Physiological day-to-day variability of select hormones at rest in exercise-trained men

Abstract

The purpose was to determine the day-to-day variability of total testosterone (tT), total T4 (tT4), total 3,5,3'-T3 (tT3), and cortisol (C) levels in exercise-trained men [no.=63, 24+/-4 yr (X+/-SD)]. Resting blood samples were collected at the same time of day (morning) over 3 consecutive days, 24 h apart, under controlled conditions. Subjects were instructed to minimize mental stress and physical activity and to maintain a consistent diet, and sleep patterns during the period of blood collections. Radioimmunoassay procedures were used to measure all hormones. Repeated measures analysis of variances were used to test for differences within each hormone across days, and intra-class correlations (ICC) and typical error were used to assess reliability of hormone concentrations across days. Results revealed resting hormonal values were within accepted clinical ranges. No significant mean differences (p>0.05) from day-to-day were found in any of the hormones. Furthermore, each hormone displayed highly significant (p<0.01) ICC values; tT 0.891, tT4 0.861, tT3 0.705, C 0.886, and consistent daily typical errors. These findings suggest resting tT, tT4, tT3, and C concentrations are not highly variable and appear reliable from day-to-day in exercise-trained men. If researchers measure any of these hormones at rest, before and after (ie, 24-48 h later) an experimental exercise treatment, they can presume that any changes seen at the 24-48 h point (that exceed the typical error appropriately) are due to their treatment and not an artifact of day-to-day variability.

Research Methodology: Endocrinologic Measurements in Exercise Science and Sports Medicine

“…1,49 Investigators should plan accordingly to carefully control and replicate the time of day in which research testing is conducted and the hormonal specimen collected. 52,53 …”

Methodology for studying Relative Energy Deficiency in Sport (REDs): a narrative review by a subgroup of the International Olympic Committee (IOC) consensus on REDs

“…Resting, fasted morning blood samples are the standard in clinical laboratory settings to control for diurnal variations in some parameters, as well as the effects of prior exercise or food intake (figure 2). Appropriate preparation by the athlete includes the following: (1) report fasted for a morning blood draw at a time that can be repeated for future tests; (2) avoid prior exercise activity for a minimum of 12 hours; (3) ensure exercise activity the day before is of easy duration and intensity (no competition or simulated competition)39 40; (4) refrain from certain dietary supplements and (5) maintain euhydration before arriving at the lab 36 41. The researcher/clinician should note the time of day and other sampling conditions to allow for future comparative sampling.…”

Recovery Rules

“…For C and T high ICCs are reported in standardized conditions. 63 CK helps with the synthesis of ATP in muscles and increases after a match as a result of muscle damage. [64][65][66] All studies that investigated CK took blood samples after a match.…”