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.