Intraindividual Relationships Between Training Loads and Heart-Rate Variability in High-Level Female Futsal Players: A Longitudinal Study.

Purpose: To investigate the internal training loads of a professional Spanish female futsal team throughout 26 weeks of training including preseason and in-season weeks and verify the impact of training period and/or training load magnitudes on heart-rate variability responses. Furthermore, we aimed to assess, intraindividually, the relationship between training load and the coefficient of variation (CV) of weekly natural log of the root mean square difference of successive normal interbeat (RR) intervals (lnRMSSD_CV), obtained from ∼5 measures per week, and recorded in the seated position. Methods: A within-subject design involved 12 high-level outfield female futsal players (mean [SD] age: 23.9 [3.4] y). Results: lnRMSSD was significantly lower and lnRMSSD_CV was significantly higher during the preseason (weeks 1–6) compared to in-season (weeks 7–26) (P <.001). Individually, players presented moderate to large negative correlations between lnRMSSD_CV and lnRMSSD during the 26 weeks of observation. Correlations ranged between r_player4 = −.41 (95% CI, −.69 to −.02) and r_player12 = −.55 (−.78 to −.18). Players also presented moderate to verylarge positive correlations between lnRMSSD_CV and session rating of perceived exertion. Correlations ranged between r_player7 =.41 (.04 to.71) and r_player1 =.71 (.45 to.86). Conclusion: Professional female futsal players in this study presented increased lnRMSSD and reduced lnRMSSD_CV during 20 weeks into the competitive season compared to 6 weeks of preseason. Furthermore, lnRMSSD_CV was negatively associated with lnRMSSD on an intraindividual basis. Finally, higher internal training loads were positively correlated with lnRMSSD_CV, indicating that heart-rate variability is responsive to weekly training loads. [ABSTRACT FROM AUTHOR]