one of the most important topics in the research on human muscles has been the brain s 
 control over maximal voluntary contractions1 .
this is related to whether the motoneuron pool has sufficient 
 excitability relative to the force the muscle attempts to generate .
this can be examined by 
 analyzing the muscular response pattern upon transmission of a maximal electrical stimulus 
 generated by a muscle undergoing a maximal voluntary contraction2 .
a single transmitted electric stimulus is referred to as an 
  interpolated twitch  , and the technique is called  the twitch interpolation technique  . as 
 the intensity of a muscular contraction increases , the amplitude of the twitch decreases ; 
 the excitability of the motoneuron pool can be measured by assessing the degree of amplitude 
 reduction .
one application of this method is measurement of the level of muscular inhibition 
 ( mi ) .
muscular inhibition refers to the amount of muscle inhibited from carrying out a 
 maximal voluntary contraction ordered by the brain .
the inhibition occurs via a process in 
 which a supramaximal electric stimulus is transmitted to the nerve connected to the muscle 
 undergoing a maximal voluntary contraction3 . in general , resisted movement , a training method to enhance muscular functions , does not 
 increase muscle strength by increasing the number of muscle fibers but rather increases 
 muscle strength by expanding them . increased muscle strength during the early stages of 
 training is merely the result of the adaptation of neural factors , not the result of muscle 
 hypertrophy4 .
such neuromuscular 
 adaptation is known to be induced by the use of submaximal stress during the initial stages 
 of training .
similarly , increased muscle strength after long - term resistance exercise is not 
 solely the result of muscle hypertrophy either , as neuromuscular factors may be 
 involved5 , 6 . walking and running  the two most representative aerobic exercises  are becoming increasingly 
 popular among people seeking to improve their health .
resistance exercise , a type of 
 anaerobic exercise , is attracting many health - seeking individuals as well .
as is evident , 
 many people are engaging in physical activities centered on enhancing cardiopulmonary and 
 muscular functions . reaping the benefits from these exercises
unfortunately , however , many fail to exploit these workouts to their 
 fullest due to an insufficient number of workout sessions , short - term and intermittent 
 workouts , and early termination .
inappropriate and sudden stress , muscular fatigue , and muscular activation may increase the 
 risk of injury by changing several properties of the muscles7 .
most of the existing research has simply focused on the changes in outcomes , such as 
 changes in muscular strength or exercise performance after resistance exercise .
any form of 
 change in outcome implies a change in the various internal environments within a muscle ; 
 that is , it signifies that there are several neuromechanical changes within the muscle , such 
 as neurological , functional , and mechanical changes , and that the features of these changes 
 are dependent on the exercise load and amount of stimulation .
therefore , it is essential to 
 analyze the internal environment of muscles against a variety of external environmental 
 factors and stimulation conditions in order to determine the causes of change .
thus , this study employed a neuromechanical approach and used the interpolated twitch 
 technique ( itt ) to conduct a comprehensive and multilateral analysis of the neurological , 
 functional , and mechanical changes in human skeletal muscles related to resistance 
 exercise .
the subjects in this study consisted of 11 healthy adult males in their 20s , none of whom 
 had any orthopedic history ( age , 23.4  1.4  years ; height , 178.5  5.2  cm ; weight , 75.6  
 8.7  kg ) at the time of the study .
the subjects received a complete explanation of the 
 objective and contents of this study , as well as the study procedures , subjects rights , and 
 safety issues , after which they voluntarily agreed to participate and signed an informed 
 consent in accordance with the ethical standards of the declaration of helsinki .
the subjects performed a standing barbell calf raise exercise to examine the changes that 
 occur in the ankle plantar flexors after resistance exercise . to ensure an equal amount of 
 resistance for all of the subjects ,
the subjects were directed to perform sufficient warm - up 
 activities and to choose a load equal to their weights .
they placed the bar on the back of 
 their shoulders with their legs apart at a distance equal to the shoulder length , placed the 
 metatarsal region of their feet on top of a 5-cm block , and raised their heels at a constant 
 speed . as they raised their heels , the subjects were directed to reach the maximum plantar 
 flexion , utilizing the maximum range of motion ( rom ) of their ankle joint , and when lowering 
 their heels , the heels were to be maintained at a point just above the ground .
the subjects 
 performed a total of five sets consisting of 10 repetitions per set .
the present study measured two types of muscular contractions : a maximal voluntary 
 isometric contraction and a supramaximal muscular contraction after resistance exercise , as 
 generated by a twitch ( that the human body can not produce voluntarily ) induced by an 
 artificial electrical stimulation .
the equipment used to transmit the electrical stimulus 
 was a grass 88 siu-5 electrical stimulator ( grass technologies , natus neurology , warwick , 
 ri , usa ) .
