Time of day effects of aerobic exercises on athletes’ cardiorespiratory and hematological quantities: systematic review and meta-analysis

ABSTRACT

Exercise induces several cardiorespiratory and hematological changes in the body. In spite of the latest advancements in exercise physiology, the effects of time-of-day on these quantities remained inconclusive. A total of 2070 potential citations were identified through PubMed, MEDLINE, SPORTDiscus, EMBASE, Physical Education index and Google Scholar searches. Based on the eligibility criteria, 17 studies remained for analysis. Using the random effect model, the overall pooled time-of-day effect of exercise on erythrocytes were, RBC= Std. MD= 0.35(95% CI, -0.008 to 0.79), I²=71%, HGB= Std. MD = 0.37(at 95% CI, -0.19 to 0.94), I²=64% and HCT=Std. MD = -0.03(at 95% CI, -0.46 to 0.39), I²=36%, leukocytes WBC=Std. MD = -1.46(at 95% CI, -1.84 to -1.07), I²=42% and NEU=Std. MD = -1.01(at 95% CI, -1.16 to -0.42), I²=69%, thrombocytes PLT=Std. MD = 0.01(at 95% CI -0.31, 0.29), I² = 0% heterogeneity and Vo₂Max=SMD = -1.15(95%CI, -2.64,0.34; P>0.13) and I² = 87 heterogeneity.  Our study partly confirms the time-of-day variations of aerobic exercise on cardiorespiratory and hematological levels in athletes. However, conducting further meta-analysis aiming to investigate the concomitant effect of aerobic exercise and time-of-day in relation to different environmental settings are imperative, such as hypoxia, tropical and neutral environments.

KEYWORDS:

• Time of day
• aerobic exercises
• cardiorespiratory and hematological quantities

Acknowledgments

During this study, the corresponding author (EK) was Exercise Physiology PhD candidate at Mekelle University. We would like to thank Mekelle University and Arba Minch College of Teachers Education.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Mekelle University [PG/CNCS/PhDRecurrent/140/2011].