Seasonal training shifts don't shake rugby players' heart health, finds study

By Hugo Francisco de SouzaOct 15 2023Reviewed by Susha Cheriyedath, M.Sc.

In a recent study published in the journal Echo Research & Practice, researchers used a combination of 2D echocardiography, electrocardiography (ECG), and speckle tracking echocardiography (STE) to investigate the variations in male rugby football league (RFL) players' cardiac function across four main time periods during an RFL season. Cardiac and training load co-evaluation during end pre-season (ENDPRE), mid-season (MIDCOMP), end-season (ENDCOMP), and end off-season (ENDOFF) revealed that, despite the highest training load during the ENDPRE phase, ECG reports and cardiac structural results were consistent across the season.

Study: Seasonal variation of cardiac structure and function in the elite rugby football league athlete. Image Credit: Jacob Lund / Shutterstock

While standard functional data largely followed this trend of season-long consistency, apical rotation, and twist results were higher during the ENDPRE phase compared to the rest of the phases, all other periods being statistically indistinguishable from one another.

Cardiac adaptation to training, AH, and the importance of PCS

High cardiac activity, especially those experienced by professional athletes, can have profound outcomes on the physiology of humans, resulting in increases in total body water, plasma volume expansion, better sustainment and/or elevation of stroke volume, reduction in heart rate, improvement in ventricular filling and myocardial efficiency, and enhanced skin blood flow and sweating responses. These physiological modifications are collectively termed 'cardiovascular adaptations to exercise' or simply 'cardiac training.'

Since most professional sports, including rugby, present variations in athletes' cardiac requirements, identifying and including any inherited condition that delays cardiac acclimatization to these varying exertion levels is essential. Historically, failure to identify these conditions promptly has resulted in sudden cardiac death (SCD).

The Rugby Football League (RFL) is the governing body for the sport in England, United Kingdom (UK). Having recognized the merits of cardiac evaluation of its member athletes, the RFL has mandated that all athletes undergo a pre-participation cardiac screening (PCS) to reduce SCD risk. This PCS aims to elucidate an athlete's cardiac adaptation to training, specifically, the structural, functional, and electrical changes associated with varying exercise levels, collectively called athletes' heart (AH). Despite being influenced by pre-existing cardiac conditions, AH is clinically delinked from general cardiac pathology.

Scientific research on PCS and AH is limited, with results mainly from electrocardiographic (ECG) or echocardiographic evaluations proving contradictory. These studies have been restricted to cyclists and soccer players, with almost no research in rugby. Since each sport has exertion requirements unique to the sport, an evaluation of AH in RFL athletes could help better understand and prepare training regimes catered to rugby, thereby improving season-wide cardiac outcomes and reducing SCD risk.

About the study

In the present study, researchers aimed to investigate the electrical, structural, and functional cardiac variations in RFL athletes across a rugby season. They employed advanced clinical evaluatory tools, including ECG, STE, and standard 2D echocardiography. The study cohort comprised professional male RFL athletes recruited from a single Super League club during RFL-mandated PCS. Study participants comprised multiple ethnicities, and data collection began via a medical questionnaire that documented cardiovascular history (personal or family), SCD, and ongoing cardiovascular symptoms.

The study design was longitudinal, and cardiac evaluations were carried out in a pre-rested state during four independent testing sessions.

"(1) End of pre-season (ENDPRE; Training period before the start of the competitive season) (2) mid-season (MIDCOMP; Middle of competitive season) (3) end-season (ENDCOMP; End of competitive season) and (4) end off-season (ENDOFF: End of the off-season with data collected on athlete return to the club after the end of season break."

Data was collected, analyzed, and reported by a specialist sports cardiologist. Athletes' cardiac history informed examinations, but analyses did not include cardiac history as a variable to avoid confounding outcomes. Retrospective training- and workload changes were collected and analyzed in tandem with cardiac reports.

Training load was computed using the Borg category ratio scale (CR10) multiplied by individual athletes' perceived exertion rating (RPE). The resulting value was expressed as an arbitrary unit (AU), computed independently for each seasonal phase.

Echocardiography comprised both ventricular assessment (using STE and 2D echocardiography), and atrial assessment, which included evaluations of left atrium (LA) and right atrium (RA) functional volumes. Finally, statistical analyses were carried out using a one-way analysis of variance (ANOVA) with post-hoc Bonferroni assessment.

Study findings

The study cohort comprised 20 male RFL athletes with a mean age of 23 years (range – 18 to 31). No cohort withdrawals were recorded, and all 20 participants met inclusion criteria and were thus included in all analyses. Training history evaluations of included participants revealed a mean training history of 13.3 years. Club-provided training regimens revealed substantial differences in exercise levels between the pre-and in-season periods.

"During a typical pre-season week, the athletes on average were taking part in 5 field training sessions (skills and conditioning) each of 70 min duration, 4 gym sessions (resistance) each of 60 min duration and 2 'wrestle' sessions each of 40 min duration. During a typical in-season week, athletes were taking part in 3 field sessions each of 45 min duration and 2 gym sessions each of 40 min duration and competitive gameplay."

Data analyses revealed that athlete heart rate (HR), blood pressure (BP), and demographic parameters remain more-or-less stable across the competitive season despite ENDPRE training loads being substantially higher than all other assessment points. ECG reports from all participants were normal across all assessment points. Left ventricular assessment largely mirrored this trend, with only apical rotation and twist depicting deviations (higher during the ENDPRE) from an otherwise uniform evaluation.

Late diastolic filling velocity was found to vary slightly across the season, with higher training loads resulting in slightly higher velocity; however, all right ventricular and atrial structural and functional parameters remained constant across the season.

Conclusions

This study presents novel data, both due to the shortage of research into the cardiac structure and functions of rugby players and because STE recorded in this study has rarely, if ever, been used in formal scientific research. Contrasting prior hypotheses, increased training load does not seem to negatively impact RFL athletes' cardiovascular health, with almost all measured parameters remaining constant despite variability in exertion across the season.

"Given that, prolonged and reduced LV twist has been reported in cardiomyopathies this study indicates the potential clinical benefit of twist and, therefore, untwist data in the PCS setting. Despite changes in twist, overall cardiac function is normal in RFL athletes."

While these results cannot be generalized given 1. the small sample size and 2. the inclusion of only male participants, these results form the basis for future research in the field and highlight the importance of STE as a tool to inform sports clinicians in settings of cardiac follow-up/secondary care.