toe flexor strength is a combination of the activity of plantar intrinsic ( flexor hallucis 
 brevis , flexor digitorum brevis , and lumbricales pedis ) and extrinsic ( flexor hallucis 
 longus and flexor digitorum longus ) muscles1 .
toe flexor muscles play important roles in arch support2 , 3 , 
 standing4 , walking / running 
 performance5,6,7,8,9 , and jump performance9 , 10 . 
 reduced toe flexor muscle force and/or volume are associated with foot and toe abnormalities 
 including plantar fasciitis11 , pes cavus 
 in charcot - marie - tooth disease12 , and 
 claw and hammer toe deformities13 . 

furthermore , reduced toe flexor strength is a risk factor of falls for elderly persons14,15,16 .
thus , estimation of toe flexor strength 
 may be important in the development of physical fitness , activities of daily living , and 
 preventive care for elderly persons .
skeletal muscle strength and volume decrease with age17 , 18 , and such decreases 
 result in reduced physical abilities in older persons19 .
the rate of the age - related reduction in skeletal muscle strength 
 and volume differs among regions and muscles . the muscle strength and volume of the lower 
 body decreases faster than those of the upper body20,21,22 .
it is hypothesized that this age - related region - specific reduction 
 is partially accounted for by an age - related reductions in physical activity21 .
specifically , it has been shown to 
 significantly reduce after the age of 50 in both men and women23 .
however , the rate of age - related reduction in toe flexor 
 strength relative to other muscle strengths is unknown .
furthermore , the relationship 
 between toe flexor strength and physical activity and inactivity in elderly men has not been 
 investigated .
thus , the purpose of the present study was to compare the toe flexor strength 
 and other muscle strengths of young and elderly men .
whether or not toe flexor strength was 
 associated with physical activity / inactivity levels was also investigated .
a total of 155 young men ( 1823  years ) and 60 elderly men ( 6588  years ) participated in 
 this study .
the elderly men were 
 recruited from among participants in events run by public bodies or the tohoku institute of 
 technology .
this study was approved by the ethical committee of the tohoku institute of 
 technology .
toe flexor strength was measured using a toe grip dynamometer ( t.k.k . 3161 , takei 
 scientific instruments co. , ltd . ,
the intra - rater and inter - rater 
 reliabilities of this apparatus have previously been reported24 .
the subjects sat on a chair with the trunk in the vertical 
 position , the hip and knee joints flexed at approximately 90 , and the ankle joints in a 
 neutral position ( at approximately 90 ) ( fig . 

1.measurement of toe flexor strength(a ) the posture adopted during measurement of toe flexor strength .
the subjects sat 
 on a chair with the trunk in the vertical position , with the hip and knee joints 
 flexed at approximately 90 , and the ankle joints in the neutral position ( at 
 approximately 90 ) .
one 
 foot was placed on the dynamometer , and the first proximal phalanx of the foot was 
 positioned on the grip bar with the heel position fixed using a heel stopper . ) .
previous studies have demonstrated that this position is the most suitable for 
 measuring toe flexor strength , because of its reliability , the stability of the knee and 
 ankle joints , and the ability of subjects to exert maximum force25,26,27,28 .
the first 
 proximal phalanx of the foot was positioned on a grip bar , and the heel position was fixed 
 using a heel stopper ( fig .
measurements were performed of the right 
 and left toes , and the mean maximum force of each foot was used in analyses .
measurement of toe flexor strength ( a ) the posture adopted during measurement of toe flexor strength .
the subjects sat 
 on a chair with the trunk in the vertical position , with the hip and knee joints 
 flexed at approximately 90 , and the ankle joints in the neutral position ( at 
 approximately 90 ) .
one 
 foot was placed on the dynamometer , and the first proximal phalanx of the foot was 
 positioned on the grip bar with the heel position fixed using a heel stopper .
measurements were made in duplicate on both hands , and the mean 
 maximum force of each hand was used in the analyses .
5715 , takei scientific instruments ) with 
 the trunk in the vertical position and the hip and knee joints flexed at approximately 90. 
 a researcher put the subject s foot through the loop of the strap connected to the strain 
 gauge , and the ankle was hooked in the loop of strap .
measurements were performed on both 
 legs , and the mean value of each leg was used in the analyses .
trunk flexibility was assessed using a sit - and - reach test using a device ( t.k.k .
the subjects sat on the floor with their hips , back , and the 
 occipital region of the head touching a wall .
they bent forward slowly , 
 and as far forward as possible , pushing the device with both hands , and the distance moved 
 by the device was measured .
the measurements were performed twice , and the maximum value was 
 used in the analyses .
measurements were made in duplicate , and the maximum value was used 
 in the analyses .
briefly , the mean 
 daily sum of standing and walking times and sitting time during the last six months were 
 requested .
values are mean  sd . the unpaired t - test was used to compare the means of the young and 
 elderly groups . to compare percent differences of the elderly group mean values with the 
 young group mean
values of hand grip , knee extensor , and toe flexor strength , one - way 
 analysis of variance ( anova ) was used .
the significance of between - group differences was 
 determined using tukey s post hoc test when the overall anova was significant .
