The aim of the present study was to investigate whether a certain time of day may be more or less catabolic or anabolic than another and therefore of greater adaptive potential after exercise. Eighteen male university students volunteered to participate in the study. Salivary specimens were collected every 60 min over a 12 h waking period and then measured with the Salimetrics HS-cortisol assay and Salimetrics HS-testosterone assay. Participants remained at rest and were fed identical meals to each other at 08:05, 13:05, and 18:05 h. Blood pressure, heart rate and core temperature were observed every 15 min. Elevated cortisol concentrations were observed in the morning between 08:00 and 09:00 h (mean concentration ± SD = 0.28 ± 0.17 ug/dL) and a nadir in the evening or early night-time, between 17:00 and 20:00 h (mean concentration ± SD = 0.12 ± 0.06 ug/dL). Post hoc analysis revealed that mean 08:00 h cortisol was significantly greater than mean cortisol at 11:00 to 20:00 h (P < 0.05) and mean 09:00 h cortisol was significantly greater than mean cortisol from 15:00 to 20:00 h (P < 0.05). However, testosterone did not change significantly during the same period. Cortisol, core temperature and systolic blood pressure correlated significantly (although not strongly) with sampling time. In conclusion, salivary sampling to assess the anabolic/catabolic status of a squad or individual or to diagnose overtraining may not be simple or feasible as the variation between individuals is high and therefore setting a threshold value would prove troublesome. Also, the episodic release of cortisol in particular increases the difficulty of deciding a value in healthy or subclinical individuals.
The aim of the present study was to establish a relationship between the diurnal variations of testosterone and cortisol with the circadian rhythm of strength and power performance. Changes in salivary cortisol and salivary testosterone were measured after two different modes of maximal exercise (back squat and maximal 5 m sprint) at two different times of day to assess diurnal fluctuations. Seventeen physically active males volunteered as subjects. A randomized cross-over design was utilized and participants were allocated to a maximal back squat protocol at 09:00 and 17:00 h, and a maximal 5 m sprint protocol at 09:00 and 17:00 h separated by at least 48 h. Saliva samples were collected before exercise, at 5 and 60 min post exercise. Exercise performance displayed no time of day effect. No significant effect of exercise mode or time of day was observed in cortisol or testosterone concentrations. Cortisol concentrations were higher in the morning (p<0.001). Testosterone did not exhibit a significant time of day effect however, higher levels tended to be observed at 09:00 h. The data suggest that non weight trained individuals do not display a time of day effect for maximum squat or 5 m sprint performance, or the subsequent salivary hormonal response.