Time of day effect on oxygen uptake changes and lung function of active female

Abstract

Various psychological and physiological functions have been shown to undergo changes within the 24-hour day. The purpose of this study was to compare the oxygen consumption changes, as well as lung function at three different times (09:00Am, 14:00 and 18:00 Pm) within the same day. Eleven female, physical education university students (age 22.27±.90 years, height 162.36± 4.20 cm and weight 56.82±6.60kg) took part in the study. The spirometric parameters (forced expiratory volume (FVC), forced expiratory volume in first second(FEV₁) FEV₁/FVC, peak expiratory flow (PEF), maximum expiratory flow(MEF_25-75%) as lung function indices determined before onset of exercise test, then progressive incremental cycle ergometer exercise test was performed until exhaustion in each time following one min of rest and two min of warm-up by cycling. The workload during the maximal test was increased 20 watts (W) every one minutes from an initial 45W until volitional subjective exhaustion. One-way repeated measures analysis of variance and bonferroni- corrected paired t-tests were used to test for differences between the times of day. Significance was set at p ≤ 0.05. A significant circadian rhythm was found for FEV₁ (p=0.05), FEV1/FVC (p=0.019), PEF (p=0.013) and MEF_25-75% (p=0.012) with the acrophases in evening. In contrast no significant circadian variation was observed for VO₂ at rest,VO₂ at 25, 45, 65, 85, 105, 125 watts, lactate threshold VO₂, VO_2max, slope of VO₂ changes curve and FVC between all measured time units (p>0.05). In summary, oxygen uptake changes didn’t vary during the time frame within which exercise is normally conducted. In contrast time of the day effect existed for lung function and it was improved from morning until evening. Therefore, it is important for coaches and athletes to be aware of how the time of day will affect their function.

Keywords

• Circadian rhythms,lung function,oxygen uptake changes,active female

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