the foot is 
 the point of direct contact between the body and the surface below .
therefore , muscle force 
 generated from the toes and ankles may play an important role in maintaining stability .
a 
 limited number of studies have reported the association between toe grasping strength and 
 postural control .
for example , two studies investigated the age - related change in toe 
 grasping strength in males and females and found that toe grasping strength is related to 
 age and declines faster than handgrip strength with increasing age1 , 2 .
in addition , handa 
 and colleagues1 reported significant 
 correlations between toe grasping strength and static balance with eyes open ( r = 0.443 , p 
 < 0.01 ) as well as tolerance to falling forward ( r = 0.620 , p < 0.01 ) .
interestingly , 
 postural sway behavior while standing improved following 8 weeks of toe grasp training 
 ( consisting of gathering a towel attached to a weight and passing small bags from one place 
 to another ) in older adults although the authors did not measure toe grasping strength3 .
perrin and colleagues4 reported that daily physical activity in older adults , even 
 if never practiced earlier in their life , had a positive effect on balance control .
gauchard 
 and colleagues5 investigated the influence 
 of two types of physical exercise ( yoga and soft gymnastics vs. jogging , swimming , and 
 cycling ) on postural sway balance in older females and found that yoga and soft gymnastics 
 appeared to have the best impact on postural control in simple postural tasks .
one 
 difference between these two types of physical exercise is how the foot contacts the ground 
 surface during the exercise .
foot muscles involved in toe grasping may be activated during 
 relatively slow movements of physical activities such as yoga and soft gymnastics .
thus , toe 
 grasping strength may be associated with the duration and intensity of daily physical 
 activity .
the purpose of the present study was to test the hypothesis that daily physical 
 activity probably contributes to toe grasping strength in middle - aged and older adults .
fifty - seven japanese women between the ages of 52 and 78  years ( mean age , 66.3  6.8  years ) 
 were recruited through printed advertisement and by word of mouth from the surrounding area 
 of the university campus in chiba . in this study ,
female volunteers were chosen because a 
 higher incidence of falls has been reported in japanese females than in japanese males7 .
all subjects were free of overt chronic 
 disease ( e.g. , diabetes , angina , myocardial infarction , arthritic and neuromuscular 
 disorders , cancer , stroke ) as assessed by self - report following a general health 
 examination .
the main types of sports activities were walking ( 17 females ) and yoga / tai chi ( 6 
 females ) .
the study was conducted according to the declaration of helsinki and was approved 
 by the ethics committee for human experiments of toyo gakuen university ( 2012 - 001 ) . written 
 informed consent was obtained from all subjects .
subcutaneous fat thickness ( ft ) was measured using b - mode ultrasound ( aloka ssd-2000 , 
 tokyo , japan ) at 9 sites , as described previously8 .
the measurements were taken while the subjects stood quietly with 
 their knees extended and relaxed .
a 5-mhz scanning head was placed on the measurement site 
 without depressing the dermal surface .
body density was estimated from ft using an 
 ultrasound - derived prediction equation8 . 

percent body fat ( % fat ) was calculated from body density using brozek s equation9 .
fat - free mass ( ffm ) was estimated as total 
 body mass minus fat mass .
body mass and standing height were measured to the nearest 0.1  kg 
 and 0.1  cm , respectively , using a height scale and an electronic weight scale .
body mass 
 index ( bmi ) was defined as body mass ( kg)/height ( m ) .
3361 , takei , 
 tokyo , japan ) , as described previously2 . 
 while barefoot , subjects were instructed to maintain a one - legged upright standing position 
 on the dynamometer , put both hands on the wall in front of them , and hold the dynamometer 
 grasping bar with their toes .
the distance between the bar and the heel was adjusted to the 
 foot size of each subject such that the distal phalanges of the great toe and fifth toe and 
 the middle phalanges of the second to fifth toes could be placed on the toe grasping bar . 

