Since the development of smart phone applications capable of accurately measuring heart rate variability (HRV), more and more teams are starting to use this marker for athlete monitoring. Though numerous studies have supported the use of HRV for reflecting recovery status and training adaptation in athletes, the real-world application of HRV in field settings can be quite confusing. This is because of the labile nature of HRV which sometimes makes interpretation of daily changes difficult. One criticism of HRV as a monitoring tool is that it is quite unreliable, meaning that it can change quite a bit on a day to day basis regardless of training load. However, it appears that the fluctuation in daily HRV may itself be a useful indicator of training status.
A new study published ahead of print in the Journal of Sports Medicine and Physical Fitness aimed at interpreting daily HRV changes among a collegiate women’s soccer team (n = 10) in response to two consecutive weeks of high and low training load. Additionally, relationships between the degree of daily HRV fluctuation and fitness parameters were assessed. Each morning, the athletes measured their HRV with the ithlete smartphone application after waking. Following the HRV measure, the athletes completed a brief wellness questionnaire where they rated perceived levels of fatigue, soreness, mood, stress and sleep quality on a 5-point scale. Training load was quantified by the session rating of perceived exertion method. Training sessions were held twice per day on Mondays and Thursdays and once per day on Wednesday and Fridays. Following the two-week training period, VO2max and YoYo IRT-1 values were assessed.
HRV showed larger reductions (moderate effect sizes) during the high load week compared to the low load week (small effect sizes), as to be expected. Large negative relationships were observed between HRV and perceived fatigue (r = -0.55) and between HRV and fitness parameters (r = -0.61 and -0.65 for VO2max and YoYo IRT-1, respectively). Therefore, it appears that lower fit athletes demonstrate less stable HRV trends compared to higher fit athletes. Furthermore, fit athletes who show unstable HRV trends are likely experiencing fatigue which may be a result of non-training related factors that are effecting their recovery. Greater reduction in HRV can be expected during high load weeks, however if athletes are still demonstrating large reductions in HRV despite reduced training loads, they may not be adequately recovering from training.
Flatt, AA, Esco, MR, Nakamura, FY & Plews, DJ. Interpreting daily heart rate variability changes in collegiate female soccer players. Journal of Sports Medicine and Physical Fitness. In Press.