Alterations in sarcoplasmic reticulum function in female vastus lateralis with eccentric exercise

This study examined the alterations in sarcoplasmic reticulum (SR) Ca2+ seq uestration function in homogenates during eccentric exercise and recovery a nd following additional eccentric exercise, and correlated these alteration s with changes in force output. Eight healthy, untrained females, aged 20-2 5 years, cycled for a total of 60 min on an eccentric cycle ergometer (30 m in at 66 +/- 3% VO2 peak and 30 min at 76 +/- 3% VO2 peak, determined durin g concentric exercise). Biopsies (extracted from the vastus lateralis) were taken before and after the exercise as well as on days 2, 6 and prior to a nd following identical exercise on day 14. Ca2+-uptake (nmol/min/mg protein ) was unaffected (p > 0.05) following the first session of eccentric exerci se; however, by day 2 a depression in uptake (p < 0.05) was observed which persisted throughout the remainder of the experiment. Maximal Ca2+-ATPase a ctivity (nmol/min/mg protein) was elevated (p < 0.05) immediately following the first exercise session, remained elevated through day 2 and returned t o pre-exercise levels by day 6 of recovery and increased again by day 14. N o changes in either Ca2+-ATPase activity or Ca2+-uptake were observed with exercise on day 14. Both eccentric sessions, performed on days 0 and 14, re sulted in similar depressions in force (p < 0.05) immediately following exe rcise. By day 2 force had recovered to pre-exercise levels. The results dem onstrate that a prolonged alteration in SR Ca2+-uptake occurs following ecc entric work that is unaccompanied by parallel changes in either SR Ca2+-ATP ase activity or mechanical performance.