Heart Rate Variability in College Football Players throughout Preseason Camp in the Heat

We aimed to characterize cardiac-autonomic responses to a 13-day preseason camp in the heat among an American college football team. Players were categorized as linemen (n=10) and non-linemen (n=18). RHR, natural logarithm of the root-mean square of successive differences multiplied by twenty (LnRMSSD), and subjective wellbeing (LnWellness) were acquired daily. Effect sizes +/- 90% confidence interval showed that for linemen, LnRMSSD decreased (moderate) on day 2 (71.2 +/- 10.4) and increased (moderate) on day 12 (87.1 +/- 11.2) relative to day 1 (77.9 +/- 11.2) while RHR decreased (small-moderate) on days 6, 7, and 12 (67.7 +/- 9.3-70.4 +/- 5.5 b center dot min-1) relative to day 1 (77.1 +/- 10.1 b center dot min-1). For non-linemen, LnRMSSD increased (small-large) on days 3-5, 7, 12, and 13 (83.4 +/- 6.8-87.6 +/- 8.5) relative to day 1 (80.0 +/- 6.5) while RHR decreased (small-large) on days 3-9, 12, and 13 (62.1 +/- 5.2-67.9 +/- 8.1 b center dot min-1) relative to day 1 (70.8 +/- 6.2 b center dot min-1). Decrements in LnWellness were observed on days 4-10 and 13 for linemen (moderate) and on days 6-9, 12, and 13 for non-linemen (small-moderate). Despite reductions in LnWellness, cardiac-autonomic parameters demonstrated responses consistent with heat-acclimation, which possibly attenuated fatigue-related decrements.