PURPOSE: Muscle overuse is characterized by inflammation, reduced strength and muscle damage. It has been proposed that calcium (Ca2+) accumulation during muscle contraction, is responsible for muscle damage. Muscle contractile properties are regulated by calcium regulatory excitation contraction coupling mechanisms. Therefore, the main aim of the present study was to investigate the effects of voluntary repetitive tasks during six weeks on the rate of sarcoplasmic reticulum (SR) Ca2+-uptake, and Ca2+-release, in young female Sprague-Dawley rats. Secondly, this study aims to evaluate the effect of the training on muscular strength and the relationship between SR Ca2+-kinetics and grip strength test performance. METHODS: Six rats were trained (EXP), using a well-established model of reaching and handle pulling with the upper extremities (2 hr/day, 3days/week, 6 weeks), six control rats (KON) were included that were not exposed to the task. Grip strength were evaluated using a grip strength meter for rodents, two weeks prior the training was initiated, and two days after the training period was concluded. Tissue samples were obtained from the supraspinatus and trapezius muscle, and the rate of SR Ca2+-uptake and SR Ca2+-release were analysed using the fluorescent Ca2+ indicator indo 1. RESULTS: The analysis revealed that EXP had a significant higher rate of SR Ca2+-uptake, in both supraspinatus (33%, P < 0,05) and trapezius (14%, P < 0,05), compared to KON. However, no significant differences in SR Ca2+-release rate were found between groups, in neither of the muscles. A decline in grip strength were found in both EXP and KON, with no significant differences between groups. No significant correlation between grip strength and the Ca2+ release uptake variables could be found. CONCLUSION: The present results suggests that repetitive voluntary reaching and handle pulling with the upper extremities during six weeks, induce extant changes in SR Ca2+-uptake rate in rats.