Title

Effects of repetitive box lifting performance on circulating measures of testosterone, cortisol, and creatine kinase in 38°C and 23°C environments

Date of Completion

January 2007

Keywords

Health Sciences, Recreation

Degree

Ph.D.

Abstract

The purpose of this investigation was to determine the effects of environmental temperature on (1) maximal isometric handgrip strength and repetitive box lifting (RBL) performance, and (2) hormonal (testosterone and cortisol) and creatine kinase (CK) responses during repeated bouts of RBL and recovery. Methods. Ten healthy males, age 21.0 ± 3.0 yr, height 176.6 ± 3.7 cm, and body mass 77.1 ± 10.3 kg, volunteered for the study. Two experimental trials (random crossover design) consisted of a 2-h exercise period (10 min sitting, 20 min standing, and 10 min RBL, repeated three times) in either 23°C or 38°C and a 3-h recovery in 23°C. Results. RBL performance was significantly reduced (P < 0.05) in 38°C over time compared to 23°C. Testosterone responses were significantly elevated during RBL and decreased at 1-h recovery at both temperatures. Significant differences (P < 0.05) in testosterone between trials were measured at 0:40, 1:20, and 2:00 during each RBL protocol. Cortisol responses were increased significantly at 1:00 in the exercise period, and stayed elevated until 2:00 in 23°C, and until 1-h recovery in 38°C. At 3-h recovery, cortisol concentrations were significantly lower compared to Pre values in both trials; significant differences were measured at 1:00 and 1:40 during the first and second rest periods, and at 24 h the next morning. The testosterone to cortisol ratio (T:C) was significantly decreased, compared to Pre, at 0, 1:00, 1:40 and 2:00 in exercise, at 1-h recovery for both trials, and increased at 3-h recovery in 38°C. There were no T:C differences between trials at any time point. During recovery, however, the T:C area-under-the-curve was significantly greater in 23°C than in 38°C. CK responses were similar between trials; significantly increased at 24 h and still elevated at 48 h. Conclusion. RBL performance over time was impaired in 38°C even with 30-min rest periods between work intervals. Catabolic effects were more pronounced during the 3-h recovery period following exercise in 38°C than during the exercise period. ^