Heart Rate Does Not Reflect the %VO 2 max in Recreational Runners during the Marathon.

Exercise physiologists and coaches prescribe heart rate zones (between 65 and 80% of maximal heart rate, HR max ) during a marathon because it supposedly represents specific metabolic zones and the percentage of V˙O 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˙O 2max , HR max , 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 %HR max remained stable after the 5th km (between 88% and 91%, p = 0.27), which was not significantly different from the %HR max at the ventilatory threshold (89 ± 4% vs. 93 ± 6%, p = 0.12). However, the %V˙O 2max and percentage of the speed associated with V˙O 2max decreased during the marathon (81 ± 5 to 74 ± 5 %V˙O 2max and 72 ± 9 to 58 ± 14 %vV˙O 2max , p < 0.0001). Hence, the ratio between %HR max and %V˙O 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.