Title

Circulating catecholamine and testosterone concentrations and their roles in muscular strength/power expression

Date of Completion

January 2004

Keywords

Biology, Animal Physiology|Health Sciences, Recreation

Degree

Ph.D.

Abstract

The role of sympathoadrenal neurohormones in strength/power expression was examined in ten resistance-trained men (22.60 ± 2.17 yrs; 89.09 ± 9.95kg; 179.06 ± 6.68cm). Following strength assessments (1RM) and familiarization trials, subjects completed two experimental conditions: (i) acute heavy resistance exercise protocol (AHREP; 6 sets of 10 repetitions of parallel barbell squats, 80% 1RM), and (ii) control condition (CONT; rest in a quiet, controlled environment). Muscular performance was assessed using ground reaction forces recorded during a maximal isometric squat preceding each set in the AHREP. Venous blood samples were collected at -24hrs, -12hrs, and -60, -30, -15, -10, and -5 minutes. Blood was collected before each set of the AHREP, as well as immediately-post and +5 minutes post-AHREP. Blood collection times were matched for CONT. Prior to AHREP, epinephrine (EPI), norepinephrine (NE), and dopamine (DA) increased above baseline 270%, 255%, and 164%, respectively. With exercise, EPI, NE, and DA increased 512%, 271%, and 38% above pre-exercise levels. Peak isometric force (Fpeak ) and the dynamic force recorded during sets decreased ∼20%. Five subjects had reductions in force (P ≤ 0.05), and were classified as ‘force reducers’ (Freduce); ‘force maintainers’ (Fmaintainers) were not different ( P > 0.05) between pre- and post-AHREP measures. Pre-exercise area under the curve (AUC) for EPI, NE, and DA were correlated (P ≤ 0.05) with baseline (pre-AHREP) Fpeak in Fmaintainers only. In response to exercise, the integrated AUC for EPI, NE, and F peak were different between Fmaintain and Freduce (EPI, t = 4.02, p = 0.00; NE, t = 3.86, p = 0.02; Fpeak, t = 5.33, p = 0.00). Exercise-induced AUC for EPI was correlated (r2 = 0.80, P = 0.01) with Fpeak AUC in Fmaintain only. The change in EPI and NE between measures was positively correlated (EPI, r2 = 0.69; NE, r2 = 0.91) with changes in Fpeak for Fmaintain only. Data indicate a biphasic catecholamine response to high-intensity resistance exercise: (i) pre-exercise ‘anticipatory’ rise, (ii) exercise stress response. Muscular force production was associated with the magnitude of change above basal catecholamine concentrations prior to, and during high intensity resistance exercise in those subjects capable of maintaining force throughout the AHREP. ^