the heel raise test is often used in a clinical setting to evaluate the function of the 
 calf muscle .
muscle activities are increased during activities such as walking , running , and 
 jumping .
the standing heel raise , called the  calf raise  , is a commonly prescribed exercise 
 for improving the strength and power of the ankle plantar flexors . in physical therapy ,
the 
 strength of the ankle plantar flexors is also measured during one - footed standing1,2,3,4,5,6,7 .
however , the single - leg heel raise can be 
 difficult for patients with ankle disorder and elderly people because of decreased balance 
 function .
therefore , the double - leg heel raise ( dhr ) is potentially useful for the clinical 
 evaluation of ankle plantar flexors8 .
there have been few studies on the maximum plantar flexion ( mpf ) moment during the dhr . 

flanagan9 reported that the mpf moment 
 for older adults was 0.85  0.18 nm / kg during the dhr and 1.50  0.23 nm / kg during the 
 single - leg heel raise .
the activity of the plantar flexor muscles increases during the single stance 
 phase : from the mid - stance to terminal stance phase .
ishikawa10 indicated that tendinous tissues of both the soleus and 
 gastrocnemius muscles slowly stretched during the single support phase and dramatically 
 recoiled during the pre - swing phase , contributing to the storage of elastic energy .
akizuki 
 et al.11 reported that the plantar flexor 
 activity was 30% of the maximum voluntary contraction ( mvc ) during normal speed walking . 

