Heart Rate Dynamics and Quantifying Physical Fatigue in Canadian Football

The cardiac response to physical exertion is linked to factors such as age, work intensity, and fitness levels. The primary objective of this study was to characterize within-session changes in cardiac response to running in Canadian football athletes, which may indicate physical fatigue. Performance profiles were collected from GPS and heart rate (HR) sensors worn by 30 male Canadian varsity football players (20–26 years old) over 28 games and practices. Running efforts with 60–180 s of rest were detected, and the maximum HR (HRmax) and peak HR recovery (HRRpk) during rest were extracted. Additionally, a new metric of cardiovascular cost (CVC) was developed to reflect the efficiency of the HR response to physical workload. HRmax was higher in games (p < 0.001) and in linemen (p < 0.001), and it increased over time (p < 0.001). HRRpk was higher in skilled players (p < 0.001) and changed over time (p < 0.001) depending on the rest period. CVC was higher in linemen (p < 0.001) and increased over time (p < 0.001). This study demonstrated the utility of HR response metrics to quantify ongoing fatigue experienced by Canadian football athletes and proposed a novel fatigue metric capable of monitoring an athlete’s fatigue state in real time.