Monitoring weekly heart rate variability in futsal players during the preseason: the importance of maintaining high vagal activity

This study aimed to compare the weekly natural log of the root-mean-square difference of successive normal inter-beat (RR) intervals (lnRMSSD(Weekly)) and its coefficient of variation (lnRMSSD(CV)) in response to 5weeks of preseason training in professional male futsal players. A secondary aim was to assess the relationship between lnRMSSD(Weekly) and lnRMSSD(CV). The lnRMSSD is a measure of cardiac-vagal activity, and lnRMSSD(CV) represents the perturbations of cardiac autonomic homeostasis, which may be useful for assessing how athletes are coping with training. Ten futsal players had their resting lnRMSSD recorded prior to the first daily training session on four out of approximately five regular training days week(-1). Session rating of perceived exertion (sRPE) was quantified for all training sessions. Despite weekly sRPE varying between 3455 +/- 300 and 5243 +/- 463 arbitrary units (a.u.), the group changes in lnRMSSD(Weekly) were rated as unclear (using magnitude-based inference), although large inter-individual variability in lnRMSSD responses was observed. The lnRMSSD(CV) in weeks 4 and 5 were likely lower than the previous weeks. A large and significant negative correlation (r=-0.53; CI 90%: -0.36; -0.67) was found between lnRMSSD and lnRMSSD(CV). Therefore, monitoring individual lnRMSSD responses is suggested since large inter-individual variations may exist in response to futsal training. In addition, higher values of lnRMSSD are associated with lower oscillations of cardiac autonomic activity.