Does training at high altitude improve cardio conditioning?
Training at high altitude is most definitely a topic of interest to athletes, and the performance gains are very debatable among researchers. To my knowledge, there have been no data-based research studies that have examined the effects of altitude training on purely anaerobic sports, outside of sprint cyclists. There is a wealth of information pertaining to aerobic sports. (All of the below recommendations are based on this research.)
Because there have been no formal research studies in this arena, no concrete conclusions can be made for anaerobic-based athletes. However, this is not to say that an anaerobic athlete could not potentially benefit from training at altitude. But because there has been no researched published on this topic, it is difficult to infer any practical applications.
Understanding the effects of altitude could prove useful to athletes of this nature. Ascending from sea level to altitude poses a stress to the body. More specifically, high altitude exposure decreases the partial pressure of inspired oxygen and the partial pressure of oxygen in arterial blood. Hematological adaptations from altitude exposure produce an increase in serum erythropoietin, red blood cells, hematocrit and hemoglobin, all of which produces an increase in oxygen delivery. Skeletal muscle adaptations include a possible increase in capillaries, myoglobin, oxidative enzymes, mitochondria and buffering capacity, all of which can improve oxygen extraction and utilization.
Traveling to altitude requires a well structured training program that includes less volume and intensity upon arriving. However, as mentioned previously, this recommendation is centered on aerobic-based sports. Anaerobic-based sports that include short bouts of high intensity training appear to not require as much of an acclimation period, if any at all.
However, if anaerobic athletes participate in aerobic conditioning as part of their overall training program at altitude, then care should be given to develop a ramp protocol including a lower duration of aerobic exercise to begin with in the first two weeks upon altitude exposure.
Because there is a decrease in VO2max at altitude, cardiovascular conditioning will not necessarily improve while at altitude, especially considering that the duration of the aerobic conditioning is less in the first two weeks of altitude exposure. Most aerobic athletes find that it is more difficult to achieve the same quality of training at altitude, which may or may not equate into better performances at sea level. The reason for this uncertainty is that it seems there are some athletes who are non-responders to altitude training and others who respond very poorly in training and competition when returning to sea level.
Because there are no scientific research on anaerobic athletes and high altitude training, it is difficult to make a conclusive statement that altitude training is of benefit for anaerobic-based athletes. Based on the physiological responses of altitude training discussed above, it can be inferred that altitude training could be of benefit in some way to anaerobic athletes, but the specific benefits as well as timelines are simply unknown. If cardiovascular conditioning is the goal, then altitude training could prove to be of benefit for some athletes given that they spend a minimum of about three weeks at higher altitude, following a ramp training program to acclimate to altitude, and they plan their competition soon after returning to sea level.
A very good reference is Altitude Training and Athletic Performance by Dr. Randy Wilbur.