however , little attention has been paid to the plantar flexor activity during walking in 
 comparison with that during the calf raise .
therefore , in the present study , we aimed to 
 evaluate the difference in the muscle activity between the dhr and walking .
thirty healthy young males participated in this study ( age 21.5  1.6  years , weight 63.6  
 9.3  kg , height 171.0  4.5  cm ) .
all the subjects provided written informed consent prior to 
 participation , and the human subjects ethics committee of tohoku bunka gakuen university 
 approved the study .
the passive rom of plantar flexion at the right ankle joint was measured with subjects in a 
 supine position using a goniometer ( ttm - kj ; sakai medical co. , ltd . ,
the 
 active rom of plantar flexion was measured in a standing position under weight - bearing 
 conditions .
emg data were simultaneously acquired from both heads of the gastrocnemius and the soleus 
 muscle of the right leg during the dhr and treadmill walking .
after shaving and scrubbing 
 the skin with alcohol , disposable ag / agcl surface electrode discs with a diameter of 10  mm 
 ( blue - sensor n-00-s , ambu , copenhagen , denmark ) were attached to the skin at locations 
 recommended by perotto and delagi12 . for 
 each muscle ,
two electrodes were placed approximately 20  mm apart , in the direction of the 
 muscle fiber .
a reference electrode , shared by the four measurement channels , was placed on 
 the bony part of the malleolus lateralis .
emg was amplified by bipolar leads with an input 
 impedance > 10 m and a gain was 80db ( mt-11 ; gehc - j , tokyo , japan ) .
the foot - switch sensors ( p002 ; dkh co. , ltd . , tokyo , japan ) were attached to the planta 
 pedis , at the center of a line between the malleolaris lateralis and the malleolaris 
 medialis .
the pressure data from the foot - switch sensors were amplified ( ph-462 ; dkh co. , 
 ltd . , tokyo , japan ) , and downloaded onto a personal computer through an a / d converter at a 
 sampling frequency of 1 khz .
after emg and the foot - switch sensors were set up , each subject performed the dhr on a flat 
 structure consisting of a load cell ( sb-200k12 ; kyowa , japan ) and hard wooden boards .
the 
 right foot was placed on the load cell and loaded as much as the leg on the other side .
the 
 subjects received feedback information from the load cell via a digital amplifier and 
 indicator ( ad-4532 ; a&d , tokyo , japan ) , and they controlled the load placed on the right 
 foot so that it was half of body weight .
the heel raise was performed under four conditions : mpf , 3/4 mpf , 2/4 mpf , and 1/4 mpf .
mpf 
 was based on the active rom in a standing position under weight - bearing conditions .
the 
 subjects followed a rhythm of 1  hz produced with an electronic metronome , raising their 
 heels for 1  s and lowering them until they touched the ground in the next second ; therefore , 
 the complete movement cycle was over 2 s. for each heel - raise condition , the dhr was 
 performed five times in succession .
the height of the heel raise was controlled using the 
 bar of a device that was adjusted to touch the dorsum pedis at the selected heel - raise 
 height .
after the dhr test , the subjects walked on a treadmill ( evolve jp ; jonson health tech 
 japan , tokyo , japan ) .
the walking speed was set at 20 , 40 , 60 , 80 , or 100 m / min , and the 
 subjects walked for 1  min at each speed .
the emg and foot - switch data were recorded during 
 the last 30  s at each speed .
the analog emg signals and foot - switch data were passed through a 16-bit a / d board 
 ( powerlab ; adinstruments , nagoya , japan ) , and all signals were sampled at 1 khz .
the onset of right heel 
 contact was determined during the dhr and treadmill walking .
the emg data were filtered with 
 a 10-hz high - pass iir digital filter and zero - phase filtering . after the signal was 
 full - wave rectified , the moving average was calculated for an 89-ms window . for the emg data 
 during the dhr
we calculated 
 the average of five peak values and adopted it as the indicator of the muscle activity 
 during the dhr . on the other hand , during treadmill walking , emg data of each gait cycle 
 were converted into 100 data using a spline ; the data for each gait cycle was interpolated 
 to 100% of gait cycle at 1% intervals . after calculating the addition average values for all 
 gait cycles ,
we adopted the peak value as 
 the indicator of the muscle activity during treadmill walking .
a within - subject one - way analysis of variance ( anova ) was used to analyze differences in 
 the activity of the three muscles .
the independent variables were the height of the heel 
 raise and the walking speed , and the dependent variable was muscle activity .
differences were assessed 
 using two - sided tests , and an alpha level of 0.05 .
the passive mpf in the supine position was 53  6 degrees , and the active mpf in the 
 standing position was 50  6 degrees .
there were significant main effects of both the height of 
 the heel raise ( p < 0.001 ) and walking speed ( p < 0.001 ) .
the muscle activity during 
 the dhr significantly increased with the increase in the height of the heel raise ( table 1table 1.peak muscle activity during the double - leg heel raise ( n=30)%mpfsoleusgastrocnemiusmedial headgastrocnemiuslateral head25% mpf0.233 0.1010.279 0.1390.110 0.04950% mpf0.269 0.1190.333 0.1990.141 0.05375% mpf0.317 0.1340.372 0.2110.192 0.072mpf0.399 0.2080.456 0.2490.304 0.128there were significant differences between all conditions in each muscle ( mv ) . ) .
in addition , there were significant differences in muscle activity between 
 walking speeds for each muscle ( p < 0.001 ) . during treadmill walking , muscle activity 
 significantly increased with the increase in the walking speed ( table 2table 2.peak muscle activity during walking ( n=30)soleusgastrocnemiusmedial headgastrocnemiuslateral head20 m / min0.078 0.0170.079 0.0180.054 0.00940 m / min0.092 0.0230.103 0.0270.064 0.01160 m / min0.104 0.0260.107 0.0250.073 0.01480 m / min0.132 0.0310.120 0.0250.098 0.018100 m / min0.179 0.0400.146 0.0280.137 0.026soleus muscle activity : there are the significant differences except for between 20 
 and 40 m / min and between 40 and 60 m / min .
gastrocnemius medial head muscle : there are 
 the significant difference except for between 40 and 60 m / min and between 60 and 80 
 m / min .
gastrocnemius lateral head : there are significant differences between all 
 speeds ( mv ) . ) .
there were significant differences in the muscle activity of the 
 gastrocnemius lateral head between all walking speeds ; however , there were no significant 
 differences in the gastrocnemius medial head activity between 40 and 60 m / min and between 60 
 and 80 m / min , and there were no significant differences in the soleus activity between 20 
 and 40 m / min and between 40 and 60 m / min .
soleus muscle activity : there are the significant differences except for between 20 
 and 40 m / min and between 40 and 60 m / min .
gastrocnemius medial head muscle : there are 
 the significant difference except for between 40 and 60 m / min and between 60 and 80 
 m / min .
gastrocnemius lateral head : there are significant differences between all 
 speeds ( mv ) .   in the comparison of the muscle activity at 1/4
mpf with that at each walking speed , the 
 activity of the soleus in 26.7% of the subjects at a walking speed of 100 m / min was higher 
 than that during the dhr , while the activity in the gastrocnemius lateral head in 80.0% of 
 the subjects was higher than that during the dhr .
however , in the comparison of the muscle 
 activity at mpf with that at a walking speed of 100 m / min , this value decreased to 23.3% for 
 the gastrocnemius lateral head .
furthermore , in the comparison of the muscle activity at mpf 
 with that at each walking speed , the activities of the soleus and gastrocnemius medial head 
 during walking exceeded those during the dhr in only 3.3% of subjects ( table 3table 3.percentage of subjects in whom walking generated higher emg activity than the dhr 
 for each plantar flexion condition at each walking speed ( n = 30)20 m / min40
m / min60 m / min80 m / min100 m / minsogmglsogmglsogmglsogmglsogmgl1/4 mpf6.70.06.73.33.320.03.36.730.010.03.356.726.720.080.01/2 mpf0.00.06.70.00.010.03.36.713.36.76.736.723.310.070.03/4 mpf3.30.03.30.03.36.70.03.310.00.03.323.310.03.333.3mpf0.00.00.00.00.03.30.00.03.30.03.310.03.33.323.3mpf : maximum plantar flexion ; so : soleus ; gm : medial head of gastrocnemius ; gl : 
 lateral head of gastrocnemius ( % ) ) .
mpf : maximum plantar flexion ; so : soleus ; gm : medial head of gastrocnemius ; gl : 
 lateral head of gastrocnemius ( % )
the heel - raise test is often used in a clinical setting to evaluate the function of the 
 calf muscles .
however , the single - leg heel raise can be difficult for the elderly and other 
 people with decreased balance function .
therefore , we proposed that the dhr test could be a 
 useful alternative to the single - leg heel raise test for the clinical assessment of ankle 
 plantar flexors .
the results of this study indicated that the dhr test is useful for 
 evaluation of the ankle plantar flexor activity necessary for walking .
there have been many studies on the plantar flexion torque of the ankle joint during 
 walking ; however , the findings have been variable , and many gait characteristics are also 
 dependent on gait velocity13 , 14 .
devita and hortobagyi15 showed that the peak torque of the ankle joint at a comfortable 
 walking velocity of 89 m / min was 136  27 nm in young subjects and 102  29 nm in elderly 
 subjects . browning and
kram13 studied 
 plantar flexion torque during walking at different velocities and found that the peak 
 plantar flexion torque was 63.9  4.85 nm at 30 m / min and 85.8  8.03 nm at 90 m / min . 

flanagan et al.9 reported that the peak 
 torque was 0.85 nm / kg during the dhr . therefore , if the body mass of the subjects ranged 
 from 60 to 80  kg , the peak torque would range from 51 to 68 nm . in that study , the plantar 
 flexion peak torque for the dhr was lower than that for walking
. however , analysis of the 
 muscle activity of the main plantar flexors in the present study provided different 
 results .
the heel - raise test involves eccentric - concentric muscle contraction of the plantar 
 flexors .
eccentric pre - activation renders an increase in performance during the concentric 
 phase , partly through the utilization of the elastic energy stored during the pre - activation 
 phase .
mueller et al.16 reported that the 
 plantar flexion peak torque , measured using an isokinetic device , accounted for 40% and 53% 
 of the variance in peak ankle moment and power during walking , respectively , and that there 
 was a strong correlation between plantar flexion peak torque and dorsiflexion rom .
the 
 authors explained that an increase in the dorsiflexion rom allows for an increase in the 
 requirement for the external dorsiflexion moment and necessarily increases the requirement 
 for internal ( muscle generated ) control of the plantar flexion moment during walking . 

however , ankle dorsiflexion during the mid - stance phase may be important for other reasons . 

ishikawa et al.10 noted that the 
 tendinous tissues of both the soleus and gastrocnemius muscles were slowly stretched during 
 the single support phase and dramatically recoiled during the pre - swing phase , contributing 
 to the storage elastic energy . in this respect ,
however , 
 during walking , the kinetics change from the closed kinetic chain of the stance phase to the 
 open kinetic chain of the swing phase . on the other hand
this suggests that humans use muscle activity more efficiently during walking . in the 
 present study ,
the activities of the soleus and gastrocnemius muscles during walking were 
 less than those of these muscles during mpf .
suzuki et al.17 reported that the 
 isometric strength of the plantar flexors was an important independent predictor for 
 habitual gait velocity in community - dwelling older women .
the plantar flexor muscles of the 
 ankle joint play an important role in the generation of torque during walking .
in addition , 
 low torque of the plantar flexor muscles has been linked to an increased risk of falling in 
 older individuals .
therefore , a simple method for evaluation of plantar flexor function is 
 important for clinical assessment , and the dhr test fulfils this role . in the present study , measurement of the plantar flexor muscle activity
however , the gastrocnemius and soleus muscles can produce a large amount of torque 
 compared with other plantar flexor muscles .
although the maximum force of the triceps surae 
 is 1620 n , the maximum force of the tibialis posterior is only 267 n18 . if a moment arm is considered , the plantar flexion torque 
 of the tibialis posterior is much smaller than that of the triceps surae .
in addition , the 
 double - leg heel raise does not allow us to evaluate the strength of the right and left calf 
 muscle independently .
however , the present study , which examined the dhr with half the body 
 weight bearing by each lower extremity , indicates that it may be used as a criterion of 
 muscle weakness if the center of gravity shifts into the left or right .
 [ purpose ] we aimed to evaluate the difference in the muscle activity between the 
 double - leg heel raise ( dhr ) and treadmill walking . [ subjects ] 
 thirty healthy males aged 
 21.5  1.6  years ( body mass 63.6  9.3  kg , height 171.0  4.5  cm ) participated in the 
 study . 
 [ methods ] electromyograms were simultaneously recorded from both heads of the 
 gastrocnemius and the soleus of the right side during the dhr and treadmill walking . 
 the 
 dhr conditions were maximum plantar flexion ( mpf ) , 3/4 mpf , 2/4 mpf , and 1/4 mpf , and the 
 walking speeds were 20 , 40 , 60 , 80 , and 100 m / min . 
 [ results ] the muscle activity during 
 the dhr and walking significantly increased with increments in the height of the heel 
 raise and walking speed , respectively . 
 comparison of the muscle activity at mpf with that 
 at each walking speed revealed that the muscle activity in the soleus and gastrocnemius 
 medial head during walking exceeded that during the dhr in less than 3.3% of cases . 
 
 [ conclusion ] the dhr test is useful for evaluating the ankle plantar flexor activity 
 necessary for walking . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION