Author(s): CHEN, S., TAN, X., LI, F., Institution: SHANGHAI UNIVERSITY OF SPORT, Country: CHINA, Abstract-ID: 1211

INTRODUCTION:
Lower-limb stiffness and ground reaction forces (GRF) are critical biomechanical factors influencing neuromuscular activation during running. While spring-mass (leg/vertical stiffness) and torsional spring (joint stiffness) models have been proposed to optimize energy efficiency and elastic energy storage in muscle-tendon units, their neuromuscular implications remain underexplored in recreational runners. This study investigates the relationship between lower-limb stiffness, GRF characteristics, and muscle activation patterns in this population.
METHODS:
Twenty-nine male recreational runners performed a 4-minute constant-speed running set at 12 km/h. Eight infrared cameras, a three-dimensional motion capture system, and a 3D force platform were used to collect lower-limb stiffness and GRF data. Surface electromyography (sEMG) signals were obtained from nine lower-limb muscles on the right leg: gluteus maximus, rectus femoris, vastus lateralis, vastus medialis, biceps femoris, tibialis anterior, gastrocnemius lateralis, gastrocnemius medialis, and soleus using a wireless sEMG system. Correlations between lower-limb stiffness, GRF, and muscle root-mean-square (RMS) were investigated using Pearson Product Moment correlations.
RESULTS:
Results revealed moderate correlations between lower peak impact force and greater gluteus maximus peak RMS (r = -0.389, p < 0.05). Lower peak active force was moderately correlated with greater gluteus maximus RMS at foot-strike (r = -0.385, p < 0.05) and larger tibialis anterior peak RMS (r = -0.431, p < 0.05). Lower peak propulsion force was moderately correlated with greater vastus lateralis RMS at foot-strike (r = -0.445, p < 0.05). Lower peak braking force was moderately correlated with greater tibialis anterior RMS at foot-strike (r = 0.369, p < 0.05). Smaller knee stiffness was moderate to largely correlated with smaller soleus and tibialis anterior RMS at foot-strike and lower soleus peak RMS (r = 0.388~0.504, p < 0.05).
CONCLUSION:
This study demonstrates that biomechanical variables (lower-limb stiffness, GRF) are associated with neuromuscular strategies in recreational runners. Gluteus maximus activation was inversely associated with impact and active forces, whereas tibialis anterior activation correlated with reduced active/braking forces, and vastus lateralis activation at foot-strike attenuated propulsion forces. Reduced knee stiffness significantly correlates with diminished soleus and tibialis anterior activation, suggesting distal muscle co-activation regulates joint rigidity. These findings imply that targeted modulation of vertical/horizontal forces and knee stiffness could optimize neuromuscular control, informing injury-prevention training paradigms.