Prior heavy exercise eliminates slow component and reduces efficiency during submaximal exercise in humans

Abstract

We investigated the hypothesis that the pulmonary oxygen uptake (V O 2 ) slow component is related to a progressive increase in muscle lactate concentration and that prior heavy exercise (PHE) with pronounced acidosis altersV O 2 kinetics and reduces work efficiency. Subjects (n = 9) cycled at 75% of the peakV O 2 (V O 2 peak ) for 10 min before (CON) and after (AC) PHE.V O 2 was measured continuously (breath-by-breath) and muscle biopsies were obtained prior to and after 3 and 10 min of exercise. Muscle lactate concentration was stable between 3 and 10 min of exercise but was 2-to 3-fold higher during AC (P < 0.05 versus CON). Acetylcarnitine (ACn) concentration was 6-fold higher prior to AC and remained higher during exercise. Phosphocreatine (PCr) concentration was similar prior to exercise but the decrease was 2-fold greater during AC than during CON. The time constant for the initialV O 2 kinetics (phase II) was similar but theV O 2 asymptote was 14% higher during AC. The slow increase inV O 2 between 3 and 10 min of exercise during CON (+7.9 ± 0.2%) was not correlated with muscle or blood lactate levels. PHE eliminated the slow increase inV O 2 and reduced gross exercise efficiency during AC. It is concluded that theV O 2 slow component cannot be explained by a progressive acidosis because both muscle and blood lactate levels remained stable during CON. We suggest that both theV O 2 slow component during CON and the reduced gross efficiency during AC are related to impaired contractility of the working fibres and the necessity to recruit additional motor units. Despite a pronounced stockpiling of ACn during AC, initialV O 2 kinetics were not affected by PHE and PCr concentration decreased to a lower plateau. The discrepancy with previous studies, where initial oxidative ATP generation appears to be limited by acetyl group availability, might relate to remaining fatiguing effects of PHE.

Effects of prior very-heavy intensity exercise on indices of aerobic function and high-intensity exercise tolerance

“…The retained hyperbolic P-t lim characteristic is consistent with its underlying determinants collectively continuing to change either linearly or exponentially with time toward some limiting value, at a rate proportional to work rate and therefore the rate of WЈ utilization (40), but with a reduction in the limiting value and/or an increase the rate at which it is approached. With regard to the latter scenario, for example, the demonstration of an increased fundamental V O 2 asymptote suggests a reduction in work efficiency (whose origin remains uncertain; see above), which would be expected to require a greater degree of PCr breakdown and therefore exacerbate depletion of a previously incompletely replenished intramuscular PCr store (48). On the other hand, the degree of exercise-induced metabolic-acidemic stress in both blood (17,18) and muscle (42,48) has been shown to be reduced.…”

“…With regard to the latter scenario, for example, the demonstration of an increased fundamental V O 2 asymptote suggests a reduction in work efficiency (whose origin remains uncertain; see above), which would be expected to require a greater degree of PCr breakdown and therefore exacerbate depletion of a previously incompletely replenished intramuscular PCr store (48). On the other hand, the degree of exercise-induced metabolic-acidemic stress in both blood (17,18) and muscle (42,48) has been shown to be reduced. An alternative scenario that is consistent with the P-t lim relationship remaining well described by a hyperbola is that, for any supra-CP work rate, V O 2max is reached prior to complete WЈ depletion, but when a constant percentage of the fully depleted WЈ is reached; i.e., the remaining portion being functionally inaccessible.…”

“…That is, the prominence of the V O 2sc and the degree of the exercise-related metabolic-acidemic stress are both reduced (e.g., 17,18,42,48). Priming exercise is generally agreed to have little or no effect on the phase 2 or fundamental V O 2 time constant ( ) for cycle ergometry (e.g., 4, 9 -11, 15, 28, 31, 38, 50; compare with 53); in contrast to knee-extensor exercise, where is typically speeded (e.g., Ref.…”

Neuromuscular and physiological variables evolve independently when running immediately after cycling

“…Furthermore, the k would suggest that the increase in O 2 was also faster during the C-R condition, indicating that steady-state could have been reached earlier following prior moderate intensity cycling exercise. The cause of the changes observed during the first minute of the C-R condition are not fully 275 understood, but may have resulted from an enhanced muscle oxygen supply (DeLorey, Kowalchuk, Heenan, Dumanoir, & Paterson, 2007), an increase in blood flow (Krustrup, Gonzalez-Alonso, Quistorff, & Bangsbo, 2001) and/or improved oxidative enzyme activity (Sahlin, Sorensen, Gladden, Rossiter, & Pedersen, 2005).…”

Physiques that perform: The interaction between body composition management, performance and calcium homeostasis in female cyclists

“…Sahlin et al (2005) have shown that GE is reduced when cycling at a moderate intensity following three high intensity (110% ̇2 max ) efforts. This suggests that efficiency is attenuated following supramaximal exercise.…”