Author(s): GASSIER, R., SOULIÉ, T., HENRY, L., STAUFFER, E., BOUVIER, J., PIALOUX, V., HINZY, F., HAUTIER, C., Institution: UNIVERSITÉ CLAUDE BERNARD LYON 1 , Country: FRANCE, Abstract-ID: 2337

INTRODUCTION:
Understanding the mechanics of impacts and vibrations induced by running is a current challenge for injury prevention, quantification of training loads and equipment design. Transient soft tissue vibrations (STV), in particular, have been linked to muscle fatigue and muscle damage (1,2,3). Yet, inconsistency in the results and limited evidence remain due to the superimposition of vibration-related effects on those induced by the muscle contraction inherent to movement, preventing a mechanistic approach. This study aimed to evaluate the influence of STV on acute neuromuscular function, using an instrumented ergometer capable of reproducing the shocks encountered when running, while eliminating the interference of voluntary contractions necessary for running (4).
METHODS:
Sixteen participants, running at least once per week, underwent nine hundred simulated running impacts at 14 to 15 km/h on one randomly selected leg. Ground reaction forces (GRF) were acquired using a force plate embedded in the ergometer. Tri-axial accelerometers recorded heel impacts and STV of the Vastus Lateralis (VL). Muscle preactivation of the VL was measured using surface electromyographic sensors (EMG). The high frequency component (>10 Hz) of GRF has been computed via Discrete Fourier Transform to quantify impact peak and loading rates. STV parameters including total magnitude, amplitude, median frequency, and damping were extracted using Continuous Wavelet Transform. Knee extensors maximal voluntary contraction torque (MVC) and voluntary activation (VA), as well as torque evoked by 10 and 100 Hz doublet (Db10 and Db100, respectively) were assessed before and immediately after the exercise, together with perceived fatigue and muscle soreness. In addition, shear wave speed of the VL was measured to assess changes in muscle mechanical properties.
RESULTS:
Immediately after the exercise, MVC decreased (-9.48 %, p = 0.001) whereas VA remained unchanged (-3.76 %, p = 0.1). Both Db100 and Db10 increased (10.31 %, p < 0.001 and 23.38 %, p < 0.001, respectively). Shear wave speed of VL rose (p < 0.05), together with elevated perceived fatigue (p < 0.001) and mild muscle soreness (p < 0.05).
CONCLUSION:
Real time recordings of force and acceleration confirmed that running impacts were accurately simulated, while preactivation values remained lower (~17% of MVC activation) than running tasks as expected. Moreover, STV induced fatigue even though there was no muscle contraction to create movement. This fatigue appears to be of central origin, as suggested by the increase in Db100 and Db10, a finding of particular interest with regard to potential positive effects related to changes in mechanical properties of the VL.
REFERENCES
1) Gassier et al., 2025
2) Ehrström et al. 2018
3) Play et al., 2024
4) Gassier et al., 2025