Diarmuid Daniels MSc., PhD Researcher, a research scientist with Orreco delves into the science of soccer, describing the crucial importance of recovery and discussing the role of blood biomarker monitoring.
The physical demands of match play in the English Premier League (EPL) have increased substantially in recent years [1, 2]. Interestingly the increases in high intensity workload reported do not appear to be attributed to improvements in players’ physical capacity . Therefore, if the physical fitness of EPL players has remained stable across time then these findings suggest players are working at a higher proportion of their physical capacity during elite matchplay , which highlights the increasing importance of player recovery.
During a regular season, EPL players occasionally compete three times per week, particularly during the winter period. Given the volume of games required to complete a season in most top leagues, and the fixtures associated with cup competitions, it has become normal for players to be exposed to these periods of fixture congestion . However, when we consider the impact of the COVID-19 era, the condensed season means playing three times a week is the new normal, and although elite players are well adapted to their sport, it is very clear that the consistent exposure to competition and limited periods of rest, places players at high risk of under recovery and its negative effects – fatigue, under-performance, higher risk of injury. The monitoring of player recovery status is therefore an important objective of sports medicine and sports science staff.
The high intensity actions of elite soccer impose distinctive physiological and mechanical loading demands on players. The performance of concentric (e.g. accelerations/maximal sprinting), isometric (e.g. shielding the ball against offensive pressure) and particularly eccentric (e.g. jumping, landing and rapid deceleration movements)
muscle contractions during the high velocity and technical actions of the game lead to various homeostatic perturbations including metabolic (i.e. muscle glycogen depletion), mechanical (i.e. muscle damage) and oxidative stress (i.e. production of reactive oxygen and nitrogen species) . These perturbations stimulate the release of a number of inflammatory mediators, which act as “cellular messengers”, activating signalling pathways and in turn regulating the molecular machinery controlling inflammatory gene expression . These “messengers” may act locally in skeletal muscle, or induce systemic effects. In this way the muscle is said to “communicate” with other organs in the body, affecting whole body health  and ultimately the rate of recovery post-game.
The production of inflammatory mediators post-game or workout is one of the fundamental features of adaptation to training. This favourable effect of inflammation may be explained by the “stress-response”hormesis theory , whereby low levels of stress can be beneficial through induction of adaptive mechanisms increasing the tolerance against future stress incidents (e.g. enhanced resistance to fatigue during a future exercise bout). However, prolonged production of inflammatory mediators can exert negative effects on muscle repair and growth by impeding muscle protein synthesis, and overwhelming the endogenous defence mechanisms of the body (e.g. anti-oxidant resources) resulting in chronic systemic inflammation. Interestingly, it has been shown that the recovery time between successive games during a three game weekly micro-cycle may not be adequate for the restoration of normal homeostasis and the resolution of the inflammatory response [9, 10]. The long-term consequences of a lack of recovery may leave many players in an energy depleted state, both emotionally and physically, and could result in an increased risk for injury . The regular measurement of blood biomarkers of muscle damage (e.g. creatine kinase), oxidative stress (biomarkers of pro-oxidant and antioxidant activity), and inflammation (e.g.C-reactive protein, pro-inflammatory cytokines) may be used to make inferences about the athletes underlying physiology and recovery before and after a game. By examining these markers it may be possible to draw some conclusion about extent of damage to the muscle as a result of the game, and provide the practitioner with “actionable” data to promote recovery in the interval between successive matches.
The intense schedule in soccer including match preparation, travel, competition, media duties and often variable rest days may realistically reduce opportunities for monitoring . However, point-of-care(POC) tests via capillary blood sampling represent a practical solution to such challenges for medical and sports science staff, and importantly may inform athlete management decisions at the time of sampling. Indeed, the simple application, small sample volume, and rapid result reporting mean that there are a number of practical advantages to POC testing. Moreover, an understanding of what is ‘normal’ and what constitutes a meaningful deviation from normal for each individual athlete is important factor as between and within player variability in biomarkers may be influenced by a number of environmental stressors and player characteristics .Statistical approaches that provide individualized ranges can be used to optimize diagnostic accuracy of blood monitoring.
Whilst such methods may assist in differentiating between normal and abnormal profiles for a given athlete, context is everything. Communication amongst key stakeholders including the sports scientist, team doctor and the athlete themselves is vital in understanding the biomarker results and defining the subsequent action required for athlete health/recovery. Using biomarker data in conjunction with workload and wellness data, assists the practitioner in understanding the real-world meaningfulness of the biomarker data. Many team sports often adopt short, customized questionnaires which can be administered on daily basis, and provide a means of capturing athlete well-being. When this subjective data is combined with blood biomarker data, the practitioner may be able to gather a holistic understanding of each individual player, gain context into the cause of disturbance in the athlete’s physiological state and inform the subsequent course of action to protect player health/recovery.
From a clinical perspective, the POC measurement of C-Reactive Protein (CRP) alongside the self-reporting of illness symptoms could be used as an indicator of infection and identify athletes that require clinical review. Moreover, it is noteworthy, that a raised CRP and the presence of fever, cough, and fatigue are among the dominant clinical features of COVID-19 , and therefore its measurement could be a high priority for tracking athlete health in the COVID-19 era.
When biomarker ‘red flags’ of physiological relevance are detected, recovery strategies can be targeted. For example, if during a period where recovery is the priority (as opposed to adaptation), and an athlete presents with an abnormal profile on a game day -1 (GD-1), pre-competition acceleration of inflammation resolution via targeted nutritional supplementation may represent a practical approach for preventing the development of excessive systemic inflammation and promote the timely recovery of the player. This may also help prevent a ‘one-size fits all’ approach to the use of antioxidant/anti-inflammatory supplementation by identifying periods where an individual may require (or not require) nutritional intervention. Ultimately, measuring blood biomarkers of recovery may aid in the individualisation of athlete management and the protection of player health.
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