Time of day effects on aerobic capacity, muscle glycogen content and performance assessment in swimming rats

Publication date: Available online 3 October 2014 Source:Science & Sports Author(s): W.R. Beck , L.F.P. Ribeiro , P.P.M. Scariot , I.G.M. dos Reis , C.A. Gobatto Objective The aims of this study were to analyze the time of day effects on aerobic capacity, time to exhaustion at this intensity and skeletal muscle glycogen concentration in swimming rats. Methods Initially, 80 animals were divided in four groups handled and tested at 12:00 and 20:00h and subjected to a lactate minimum test. For 12:00 and 20:00h, the lactate minimum intensity was successfully determined in 65 vs 85% of the animals, respectively, and no significant differences (P =0.15) were found between groups for this variable (4.95±0.40 vs 4.83±0.48% body weight, respectively). Forty-eight hours after, exercised groups (at 12:00h or 20:00h) performed an exhaustive swim bout at lactate minimum intensity. Results Time to exhaustion was significantly greater (P =0.03) for rats exercised in the dark vs light period (108.89±46.33 vs 77.96±30.81min, respectively). In addition, higher skeletal muscle glycogen concentrations were found in control group at 20:00h when compared to all other groups, probably playing an important role on time to exhaustion. These results suggest that although rat's aerobic capacity is not affected by the time of day, swimming performance is improved in the dark when compared to light period.
Source: Science and Sports - Category: Sports Medicine Source Type: research