Acute short-term dim light exposure can lower muscle strength endurance

Background: Since it has been shown that spending 18 h under dim light conditions can result in reduced handgrip endurance, it was questioned whether or not a shorter exposure to dim light (i.e., 1 h) would have similar influence upon muscular endurance. Therefore this study compared the number of weighted knee extension lifts that could be done after spending 1 h in either dim or bright light. Methods: Participants (5 women, 11 men, college students 19-26 years) performed knee extension lifts to exhaustion with a load approximating 40% of their body weight. The lifts to exhaustion were measured immediately following 1 h of exposure to each of the following three conditions: dark (DL), room light (RL), and room light plus 5 mg melatonin (RLM). A minimum of 48 h separated each condition, and all participants started the exposures in a rested fed condition. Results: Average (+/-SD) number of knee extension lifts for RL (62.0 +/- 22.0) was significantly (p < 0.05) greater than DL (51.4 +/- 14.7) and RLM (57.8 +/- 22.9). The number of RLM knee extension lifts was not significantly different from DL. Exposure to 1 h of dim light immediately prior to activity can result in a reduction in thigh muscle endurance. The decline in performance to short-term dim light exposure was similar to that found following longer-term exposure. Conclusion: It appears that light intensity can influence muscle endurance, however, at this time this effect cannot be directly related to endogenous melatonin production. Copyright (C) 2014, Shanghai University of Sport. Production and hosting by Elsevier B.V. All rights reserved.