Abstract

Objectives: To analyse the heart rate (HR) response and estimate the ultraendurance threshold—the optimum maintainable exercise intensity of ultraendurance cycling—in ultraendurance elite cyclists competing in the Race across the Alps.

Methods: HR monitoring was performed in 10 male elite cyclists during the first Race across the Alps in 2001 (distance: 525 km; cumulative altitude difference: 12 600 m) to investigate the exercise intensity of a cycle ultramarathon and the cardiopulmonary strains involved. Four different exercise intensities were defined as percentages of maximal HR (HR_max) as follows: recovery HR (HR_re), <70% of HR_max; moderate aerobic HR (HR_ma), 70–80%; intense aerobic HR (HR_ia), 80–90%; and high intensity HR (HR_hi), >90%.

Results: All athletes investigated finished the competition. The mean racing time was 27 hours and 25 minutes, and the average speed was 18.6 km/h. The mean HR_max was 186 beats/min, and the average value of measured HRs (HR_average) was 126 beats/min resulting in a mean HR_average/HR_max ratio of 0.68, which probably corresponds to the ultraendurance threshold. The athletes spent 53% (14 hours 32 minutes) of total race time within HR_re, 25% (6 hours 51 minutes) within HR_ma, 19% (5 hours 13 minutes) within HR_ia, and only 3% (49 minutes) within HR_hi, which shows the exercise intensity to be predominantly moderate (HR_re + HR_ma  =  78% or 21 hours 23 minutes). The HR response was influenced by the course profile as well as the duration. In all subjects, exercise intensity declined significantly during the race, as indicated by a decrease in HR_average/HR_max of 23% from 0.86 at the start to 0.66 at the end.

Conclusions: A substantial decrease (10% every 10 hours) in the HR response is a general cardiovascular feature of ultramarathon cycling, suggesting that the ultraendurance threshold lies at about 70% of HR_max in elite ultramarathon cyclists.