1Unfallkrankenhaus Berlin Klinik f. Innere Medizin / Kardiologie Berlin, Deutschland; 2Technische Universität München (TUM) München, Deutschland
Maximum heart rate (HRmax) and percentages hereof are regularly applied to calculate target heart rate zones when prescribing exercise intensity in preventive and sports cardiology. The most commonly used age-based HRmax equation is “HRmax = 220 – Age” [Fox equation]. However, this approach has been addressed to have large prediction errors, age, sex and fitness being significant factors. As a consequence, exercise intensity prescription may be under or overestimated in certain individuals, thereby reducing the benefits of cardiovascular and metabolic adaptations.
To resolve this, we examined HRmax during maximal exercise testing in male and female subjects with a wide age range (12-39 yrs) of both sexes and different fitness levels (untrained to elite athletes) and compared the calculated HRmax (Fox-HRmax) with measured HRmax (Real-HRmax).
A total of 17.390 subjects (age 31.0±15.1 yrs, 69.3 % males, 49.5 % athletes) were included. Real-HRmax was measured during maximal exercise test (cycle ergometer or treadmill, Lactatemax ≥8 mmol/L, RPE ≥18). Age-based HRmax was predicted using the Fox formula. Aerobic fitness categories were defined according to lactate thresholds at 3 mmol/L [P(3)]: <1 W/kg, 1.0-1.9 W/kg, 2.0-2.9 W/kg, 3.0-3.9 W/kg, ≥ 4 W/kg (in total 6.528 cycle ergometer data).
Overall, the Fox equation overestimates HRmax both for men (Fox-HRmax: 188±16 bpm, Real-HRmax: 186±16 bpm, p<0.001) and women (Fox-HRmax: 192±14 bpm, Real-HRmax: 188±14 bpm, p<0.001), this in particular among athletes (Fox-HRmax: 192±14 bpm, Real-HRmax: 188±14 bpm, p<0.001). Notably, with increasing age Fox-HRmax tends to be underestimated (e.g., age 20-29 yrs: Fox-HRmax: 196±3 bpm, Real-HRmax: 191±9 bpm, p<0.001; age 50-59 yrs: Fox-HRmax: 166±3 bpm, Real-HRmax: 170 ± 14 bpm, p<0.001). Also, aerobic performance influenced Real-HRmax (e.g., age group 40-49 yrs: P(3) 1.0-1.9 W/kg: 175 ± 14 bpm, P(3) 2.0-2.9 W/kg: 178 ± 11 bpm, P(3) 3.0-3.9 W/kg: 180 ± 10 bpm, P(3) ≥ 4 W/kg: 182 ± 9 bpm, p<0.001).
The results showed the well-known age-dependent decline of HFmax. Calculated values become imprecise, especially with increasing age. We disputed the assumption that athletes have lower HFmax, but in contrast demonstrated a positive association between performance and HFmax. These results have clinical implications in that exercise intensity prescription should rather be measured than calculated. Data from this large data set will enable to refine the Fox equation.