Isokinetic dynamometry assessment of the transition period between eccentric and concentric hamstring contractions in athletes with a history of hamstring injury.

Background: Hamstring (Hs) injuries are frequent in sports involving explosive efforts. While eccentric deficits and strength imbalances are known risk factors, the role of the transition period between eccentric and concentric contractions remains unexplored. Objective: To determine whether the transition period between eccentric and concentric contractions of the hamstrings, measured using an isokinetic dynamometer, differs between athletes with a history of Hs injury and healthy controls. Methods: This observational retrospective study included 57 participants (26 previously injured athletes and 31 healthy controls) assessed with standard and plyometric isokinetic tests. The primary outcome was the transition period between eccentric (30°/s) and concentric (240°/s) Hs contractions. Secondary outcomes included torque measurements and calculated ratios (Croisier and Plyometric). Results: The transition period did not differ significantly between groups. Injured athletes demonstrated higher concentric Hs peak torque at 240°/s ( Conclusion: The transition period, as measured by isokinetic testing, does not appear to be influenced by a prior Hs injury and may lack clinical utility in guiding rehabilitation. However, plyometric evaluation may help reveal residual eccentric deficits in previously injured athletes. Future studies using electrophysiological techniques could provide more precise insight into neuromuscular latency during explosive efforts. Levels of evidence: 3b.