Impaired calcium pump function does not slow relaxation in human skeletal muscle after prolonged exercise

John Booth 1 , Michael J. McKenna 2 , Patricia A. Ruell 1 , Tom H. Gwinn 1 , Glen M. Davis 3 , Martin W. Thompson 1 , Alison R. Harmer 1 , Sandra K. Hunter 1 , and John R. Sutton 1 1 School of Exercise and Sport Science and 3 Rehabilitation Research Centre, Faculty of Health Science, University of Sydney, New South Wales 2141; and 2 Department of Human Movement, Recreation, and Performance, Centre for Rehabilitation Exercise and Sports Science, Victoria University of Technology, Melbourne, Victoria 8001, Australia Received 16 January 1996; accepted in final form 5 March 1997. Booth, John, Michael J. McKenna, Patricia A. Ruell, Tom H. Gwinn, Glen M. Davis, Martin W. Thompson, Alison R. Harmer, Sandra K. Hunter, and John R. Sutton. Impaired calcium pump function does not slow relaxation in human skeletal muscle after prolonged exercise. J. Appl. Physiol. 83(2): 511-521, 1997. This study examined the effects of prolonged exercise on human quadriceps muscle contractile function and homogenate sarcoplasmic reticulum Ca 2+ uptake and Ca 2+ -adenosinetriphosphatase activity. Ten untrained men cycled at 75 ± 2% (SE) peak oxygen consumption until exhaustion. Biopsies were taken from the right vastus lateralis muscle at rest, exhaustion, and 20 and 60 min postexercise. Peak tension and half relaxation time of the left quadriceps muscle were measured during electrically evoked twitch and tetanic contractions and a maximal voluntary isometric contraction at rest, exhaustion, and 10, 20, and 60 min postexercise. At exhaustion, homogenate Ca 2+ uptake and Ca 2+ adenosinetriphosphatase activity were reduced by 17 ± 4 and 21 ± 5%, respectively, and remained depressed after 60 min recovery ( P 0.01). Muscle ATP, creatine phosphate, and glycogen were all depressed at exhaustion ( P 0.01). Peak tension during a maximal voluntary contraction, a twitch, and a 10-Hz stimulation were reduced after exercise by 28 ± 3, 45 ± 6, 65 ± 5%, respectively ( P 0.01), but no slowing of half relaxation times were found. Thus fatigue induced by prolonged exercise reduced muscle Ca 2+ uptake, but this did not cause a slower relaxation of evoked contractions. fatigue; muscle contractile function; sarcoplasmic reticulum; calcium uptake; calcium adenosinetriphosphatase activity 0161-7567/97 $5.00 Copyright © 1997 the American Physiological Society