Declines in muscle contractility and activation during isometric contractions of the knee extensors vary with contraction intensity and exercise volume

New Findings What is the central question of this study? Is there a critical threshold beyond which the loss of muscle contractility is regulated by the level of muscle activation during single‐limb exercise of differing intensities and volumes? What is the main finding and its importance? Plateaus in the decline in muscle contractility during single‐limb knee extension depended on both exercise volume and contraction intensity. A plateau was only evident with an increase in exercise volume. Muscle activation increased and did not decline despite substantial reductions in contractility. The findings indicate that the decrease in muscle contractility exhibited by resistance‐trained men during the performance of submaximal isometric contractions with the knee extensors was not regulated by the level of muscle activation. Our study examined the influence of contraction intensity and exercise volume on changes in muscle contractility and activation of the knee extensor muscles. Maximal voluntary torque (MVT) and rate of change in torque, surface electromyograms, voluntary activation, V‐waves and quadriceps resting twitch measures were assessed in 10 resistance‐trained men during two experimental sessions. Each session began with an initial baseline series of contractions at a fixed intensity of 40% or 80% MVT. The 40%‐only session continued with five contractions to task failure at 40% MVT. The 80% session continued with five contractions to failure each at 80%, 60% and 40% MVT. Greater reductions in MVT were observed during the baseline contractions of the 40%‐only session compared with the 80% session at each matched‐volume time point (P 40% (P