Abstract
The slow component () that develops during high-intensity aerobic exercise is thought to be strongly associated with locomotor muscle fatigue. We sought to experimentally test this hypothesis by pre-fatiguing the locomotor muscles used during subsequent high-intensity cycling exercise. Over two separate visits, eight healthy male participants were asked to either perform a non-metabolically stressful 100 intermittent drop-jumps protocol (pre-fatigue condition) or rest for 33 min (control condition) according to a random and counterbalanced order. Locomotor muscle fatigue was quantified with 6-s maximal sprints at a fixed pedaling cadence of 90 rev·min−1. Oxygen kinetics and other responses (heart rate, capillary blood lactate concentration and rating of perceived exertion, RPE) were measured during two subsequent bouts of 6 min cycling exercise at 50% of the delta between the lactate threshold and determined during a preliminary incremental exercise test. All tests were performed on the same cycle ergometer. Despite significant locomotor muscle fatigue (P = 0.03), the was not significantly different between the pre-fatigue (464 ± 301 mL·min−1) and the control (556 ± 223 mL·min−1) condition (P = 0.50). Blood lactate response was not significantly different between conditions (P = 0.48) but RPE was significantly higher following the pre-fatiguing exercise protocol compared with the control condition (P < 0.01) suggesting higher muscle recruitment. These results demonstrate experimentally that locomotor muscle fatigue does not significantly alter the kinetic response to high intensity aerobic exercise, and challenge the hypothesis that the is strongly associated with locomotor muscle fatigue.
Highlights
The oxygen uptake (V O2) kinetics during aerobic exercise is characterized by a tri-phasic response profile (Whipp and Ward, 1990)
The V O2 slow component (V O2sc) that develops during high-intensity aerobic exercise is thought to be strongly associated with locomotor muscle fatigue because of shared mechanisms like decreased “metabolic stability,” muscle metabolite accumulation, decreased free energy of ATP breakdown, limited O2 or substrate availability, increased glycolysis, pH disturbance, increased muscle temperature, ROS production, and altered motor unit recruitment patterns (Grassi et al, 2015)
They found that, across exercise intensities, the overall reduction in maximal voluntary cycling power (MVCP) was significantly correlated with the magnitude of the V O2sc. This finding suggests that locomotor muscle fatigue might be a pre-requisite for the development of the V O2sc observed during high-intensity aerobic exercise
Summary
The oxygen uptake (V O2) kinetics during aerobic exercise is characterized by a tri-phasic response profile (Whipp and Ward, 1990). V O2max , the exponential kinetics are complicated by an additional component resulting in a slow rise V O2 above that expected from the sub-LT linear relationship between V O2 and power output This phase, termed the V O2 “slow component” (Whipp, 1994), is a manifestation of reduced muscle efficiency during exercise above LT. In a seminal study, Cannon et al (2011) quantified locomotor muscle fatigue induced by cycling exercise at various intensities (80% LT, 20 and 60% ) using 5-s isokinetic sprints to measure maximal voluntary cycling power (MVCP) at three different pedaling cadences (60, 90, and 120 rev·min−1) They found that, across exercise intensities, the overall reduction in MVCP (i.e., the magnitude of locomotor muscle fatigue) was significantly correlated with the magnitude of the V O2sc.
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