5.9163.4  4.5*body weight ( kg)66.3  10.462.4  8.7*bmi ( kg / m)22.6  3.223.3  2.9hand grip strength ( kg)44.5  7.035.2  6.0*knee extensor strength ( kg)41.4  10.726.6  7.9*toe flexor strength ( kg)15.2  4.88.4  3.9*sit - and - reach ( cm)40.3  9.931.2  13.3*functional reach ( cm)44.2  9.432.2  9.9*standing / walking time ( hr / day)6.0  3.23.9  2.4*sitting time ( hr / day)7.4  3.76.2  3.3*bmi : body mass index .
the mean height and body weight of 
 the elderly group were significantly lower than those of the young group ; body mass index 
 ( bmi ) was not different between the two groups . regarding the physical fitness parameters , 
 all five measures of the elderly group ( hand grip strength , knee extensor strength , toe 
 flexor strength , sit - and - reach , and the functional - reach test ) were significantly lower than 
 those of the young group .
both the times spent standing / walking and sitting by the elderly 
 group were significantly shorter than those of the young group .
* p<0.05 vs. young group table 2table 2.proportional differences in muscle strength of elderly men compared with the mean 
 values of young menhand gripknee extensortoe flexorproportional difference from young mean , % 79.2  13.464.3  19.0 * 55.2  22.4* n=60 . proportional difference from young mean was calculated using the formula 
 bellow : proportional difference from young mean ( % ) =  kg old groupkg mean value of young 
 group100 .
p<0.05 vs. 
 knee extensor strength demonstrates the percent differences in the muscle strengths of the elderly 
 men compared with the mean values of the young men .
the rank - order of relative values of 
 muscle strength was : toe flexor < knee extensor < hand grip ( p<0.05 ) .
proportional difference from young mean was calculated using the formula 
 bellow : proportional difference from young mean ( % ) =  kg old groupkg mean value of young 
 group100 .
p<0.05 vs. 
 knee extensor strength table 3table 3.correlation coefficients ( r ) between toe flexor strength and the other parameters 
 of both groupsyoungelderlyage0.174*0.390*height0.1260.138body weight0.225 * 0.216bmi0.187 * 0.194hand grip strength0.317 * 0.509*knee extensor strength0.246 * 0.590*sit - and - reach0.1080.389*functional - reach0.240 * 0.395*standing / walking time0.1130.276*sitting time0.0570.066bmi : body mass index . *
significant correlation with toe flexor strength 
 ( p<0.05 ) shows the correlation coefficients between toe flexor strength and other 
 parameters in each group . in the young group ,
toe flexor strength was found to have 
 significant positive correlations with age , body weight , bmi , hand grip strength , knee 
 extensor strength and functional reach , but not height , sit - and - reach , and standing / walking 
 and sitting times . in the elderly group , toe flexor strength was found to have a significant 
 negative correlation with age , and significant positive correlations with hand grip 
 strength , knee extensor strength , sit - and - reach , functional - reach , and standing / walking 
 time ; no correlation was found between toe flexor strength and height , body weight , bmi , or 
 sitting time .
this study found that toe flexor strength decreases with increasing age , and hand grip and 
 knee extensor strength also decrease .
the rate of decrease of toe flexor strength with age 
 was greater than those of other muscle strengths .
in addition , toe flexor strength was 
 positively associated with physical activity levels assessed by daily standing / walking 
 time .
the rate of age - related reductions in toe flexor and knee extensor strengths were found to 
 be greater than in hand grip strength .
this is consistent with results reported by previous 
 studies , which suggests that the muscle strength of the lower body decreases faster than the 
 upper body20 , 22 .
moreover , the rate of age - related reduction in toe flexor strength 
 was greater than that of knee extensor strength .
the obvious conclusion to be drawn from 
 this is that the aging process is reflected more by toe flexor strength than by other muscle 
 strengths .
however , the results do not mean that age - related decay in muscles involving toe 
 joint movement is greater than in muscles involving knee joint movement , because this study 
 did not measure toe extensor or knee flexor strength .
the rate of age - related reduction in 
 muscle volume differs among joint movement types .
for example , the volume of the elbow 
 flexor muscle decreases with age , whereas elbow extensor muscle volume does not30 .
additionally , the age - related reduction 
 in knee extensor muscle volume is greater than that in knee flexor muscle volume31 .
thus , it is likely that the rate of 
 age - related decline in force production also differs among joint movement types . 

