Evaluating individual training adaptation with smartphone-derived heart rate variability in a collegiate female soccer team

Monitoring individual responses throughout training may provide insight to coaches regarding how athletes are coping to the current program. It is unclear if the evolution of heart rate variability (HRV) throughout training in team-sport athletes can be useful in providing early indications of individual adaptation. This study evaluated relationships between changes in resting cardiac autonomic markers derived from a novel smartphone device within the first 3 weeks of a 5-week conditioning program and the eventual change in intermittent running performance at week 5 among 12 collegiate female soccer players. Change variables from weeks 1 to 3 of the weekly mean and weekly coefficient of variation for resting heart rate (δRHRmean and δRHRcv, respectively) and logtransformed root mean square of successive R-R intervals multiplied by 20 (δLn rMSSDmean and δLn rMSSDcv, respectively) were compared with changes in Yo-Yo Intermittent Recovery Test Level 1 performance (δYo-Yo). A very large and significant correlation was found between δYo-Yo and δLn rMSSDcv (r = 20.74; p = <0.01) and a large nonsignificant correlation was found with δLn rMSSDmean (r = 0.50; p = 0.096). This study suggests that a decrease in Ln rMSSDcv within the first 3 weeks of training is a favorable response, indicative of positive adaptation. Collecting daily HRV data with a smartphone application using ultrashort HRV measures seems useful for athlete monitoring.