The majority of training load research typically involves only male athletes. Females are a very underrepresented group in this area of study. It’s important to understand that women are quite different from men, particularly from a hormonal perspective. Significantly less testosterone and higher estrogen in women really separate them from men when it comes to training adaptation. Therefore, we need to be careful when applying research performed in men, to women.
Some new research published ahead of print in the International Journal of Sports Physiology and Performance evaluated the impact of 3 weeks of varying training load on HRV and Wellness scores in a team of collegiate female athletes. A novel aspect of this study was that the athletes self-recorded HRV measures with a smartphone application. Additionally, the measurement duration for HRV tests was approximately one minute, which is substantially shorter than traditional measures of 5-minutes.
The athletes were put through moderate, high and low training load weeks during their spring season. Conditioning sessions and resistance training sessions took place twice per week on the same day, separated by at least 4 hours. Soccer practices occurred 3 times a week on separate days. Training load was quantified via the session rating of perceived exertion method. Wellness surveys were administered 3 times per week which involved having the athletes rate their perceived level of soreness, sleep quality, fatigue, mood and stress on a 5 point scale. All wellness, training load and HRV data was collected via smartphone.
The weekly mean and coefficient of variation were calculated from the daily HRV values. The authors found that the mean and CV values were lowest and highest, respectively, during the high load week. In contrast, the mean and CV values were highest and lowest, respectively, during the low load week. Wellness values were lowest during the high load week and higher during the moderate and low load weeks.
Retrospectively, the authors then assessed if the weekly values (mean and CV) could be accurately captured in as few as 3 or 5 days per week. At this time, the authors advise a minimum of 5 HRV measures per week to reflect weekly values, though the 3 day measures faired quite well. But until more research is available to corroborate these findings, 5 days is the recommended minimum.
The authors concluded that smart-phone derived HRV provided a simple, non-invasive and objective physiological marker that related to training load and wellness throughout the three week period. The CV in particular was the most sensitive marker to the changes in training load. This means that the athletes experience greater day-to-day fluctuation in their HRV scores as a result of high training load. During the moderate and low training load weeks, the CV was smaller, indicative of less homeostatic perturbation. Practitioners are therefore advised to monitor CV changes, in addition to the mean, throughout training for insight on individual training adaptation.
Flatt, A. A., & Esco, M. R. (2015). Smartphone-derived Heart Rate Variability and Training Load in a Female Soccer Team. International Journal of Sports Physiology and Performance. Ahead of print.