During high intensity exercise, metabosensitive muscle afferents are thought to inhibit the command motor drive. However, this paradigm cannot explain the high motor drive inhibition despite low metabolic stress observed during high force level contractions. A better comprehension of the etiology of central fatigue under various mechanical stresses is particularly relevant in rugby where players performed tasks involving force (scrums, mauls) power (sprint start) or even speed (sprint).
Thirteen active men completed two maximal intensity isokinetic knee extension tests (160 contractions) under conditions of low or high force by manipulating the contraction velocity. Neuromuscular testing procedures including evoked torque and voluntary activation were performed every 20 contractions. The exponential modeling of these variable over time allowed to extract the rate of decrease (i.e. curvature constant).
The voluntary activation decreased quicker for the high force condition (curvature constant: 31±14s vs. 51±21s for low force condition; p<0.05). For high force contractions, the evoked torque and voluntary activation curvature constant are negatively correlated (R=-0.80) while they are positively correlated for low force condition (R=0.54).
These results may provide interesting results for rugby. High central fatigue rate of development during scrums and mauls (high force) may be govern by different mechanisms than during sprints (high power), possibly involving mechanosensitive afferents. This should be taken into consideration when testing or training athletes.