Stress and recovery in sports: Effects on heart rate variability, cortisol, and subjective experience

This study aimed to investigate (1) the time-variations and (2) the repeated measures relationship between training load (TL) and psychological and physiological parameters and performance. Data were collected around 12-weeks of training in fifteen national swimmers. Psychological states were assessed using the RESTQ-36-R-Sport Questionnaire and the Sport Emotion Questionnaire. Subjects collected four saliva samples throughout the day at 1) 7 a.m. immediately after waking, 2) 30 min after waking, 3) 60 min after waking, and 4) 8 p.m., allowing us to calculate the area under the curve with respect to ground (AUCg) and the sAA over cortisol ratio (AOC). Finally, heart rate variability was computed using a submaximal 5'-5' running test. Time variations were analyzed throughout repeated measures ANOVA and repeated measures correlations were run using the ``rmcorr'' R package. Recovery-stress states and emotional markers showed quadratic curves, while parasympathetic markers showed linear trajectories over time. Significant associations over time were found between TL and recovery, stress, emotional states, lnRMSSD and the AOC. Taken together, these results provided evidence that psychological and physiological states do not follow the same dynamics (i.e., linear vs. quadratic vs. no variation) in the functional training periodization condition. Our study also provided evidence that recovery-stress states, emotional states, lnRMSSD, and the AOC were of interest due to their intra-individual associations around the time with TL.