HEART RATE RESPONSES TO DOWNHILL MOUNTAIN BIKING IN DOWNHILL AND CROSS COUNTRY CYCLISTS

Abstract

Mountain biking has become more popular as a leisure activity over the past decade (Baron, 2001). The sport has several disciplines, of which downhilling is rapidly becoming one of the most popular. Riders compete over a measured downhill course against the clock. Despite the popularity of the downhill discipline, there is a dearth of research into this area. The aim of this study was to evaluate the heart rate responses of downhillers (DH) and cross-country (XC) mountain bikers, during downhill riding. Six DH riders (age 27.1 ± 5.4 years) and seven XC riders (age 43.0 ± 9.2 years) each performed two timed runs down a measured downhill course (distance - 1.7km, vertical interval - 180 m). Heart rates were recorded using a short-range telemetry system (Vantage NV, Polar, Kempele, Finland). The sampling rate was set to record the R-R interval. Subjects were allowed to use their own cycle (seven full suspension, six front suspension only). Mean heart rates were recorded for ten successive fifteen second intervals (P1 to P10). Overall performance time was also recorded. An independent t-test was used to assess differences in the heart rate response, and performance time, between groups. A One-Sample Kolmogorov-Smirnov test revealed that all test variables were normally distributed. Results showed a significant difference in heart rates, by discipline, at the first and second data points (p<0.05 at P1 and P2). No significant differences were identified between data points at any other part of the timed trial. DH riders performed the timed run significantly faster (p<0.05). The measured differences, at P1 and P2, may be due to an increased power output at the start of the runs. Though the sport sees an intermittent intensity pattern, heart rates were consistently very high. The mean heart rates for both groups were higher during downhilling than those found by research on cross-country riding (Wilber et al., 1997). Intensity may remain high due to the muscular activity of the arms and legs during the non-pedalling phases. This can help to dampen the impact of the course, and
assist in manoeuvring the bicycle over obstacles. Further research using SRM power cranks will help to determine whether DH riders do produce more power than XC. The quicker times by the DH riders are more likely to be a result of greater downhill-specific riding skills. Anstiss (1997) also reported that DH riders took more risks than XC both in sport and in other aspects of their lifestyles. This risk-taking tendency of downhillers may be a factor in the faster times between groups. In conclusion, DH riders performed at a higher heart rate level than XC during the trial. Factors such as power output, skill and attitudes to risk are likely to be influential in downhilling performance.