Mechanical work and physiological responses to simulated cross country mountain bike racing

Abstract

The purpose was to assess the mechanical work and physiological responses to cross country mountain bike racing. Participants (n = 7) cycled on a cross country track at race speed whilst VO2, power, cadence, speed, and geographical position were recorded. Mean power during the designated start section (68.5 ± 5.5 s) was 481 ± 122 W, incurring an O2 deficit of 1.58 ± 0.67 L - min(-1) highlighting a significant initial anaerobic (32.4 ± 10.2%) contribution. Complete lap data produced mean (243 ± 12 W) and normalised (279 ± 15 W) power outputs with 13.3 ± 6.1 and 20.7 ± 8.3% of time spent in high force-high velocity and high force-low velocity, respectively. This equated to, physiological measures for %VO(2max) (77 ± 5%) and % HR(max) (93 ± 2%). Terrain (uphill vs downhill) significantly (P < 0.05) influenced power output (70.9 ± 7.5 vs. 41.0 ± 9.2% W(max)),the distribution of low velocity force production, VO2 (80 ± 1.7 vs. 72 ± 3.7%) and cadence (76 + 2 vs. 55 ± 4 rpm) but not heart rate (93.8 ± 2.3 vs. 91.3 ± 0.6% HR(max)) and led to a significant difference between anaerobic contribution and terrain (uphill, 6.4 ± 3.0 vs. downhill, 3.2 ± 1.8%, respectively) but not aerobic energy contribution. Both power and cadence were highly variable through all sections resulting in one power surge every 32 s and a supra-maximal effort every 106 s. The results show that cross country mountain bike racing consists of predominantly low velocity pedalling with a large high force component and when combined with a high oscillating work rate, necessitates high aerobic energy provision, with intermittent anaerobic contribution. Additional physical stress during downhill sections affords less recovery emphasised by physiological variables remaining high throughout.

Time of VO2max Plateau and Post-Exercise Oxygen Consumption During Incremental Exercise Testing in Young Mountain Bike and Road Cyclists

“…Concomitantly, the lower RERpost in group MC (approaching a value of 1) suggests the greater use of Laas a substrate in oxidative metabolism (Emhoff et al 2013, Gladden 2008, Robergs et al 2004 and also improvements in the shuttling of lactate at the intracellular and extracellular level so to be utilized via oxidation or converted to glucose and glycogen (Brooks 2000, Brooks 2007. It is therefore possible that the specificity of cross-country MTB training and competition can enhance lactate production and oxidization during exercise and improve post-exercise lactate transport capacity from muscle to blood (Impellizzeri et al 2002, MacDermid andStannard 2012). Conversely, the longer endurance steady-state activity typical of road cycling could be less conducive to lactate production and efficient disposal.…”

“…Hence, the specificity of each cycling discipline suggests differences in those physiological and performance characteristics that relate to performance. MacDermid and Stannard (2012) quantified the power output of a simulated mountain biking race to find that highest power was produced immediately after the start and during uphill segments, incurring a significant oxygen deficit. Therefore, the high-intensity yet intermittent nature of MTB racing has led to suggestions that anaerobic metabolism is just as an important determinant of performance as aerobic metabolism (Impellizzeri and Marcora 2007, MacDermid and Stannard 2012, Stapelfeldt et al 2004.…”

“…MacDermid and Stannard (2012) quantified the power output of a simulated mountain biking race to find that highest power was produced immediately after the start and during uphill segments, incurring a significant oxygen deficit. Therefore, the high-intensity yet intermittent nature of MTB racing has led to suggestions that anaerobic metabolism is just as an important determinant of performance as aerobic metabolism (Impellizzeri and Marcora 2007, MacDermid and Stannard 2012, Stapelfeldt et al 2004. Inoue et al (2012) reported a significant correlation between MTB race times and maximal peak power and mean average power attained in a variant of the Wingate anaerobic test involving five 30-s all-out bouts interspersed with 30-s of recovery.…”

Cyclists and triathletes do not differ in muscle volume, muscle recruitment or pedal force effectiveness

“…Furthermore, we did not include mountain bikers in our comparisons. Mountain bikers tend to opt for reduced pedaling cadence [32] and longer crank arms [33] than road cyclists, which would require larger muscle force per pedal stroke. On the other hand, track cyclists use higher pedaling cadence [34] and sustain larger power outputs which may lead, in turn, to large force produc-tion per pedal stroke.…”

Predictive Validity of Critical Power, The Onset of Blood Lactate and Anaerobic Capacity for Cross-Country Mountain Bike Race Performance

“…1 Un-typical of other endurance sports starting on mass, XCO-MTB requires maximal effort from the start to gain or hold positional advantage so as not to impair overall performance. As such initial field based research identifies that 82% of total race time corresponds to power outputs greater than the Lactate Threshold (LT) equating to 90% HR max and 84% VO 2max .…”