subjects were allowed to perform one test trial , followed by 3 maximum trials , and the best 
 values for right and left feet were averaged and used for data analysis .
maximal toe 
 grasping strength divided by body weight was calculated for evaluating relative toe grasping 
 strength .
test - retest reliability of toe grasping strength has been reported in a previous 
 study10 .
maximum voluntary isometric strength of the knee extensors was determined using a biodex 
 system 3 dynamometer ( shirley , new york , usa ) .
subjects were carefully familiarized with the 
 testing procedures of voluntary force production approximately one week before testing .
each 
 subject was seated on a chair with the hip joint angle positioned at 85. the center of 
 rotation of the knee joint of the right leg was visually aligned with the axis of the lever 
 arm of the dynamometer , and the ankle of the right leg was firmly attached to the lever arm 
 of the dynamometer with a strap .
after a warm - up consisting of submaximal contractions , the 
 subject was instructed to perform maximal isometric ( mvc ) knee extension at a knee joint 
 angle of 80. a knee joint angle of 0 corresponded to full extension of the knee . if mvc 
 strength for the first two trials varied by > 5% , an additional mvc was performed .
knee extension mvc divided 
 by body weight was calculated for evaluating relative knee extension strength . during orientation
, participants were shown how to attach the accelerometer ( lifecorder ex , 
 suzuken , nagoya , japan ) on an elastic belt over their left or right hip and were instructed 
 to record their daily physical activity for 30 days , beginning on the following day .
if 
 participants did not use the accelerometer for a couple of days during the testing period , 
 they were requested to record their activity for additional days . to achieve > 90% 
 reliability for estimating the yearly physical activity in older adults , > 30 consecutive 
 observation days are required11 .
after 
 the measurements were taken , the recorded activity level data were downloaded to a personal 
 computer .
the data were classified into different intensities using 10 activity levels , 
 ranging from 0 to 9 , based on the accelerometer signal .
level 0 ( corresponding to < 0.06 
 g ) denotes immobility , and levels 1 to 9 ( corresponding to  0.06 g ) denote subtle to 
 vigorous movements . in this study ,
exercise intensity was categorized into one of 3 activity 
 levels on the basis of the accelerometer signal : light physical activity ( levels 13 , < 3 
 metabolic equivalents [ met ] ) , moderate physical activity ( levels 46 , 36 met ) , and vigorous 
 physical activity ( levels 79 , > 6 met ) according to a previous study12 .
in addition , the total duration of each 
 level of exercise intensity was calculated .
participants were 
 separated into two groups on the basis of daily step counts measured by an accelerometer : 
 low ( n = 28 , < 8,000 steps per day ) and high ( n = 29 ,  8,000 steps per day ) . before 
 comparisons were made , dependent variables were tested for normality of distribution by the 
 shapiro - wilk test . the difference between low and high groups
was tested for significance by 
 using unpaired student s t - tests , and if any variables were not normally distributed , the 
 mann - whitney u test was used .
pearson product correlations were performed to determine the 
 relationships between accelerometer - determined physical activity level and relative maximum 
 strength ( divided by body weight ) of toe grasping and knee extension .
if any variables were 
 not normally distributed , then spearman s rho correlation was used . because age was 
 different between the two groups , partial correlations of relative strength with physical 
 activity levels adjusted for age
although the high group was approximately 5  years younger than the low group ( p < 0.01 ) , 
 bmi and body composition ( % fat and ffm ) were similar between the two groups .
absolute and 
 relative toe grasping maximal strength were greater ( p < 0.001 ) in the high group than in 
 the low group .
however , both absolute and relative knee extension strength were similar 
 between the two groups .
all 3 intensities ( light , moderate , and vigorous ) of physical 
 activity were higher in the high group compared with the low group ( table 1table 1.body composition , physical activity , and muscle strength in middle - aged and older 
 womendaily step counts ( steps / day)overalllow ( < 8,000)high ( 8,000)n282957age , yrs69 ( 7)64 ( 6)66.3 ( 6.8)height , m1.53 ( 0.05)1.53 ( 0.06)1.53 ( 0.05)body weight , kg52.9 ( 6.1)51.7 ( 4.5)52.3 ( 5.4)body mass index , kg / m22.7 ( 2.9)22.1 ( 2.0)22.4 ( 2.5)body fat , % 27.3 ( 5.1)26.9 ( 5.2 ) 27.1 ( 5.1)fat - free mass , kg38.3 ( 3.1)38.2 ( 3.2)38.2 ( 3.2)muscle strengthfoot grasping , kg11.9 ( 3.1)14.9 ( 3.3)13.4 ( 3.5)knee extension , nm104 ( 28)106 ( 22)105 ( 25)relative muscle strengthfoot grasping / wt , kg / kg0.23 ( 0.06)0.29 ( 0.07)0.26 ( 0.07)knee extension / wt , nm / kg1.96 ( 0.48)2.07 ( 0.45)2.01 ( 0.46)physical activity , min / daylow48.3 ( 14.6)71.4 ( 19.1)60.1 ( 20.5)moderate10.6 ( 7.7)33.3 ( 13.7)22.2 ( 15.9)vigorous0.6 ( 0.9)2.4 ( 1.7)1.54 ( 1.65)low + moderate59.0 ( 17.2)104.7 ( 18.3)82.2 ( 29.1)moderate + vigorous11.2 ( 8.1)35.8 ( 14.6)23.7 ( 17.1)step counts , steps / day5,456 ( 1,588)10,406 ( 1,898)7,974 ( 3,041)significant difference from low group p<0.01 , p<0.001 .
