The majority of research evaluating recovery status in American football players has evaluated endocrine markers, biochemical markers (i.e., creatine kinase) and subjective ratings of well-being. However, little attention has been given to cardiovascular markers. Football is often thought of as a predominantly anaerobic sport which may cause some to under appreciate the importance of having a well developed cardiovascular system for meeting the physical demands of training. Moreover, the cardiovascular system plays an important role in facilitating recovery between intermittent bouts and in the post-exercise period. A popular marker of cardiovascular recovery among sports teams is resting heart rate variability (HRV). HRV reflects autonomic regulation of the heart with specific parameters representing parasympathetic influence. It is thought that cardiovascular homeostasis is attained following exercise when parasympathetic indices of HRV return to baseline values.
A new study published ahead of print in the Journal of Strength and Conditioning research evaluated resting HRV throughout spring camp among a group of NCAA Division 1 football players. The primary aim of the study was to determine if HRV returned to baseline between consecutive day training sessions. Twenty-five players were grouped according to playing position: receivers and defensive backs (Skill), running backs, linebackers and tight-ends (Mid-Skill) and linemen. HRV was recorded approximately 90 minutes before practices using a validated pulse-wave finger sensor synced to an iPad. Baseline HRV was compared with HRV following ~20 hours of recovery, prior to the next day training session. Training load was quantified via tri-axial accelerators. The parameter used in this study was total PlayerLoad.
The results showed that at the group level, HRV returned to baseline among Skill by next day training. HRV values trended back toward baseline for Mid-Skill, though considerable inter-individual variability was observed. For linemen, HRV values were significantly below baseline. This was observed despite the fact the linemen experienced significantly lower PlayerLoad values than Skill and Mid-Skill players. Changes in HRV were significantly related with body mass (r = -0.62) where larger players experienced the largest HRV reductions. The authors speculate that these findings may have important implications for the competitive season. Because linemen showed inadequate cardiovascular recovery between sessions, this may make them more susceptible to autonomic nervous system imbalance (an indicator of overtraining) during more intensive periods.
Flatt, AA. et al. Heart rate variability and training load among NCAA division 1 college football players throughout spring camp. Journal of Strength and Conditioning Research. In press.