The Effect of Exercise Priming on V̇O2 Kinetics, Muscle Torque Complexity and Exercise Tolerance during Intermittent Isometric Contractions.

Exercise priming can alter V̇O2 kinetics and improve the performance of subsequent exhaustive heavy exercise. During fatiguing isometric exercise there is a reduction in the

complexity of muscle torque output, which correlates with metabolic changes observed in the same exercise domain. This study aims to investigate the effect of exercise priming on V̇O2

kinetics, muscle torque complexity and exercise tolerance during intermittent isometric exercise.

Five males and five females (25 ± 6 years, 171.4 ± 9.3 cm, 69.2 ± 12.0 kg) completed three experimental trials in a randomised order. The trials consisted of a six-minute priming exercise bout or rest period, followed by 20 minutes of rest, before completing a second exhaustive exercise bout. Participants performed intermittent isometric contractions of the knee extensors at 40% maximal voluntary contraction (MVC) with a duty cycle of 0.6. Participants' rate of perceived exertion (RPE) and muscle oxygen consumption were measured at regular intervals throughout the exercise.

There was no difference in the time to task failure between primed and non-primed exercise. There was a higher EMG amplitude at the start of the primed exhaustive bout compared to the non-primed exercise bout. The V̇O2 response to exhaustive exercise was not different between the primed and non-primed conditions. Peripheral fatigue was present at the onset of exercise following priming and a significant loss of muscle torque complexity with priming.

There was no improvement in performance of subsequent intermittent isometric contractions with prior exercise, nor was there change in the V̇O2 response. Loss of complexity could be attributed to the increase in arEMG at the onset of the exhaustive exercise, more specifically an increase in motor unit recruitment with the development of fatigue. These results suggest that there is some effect of high-intensity prior exercise on exhaustive isometric contractions of the knee extensors.