wt : body weight a negative correlation was observed between age and relative toe grasping strength ( r = 
 0.480 , p < 0.001 ) and between age and relative knee extension strength ( r = 0.307 , p 
 < 0.05 ) .
relative toe grasping strength correlated positively with light ( r = 0.320 , p 
 < 0.05 ) , moderate ( r = 0.345 , p < 0.01 ) , and vigorous ( r = 0.296 , p < 0.05 ) 
 physical activity . relative knee extension strength correlated positively with moderate ( r = 
 0.298 , p < 0.05 ) , and vigorous ( r = 0.358 , p < 0.01 ) physical activity , but not with 
 light ( r = 0.203 , p = 0.131 ) physical activity . similarly , both toe grasping and knee 
 extension strength correlated with light plus moderate physical activity as well as moderate 
 plus vigorous physical activity ( table 
 2table 2.pearsons and partial ( adjusted for age ) correlation coefficients between muscle 
 strength and physical activity in middle - aged and older womenpearson s correlationpartial correlationgraspingknee exgraspingknee ex light + moderate0.4150.306 * 0.290 * 0.217 moderate + vigorous0.350 0.312 * 0.228 0.233 step counts0.4120.330 * 0.283 * 0.242*p<0.05 , p<0.01 . grasping , foot grasping strength / body weight ; knee ex , knee 
 extension strength / body weight ) .
average step count also correlated with both toe grasping and knee extension 
 strength ( table 2 ) . after adjusting for age , 
 only the duration of light plus moderate physical activity and average step count correlated 
 to toe grasping strength ( table 2 ) .
* p<0.05 , p<0.01 . grasping , foot grasping strength / body weight ; knee ex , knee 
 extension strength / body weight
in the present study , we tested our hypothesis that daily physical activity may contribute 
 to toe grasping strength in middle - aged and older females .
the primary findings of this 
 study were that : 1 ) the high group (  8,000 steps / day ) had significantly greater toe 
 grasping strength , but not knee extension strength , when compared with the low group ( < 
 8,000 steps / day ) strength , 2 ) toe grasping strength was significantly associated with daily 
 step count , and 3 ) toe grasping strength significantly correlated with light plus moderate 
 intensity physical activity , but not moderate plus vigorous intensity physical activity .
it has previously been reported that accelerometer ( or pedometer)-determined physical 
 activity levels dramatically decrease later in life13,14,15 . in japanese , for example , average yearly step counts were 
 approximately 7,000 steps / day for ages 6574 and 5,000 steps / day for ages 758413 .
kitagawa et al.16 reported a mean value of 8,401 ( sd 3404 ) steps / day in 
 older japanese females aged 6187  years ( mean age 71  6  years ) .
similarly , yoshioka et 
 al.17 reported an average number of 
 7,922 steps / day in middle - aged and older adults ( females and males ) aged 5069 .
physical 
 activity levels of our subjects were similar to the previous studies with an average value 
 of approximately 8,000 steps / day ( mean and sd , 7,974  3,041 ) in middle - aged and older 
 females ( mean age 66  7  years ) .
it is generally believed that participation in regular physical activities may be 
 associated with greater maintenance of muscular strength . in the present study , active 
 females (  8,000 steps / day ) had 26% higher toe grasping strength compared with females who 
 were not as physically active ( < 8,000 steps / day ) , while knee extension strength was 
 similar between the two groups .
furthermore , both knee extension and toe grasping strength 
 correlated significantly to average step count , although the correlation coefficient between 
 step count and toe grasping strength was only significant after adjusting for age .
al.18 investigated the influence of 
 physical activity on muscular strength of knee extensors , plantar flexors , and handgrip in 
 females aged 20 to 89  years .
they found that self - reported physically active females were 
 stronger than physically inactive females when absolute strength of the leg muscles was 
 normalized for body weight ; however , knee extension strength at ages 6064 , 6569 , and 7074 
 were probably similar between the active and inactive females .
leskinen et al.19 reported that active twins had 20% higher 
 knee extension strength than their inactive co - twins , while the active twins had only 4% 
 higher mid - thigh muscle cross - sectional area than that of the inactive twins .