the pulse duration ( 0.5  s ) was equally applied to all subjects with an 
 inter - pulse duration of 20  ms . to determine the optimal stimulation point ,
the ankle was fixed at 10 in the plantar 
 flexion position , and an anode was attached to the femur above the patella , while a cathode 
 was attached to posterior tibial nerve , which shows the maximum response in the posterior 
 popliteal region .
the maximum stimulation point was found by means of singlet stimulation , 
 after which doublet stimulation was applied to induce a supramaximal contraction .
the electrical stimulus was given two times each in consideration of the potentiated 
 effect , and the information about the torques and angles was saved on a personal computer 
 after computing the voltage value from a dynamometer and running it through an 
 analogue - digital ( a / d ) converter .
a bagnoli 8-channel wireless electromyography ( emg ) system ( delsys , boston , ma , usa ) with a 
 sampling rate of 200  hz and band - pass filter of 2045  hz was used to collect 
 electromyographic signals .
the electromyography system was used to measure the level of 
 supramaximal contraction via stimulation of the posterior tibial nerve and the levels of 
 agonist and antagonist activation during a maximal voluntary isometric contraction ( mvic ) . 

the electrodes were placed parallel to the muscle fibers located in the center of the 
 muscle belly of the tibialis anterior , soleus , lateral gastrocnemius , and medial 
 gastrocnemius muscles . before placing the electrodes ,
the surfaces were shaved and 
 sterilized with alcohol to minimize the skin resistance levels .
the electromyographic 
 signals were fed into an a / d converter and later saved on a personal computer .
this study used the labview 8.0 ( national instruments , austin , tx , usa ) software to collect 
 measurement data and save it onto a personal computer .
torques and angle signals were 
 received from the dynamometer , the signals from the four muscles were received from the 
 electromyography system , and synchronization signals were received from the electrical 
 stimulator .
these data were fed into the a / d converter , and the resulting digital data were 
 saved on a personal computer .
the voltage value received from the dynamometer was 
 recalibrated and converted to an nm value for analysis , while the remaining signals were 
 extracted as real data using chart 5 for windows ( adinstruments , colorado springs , co , usa ) 
 program .
the collected data were statistically analyzed using the spss for windows , version 12.0 , 
 software .
the mean ( m ) and standard deviation ( sd ) were calculated , and a paired t - test was 
 conducted to compare the difference in each variable before and after the resistance 
 exercise .
the mvic torque was found to have decreased from 122.06  21.05 nm ( before exercise ) to 
 116.80  19.71 nm ( after exercise ) , but the change was not statistically significant .
the resting twitch torque also decreased , from 37.04  10.14 nm ( before exercise ) to 31.46 
  8.61 nm ( after exercise ) , and the change was statistically significant ( p<0.01 ) .
mi appeared to have increased from 5.83  6.16% ( before exercise ) to 7.18  5.05% ( after 
 exercise ) , but the increase was not statistically significant .
moreover , muscle activation 
 slightly decreased from 0.144  0.066 v ( before exercise ) to 0.139  0.065 v ( after 
 exercise ) , but there was no statistical significance .
the muscle contraction time decreased from 0.13  0.01  msec ( before exercise ) to 0.12  
 0.01  msec ( after exercise ) , and the change was statistically significant ( p<0.001 ) . 

similarly , the half relaxation time was also decreased , from 0.09  0.01  msec ( before 
 exercise ) to 0.07  0.01  msec ( after exercise ) , and the difference was statistically 
 significant ( p<0.001 ) ( table 1table 1.changes in muscle properties of the ankle plantar flexor after heel raise 
 exercise ( meansd)variableprepostmvic ( nm)122.06  21.05116.80  19.71rtt ( nm)37.04  10.1431.46  8.61**mi ( % ) 5.83  6.167.18  5.05rms ( v)0.144  0.0660.139  0.065ct ( msec)0.13  0.010.12  0.01***hrt ( msec)0.09  0.010.07  0.01***mvic : maximal voluntary isometric contraction ; rtt : resting twitch torque ;
mi : muscle 
 inhibition ; rms : root mean square of muscle activation ; ct : contraction time ; hrt : 
 half relaxation time . * * p<0.01 ; * * * p<0.001 ) .
mvic : maximal voluntary isometric contraction ; rtt : resting twitch torque ; mi : muscle 
 inhibition ; rms : root mean square of muscle activation ; ct : contraction time ; hrt : 
 half relaxation time . * * p<0.01 ; * * * p<0.001
the present study sought to conduct a comprehensive and multilateral analysis of acute 
 neurological , functional , and mechanical changes in human skeletal muscles after resistance 
 exercise through a neuromechanical approach .
the itt was developed by merton in 19548 
 as a means of measuring the inactivation of the adductor pollicis muscle .
it has been used in several studies 
 that have reported the level of muscular activation ( prominently in the ankle dorsiflexor 
 and plantar flexor9 , the quadriceps 
 femoris muscle10 , and the elbow joint 
 flexor4 ) during a maximal voluntary 
 contraction .
