Abstract
Information about anaerobic energy production and mechanical efficiency that occurs over time during short-lasting maximal exercise is scarce and controversial. Bilateral leg press is an interesting muscle contraction model to estimate anaerobic energy production and mechanical efficiency during maximal exercise because it largely differs from the models used until now. This study examined the changes in muscle metabolite concentration and power output production during the first and the second half of a set of 10 repetitions to failure (10RM) of bilateral leg press exercise. On two separate days, muscle biopsies were obtained from vastus lateralis prior and immediately after a set of 5 or a set of 10 repetitions. During the second set of 5 repetitions, mean power production decreased by 19% and the average ATP utilisation accounted for by phosphagen decreased from 54% to 19%, whereas ATP utilisation from anaerobic glycolysis increased from 46 to 81%. Changes in contraction time and power output were correlated to the changes in muscle Phosphocreatine (PCr; r = −0.76; P<0.01) and lactate (r = −0.91; P<0.01), respectively, and were accompanied by parallel decreases (P<0.01-0.05) in muscle energy charge (0.6%), muscle ATP/ADP (8%) and ATP/AMP (19%) ratios, as well as by increases in ADP content (7%). The estimated average rate of ATP utilisation from anaerobic sources during the final 5 repetitions fell to 83% whereas total anaerobic ATP production increased by 9% due to a 30% longer average duration of exercise (18.4±4.0 vs 14.2±2.1 s). These data indicate that during a set of 10RM of bilateral leg press exercise there is a decrease in power output which is associated with a decrease in the contribution of PCr and/or an increase in muscle lactate. The higher energy cost per repetition during the second 5 repetitions is suggestive of decreased mechanical efficiency.
Highlights
Whereas the physiological and metabolic responses to maximal running, cycling and knee extension exercise using the leg extension ergometer have been well documented, to our knowledge, careful investigations examining substrate utilisation across a single set of bilateral leg press exercise have not been performed
A limited number of studies that employ cycle exercise [5,6], static knee-extension [7,8,9] or dynamic one-legged knee-extensor [4,10,11,12] exercise at a constant work rate [10] have estimated that ATP utilisation per work unit either decreased [7,8,9,10] or increased over time [4] during exercise
10.9 as the exercise progresses, implying that mechanical efficiency is reduced during the second half of the exercise
Summary
Whereas the physiological and metabolic responses to maximal running, cycling and knee extension exercise using the leg extension ergometer have been well documented, to our knowledge, careful investigations examining substrate utilisation across a single set of bilateral leg press exercise have not been performed. A limited number of studies that employ cycle exercise [5,6], static knee-extension [7,8,9] or dynamic one-legged knee-extensor [4,10,11,12] exercise at a constant work rate [10] have estimated that ATP utilisation per work unit either decreased [7,8,9,10] or increased over time [4] during exercise This may be partly due to the variety of experimental conditions, the mode of exercise chosen to estimate mechanical efficiency and the difficulties of quantifying anaerobic energy production based on the decrease in muscle adenosine triphosphate and PCr, as well as the accumulation of metabolites such as lactate. It is still uncertain whether mechanical efficiency changes over time during short-lasting maximal dynamic exercise such as the leg press model
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