Anaerobic Energy Supply During Maximum-Intensity Short-Term Voluntary Sustained Exercise in Man.

Abstract

The purpose was to directly assess the relative contributions of the anaerobic energy releasing pathways to ATP provision during very brief (2-14s) maximal isometric contractions in human skeletal muscle, and to examine the recovery processes following such exercise. Eleven males performed unilateral sustained maximal isometric contractions of the knee-extensor muscles. Ten needle biopsy samples [2 pre-exercise (PreEx), 4 exercise (Ex), and 4 recovery (Rec) samples] were obtained from each subject over 3 separate testing sessions. Circulation was occluded at the upper thigh prior to all biopsies. Ex samples were taken immediately following 2-14s of maximal voluntary contraction. Contraction times were randomly pre-determined such that 6 biopsies were obtained following each of 2, 4, 6, 8, 10, 12, and 14s of contraction. Rec samples were collected 10, 20, 30, 40, 60, 120, and 180s following 14s maximum contractions. Significant changes occurred for both phosphocreatine (PCr) and lactate concentration within the initial 2s (n=7, p≤0.05) of contraction. In 14s, PCr concentration decreased to 53.3% of the PreEx value at a rate of 2. 53±0 .18 mmol· kg⁻¹dm · s⁻¹, while muscle lactate increased to approximately 8 times the initial value, at a steady rate of 1. 52±0 .10 mmol ·kg⁻¹ s⁻¹. Following contraction, PCr returned to the PreEx value within 60s of recovery (n=4, p>O. OS) , but muscle lactate concentration was still significantly elevated above resting after 180s of recovery (n=4, ≤0.05). Total ATP production over 14s was 69.03±4.47 ⁻¹dm, with an average turnover rate of 4.93±0.32 mmol·kg⁻¹dm·s⁻¹. The initial ATP turnover rate was 7. 26±1. 94 mmol· kg⁻¹ dm· s⁻¹ with 67% of the ATP being derived from PCr degradation and 33% from glycogenolysis. As contraction continued, however, there was an almost equal contribution to ATP provision from the 2 anaerobic energy delivery pathways, and (with the exception of the first 2 seconds) the proportion changed very little over time. This study was supported by the Natural Sciences and Engineering Research Council of Canada.