furthermore , the itt has been used in analyzing the mechanisms of muscular 
 fatigue and muscle weakness induced by a range of causes . in particular ,
the itt has been utilized in studies of neural adaptation during a maximal 
 isometric contraction in relation to physical training1 .
this study used a dynamometer and electrical stimulator to compare and analyze the mvic 
 torques and twitch torques before and after resistance exercise in an attempt to ascertain 
 the changes in muscular strength induced by resistance exercise .
the mvic was interpreted as 
 a voluntary contraction produced by neural control , and the twitch torque was interpreted as 
 a contraction dependent on the mechanical properties of peripheral nerves without any neural 
 control .
the resting twitch torque value was calculated by averaging the two twitches 
 induced by the electrical stimuli , and the resting mvic torque value was the value at the 
 point of maximum contraction based on the passive torque11 .
the measurements showed that the mvic torque was lower after resisted exercise , but the 
 change was statistically insignificant .
these results indicate that there is a greater reduction in muscular strength ( after 
 resistance exercise ) due to the peripheral mechanical systems of muscles than due to 
 neurological factors12 .
they also signify 
 that although fatigue has an effect on both factors , it has a greater impact on the 
 mechanical factors13 .
future researchers 
 should conduct further studies on long - lasting fatigue and fatigue reduction or recovery 
 factors .
muscle activation was measured using an electromyography system and the mi value to analyze 
 neuromuscular properties .
the mi value was calculated by measuring the twitching plantar 
 flexor torque induced by a supramaximal electrical stimulus applied to the posterior tibial 
 nerve when the plantar flexor muscles were undergoing a maximal voluntary isometric 
 contraction .
the root mean square ( rms ) of muscular activation was computed by running the 
 measured waveform through the emgwork 4.1 software ( delsys , boston , ma , usa ) .
the results 
 indicated no significant changes in the mi or rms in relation to resisted training .
the statistical insignificance pertaining to muscle inhibition and activation should be 
 examined in association with similar statistically insignificant changes ( caused by 
 neurological factors ) in muscular strength during an mvic14 .
neurological factors not only generate muscle strength but also 
 play a role in the acute effects of resistance exercise . in fact , it can be said that 
 peripheral neurological factors sustain the functional decline of mechanical factors induced 
 by twitching stimulations and that they are less influenced by acute effects overall .
the 
 muscle contraction time and half relaxation time were analyzed to examine the functional 
 properties of skeletal muscles .
the contraction time refers to the period from rest to the 
 onset of maximum torque , and the half relaxation time refers to the time it takes for the 
 maximum torque value to decline by half .
generally , muscle contraction times and half 
 relaxation times are thought to be prolonged as muscular fatigue accumulates15 .
likewise , the reductions in contraction time and half relaxation time found in this study 
 appear to stem from muscular fatigue induced by the resistance exercise .
similar to other 
 factors , the measurement variables induced by twitch stimuli all have a statistically 
 significant impact on the acute effects noted during resistance exercise . in summary , the acute effects of resistance exercise have a temporary impact on the 
 peripheral mechanical system itself , not on the neurological factors , in terms of reducing 
 muscle strength .
future studies should more closely examine the roles of neurological 
 factors in intensifying fatigue and several neuromechanical factors in relation to the 
 periods and lengths of recovery exercises .
 [ purpose ] the purpose of this study was to perform a quantitative assessment of 
 neuromechanical adaptation in skeletal muscles and to propose the scientific underpinnings 
 of the acute effects induced by resistance exercise . 
 [ subjects ] the subjects in this study 
 were 11 healthy adult men in their 20s who had no orthopedic history at the time of the 
 study . to examine any signs of resistance exercise - induced changes in the ankle plantar 
 flexor , 
 the subjects were directed to perform a standing barbell calf raise routine . 
 
 [ methods ] subjects were to carry a load equal to their weights and to perform five sets of 
 ten repetitions . the maximal voluntary isometric contraction torque , resting twitch 
 torque , muscle inhibition , root mean square of muscular activation , contraction time , and 
 half relaxation time were analyzed by synchronizing a dynamometer , an electrical 
 stimulator , and an electromyography system . [ results ] the maximal voluntary isometric 
 contraction torque appeared to decline , but the change was not statistically significant . 
 the decline of resting twitch torque , on the other hand , was found to be statistically 
 significant . muscle inhibition and root mean 
 square of muscular activation were both 
 reduced , but both changes were not statistically significant . 
 lastly , contraction time and 
 half relaxation time both statistically decreased significantly after resistance exercise . 
 
 [ conclusion ] these results indicate that the acute effects of resistance exercise have a 
 greater impact on the peripheral mechanical system itself , rather than on neurological 
 factors , in terms of the generation of muscle force . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION