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

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. The aim was to test the effects of force-velocity condition and power output on strength-endurance. Fourteen sportsmen performed i) force- and power-velocity relationships evaluation in squat jumps and ii) strength-endurance evaluations during repeated squat jump tests in ten 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 ten conditions. The effects of %P-max, %P(max)v, and R-Fv on SJ(Rep) and Wtot were tested via stepwise multiple linear regressions and two-way ANOVAs. SJ(Rep) exhibited almost perfect intra- and inter-day reliability (ICC=0.94 and 0.93, respectively). SJ(Rep) and W-tot were influenced by % P(max)v and R-Fv (R-2=0.975 and 0.971; RSME=0.242 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 regression's 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). 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.