Last updated: 3 August 2026
Reviewed by Jordan Makin, FA Level 2 Football Coach
VO2 reserve (VO2R) is the range between resting VO2 and VO2 max. The Karvonen formula applies the same principle to heart rate: HRR = max HR − resting HR; target HR = resting HR + (intensity% × HRR). Training at 60-70% of HRR (heart rate reserve) corresponds to Zone 2 aerobic base work. This method accounts for individual resting heart rate variation — a person with a low resting HR (45 bpm) has a larger HRR and thus higher training zones than someone with a resting HR of 70 bpm at the same max HR.
Key points
- HRR = max HR − resting HR
- Target HR = resting HR + (intensity% × HRR)
- More accurate than %max HR alone
- Karvonen formula (also called heart rate reserve method)