Neuromuscular fatigability of plantar flexors following continuous and intermittent contractions.

The purpose of this study is to investigate if a continuous muscle contraction (CON) is more fatiguing than an intermittent exercise (INT) performed until task failure. To get a more comprehensive picture of neuromuscular fatigability, in addition to the commonly used maximal voluntary contraction (MVC), we assessed the maximal torque sustainability (i.e., the ability to maintain a high level of torque for 1 min). Fourteen subjects performed a plantar flexors MVC of 1-min duration (MVC) before and after CON or INT contractions at 40% MVC until task failure. Despite a greater torque-time integral for the INT task, a similar MVC reduction was found after both exercises. On the contrary, a greater torque loss during the MVC was observed after the CON exercise and it was positively correlated to the mean exercise torque. These results reveal that, for exercises performed until exhaustion, the contraction pattern (i.e., CON vs. INT) affects the ability to maintain a high level of torque, but does not influence the maximal torque production capacity. Thus, we demonstrate that maximal torque production and sustainability are two distinct and complementary characteristics of neuromuscular fatigability. Consequently, when considering both capacities, it results that, an exhausting CON contraction is more fatiguing than an exhausting INT effort. This highlights the importance of simultaneously evaluating both capacities when exploring neuromuscular fatigability. This study provides new information about the influence of the contraction pattern (i.e., continuous and intermittent) on the development of neuromuscular fatigability when exercise is performed until exhaustion. Maximal torque production is similarly reduced by both exercises, whereas maximal torque sustainability is impaired only after the continuous exercise. To evaluate neuromuscular fatigability, we then recommend using a sustained maximal voluntary contraction since this measure allows to concurrently collect information on complementary aspects of neuromuscular fatigability.