Heart Rate Does Not Reflect the %VO2max in Recreational Runners during the Marathon

Exercise physiologists and coaches prescribe heart rate zones (between 65 and 80% of maximal heart rate, HRmax) during a marathon because it supposedly represents specific metabolic zones and the percentage of (V) over dotO(2max) below the lactate threshold. The present study tested the hypothesis that the heart rate does not reflect the oxygen uptake of recreational runners during a marathon and that this dissociation would be more pronounced in the lower performers' group (>4 h). While wearing a portable gas exchange system, ten male endurance runners performed an incremental test on the road to determine (V) over dotO(2max), HRmax, and anaerobic threshold. Two weeks later, the same subjects ran a marathon with the same device for measuring the gas exchanges and HR continuously. The %HRmax remained stable after the 5th km (between 88% and 91%, p = 0.27), which was not significantly different from the %HRmax at the ventilatory threshold (89 +/- 4% vs. 93 +/- 6%, p = 0.12). However, the %(V) over dotO(2max) and percentage of the speed associated with (V) over dotO(2max) decreased during the marathon (81 +/- 5 to 74 +/- 5 %O-2max and 72 +/- 9 to 58 +/- 14 %v(V) over dotO(2max), p < 0.0001). Hence, the ratio between %HRmax and %(V) over dotO(2max) increased significantly between the 5th and the 42nd km (from 1.01 to 1.19, p = < 0.001). In conclusion, pacing during a marathon according to heart rate zones is not recommended. Rather, learning about the relationship between running sensations during training and racing using RPE is optimal.