Biomarkers of Physiological Responses to Periods of Intensified, Non-Resistance-Based Exercise Training in Well-Trained Male Athletes: A Systematic Review and Meta-Analysis
Intensified training is important for inducing adaptations to improve athletic performance, but detrimental performance effects can occur if prescribed inappropriately. Monitoring biomarker responses to training may inform changes in training load to optimize performance.
This systematic review and meta-analysis aimed to identify biomarkers associated with altered exercise performance following intensified training.
Embase, MEDLINE, CINAHL, Scopus and SPORTDiscus were searched up until September 2017. Included articles were peer reviewed and reported on biomarkers collected at rest in well-trained male athletes before and after periods of intensified training.
The full text of 161 articles was reviewed, with 59 included (708 participants) and 42 (550 participants) meta-analysed. In total, 118 biomarkers were evaluated, with most being cellular communication and immunity markers (n = 54). Studies most frequently measured cortisol (n = 34), creatine kinase (n = 25) and testosterone (n = 20). Many studies reported decreased immune cell counts following intensified training, irrespective of performance. Moreover, reduced performance was associated with a decrease in neutrophils (d = − 0.57; 95% confidence interval (CI) − 1.07 to − 0.07) and glutamine (d = − 0.37; 95% CI − 0.43 to − 0.31) and an increase in urea concentration (d = 0.80; 95% CI 0.30 to 1.30). In contrast, increased performance was associated with an increased testosterone:cortisol ratio (d = 0.89; 95% CI 0.54 to 1.24). All remaining biomarkers showed no consistent patterns of change with performance.
Many biomarkers were altered with intensified training but not in a manner related to changes in exercise performance. Neutrophils, glutamine, urea and the testosterone:cortisol ratio exhibited some evidence of directional changes that corresponded with performance changes therefore indicating potential to track performance. Additional investigations of the potential for these markers to track altered performance are warranted.
Grace Greenham was supported by an Australian Government Research Training Program Scholarship and a research scholarship from the Adelaide Football Club. Joel Garrett was supported by an Australian Government Research Training Program Scholarship and a research scholarship from the Port Adelaide Football Club.
Compliance with Ethical Standards
No sources of funding were used to assist in the preparation of this article.
Conflict of interest
Grace Greenham, Jonathan D Buckley, Joel Garrett, Roger Eston, and Kevin Norton have no conflicts of interest.
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