Author(s): DEMANUELE, S., GHIOTTO, L., AMINI, M., PILERI, A., BOCCIA, G., SCHENA, F., TARPERI, C. , Institution: UNIVERSITY OF VERONA, Country: ITALY, Abstract-ID: 782

INTRODUCTION:
Eccentric muscle actions, which generate high force at relatively low metabolic cost, often induce muscle damage and prolonged neuromuscular fatigability. The results of these mechanisms are evident in ecological situations, such as mountain trail running and other eccentric-intensive tasks. Such eccentric-induced deficits have important functional consequences: for instance, the ability to quickly manage terrain roughness to avoid potential accidents/injuries or the balance recovery after a sudden slip must occur within ≈100 ms. Thus, the ability to develop force rapidly, quantified as the rate of force development (RFD), is often more critical than maximal strength alone. Moreover, many real-world gestures involve submaximal forces. To address this, the RFD scaling factor (RFD-SF) has been proposed as a novel metric to assess rapid force capacity across submaximal intensities. We aimed to analyze the impact of a fatiguing incremental eccentric cycling task on muscle voluntary force (MVF), RFD (peak and time-locked window), and RFD-SF.
METHODS:
A within-subject, repeated-measures design was used to quantify the acute effects on knee extensor neuromuscular function. 38 healthy participants (31 men, 7 women; 23 ± 1 years) completed two sessions 10–15 days apart. Visit 1 served as a familiarization and Visit 2 as a neuromuscular assessment before and immediately after the incremental eccentric cycling task, until voluntary exhaustion (from 100W for males and 50W for females + 25W·min⁻¹). The primary dependent variables were MVF, RFDpeak, time-locked RFD50, 100, 150, and RFD-SF, derived from ≥ 48 ballistic isometric knee-extension contractions performed across 20, 40, 60, and 80% MVF targets in blocks randomized across participants and matched PRE–POST within participants.
RESULTS:
Linear mixed models indicated that, even after a prior identical eccentric exposure (to account for the repeated-bout effect), MVF decreased by ≈16% (p < 0.001; d = −3.34), RFD declined across all windows (RFD50: −9.3%, p < 0.05, d = −0.53; RFD100: −7.5%, p < 0.001, d = −1.00; RFD150: −8.4%, p < 0.001, d = −1.49) and RFDpeak decreased by −9.1% (p < 0.01; d = −0.84); additionally, the RFD-SF slope decreased by ≈5% (p < 0.01; d = −0.68), indicating reduced rapid force capacity across submaximal targets.
CONCLUSION:
An incremental eccentric cycling task induced marked reductions in MVF and in the ability to generate force rapidly, even after a prior eccentric exposure, highlighting RFD and RFD-SF as sensitive markers of acute fatigability. Because many athletic tasks have a large eccentric component, these impairments may compromise rapid reactive actions on technical terrain or during repeated decelerations. From a practical perspective, coaches should therefore monitor and periodize eccentric load, avoiding exhaustive bouts before power/agility-demanding sessions; conversely, eccentric pre-conditioning may be used strategically to elicit adaptation while attenuating damage on subsequent exposures.