AUTHOR=Rivière Jean Romain , Peyrot Nicolas , Cross Matthew R. , Messonnier Laurent A. , Samozino Pierre 

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

JOURNAL=Frontiers in Physiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2020.576725

DOI=10.3389/fphys.2020.576725

ISSN=1664-042X

ABSTRACT=<sec><title>Context</title><p>Strength-endurance mainly depends on the power output, which is often expressed relative to the individual’s maximal power capability (<italic>P</italic><sub>max</sub>). 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 (<italic>P</italic><sub>max</sub><italic>v</italic>), associated with a change in the power reserve. So far, the effect of these changing conditions on strength-endurance remains unclear.</p></sec><sec><title>Purpose</title><p>We aimed to test the effects of force-velocity condition and power output on strength-endurance.</p></sec><sec><title>Methods</title><p>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 (%<italic>P</italic><sub>max</sub>), (ii) velocity-specific relative power (%<italic>P</italic><sub>max</sub><italic>v</italic>), and (iii) ratio between force and velocity (<italic>R</italic><sub>Fv</sub>). Strength-endurance was assessed by the maximum repetitions (<italic>SJ</italic><sub>Rep</sub>), and the cumulated mechanical work (<italic>W</italic><sub>tot</sub>) performed until exhaustion during repeated squat jump tests. Intra and inter-day reliability of <italic>SJ</italic><sub>Rep</sub> were tested in one of the 10 conditions. The effects of %<italic>P</italic><sub>max</sub>, %<italic>P</italic><sub>max</sub><italic>v</italic>, and <italic>R</italic><sub>Fv</sub> on <italic>SJ</italic><sub>Rep</sub> and <italic>W</italic><sub>tot</sub> were tested via stepwise multiple linear regressions and two-way ANOVAs.</p></sec><sec><title>Results</title><p><italic>SJ</italic><sub>Rep</sub> exhibited almost perfect intra- and inter-day reliability (ICC=0.94 and 0.92, respectively). <italic>SJ</italic><sub>Rep</sub> and <italic>W</italic><sub>tot</sub> were influenced by %<italic>P</italic><sub>max</sub><italic>v</italic> and <italic>R</italic><sub>Fv</sub> (<italic>R</italic><sup>2</sup> = 0.975 and 0.971; RSME=0.243 and 0.234, respectively; both <italic>p</italic> &lt; 0.001), with the effect of <italic>R</italic><sub>Fv</sub> increasing with decreasing %<italic>P</italic><sub>max</sub><italic>v</italic> (interaction effect, <italic>p</italic> = 0.03). %<italic>P</italic><sub>max</sub> was not considered as a significant predictor of strength-endurance by the multiple regressions analysis. <italic>SJ</italic><sub>Rep</sub> and <italic>W</italic><sub>tot</sub> were higher at lower %<italic>P</italic><sub>max</sub><italic>v</italic> and in low force-high velocity conditions (i.e., lower <italic>R</italic><sub>Fv</sub>).</p></sec><sec><title>Conclusion</title><p>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 %<italic>P</italic><sub>max</sub><italic>v</italic> and <italic>R</italic><sub>Fv</sub>). 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.</p></sec>