Increases in training load are often used by coaches to stimulate adaptations in athletes. Overload periods are common in periodized training structures and often precede a taper leading into competition. Despite being exposed to the same training schedule, not all athletes respond the same way to intensified training. Some athletes will respond well and improve performance while others may become fatigued and present with overuse issues. Baseline fitness level, stress, sleep quality and dietary factors may contribute to the individuality in training responses. It would be useful for coaches to have an objective physiological marker that they can use to evaluate how athletes are responding. This would enable coaches to identify those responding poorly to training and thus can modify training loads accordingly for them. Heart rate variability (HRV) is an objective, physiological marker that can be acquired daily via smartphone applications and is emerging as a useful training status marker among sports teams. While HRV has been shown to identify positive from negative responders based on performance changes, it is unknown whether HRV relates at all with overuse injuries.
A new study published ahead of print in the Journal of Sports Science and Medicine monitored incidence of overuse injuries, changes in training load and heart rate variability in a small sample of high level competitive CrossFit athletes. Training load was quantified via the session rating of perceived exertion method. From this, the exponentially-weighted moving average for the acute to chronic workload ratio was derived to determine when training loads were high. Vagally-mediated heart rate variability was measured daily by the athletes with a commercially available smartphone application. A brief questionnaire was emailed to each subject once per week to assess overuse injuries. The observation period spanned a sixteen week training cycle.
The results showed that there was a significant interaction effect between the weekly HRV average and acute to chronic workload ratio on reported overuse injuries the subsequent week. There was a substantially greater risk of overuse issues when individuals demonstrated lower HRV during a high load training week. In contrast, when athletes were able to maintain HRV within baseline ranges during a high load week, less overuse injuries were reported. Therefore, when monitoring HRV responses in athletes during intensified training, coaches should follow-up with athletes demonstrating reduced values to ensure overuse issues aren’t occurring.
Marco Altini, Sean Williams, Matthew Watson, Daniel Rowland, Thomas Booton, (2017) Heart Rate Variability is a Moderating Factor in the Workload-Injury Relationship of Competitive CrossFit™ Athletes. Journal of Sports Science and Medicine (16), 443 – 449.