Examining the Cross-Education Phenomenon in Lower Limbs: Insights from the Force-Velocity Profile

This study explored whether the cross-education (CE) phenomenon could be examined through the force-velocity (FV) profile obtained from unilateral leg extension. Nineteen participants completed 5 weeks of unilateral knee extension interventions differing in set configuration. A traditional training group (TT) carried out four sets of 8 repetitions with 3 min of rest between sets, whereas an inter-repetition training group (IRT) completed 32 repetitions with 17.4 s of rest between repetitions. Exercise was performed with the 10-repetition maximum load on the dominant limb. Individual linear FV profiles (slope: S_FV; theoretical maximum force and velocity: F₀ and V₀; and maximum estimated power: P_max) were obtained for trained and untrained legs pre-post intervention. The trained limb showed significant increases in the post-test for F₀, P_max, and a steeper S_FV (p < 0.05). In the untrained limb, F₀ (p = 0.042) and P_max (p = 0.010) also improved, whereas no changes were observed in V₀ or S_FV. Set configuration did not modulate the FV adaptations in the trained or untrained limb. CE was only observed for specific estimated force and power parameters. These findings indicate that strength and power transfer can be accomplished with low-fatigue training protocols, which may offer a more tolerable and practical option in clinical and performance settings.