Effects of Position and Injury Status on Associations Between Preseason Workload and Heart-Rate Variability Profiles in American College Football Players

PURPOSE: To quantify position-specific associations between heart-rate-variability profile characteristics and external-workload parameters in American college football players during preseason camp while accounting for injury-related participation status. METHODS: Twenty-seven players categorized into skill (n = 15) and midskill (n = 12) position groups participated in the study. Players were further categorized as having "full go" (n = 15) or "go as can" (n = 12) participation status. The camp mean and coefficient of variation (CV) (indexing daily variation) for various workload parameters and resting heart rate and the natural log of the root mean square of successive differences (LnRMSSD) were quantified. RESULTS: Skill players who consistently performed higher total workloads (total distance and player load) exhibited the most stable LnRMSSD (ie, lower CV; P < .05), while midskill players with the highest total workloads exhibited greater daily variation in LnRMSSD (ie, higher CV; P < .05). These associations persisted after injury-status adjustment. However, consistent between position groups, players with greater daily variation in select workload parameters also showed greater daily variation in LnRMSSD (P < .05). No between-groups differences for injury status were observed (P > .05), although effect-size analysis showed that LnRMSSD was moderately greater in "full go" players (effect size = 0.73, P < .07). CONCLUSIONS: Daily LnRMSSD variation better reflected position-specific workload responses, whereas mean LnRMSSD may affect or be affected by injury status. While skill players tolerated high total workloads with stable LnRMSSD, midskill players exhibited less day-to-day variation in LnRMSSD and high-intensity outputs at moderate workloads.