NOCTURNAL HORMONAL RESPONSES TO RESISTANCE EXERCISE

The effects of resistance exercise on the nocturnal responses of corti sol (CO), testosterone (TEST), human growth hormone (hGH), and thyroid hormones (T-3, T-4) were examined in eight trained weight lifters. Ea ch subject completed two trials using a counterbalanced design: a cont rol, no exercise trial (CON) and a heavy resistance exercise session o f three sets of six exercises to exhaustion (RE). The exercise session took place between 1900 and 2000 hours. Blood was sampled prior to an d at 20-min intervals after RE. For both trials blood was sampled at h ourly intervals from 2100 hours until 0700 hours. The hGH and CO conce ntrations were increased up to 40-min post-exercise (P < 0.05), but re turned to resting levels 1 h post-exercise. Nocturnal hGH concentratio n was not affected by RE (P > 0.26) and peaked at 0200 hours and decli ned until 0700 hours. Similarly, the CO responses were similar between the trails (P > 0.14). This CO concentrations declined from 2200 hour s until 0100 hours, then increased steadily until 0700 hours. The TEST concentrations during both trials rose steadily from 2200 hours until 0700 hours; however, the rise in TEST from 0500-0700 hours during RE was greater than during the CON trails (P = 0.059). The T-3 concentrat ions were unchanged by exercise and were similar at all times between trails. The T-4 concentrations were elevated for 20 min after RE; howe ver nocturnal T-4 concentrations were lower after RE than during CON. These results would suggest that hGH and CO may have limited nocturnal reactivity to resistance exercise. However, the nocturnal alterations of TEST and T-4 after resistance exercise, although small, may have i mplications for muscle anabolism.