Author(s): BELECHRIS, N., BOGDANIS, G., TERZIS, G., DALLAS, G., PARADISIS, G. , Institution: NATIONAL AND KAPODISTRIAN UNIVERSITY OF ATHENS, Country: GREECE, Abstract-ID: 1293

INTRODUCTION:
Leg (Kleg) and vertical stiffness (Kvert) are biomechanical properties that influence running performance by modulating force transmission and elastic energy return [1]. The spring-mass model suggests that alterations in mechanical load can affect lower limb stiffness [2]. Running with weighted vests (WV) can increase mechanical load [3]. Symmetrical loading is assumed, but there is limited evidence on the effect of WV on bilateral symmetry. This study examined how WV influences Kleg, Kvert and their respective asymmetries (ASI).
METHODS:
Participants (N = 15; age = 21.4 ±2.9 years; body weight (BW) = 68.9 ± 7.6 kg; height = 1.77 ± 0.04 m; maximal oxygen uptake (VO2max) = 60.9 ± 5.8 ml/kg/min; maximal aerobic speed (MAS) = 4.96 ± 0.46 m·s⁻¹) completed 2 min running bouts under three loading conditions, Unloaded, 5% BW and 10% BW with a WV at MAS. During each condition, spatiotemporal parameters were recorded using a high-speed camera (300 fps) at the last 30 s of each condition. Kvert and Kleg were calculated from the spring-mass model [1]. The dominant leg of each participant was defined by the triple jump test [4]. ASI was determined using the formula: ASI = 2 * |Dominant - NonDominant| / (Dominant + NonDominant) * 100. Differences were assessed via two-way and one-way repeated measures ANOVAs. Post hoc analysis utilized Bonferroni adjustments, while Cohen’s d and percentage changes (Δ%) characterized the magnitude of effects.
RESULTS:
Both Kvert and Kleg showed significant main effects of Load (p < 0.001), but only Kvert showed for Dominance (p = 0.05) at 10% BW (Δ% = -1.6%, d = 0.15), while no interactions were significant. A significant main effect of Load was found only for ASI-Kleg (p = 0.030, partial η2 = 0.22). Post hoc comparisons revealed a negligible change at 5% BW (Δ% = -12.18%, d = -0.14) but a large reduction in ASI-Kleg at 10% BW (Δ% = -64.72%, d = -0.87).
CONCLUSION:
WV influence stiffness variables by triggering acute adaptations to control the increased mechanical demands. The decrease in stiffness contradicts existing literature [3], but it is hypothesized that it was a compensatory reduction in force transmission to attenuate initial impact. The significant reduction of ASI-Kleg can show that this accommodation promotes greater mechanical symmetry by adopting a more symmetrical force attenuation strategy.
REFERENCES:
1. Morin, J., Dalleau, G., Kyrolainen, H., Jeannin, T., & Belli, A. (2005). A simple method for measuring stiffness during running. Journal of Applied Biomechanics, 21, 167–180.
2. Blickhan, R. (1989). The spring-mass model for running and hopping. Journal of Biomechanics, 22, 1217–1227.
3. Silder, A., Besier, T., & Delp, S. L. (2015). Running with a load increases leg stiffness. Journal of biomechanics, 48(6), 1003-1008.
4. Risberg, M. A., Holm, I., & Ekeland, A. (1995). Reliability of functional knee tests in normal athletes. Scandinavian journal of medicine & science in sports,5(1), 24-28.