Research On Lower Extrimity Stiffness And Muscle Neuromuscular Strength Training Adaptability Related To Running Economy

Objective: This study aims to:(1) explore the relationships between factorsaffecting the lower extremity stiffness and running economy (RE), determinebiomechanical index for running economy evaluation, compensate for the shortageof physiological index of running economy evaluation;(2) explore the effect of strengthtraining on skeletal muscle work economy, mechanical properties and surface EMGsignal characteristics, reveal the mechanism of strength training to improve RE,compensate for the current research shortage, provide reference to draw up targetedtraining plan for runners’ RE improvements.Methods:(1) In order to explore the relationship between running economy andthe lower extremity stiffness, avoid physiology and kinesiology factors have effect onexperimental results,14well trained middle and long distance runners(with4.55±0.96years of professional aerobic endurance training experience) were recruited into thisstudy and were distributed into two groups according to their RE, MTU stiffness oflower extremity and pre-motion time of the achilles tendon reflex were measured forgroup comparisons, three dimension motion and force analysis were used to calculatethe leg stiffness and joint stiffness of the lower extremity during contact phase ofrunning, stable VO2of running at the speed of12km/h were collected to calculate REvalue. Pearson correlation analysis method was used to explore the relationship betweenRE and leg stiffens, joint stiffness of the lower extremity. Independent-samples T testwas used to compare the differences of the lower extremity stiffness between differentRE groups.(2) In order to explore the mechanisms of strength training to improve REand the effect of strength training on muscle exercise economy and mechanicalproperties,30untrained healthy men with no previous strength training experience andparticipate physical exercise less than once a week were recruited into this study, andwere distributed into training and control group, only training group received10weeks progressive strength training intervention. Parameters relate to muscle exerciseeconomy and mechanical properties were measured and before and after the strengthtraining intervention for statistical analysis.(3) In order to reveal the mechanisms ofstrength training to improve RE, explore the impact of muscle strength decrease onmuscle exercise economy and neuromuscular sEMG characteristics,17well trainedathletes with long term high load explosive strength training experiences were recruitedinto this study, all subjected endured5sets (10repetitions per set) high load resistantknee extension exercise. Force and sEMG characteristic response of the muscle-tendonunit of quadriceps femoris (MTU-QF) to5*10high load resistant knee extensionexercises were investigated by pre and post comparisons.Results:（1）When subjects running on the treadmill at the speed of10km/h and12km/h,they reached their stable oxygen consumption on the fifth minute, the VO2differencebetween the fourth and the fifth minute is less than2ml/kg.（2）Lower extremity MTU stiffness embodies certain adaptations to training, andshows high stiffness value in achilles tendon and tibialis anterior, low stiffness value ingastrocnemius medialis, no significant correlation was found between lower extremityMTU and RE.（3）Leg, knee and ankle joints show high stiffness during early stance phase butsignificant lower stiffness during late stance phase, no stiffness changes was found inknee joints, leg stiffness during early stance phase significant correlate with RE.（4）In this study, the self-made achilles tendon reflex(ATR) trigger combinationwith sEMG techniques perform ATRT measurements in a visual mode, with thesatisfying accuracy of the test results. A shorter pre-motor time (PMT) of ATRT in highRE group vs. a longer PMT in low RE group, but neither significant difference betweengroups nor significant correlation between ATRT and RE was found.（5）10weeks progressive resistant strength training can significant improveskeletal muscle mechanical properties with the significant increases of maximal strength,speed strength and muscle elastic energy utilization capacities in SSC cycle. Adaptionsof skeletal muscle mechanical properties indicate that10weeks progressive resistancestrength training intervention is helpful to improve muscle exercise economy. （6）Acute muscle fatigue induced by5sets high load explosive knee extensionexercise significant decreased maximal strength, speed strength and muscle workefficiency of the working muscle. The decrease of the muscle working efficiency ismainly susceptible to impaired peripheral muscle function not the divergence ofneuronal coding mechanisms in the central nervous system. Neuromuscularpre-activation of the working muscle was enhanced to compensate for acute musclefatigue.Conclusions（1）In this study, significant positive correlation was found between leg stiffnessduring contact phase and RE at the running speed of12km/h, it is the first time toestablish a biomechanical index to evaluate running economy comprehensively,indicating that evaluation of running economy will never limited to physiologicalindexes.（2）In this study, the self-made ATR trigger in combination with sEMGtechniques perform ATRT measurements in a visual mode, with the satisfying accuracyof the test results. This is an innovation, but the function of the instrument needs to befurther improved（3）The increase or decrease of the muscle strength can make muscle workefficiency produce synchronous changes, which affects the muscle exercise economy.The improvement of muscle exercise economy by strength training was due to muscleitself function adaption.