our findings 
 in toe grasping strength support the previous studies , whereas the reasons for the 
 difference in knee extension strength between the present and previous studies are not well 
 known .
one possible explanation is that most of the previous studies used questionnaires for 
 evaluating the frequency and/or duration of a given type of physical activity during a 
 typical week , and determination of physical activity profile based on questionnaires may or 
 may not be accurate , especially regarding exercise intensity20,21,22 .
thus , this methodological concern may have affected the results 
 reported by the previous studies . in the present study ,
toe grasping strength was associated with light plus moderate 
 intensity physical activity . in terms of foot - ground contact time ,
foot muscles involved in 
 toe grasping may be better activated during light / moderate intensity slow movements than 
 during vigorous intensity fast movements although this may depend on footwear .
a previous 
 study examined the effects of low - intensity toe grasp training ( which consisted of gathering 
 a towel attached to a weight and passing small bags from one place to another ) in older 
 adults and found that postural sway behavior while standing improved following the 
 training3 .
although that study did not 
 measure the change in toe grasping strength , it is expected that muscular functions involved 
 in toe grasping may be improved by relatively low - intensity exercise training .
therefore , 
 results from the present and previous studies together suggest that relatively low - intensity 
 exercise would be suitable for improving toe grasping strength .
another previous study investigated the effect of accelerometer - determined daily physical 
 activity on lower body muscular power in adolescents23 .
the results showed positive correlations between muscular power 
 and vigorous intensity physical activity but not with moderate or light intensity physical 
 activity . in that study ,
the duration of vigorous intensity physical activity was 
 approximately 14 minutes for female adolescents and 25 minutes for male adolescents . in the 
 present study ,
the average duration of vigorous intensity physical activity was only 1.5 
 minutes in middle - aged and older females , and the effect of vigorous intensity exercise on 
 knee extension strength appeared to be limited .
therefore , for improving knee extension 
 strength , the advantage of regular physical activity may depend on the intensity and 
 duration of exercise .
it is possible that older adults with high levels of physical activity in daily life have 
 better balance control compared with less active individuals .
although aoyagi et al.24 reported no significant association 
 between body sway and level of daily physical activity , many intervention studies have 
 revealed a number of factors that contribute to better balance25 . in particular ,
gauchard et al.5 reported more improvement in static postural control with 
 yoga / soft gymnastics ( proprioceptive exercise ) than with jogging / swimming / cycling 
 ( bioenergetic exercise ) .
it has been reported that toe grasping strength is associated with 
 static balance with eyes open as well as with tolerance to falling forward1 .
our results , along with those of previous 
 studies , suggest that toe grasping strength may be a contributing factor to the connection 
 between the effects of daily physical activity and balance control .
several limitations of this study should be mentioned . because patterns of daily physical 
 activity differ between women and men and our subjects were only women
although the duration of light / moderate physical activity was 
 associated with toe grasping strength , we did not consider the type of exercise performed 
 during daily physical activity .
additional research into these issues is needed . in summary , active middle - aged and
older women had higher toe grasping strength compared 
 with females who were relatively physically inactive .
significant correlations were observed 
 between toe grasping strength and accelerometer- determined physical activity levels , 
 especially the duration of light plus moderate physical activity .
these results suggest that 
 toe grasping strength may be associated with the amount of light daily physical 
 activity .
 [ purpose ] to test the hypothesis that toe grasping strength is associated with daily 
 physical activity in older adults . 
 [ subjects ] fifty - seven japanese women , aged 
 5278  years , volunteered . 
 [ methods ] toe grasping and knee extension strength were 
 measured . 
 physical activity was also measured , using an accelerometer , and the total 
 duration of each level of exercise intensity ( light , moderate , and vigorous ) and average 
 step counts were calculated . 
 subjects were separated into two groups on the basis of 
 accelerometer - determined step counts : low ( n=28 , < 8000 steps / day ) and high ( n=29 , 8000 
 steps / day ) . [ results ] body mass index and body composition ( % fat and fat - free mass ) were 
 similar between the two groups . 
 absolute and relative toe grasping strengths ( divided by 
 body weight ) were greater in high than in low . however , 
 both absolute and relative knee 
 extension strength were similar between the groups . 
 relative toe grasping and knee 
 extension strength correlated with all 3 intensities of physical activity and average step 
 count . 
 after adjusting for age , the duration of light plus moderate physical activity and 
 average step counts correlated to toe grasping strength but not to knee extension 
 strength . 
 [ conclusion ] our results suggest that toe grasping strength may be associated 
 with the amount of light intensity daily physical activity . 