Effect of Time of Day on Performance, Hormonal and Metabolic Response during a 1000-M Cycling Time Trial

Abstract

The aim of this study was to determine the effect of time of day on performance, pacing, and hormonal and metabolic responses during a 1000-m cycling time-trial. Nine male, recreational cyclists visited the laboratory four times. During the 1st visit the participants performed an incremental test and during the 2nd visit they performed a 1000-m cycling familiarization trial. On the 3rd and 4th visits, the participants performed a 1000-m TT at either 8 am or 6 pm, in randomized, repeated-measures, crossover design. The time to complete the time trial was lower in the evening than in the morning (88.2±8.7 versus 94.7±10.9 s, respectively, p<0.05), but there was no significant different in pacing. However, oxygen uptake and aerobic mechanical power output at 600 and 1000 m tended to be higher in the evening (p<0.07 and 0.09, respectively). There was also a main effect of time of day for insulin, cortisol, and total and free testosterone concentration, which were all higher in the morning (+60%, +26%, +31% and +22%, respectively, p<0.05). The growth hormone, was twofold higher in the evening (p<0.05). The plasma glucose was ∼11% lower in the morning (p<0.05). Glucagon, norepinephrine, epinephrine and lactate were similar for the morning and evening trials (p>0.05), but the norepinephrine response to the exercise was increased in the morning (+46%, p<0.05), and it was accompanied by a 5-fold increase in the response of glucose. Muscle recruitment, as measured by electromyography, was similar between morning and evening trials (p>0.05). Our findings suggest that performance was improved in the evening, and it was accompanied by an improved hormonal and metabolic milieu.

Expectancy of ergogenicity from sodium bicarbonate ingestion increases high-intensity cycling capacity

“…Participants attended the laboratory at the same time of the day for each visit to minimise the influence of circadian changes on exercise performance (Fernandes et al 2014). Trials were carried out 3 to 7 days apart.…”

The behavior of an opponent alters pacing decisions in 4-km cycling time trials

“…Table 2. RPE scores (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) before, during and after the 4-km time trial (TT). In addition, the average % completion time (Compl time %) at the moment of asking RPE is given.…”

“…Time-trials were completed at the same time of the day (±2 h), and the same day of the week to minimize circadian variation [15,16]. Participants were asked to maintain normal activity and sleep pattern throughout the testing period.…”

Circadian Rhythms, Exercise, and Cardiovascular Health

“…During the day, the adrenal gland follows a diurnal rhythm through the release of cortisol, which raises blood pressure and heart rate [3]. Due to the morning peak in cortisol levels and gradual decrease throughout the day [47], early morning release of hormones such as cortisol could contribute to this increase in blood pressure and resulting cardiovascular events [34]. Similarly, melatonin release is highly responsive to circadian rhythms and thus displays diurnal variation [23].…”