Energy System Contributions During XC Mountain Biking

This article will briefly discuss the contributions of the anaerobic and aerobic energy systems during mountain biking.  More specifically long, off road cross country races as opposed to downhill oriented mountain biking.

Cross country mountain bike racing (CCMBR) is characterized by riding on narrow sections of dirt or rock trail, involves significant amounts of climbing and descending, and races can vary in time from two hours up to twenty-four hours or longer. Although CCMBR primarily derives energy from the aerobic energy system due to the length and intensities required to complete a race successfully, the anaerobic system also plays a significant role in energy production. 

For example, at the start of a race, it is advantageous for the mountain biker to sprint to obtain a favorable position before entering the single track portion of the trail where passing becomes more difficult.  Furthermore, there are multiple times during the race where the anaerobic system comes in to play such as technically demanding ascents, breakaway attempts, and sprints to the finish. Research by Zarzency, Podlesny, and Polak (2013) found that during cross country mountain bike races that the time spent at an exercise intensity above the anaerobic threshold was 31% of the total competition time whereas time spent below aerobic threshold and between aerobic and anaerobic thresholds accounted for 18% and 51% of total competition time. 

This research agrees with Wirnitzer and Kornexl (2008) who found participants in a strenuous eight-day mountain bike race spent 36% of competition time in a high and very high-intensity zone which indicates utilization of the anaerobic energy system, while the remaining time was spent in the low to moderate intensity zone which primarily involved the aerobic energy system. These studies make it apparent that success as a mountain biker relies on both the aerobic and anaerobic energy systems.

When the aerobic energy system is utilized during mountain biking ATP (energy) is produced from the generation of acetyl-CoA via the oxidation of carbohydrates and fats (and in some cases proteins). Acetyl-CoA is then oxidized in the Krebs cycle which leads to oxidative phosphorylation and ATP formation in the electron transport chain (Powers & Howley, 2015).

When the anaerobic system is utilized during mountain biking energy is primarily produced via glycolysis which involves the breakdown of glucose or glycogen to form pyruvate or lactate which ultimately leads to rapid ATP production (Powers & Howley, 2015). Also, the ATP-PC system may contribute energy during short bouts (lasting a few seconds) of intense exercise such as surging to pass a competitor.

The take home points from this article are really quite simple.  To perform your best during a mountain bike race, the majority of your training miles (60-70%) should be done at a relatively low intensity (75% maximum heart rate or lower) to develop your aerobic capacity, while two to three workouts a week should be included that involve threshold, interval, and VO2 Max training to develop anaerobic capacity. 

 

References

Zarzeczny, R., Podleśny, M., & Polak, A. (2013). Anaerobic capacity of amateur mountain bikers during the first half of the competition season. Biology of sport, 30(3), 189.

Wirnitzer, K. C., & Kornexl, E. (2008). Exercise intensity during an 8-day mountain bike marathon race. European journal of applied physiology, 104(6), 999-1005.

Powers, S. K., & Howley, E. T. (2015). Bioenergetics. Exercise physiology: Theory and application to fitness and performance (pp.39-65).  (9th ed.). New York, NY: Human Kinetics.

 



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