Effect of time of day on performance, hormonal and metabolic response during a 1000-M cycling time trial

PLoS One. 2014 Oct 7;9(10):e109954. doi: 10.1371/journal.pone.0109954. eCollection 2014.

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.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Bicycling / physiology*
  • Blood Glucose / metabolism*
  • Circadian Rhythm / physiology*
  • Cross-Over Studies
  • Electromyography
  • Epinephrine / blood
  • Exercise / physiology
  • Glucagon / blood
  • Growth Hormone / blood*
  • Humans
  • Hydrocortisone / blood
  • Insulin / blood
  • Lactic Acid / blood
  • Male
  • Muscle, Skeletal / physiology
  • Norepinephrine / blood
  • Oxygen Consumption / physiology
  • Photoperiod
  • Testosterone / blood*

Substances

  • Blood Glucose
  • Insulin
  • Lactic Acid
  • Testosterone
  • Growth Hormone
  • Glucagon
  • Hydrocortisone
  • Norepinephrine
  • Epinephrine

Grant support

This work was supported by Alagoas Research Foundation (FAPEAL, process number: 20110825-011-0025-0004). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.