Strength-Endurance: Interaction Between Force-Velocity Condition and Power Output

CONTEXT: Strength-endurance mainly depends on the power output, which is often expressed relative to the individual’s maximal power capability (P(max)). However, an individual can develop the same power, but in different combinations of force and velocity (force-velocity condition). Also, at matched power output, changing the force-velocity condition results in a change of the velocity-specific relative power (P(max)v), associated with a change in the power reserve. So far, the effect of these changing conditions on strength-endurance remains unclear. PURPOSE: We aimed to test the effects of force-velocity condition and power output on strength-endurance. METHODS: Fourteen sportsmen performed (i) force- and power-velocity relationships evaluation in squat jumps and (ii) strength-endurance evaluations during repeated squat jump tests in 10 different force-velocity-power conditions, individualized based on the force- and power-velocity relationships. Each condition was characterized by different (i) relative power (%P(max)), (ii) velocity-specific relative power (%P(max)v), and (iii) ratio between force and velocity (R(Fv)). Strength-endurance was assessed by the maximum repetitions (SJ(Rep)), and the cumulated mechanical work (W(tot)) performed until exhaustion during repeated squat jump tests. Intra and inter-day reliability of SJ(Rep) were tested in one of the 10 conditions. The effects of %P(max), %P(max)v, and R(Fv) on SJ(Rep) and W(tot) were tested via stepwise multiple linear regressions and two-way ANOVAs. RESULTS: SJ(Rep) exhibited almost perfect intra- and inter-day reliability (ICC=0.94 and 0.92, respectively). SJ(Rep) and W(tot) were influenced by %P(max)v and R(Fv) (R(2) = 0.975 and 0.971; RSME=0.243 and 0.234, respectively; both p < 0.001), with the effect of R(Fv) increasing with decreasing %P(max)v (interaction effect, p = 0.03). %P(max) was not considered as a significant predictor of strength-endurance by the multiple regressions analysis. SJ(Rep) and W(tot) were higher at lower %P(max)v and in low force-high velocity conditions (i.e., lower R(Fv)). CONCLUSION: Strength-endurance was almost fully dependent on the position of the exercise conditions relative to the individual force-velocity and power-velocity relationships (characterized by %P(max)v and R(Fv)). Thus, the standardization of the force-velocity condition and the velocity-specific relative power should not be overlooked for strength-endurance testing and training, but also when setting fatiguing protocols.