Abstract
The experiment examined the effects 4 weeks of vitamin D (Vit D) supplementation versus placebo on musculoskeletal and psychomotor performance. Thirty-two college age males (Age: 22 +/- 4 y, Height: 177.7 +/- 8.3 cm, Weight: 81.5 +/- 14.6 kg, BF%: 19.6 +/- 7.9, Vit D: 20.0 +/- 7.2 ng/ml). Participants were assigned to group (Vit D vs placebo) and remained blind throughout the study. The treatments were 4000 IU of Vit D3 or placebo (dextrose) administered daily for 4 weeks. The participants underwent baseline testing for isometric strength, explosive ability and psychomotor performance, which was repeated at week 2 and week 4. Isometric tests consisted of an Isometric Mid Thigh Pull on a Force Plate (IMTP) and an upper body isometric test (UBIST) using a load cell. Peak force during a countermovement jump (CMJ) was also determined via force plate. A psychomotor vigilance test (PVT) was used to measure sustained reaction time. Analysis of the UBIST data did not reveal a significant group x time interaction (p = 0.14; Vit D pre: 553.7 +/- 168.3 N, post: 585.5 +/- 150.2 N; Placebo pre: 677.7 +/- 182.3 N, post: 649.8 +/- 236.9 N). For IMTP no significant group x time interaction (p = 0.83; Vit D pre: 2596.4 +/- 342.3 N, post: 2606.9 +/- 378.3 N; Placebo pre: 2684.0 +/- 432.9 N, post: 2762.6 +/- 440.4 N) was found. CMJ analysis did not reveal interaction effects for group x time (p = 0.21; Vit D pre: 4429.7 +/- 1619.0 N, post: 4938.5 +/- 2374.8 N; Placebo pre: 5537.3 +/- 3027.0 N, post: 6266.9 +/- 4577.3 N). For PVT (mean reaction time) there was no significant interaction effects for group x time (p = 0.35; Vit D pre: 0.304 +/- 0.041 sec, post: 0.301 +/- 0.053 sec; Placebo pre: 0.295 +/- 0.044 sec, post: 0.284 +/- 0.029 sec). In conclusion, four weeks of Vit D supplementation was not effective in increasing musculoskeletal or psychomotor performance.