 prevent this , it is thought that the knee joint is immobilized by contraction of the rectus 
 femoris , that is , we think the rectus femoris during exertion of toe - gripping strength acts 
 in order to control the action of knee joint flexion by the gastrocnemius . first , we were unable to avoid the common problems that 
 negatively affect surface emg recording , such as skin resistance , artifacts , and the effects 
 of proximal muscles . second , as only healthy young women participated in this study , it is 
 difficult to extend our findings to the general population . in future studies , we need to 
 consider this aspect , and involve healthy young men and individuals of different age 
 groups .
[ purpose ] in the present study , we investigated femoral muscle activity during 
 toe - gripping , and the role of the femoral muscles in toe - gripping strength . 
 [ subjects ] 
 fourteen healthy young women were selected . 
 [ methods ] we measured the maximum voluntary 
 contraction of the rectus femoris and long head of the biceps femoris muscles . 
 we then 
 calculated the percent integrated emg ( % iemg ) during the toe - gripping action . 
 [ results ] we 
 found that the % iemg of the biceps femoris was significantly higher than that of the 
 rectus femoris . 
 moreover , a significant positive correlation was found between the % iemg 
 of the rectus femoris and that of the biceps femoris . 
 [ conclusion ] these results suggest 
 that femoral muscles co - contract during the toe - gripping action , and thus possibly 
 contribute to knee joint stability .