Author(s): ALAUX, H., BARRUÉ-BELOU,S., DUCLAY,J., Institution: TOULOUSE NEURO IMAGING CENTER (TONIC), Country: FRANCE, Abstract-ID: 2277

INTRODUCTION:
Persistent quadriceps weakness after ACL rupture is well documented and hinders functional recovery. These deficits likely reflect structural and neuromuscular alterations, with neural activation impairments evolving from predominantly spinal to more central mechanisms from acute to subacute phases [1]. However, neural activation has been mainly studied during isometric contractions and after reconstruction rather than after rupture alone. This study aimed to extend knowledge on neuromuscular contributions to strength asymmetries during anisometric contractions in patients following ACL rupture.
METHODS:
This abstract reports preliminary data from sixteen patients assessed 2-6 weeks after ACL rupture and sixteen healthy subjects. Participants performed maximal quadriceps contractions under three conditions: isometric at 80° knee flexion, and concentric and eccentric at 20°/s from 60° to 100° knee flexion. For each condition, we measured at 80°: torque, voluntary activation, electromyographic activity (RMS) of knee extensor muscles, and doublet-evoked torque. For each variable, side-to-side asymmetries were calculated using the asymmetry index ((stronger − weaker)/stronger) and analyzed with a two-way repeated-measures ANOVA with contraction mode (isometric, concentric, eccentric) as a within-subject factor and group (patients, controls) as a between-subject factor. Finally, we assessed covariations between torque asymmetries and asymmetries in doublet evoked torque and voluntary activation in patients and healthy controls using a linear mixed effects model.
RESULTS:
Repeated-measures ANOVA revealed significant group effects for asymmetries in torque, doublet-evoked torque, and voluntary activation (p ≤ 0.05), with greater side-to-side asymmetries in patients than controls, but no main effect of mode or mode × group interaction. RMS EMG asymmetries showed no significant group or mode effects and no group × mode interactions (p ≥ 0.05). For both patients and healthy subjects, torque asymmetry was positively associated with both voluntary activation and doublet-evoked torque asymmetries (p ≤ 0.05), and was not influenced by contraction mode (p ≥ 0.05). Model explained 65% of the variance (R² = 0.65).
CONCLUSION:
Our results indicate that the side-to-side deficits in torque and neuromuscular factors previously reported during isometric contractions in post-operative patients [2] extend to anisometric contractions early after ACL rupture. Furthermore, deficits in activation level and muscle capacity appear to contribute to torque asymmetries in both patients with ACL rupture and healthy controls, consistent with previous isometric findings [3]. This contribution was similar across isometric, concentric, and eccentric modes.

REFERENCES
1. Lepley, A. S., et al. Scandinavian Journal Of Medicine And Science In Sports, 2015.
2. Lisee, C., et al. Sports Health, 2019.
3. Maffiuletti, N. A., et al. Journal Of Electromyography And Kinesiology, 2016.