Heart Rate Variability (HRV) is a widely-accepted as a measure for recovery after workouts. As runners are always looking to work harder (read: get faster) and avoid injury, research continues to expand. When considering how to improve performance, training sessions are almost always the first thought. HRV came into play once we started considering how well athletes were recovering after their workouts. Were they setting themselves up for injury? For burnout? For the most optimal performance?

As HRV has been established as a means to evaluate the quality of an athlete’s recovery, researchers are able to assess how well and how quickly athletes recover from different types of training. A recent article published in the Journal of Strength and Conditioning Research compared recovery for two different types of high-intensity interval training (HIIT) training sessions.

The researchers recruited twelve young, physically active men to participate in two exercise sessions. One session was a HIIT cycle ergometer workout: eight twenty second bouts of 170% max power cycling with 10 seconds of recovery between each bout. The other session was a total body HIIT workout compromised of burpees, mountain climbers, jumping jacks, and squat plus kettlebell thrusts. Each exercise was performed for 2 reps, and the same schematic was used: eight twenty bouts with ten seconds of recovery between each bout. The participants were randomized into two groups so that half performed the total body workout first and half did the cycle ergometer workout first.

HRV was assessed immediately prior, immediately after, and 24 hours after the sessions. The results showed that HRV returned to baseline measurements 24 hours after both protocols. This indicates that the cardiovascular system is properly recovered from the HIIT workout and that athletes are able to perform another HIIT workout - from a cardiovascular standpoint, at least. It is important to be aware that other systems, such as the neuromuscular or the metabolic, might not be recovered. Further research is needed to assess these systems.

However, it was unexpected that the cardiovascular system recovered so quickly. This is important data for those with workouts scheduled close together or those squeezing in two a days. Hopefully, more research will be conducted to show us exactly when the athlete’s cardiovascular system is recovered. Is it 12 hours? 18? 10? In the meantime, 24 hours is a working guideline for cardiovascular recovery after a HIIT session.

Dr. Cathlin Fitzgerald, PT, DPT, CSCS, CAFS


Schaun Gustavo Z Del Vecchio Fabrico. “High-intensity interval exercises’ acute impact on heart rate variability: comparison between whole-body and cycle ergometer protocols”. Journal of Strength and Conditioning Research; 32(1): 223-229.