unfortunately , there are few accurate methods to measure toe muscle strength other than that 
 for toe flexion1 .
further studies are 
 needed to estimate and compare the rates of age - related reductions in the muscle strengths 
 of various types of actions and joints .
for example , toe flexor 
 strength was found to positively associate with walking performance such as walking speed , 
 percentage of swing time in a gait cycle , and stride length during walking at maximal speed , 
 in elderly men and women5 .
study also 
 found that toe flexor strength showed a positive correlation with the physical activity 
 level , estimated from the self - reported daily standing / walking time in elderly men .
one 
 plausible explanation for this correlation is that toe flexor muscles are intensely 
 recruited during standing and/or walking actions leading to improvement of force production 
 in these muscles .
indeed , activity of the flexor digitorum brevis muscle , estimated from 
 intra - muscular electromyography , was shown to increase with increasing postural demand 
 during standing32 .
furthermore , the long 
 and short toe flexor muscles were shown to exert forces of approximately 61% and 49% of body 
 weight , respectively , during the second peak of ground reaction force in the gait cycle33 .
another potential explanation is that 
 higher toe flexor strength supports activities of daily living , leading to an increase in 
 standing / walking activity .
our 
 study also found that the mean daily standing / walking time of elderly men was 35% lower than 
 that of young men .
it is likely that the age - related reduction in standing / walking activity 
 has a greater impact on toe flexion strength than reductions in hand grip or knee extensor 
 strength , leading to earlier loss of toe flexor strength than in other muscle strengths . 

additionally , age - related decline in muscle strength is multifactorial18 , 34 , and the rate 
 of decline in neuromuscular anatomical factors differs between the upper and lower body .
for 
 example , the proportion of fast - twitch type ii fiber areas in the vastus lateralis muscle 
 reduces with age faster than in the biceps brachii muscle35 .
moreover , the number of muscle fibers in the vastus lateralis 
 muscle reduces with age36 , but does not 
 in the biceps brachii muscle37 .
the 
 number of medial gastrocnemius motoneurons decreases with age , but the number of ulnar 
 motoneurons in rats does not38 .
although 
 the present and other previous studies have not investigated such factors with regard to toe 
 flexion , it is possible that such factors are associated with the early reduction of toe 
 flexor strength observed in this study .
first , the cross - sectional 
 nature of this study limits our ability to draw causal inferences from the relationships 
 observed .
it is still unclear whether increasing the physical activity level promotes the 
 enhancement of toe flexor strength , or whether higher toe flexor strength promotes increases 
 in the physical activity of elderly men .
further longitudinal studies are needed to fully 
 understand the relationship between toe flexor strength and physical activity .
second , 
 participants were not randomly sampled , as all of the participants were volunteers and 
 able - bodied community - dwelling persons .
it is still not known 
 whether the differences in the rate of age - related reduction in muscle strength among toe 
 flexion , hand grip , and knee flexion are the same for women .
gender differences concerning 
 age - related reductions in muscle force generation and volume have not been previously 
 reported21 , 39 . additionally , a previous study showed that toe flexor strength of 
 male subjects in their 70s was 38.5% lower than in that of the males in their 20s , but 29.8% 
 lower in women23 , suggesting that the 
 age - related reduction in toe flexor strength could be lower in women than in men .
fourth , 
 this study examined young ( 1823  years ) and elderly ( 6588  years ) men , but not middle - aged 
 men .
lynch et al.40 demonstrated that 
 elbow flexion force linearly decreased with age , whereas knee extension force decreased in a 
 quadratic way .
the possibility that different relationships of age - related decline among 
 muscle groups impact the relative decline levels of the toe flexor , hand grip , and knee 
 extensor strengths can not be ruled out .
fifth , physical activity was estimated using a 
 self - administered questionnaire which is considered a less reliable and valid method .
it has 
 been reported that questionnaires often over- or underestimate physical activity level due 
 to recall bias41 . despite these limitations ,
this study is the first to demonstrate the early loss of toe 
 flexor strength compared to other muscle strengths , and the relationship between toe flexor 
 strength and the physical activity levels of elderly men .
it has been reported that elderly 
 persons with poor toe flexor strength have difficulty walking safely under certain 
 conditions5 .
thus , toe flexor strength 
 should be considered a good indicator of muscle function and the physical fitness of elderly 
 persons .
 [ purpose ] to compare the toe flexor , hand grip and knee extensor strengths of young and 
 elderly men , and to examine the association between toe flexor strength and physical 
 activity or inactivity levels . 
 [ subjects and methods ] young ( n=155 , 1823  years ) and 
 elderly ( n=60 , 6588  years ) men participated in this study . 
 toe flexor , hand grip , and 
 knee extensor strength were measured . physical activity ( time spent standing / walking per 
 day ) and 
 inactivity ( time spent sitting per day ) were assessed using a self - administered 
 questionnaire . 
 [ results ] toe flexor , hand grip , and knee extensor strength of the elderly 
 men were significantly lower than those of the young men . 
 standing / walking and sitting 
 times of the elderly men were lower than those of the young men . 
 toe flexor strength 
 correlated with hand grip and knee extensor strength in both groups . in elderly men , toe 
 flexor strength correlated with standing / walking time . in comparison to the young men s 
 mean values , toe flexor strength was significantly lower than knee extensor and hand grip 
 strength in the elderly group . 
 [ conclusion ] the results suggest that age - related reduction 
 in toe flexor strength is greater than those of hand grip and knee extensor strengths . 
 an 
 early loss of toe flexor strength is likely associated with reduced physical activity in 
 elderly men . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION