human movement can be classified into walking and running , the latter of which easily 
 fatigues the lower limb muscles1,2,3,4 . during running
, the lower limbs must cope with the repeated 
 transient impact of vertical ground reaction force ( grf ) , which is an abrupt collision force 
 equal to about 1.5- to 3-fold the body weight5 .
such repeated impacts are considered to cause lower limb muscle 
 fatigue via chronic irritation .
the incidence of running injury is affected by the running 
 velocity and distance ran .
investigated 17,000 patients6 and found a significantly higher incidence of osteoarthritis 
 in men who were involved in running > 20 miles per week .
koplan et al . found that the 
 risk of injury increased with increasing weekly distance3 .
on the other hand , imai et al.7 found that the number of marathon athletes who stopped running 
 within four hours was significantly high .
running 
 faster generally produces greater ground reaction force ( grf ) and imposes greater stress on 
 various parts of the body8 , 9 .
running injuries occur most frequently in the knee , 
 foot / ankle , and lower leg according to taunton , et al.10 , who found that the most common overuse injuries included 
 patellofemoral pain syndrome , iliotibial band friction syndrome , and plantar fasciitis . running velocity is affected by various conditions including individual running ability .
we 
 postulated that the load imposed on the lower limbs would change at different running 
 velocities . furthermore , because portion failure differs among individuals , the load applied 
 to each muscle is probably not uniform .
therefore , we analyzed muscle 
 activity under free walking , jogging (  8.7  km / h ) , and running (  8.8  km / h ) conditions on a 
 treadmill .
ten male students without leg injuries ( age , 23.2  6.5 y ; height , 170.4  5.7  cm ; weight , 
 67.6  11.1  kg ; bmi , 23.3  3.2 ) provided written informed consent to participate after 
 receiving an oral and written explanation of the study and its purpose .
the ethics review 
 board at heisei college of health sciences approved this study ( no .
the 
 participants did not routinely run but participated in recreational sports once or twice 
 each week .
muscle activity was measured by surface electromyography using a telemyo g2 and 
 myoresearch xp ( noraxon usa inc . ,
scottsdale , az , usa ) with disposable m-00-s blue sensor 
 polymer electrodes ( ambu a / s , ballerup , denmark ) attached to the belly of the muscle while 
 the participants moved on a gait trainer system 2 treadmill ( biodex medical systems inc .
muscle output was recorded at 30 frames / sec using a video camera to 
 synchronize the movements with the electromyographic data .
activity was assessed at the left 
 vastus medialis , vastus lateralis , hip adductors , tibialis anterior , lateral head of 
 gastrocnemius , medial head gastrocnemius , and soleus .
maximum voluntary isometric contraction ( mvc ) was determined as manual resistance against a 
 maximally contracted muscle .
the participants walked , jogged , and ran for 10 minutes in 
 random order , and the myogenic potentials were measured for 30 seconds 10 minutes later . 

analog signals of myogenic potential were processed using a band - pass filter ( 10500  hz ) at 
 a sampling frequency of 1,000  hz . the greater trochanter , lower limb joint space , and lateral malleolus of the left hip , 
 knee , and ankle were marked with tape to measure the range of motion .
one 30-second cycle of 
 walking , jogging , and running recorded with the video camera was selected , and then initial 
 contact , mid stance , toe off , and the range of motion of hip flexion , knee flexion , and 
 ankle dorsiflexion were measured on printouts .
in addition , using the time required for one 
 cycle , stride was calculated .
electromyographic data were analyzed using the average value of each muscle output and 
 central frequency .
the average activity was calculated from 30-second cycles of walking , 
 jogging , and running , including both the swing and stance phases .
these output values were 
 divided by the mvc to determine the % mvc of each muscle .
in addition , lower limb joint 
 angles on printouts were measured using a protractor .
the data were analyzed using a one - way 
 analysis of variance , and statistical significance was accepted at p < 0.05 .
the average walking , jogging , and running speeds were 3.6  0.4 , 6.7  0.6 , and 10.4  
 1.3  km / h , respectively .
the average electromyographic activities of the vastus medial , tibialis anterior , medial 
 head of the gastrocnemius , and lateral head of the gastrocnemius were significantly higher 
 during jogging and running compared with walking .
the hip adductors and vastus lateralis did not significantly 
 differ ( table 1table 1.average % mvc of muscles ( n=10)walkingjoggingrunningvastus medialis12.52.735.85.3 * 38.84.6*vastus lateralis17.16.136.38.137.76.8hip adductors31.26.741.07.250.17.1tibialis anterior14.31.329.33.8 * 37.63.0*lateral head of the gastrocnemius16.03.042.68.5 * 40.86.2*medial head of the gastrocnemius30.83.758.17.6 * 63.35.3*soleus18.45.039.67.844.86.2*values are meansse . * p<0.05 , vs. walking . ) .
the maximal electromyographic activities of the vastus medialis during jogging and running 
 and medial head of the gastrocnemius during running were significantly higher than during 
 walking ( table 2table 2.maximum % mvc of muscles ( n=10)walkingjoggingrunningvastus medialis54.87.6105.915.2 * 135.711.5*vastus lateralis68.129.0103.117.0134.423.6hip adductors147.231.598.620.2137.320.0tibialis anterior54.16.385.820.787.87.9lateral head of the gastrocnemius69.014.4125.527.7136.515.1medial head of the gastrocnemius129.921.6190.427.8224.226.0*soleus103.351.8113.625.9179.028.6values are meansse .
the central frequency did not significantly differ ( table 3table 3.average central frequency of muscles ( n=10)walkingjoggingrunningvastus medialis23.16.437.95.932.46.4vastus lateralis29.75.840.35.641.86.9hip adductors15.24.120.44.123.33.4tibialis anterior59.86.066.06.566.17.4lateral head of the gastrocnemius34.37.142.77.255.76.0medial head of the gastrocnemius50.07.362.59.963.19.2soleus61.27.645.18.259.711.8values are meansse ) .
the angle of the knee at initial contact , mid stance , and toe off significantly differed , 
 with the knee being more flexed during jogging and running than walking the knee being more 
 flexed during running than jogging at mid stance and toe off ( table 4table 4.average left lower limb joint angles ( n=10)walkingjoggingrunninghip joint flexionic20.52.424.52.228.02.9ms10.51.623.51.5 * 28.51.7*to6.02.23.02.6 * 5.51.9*knee joint flexionic4.22.114.82.2 * 17.22.0*ms15.02.141.51.5 * 48.01.5*,**to57.11.338.92.4 * 25.42.4*,**ankle joint dorsiflexionic2.23.64.02.06.21.1ms6.51.320.01.7 * 22.01.3*to14.82.214.82.720.13.5values are meansse . * p<0.05 , vs. walking . * * p<0.05 , vs. jogging .
ic : initial 
 contact , ms : mid stance , to : toe off ) .
ic : initial 
 contact , ms : mid stance , to : toe off the average lengths of the running stride were significantly longer than those of jogging 
 and walking . also , that of jogging was significantly longer than that of walking ( table 5table 5.average length of stride ( n=10)walkingjoggingrunningstride ( m)1.240.041.460.06 * 2.140.08*,**values are meansse .
hreljac identified training , anatomy , and biomechanical factors as risk factors associated 
 with running , since fast running generates considerable grf and training to run stresses the 
 joints , muscles , and ligaments12 .
the 
 present study investigated differences in the amount of muscle activity during walking , 
 jogging , and running .
all participants walked freely at their own pace and then jogged at  
 8.7  km / h and ran at  8.8  km / h .
the central frequency of each muscle seemed to remain essentially unchanged between running 
 and jogging compared with walking , and fatigue did not arise .
the vastus lateralis and 
 vastus medialis of the quadriceps not only act on the lower limb during running or walking 
 but also suppress damage to the knee during weight - bearing in the stance phase .
therefore , 
 we speculated that the amount of muscle activity would increase as the grf increases .
the 
 averaged values of the vastus medialis were significantly higher during running and jogging 
 compared with walking .
brownstein et al.13 found that a knee position that is more flexed than extension is 
 due to the amount of activity of the vastus medialis .
the present study found that the knees 
 were flexed significantly more during running and jogging compared with walking at initial 
 contact and during mid stance .
these findings support the notion that the vastus medialis 
 works easily during jogging and running .
in addition , kim et al.14 showed that the amount of activity in the vastus medialis 
 rose in response to an elevated walking speed .
furthermore , in a previous study15 , we compared the muscle activity during 
 jogging and walking at the same velocity . in this study , the activity of the vastus medialis 
 during jogging was significantly higher , and the knee joints exhibited significant flexion 
 during jogging .
load was 
 especially applied in the direction of internal rotation in the stance phase . a study by ono 

et al.17 showed that the output of the 
 vastus medialis was increased in the lower leg during internal rotation . on the other hand , 
 the output at 90 of flexion between knee extension from the vicinity of the vastus 
 lateralis muscle did not significantly change13 .
in addition , the activity of the vastus lateralis muscle during 
 walking was significantly higher , which could account for the small difference between 
 walking and running .
the average 
 values of the adductor muscles did not significantly differ among walking , jogging , and 
 running .
along with the outer muscles of the hip joint such as the gluteus medius , the 
 adductor muscles maintain the inner - outer intermediate position of the lower limb during 
 running .
the types of hip movement involved in running are primarily flexion and extension , 
 with minimal adduction and abduction . in addition , because the treadmill floor is 
 horizontal , the trunk is also likely to become upset .
therefore , we considered that the 
 adductor muscles do not play significant roles in walking , jogging and running .
the averages values for the tibialis anterior muscle were significantly higher during 
 running and jogging compared with walking .
the tibialis anterior muscle contracts either 
 centrifugally or isometrically before and after initial contact to control the foot to 
 prevent falling18 , 19 .
this muscle was significantly more contracted during running and 
 jogging , perhaps because movement was faster .
the average values of the lateral and medial heads of the gastrocnemius were significantly 
 higher during running and jogging compared with walking .
the gastrocnemius works from the 
 loading response to the terminal stance between the stance phase18 .
the knee joint extends in the late stance phase of the 
 running stride via plantar flexion of the ankle joint .
the force exerted on the achilles 
 tendon during running exceeds 12-fold the weight of the runner20 .
a large output by the gastrocnemius is required to 
 advance the body during running .
the average value of the soleus muscle was significantly higher during running than during 
 walking .
the soleus is a single joint muscle that runs from the proximal portion of the 
 tibia and fibula to the achilles tendon .
thus , the amount of muscle activity is not affected 
 by the angle of the knee joint . because the knee flexes deeply in mid stance during running , 
 more extension is required at toe off , and thus a large force is required for the triceps 
 surae muscle . under such conditions
, the soleus muscle works more easily than the 
 gastrocnemius , which is a biarticular muscle . according to mann et al.21 , the angle of 
 the lower limbs and the amount of muscle activity increases during running at higher 
 velocities compared with walking .
the stance phase is longer than the swing phase during 
 walking but is shorter during running . according to kluitenberg et al.22 , grf on a treadmill and on the ground increases in the 
 same way when
aramptzis et al.23 reported that the mechanical power of the knee joint and 
 ankle joint increases with increasing running velocity , and the present study found that , 
 the stride was extended in accordance with the increase in velocity .
we considered that 
 exercise load is greater during running compared with walking due to these factors .
the 
 present study found that the amount of activity in the soleus muscle was significantly 
 higher during running and jogging compared with the amounts of activity in the vastus 
 medialis , tibialis anterior , and gastrocnemius muscle , which are involved in walking . 

therefore , it was suggested that an increase in velocity causes these muscles to carry a 
 heavier load .
 [ purpose ] the present study aimed to determine changes in muscle activity while moving on 
 a treadmill at various speeds . 
 [ subjects ] the activities of the left vastus lateralis , 
 vastus medialis , hip adductors , lateral head of gastrocnemius , medial head gastrocnemius , 
 soleus , and tibialis anterior of 10 healthy male university students were analyzed . 
 
 [ methods ] university students walked , jogged , and ran for 10 minutes each in random order , 
 and then myogenic potentials were measured 10 minutes later for 30 seconds . 
 the flexion 
 angle of the lower limb upon initial contact , mid stance , and toe off were measured . 
 
 [ results ] the average walking , jogging , and running speeds were 3.6  0.4 , 6.7  0.6 , and 
 10.4  1.3  km / h , respectively . 
 the average electromyographic activities of the vastus 
 medial , tibialis anterior , medial head of gastrocnemius , and lateral head of gastrocnemius 
 significantly differed . 
 all muscles were more active during jogging and running than 
 walking . 
 only the soleus was more active during running than walking , and the activities 
 of the hip adductors and vastus lateralis did not significantly differ . 
 [ conclusion ] 
 velocity is faster and the angles of the lower limbs and ground reaction force ( grf ) are 
 larger during running than walking . the vastus medialis and soleus worked more easily 
 according to the angle of the knee joint , whereas the tibialis anterior worked more easily 
 at faster velocities and the medial and lateral heads of the gastrocnemius worked more 
 easily with an increased grf . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION