Author(s): MANENTE, A., CORONA, E., MARCANTONI, L., BOLDRINI, M., FORMENTI, D., DE DONATO, S., CASTIGLIONI, P., CAVAGGIONI, L., RONCHETTI, D., MERATI, G., Institution: UNIVERSITY OF INSUBRIA (VARESE-COMO), Country: ITALY, Abstract-ID: 2682

INTRODUCTION:
Delayed neuromuscular pre-activation is a key contributor to instability and fall risk, particularly in older adults. Static stretching is widely used in exercise and rehabilitation programs, however its acute effects on anticipatory muscle activation remain debated. This study investigated whether static quadriceps stretching alters muscle pre-activation timing during a controlled drop-landing task in young adults, simulating a single-leg descent from a standard stair step. The aim was to provide an insight for fall-prevention strategies in aging populations.
METHODS:
Fifteen healthy adults (18–30 years) performed a single-leg landing from a 19-cm step. Fall time was recorded using an IMU (G-sensor, BTS, Italy) positioned near the body’s centre of mass, at the level of the L5-S1 vertebrae. Surface wireless electromyography (FreeEMG, BTS, Itay) recorded pre-activation timing of the rectus femoris, vastus medialis, biceps femoris, and semitendinosus muscle. After three baseline trials, participants completed a static quadriceps stretching protocol (2×45 s with 30 s rest), followed by three post-stretch trials. Pre-activation timings (ms before ground contact) pre- and post-stretching administration were compared using paired t-tests. Correlations between anthropometric variables and pre-activation timings were also explored. Significance was set at p<0.05.

RESULTS:
Inter-individual variability in pre-activation values was high, ranging from 10 to >1000 ms across subjects. Static stretching significantly delayed rectus femoris pre-activation (mean increase ≈ +40–60 ms; p<0.05). No significant changes were observed for the vastus medialis (p=0.349), biceps femoris (p=0.431), or semitendinosus (p=0.123), although a non-significant trend toward delayed activation was noted. A significant positive correlation was found between body weight and vastus medialis pre-activation timing post-stretching (R²=0.27; p=0.05).
CONCLUSION:
A single session of static quadriceps stretching appeared to induce a significant delay in rectus femoris pre-activation during single-leg landing, suggesting a temporary reduction in neuromuscular readiness. Although other muscles showed no significant changes, the observed trend toward delayed activation may have functional relevance. These findings indicate that prolonged static stretching immediately before dynamic balance tasks may transiently impair anticipatory stabilization. When translated to older adults, such effects could increase fall risk, for example during stair descent. Integrating dynamic warm-up, neuromotor training, and carefully timed stretching may help optimize fall-prevention exercise programs.