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

Abstract

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.

Keywords: endurance; energy cost of running; exercise physiology; pacing; running performance; self-pace run.

Figure 1

Averages speeds during the marathon of the faster and slower marathoners’ groups expressed in % of v$\dot{\mathit{V}}$O_2max. For the slower group, the speed was stable until the 15th km and then decreased significantly in between, while for the fastest group, the speed decreased significantly at the 25th km. ** p < 0.02).

Figure 2

Averages % of HR_max during the marathon of the faster and slower marathoners’ groups expressed in % of HR_max. The % of HR_max at the Respiratory Compensatory Point (RCP) was indicated as a reference for each group.

Figure 3

Averages % of $\dot{V}$O_2max during the marathon of the faster and slower marathoners’ groups expressed in % of $\dot{V}$O_2max. The % of $\dot{V}$O_2max at the Respiratory Compensatory Point (RCP) was indicated as a reference for each group.

Figure 4

The energy cost of running (Cr) during the marathon of the fastest and slower marathoners’ groups expressed in mL·kg⁻¹·km⁻¹. The energy cost of running during the below the Respiratory Compensatory Point (RCP) measured in the UM-TT was indicated as a reference for each group.