When you ride your bike in the mountains it will be more difficult when altitude increases. Because of the altitude, your power output will be lower for the same relative intensity. This is caused by the thinner air at higher altitudes. By spending a longer period at altitude, your body can adapt to the thinner air, reducing performance losses.
as altitude increases during exercise the pO2 (partial oxygen pressure) decreases. With each breath, less oxygen reaches your lungs, meaning there is also less oxygen available in your blood for transport to your muscles.
Your heart rate increases to transport more oxygen to your muscles. This means that the heart quickly reaches its maximum output and your threshold power decreases. At altitude, post-exercise recovery is also slower.
Power output decreases at altitude
As altitude increases, your power output declines at the same relative intensity. Various models try to estimate the theoretical decrease in aerobic power output1 2. These models are based on well-trained athletes. When athletes remain at altitude for at least two weeks, their bodies adapt to the thinner air, resulting in a smaller decline in power output.
he summit of Alpe d’Huez is at 1,850m, meaning the final 4 km of the climb are above 1,500m. When your threshold power at sea level is 250 Watts, it will be about 8,7% lower (228 Watts) at 1500m. This also means that your power zones change.
VO2max also decreases at altitude
Several scientific studies show that VO2max also decreases when altitude increases. The exact decrease is not clear because there are many differences between the study design and the subjects involved in the different studies.
Even at an altitude of 589m, a slight reduction in VO₂max has been observed compared to sea level values. If altitude increases, the amount of oxygen that can be absorbed into the blood decreases, causing the VO2max of men and women to decrease about 7-9% per 1000m 3. The extent of VO₂max reduction varies significantly between individuals4.
Will your performance also decrease?
To determine performance, gross efficiency, pacing strategy, and aerodynamics are, in addition to power and VO2max, also important. Research shows that altitude does not affect gross efficiency2. At altitude, air resistance is lower, which means that you have to produce less power to attain a certain velocity.
he key question is whether the power loss is sufficiently offset by the reduced air resistance. Research shows that performance over 1000m decreases by 2-4% in medium and long distance runners and above 2000m with> 4% <6/sup>.
Applied to cycling, this suggests you could theoretically be 2-4% faster on a climb starting at sea level compared to the same climb beginning at 1,000m.
1. Basset, D., Kyle, C., Passfield, L., Broker, J., & Burke, E. (1999). Comparing cycling world hour records, 1967-1996: modeling with empirical data. Medicine and science in sports and exercise, 31(11):1665-76.
2. Péronnet, F., Thibault, G., & Cousineau, D. (1991). A theoretical analysis of the effect of altitude on running performance. Journal of applied physiology, 70(1):399-404.
3. Fulco, C., Rock, P., & Cymerman, A. (1998). Maximal and submaximal exercise performance at altitude. Aviation, space, and environmental medicine, 69:793.
4. Robergs, R., Quintana, R., Parker, D., & Frankel, C. (1998). Multiple variables explain the variability in the decrement in VO2max during acute hypobaric hypoxia. Medicine and science in sports and exercise, 30:869.
5. Clark, S., Bourdon, P., Schmidt, W., Singh, B., Cable, G., Onus, K., Woolford, S., Stanef, T., Gore, D., Aughey, R. (2007). The effect of acute simulated moderate altitude on power, performance and pacing strategies in well-trained cyclists. European journal of applied physiology, 102(1):45-55.
6. Hamlin, M., Hopkins, W., & Hollings, S. (2015). Effects of altitude on performance of elite track-and-field athletes. International journal of sports physiology and performance., 10(7):881-7.
