The physiological and physical determinants of mountain bike cross country cycling

PURPOSE: The purpose of this investigation was to establish the physical and physiological determinants of mountain bike (MTB) cross-country (XC) cycling, and to elucidate the technique adopted in riding off road. As there is minimal data outlining the sport of XC cycling, the design and results of elite races were documented and analysed. This was undertaken to summarise event information and review technical race characteristics that impact on the performer. These analyses allowed the construction of a XC time trial (F.1) course, which was employed to profile the physical and physiological demands of completing it. A model was developed based on test measures, with the purpose of predicting XC performance and validating its production method. The purpose of the final section in this research was to determine if elite XC cyclists perform similarly to competitive riders. METHOD: Twenty nine World Cup and Title XC races were documented and averaged for winning time, race ascension, race speed, race duration, mean gradient, % time to 20th place and % of breakdown of technical course content. This established broadly the demands of XC cycling at the highest level and allowed a representative off road course to be constructed. Laboratory cycle maximum test (CMT) and IT measures were compared to determine which variables best described performance. Eleven experienced male XC cyclists (25.1 ± 4.9 y, 71.4 ± 6.7 kg, VO2max 64.7 ± 8.2 mLkg-1min-1 ) completed CMT, followed by a XC TT (15.52 km, 624 — m elevation gain). CMT values were related to the physiological responses and ride times recorded from the TT. TT power output was measured with the SRM Tm training system, with blood lactate (Bla) and perceived exertion (RPE) taken each lap. To construct the XC model the TT course was divided into 8 discrete terrain categories, with the relationships between category speed and % of peak power output (PPO) established. The model tested relationships established between CMT and the XC TT by comparing real performances to predicted ones. Five elite male cyclists (28 ± 3.3 y, 68.8 ± 6.2 kg, VO2max 75.4 ± 2.3 mLkg-l min-1 ) completed laboratory testing, whilst three cyclists performed XC TT's (13.8 km, 646-m elevation gain). Power output was measured by the SRM Tm training system. TT values were compared to competitive cyclists, which established similar ride patterns. RESULTS: Race analysis revealed: a duration of 141 ± 11 min. for elite men (M) and 119 ± min. for elite women (W), a race ascension of 1942 ± 245m (M) and 1402 ± 175 (W), an average speed of 21.2 ± 1.7 km.hr-1 (M) and 17 ± 1.7 km.hr-1 (W) and a mean gradient of 4.11 ± 0.52%. Percentage of fast downhill (DH) (12.8 ± 6.3%), technical DH (9.1 ± 4.1%) and single track (44.9 ± 10%) was measured. Mean gradient in 1999 (4.46 ± 0.36%) was significantly higher (P<0.05) than in 1997 (3.99 ± 0.53%) and 1998 (3.91 ± 0.53%) No differences (P>0.05) were observed between the mean XC TT and values at individual anaerobic threshold (IAT) for heart rate (174 ± 7 bpm vs 173 ± 8 bpm) and power output (315 ± 39W vs 309 ± 27W). Significantly higher (P<0.05) Bla concentration was observed during the XC TT than calculated at [AT (8.1 mmolL -I± 2.1 vs 4.0 ± 1.0 mmolL-1). Significant differences (P<0.01) were observed in power output, cadence and speed between TT laps and terrain categories. Strong relationships were established between CMT values and TT performance. Peak power output (PPO) to total mass was strongly correlated (r= -0.93) to XC TT time, whilst PPO was less strong (r= 0.64). The difference between modelled XC TT time and actual performance time for two subjects was -2.65% and 2.27%, respectively. Elite XC cyclists showed an ability to sustain a high power output in a lab based TT (362.8 ± 23W) and maintained a high percentage of peak HR (93.3 ± 1.5%). During XC TT's elite cyclists averaged 306.8 ± 14.5W, 68.3 ± 4.3 rpm and maintained 90.7 ± 0.80% of peak HR. For "15-20% Ascent", "10-15% Ascent" and "5-10% Ascent" categories percentage of PPO between elite and competitive cyclists was not different (P>0.05) (114.4 ± 8.8% vs 115.1 ± 8.2%; 100.3 ± 7.8% vs 102.2 ± 9.5%; 89.8 ± 7.7% vs 88.5 ± 2.8%). Significantly greater (P<0.05) speed and power output was observed between elite and competitive cyclists in seven and six of the eight terrain categories, respectively. Modelling between actual and predicted times revealed small mean differences (4.62% of mean performance time) and median absolute differences (4.67%). CONCLUSION: This investigation has established with novel ways the primary determinants of off road cycling, showing that MTB XC places considerable endurance and technique demands on the performer. The nature of a XC course appears to dictate the physical responses observed and techniques adopted. Strong relationships established between test variables relative to mass and XC TT performance indicate the marked influence of gradient in off road cycling. This investigation demonstrates that MTB XC is an intermittent and high intensity cycling discipline, which despite requiring significant technical skill, is dependent on physiological measures related to mass.