The Power Output Characteristics of Downhill Mountain Biking

Abstract

Purpose:
To determine the performance characteristics of field-based
Downhill Mountain biking (DH) and to identify the best methods of assessment for DH type activity.

Methods:
Twelve trained male cyclists of differing experience
levels (age 31.4 ± 9.8 yrs, mean ± s.d.), performed a single laboratory-based intermittent cycle test consisting of 12 all out efforts, separated by periods of passive
recovery ranging from 5 to 15 seconds and a continual incremental ramp test to exhaustion. Power output was recorded using a Polar S710 heart rate monitor and
power sensor kit and a Schoberer Rad Messetechnik (SRM) Powermeter systemduring each test. Additionally, seventeen national level trained, male downhill cyclists (age 27.1 ± 5.1 yrs) performed two timed field-based runs of a measured DH course. An SRM Powermeter was used to record power, cadence and speed. Heart rate was again recorded via a Polar S710 monitor.

Results:
During intermittent tests significant differences (p<0.05) in power were found at 8 of the 12 efforts. A significant difference (p<0.001) was also found when power was averaged over all 12 intervals. Mean power was 556 ± 102 W and 446 ± 61 W for the SRM and S710 respectively. The 5710 underestimated power by an average of 23% with random errors of */ 24% when compared to the SRM. Random errors ranged from 36% to 141% with the median being 51%. Significant differences (p<0.001) were also found between the two systems during the incremental ramp tests. Mean power output was 189 ± 51 W and 212 ± 49 W for the SRM and S710 respectively. The 5710 overestimated power by an average of 11% over the SRM. Random errors ranged from 21% to 67% with the median being 13%. During field-testing peak power was 834 ± 129 W. Mean power (75 W) accounted for only 9% of peak values. Paradoxically, mean heart rate was 168 ± 9 beats.min-1, accounting for 89% of agepredicted maximum heart rate. Mean cadence (28 ± 20 revs.min -1) was significantly related to speed (r = 0.51; p<0.01). Power and cadence were not significantly related to run time or any other variable.

Conclusions:
Results indicated there was little agreement between the two ergometer systems. The Polar S710 did not provide a valid measure of power during intermittent DH type cycling activity, nor did it provide a valid measure for scientific/elite use during continuous type cycling activity. Errors in the 5710 system were potentially influenced by chain vibration and sampling rates. Field results support the intermittent nature of DH Mountain biking. The poor relationships between power and cadence to run time suggest they are not essential pre-requisites to performance in DH and indicate the importance of riding dynamics to overall performance.

Keywords: Downhill, Mountain biking, power output