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Abstract

Blood test data were traditionally confined to the clinic for diagnostic purposes, but are now becoming more routinely used in many professional and elite high-performance settings as a physiological profiling and monitoring tool. A wealth of information based on robust research evidence can be gleaned from blood tests, including: the identification of iron, vitamin or energy deficiency; the identification of oxidative stress and inflammation; and the status of red blood cell populations. Serial blood test data can be used to monitor athletes and make inferences about the efficacy of training interventions, nutritional strategies or indeed the capacity to tolerate training load. Via a profiling and monitoring approach, blood biomarker measurement combined with contextual data has the potential to help athletes avoid injury and illness via adjustments to diet, training load and recovery strategies. Since wide inter-individual variability exists in many biomarkers, clinical population-based reference data can be of limited value in athletes, and statistical methods for longitudinal data are required to identify meaningful changes within an athlete. Data quality is often compromised by poor pre-analytic controls in sport settings. The biotechnology industry is rapidly evolving, providing new technologies and methods, some of which may be well suited to athlete applications in the future. This review provides current perspectives, limitations and recommendations for sports science and sports medicine practitioners using blood profiling and monitoring for nutrition and performance purposes.

1 Introduction

Many professional and Olympic-level athlete settings comprise comprehensive sports medicine and sports science support services, with an objective of: (1) achieving the highest possible level of performance with the lowest number of days lost to injury or illness [1], and (2) a duty of care to protect athletes from long-term negative health consequences of their sport [2]. A wealth of measurable variables of task-specific performance, training load, physiology, health and wellness exist to facilitate this, which can be used to guide coaches and athletes. In many cases this now includes blood profiling and monitoring, yet there has been no recent review of the practical application of blood profiling and monitoring in sport aimed at this interdisciplinary team. Here, we define ‘blood profiling’ as any blood testing where the data are applied beyond a medical diagnostic or anti-doping purpose. This includes the use of biomarkers to assess the efficacy of training interventions, inform nutritional strategies, and assess the capacity to tolerate training load. We define ‘blood monitoring’ as tests that are conducted frequently (e.g. once per micro-cycle) in order to describe the recovery status of the athlete.

There are a host of positive and negative outcome indicators that can be found within the blood that may corroborate or contrast with subjective athlete reports of performance readiness and symptoms, or other objective test data. These can help the practitioner decide whether an athlete is likely to be able to sustain or adapt to training/high performance or to assess the efficacy of an intervention. For example, a high testosterone-to-cortisol ratio suggests greater anabolic drive and has been strongly associated with positive training and performance outcomes [3]; chronically low energy availability (evident in a reduction in triiodothyronine as an example) reduces the ability to adapt to training [4], while also being a risk factor for bone stress injuries [5]; low iron status compromises the erythropoietic effects of altitude linked to endurance performance [6]; and vitamin D deficiency is known to compromise immunity, muscle repair and bone health [7, 8].

The aim of this review is to provide a useful practical guide to blood biomarker profiling and monitoring; it is not intended to be an exhaustive summary of the literature. It is beyond the scope of the present review to discuss sampling of other body fluids such as saliva, urine and tear fluid [9], or to discuss advanced techniques emerging in sports science such as metabolomics and ‘athleticogenomics’ [10, 11, 12]. However, this is not intended to diminish their future importance.

Importantly, there are a number of considerations that are often overlooked in the application of blood biomarker measurement in sport, including: (1) consideration given to what is ‘normal’ and what constitutes a meaningful deviation from normal for each individual athlete; (2) pre-testing considerations such as the time of day, posture, fasting/hydration status, transportation and storage of samples, the effects of recent training sessions (i.e. timeline for the restoration of homeostasis for each analyte); (3) sports-specific expertise present to interpret and address actions arising from testing; (4) appreciation of plasma volume shifts where the biomarker is volumetric in nature, e.g. hemoglobin.

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