Allan Phillips and myself have greatly discussed altitude training in previous articles (Does Altitude Training Work? and High-Altitude Training Does Not Improve Swimming Performance). Overall, we've concluded altitude training yields minimal alterations on oxygen consumption and blood markers. However, we've suggested this form of training likely results in improvement due to other aspects from the training camp (biomechanical analysis, team bonding, etc.).
As with all research, new information is uncovered all the time and for this topic, a lot more research is necessary. Specifically, controlled long-term studies are necessary to monitor and track performance alterations, as Allan Phillips discussed in the aforementioned article.
Moreover, it is uncertain whether blood and oxygen adaptations are the necessary parameters to study, as a recent study by Chia (2013) found high-altitude training resulted in a decrease of fat mass with an increase in lean mass during 3-weeks of high-altitude training with the same training volume and intensity.
Chia et al. conducted a second experiment in the course of which the
"effects of hypoxia (at 16% oxygen) on blood distribution to the skeletal muscle were assessed under glucose-ingested condition (i.e. insulin-stimulated condition) after training at sea level. Skeletal muscle blood distributions were measured using near infrared spectroscopy (NIRS) to detect changes in hemoglobin concentrations under hypoxic (16% oxygen) and normoxic conditions for 90 min after oral glucose ingestion." (Chia. 2013)
Aside from the expected change in oxygen saturation and more constant hemoglobin levels during the hypoxia condition, Chia et al. also observed an increase in lactate production and a decreased glucose clearance from the blood, which was compensated by an increased insulin response.
Theoretically, during hypoxia the body's mitochondria would increase their fatty acid uptake and beta-oxidation, which would release more fat from storage. To test this, one must measure the respiratory exchange ratio (RER) to monitor fuel usage. However, oxygen is used during this process, something lower at high-altitude. For this reason, Chia et al. feel the increase in insulin was the main reason for the body composition adaptations.
Overall, the research still indicates high-altitude training and hypoxia do not result in swimming performance improvements. However, the alterations in body composition during hypoxia may allow a swimmer to create more force and swim faster. Unfortunately, if these competitors are using fatty oxidation as a fuel source instead of glucose, it may hinder performance in events where glucose is the necessary fuel (races between 20 - 120 seconds). Future studies must analyze the fuel use in response to hypoxic training in high-altitude venues and look at performance results in swimming specialist in all distances, as high-altitude may provide benefits, but potentially only in events minimally using glucose (potentially the 50 free, 400 free, 800 free, and 1500 free). On last point, the longer events likely don't yield benefit from this alteration in body composition and fuel utilization, as less fat may impair floating and increase energy requirements.
- Chia M, Liao CA, Huang CY, Lee WC, Hou CW, Yu SH, Harris MB, Hsu TS, Lee SD, Kuo CH. Reducing Body Fat with Altitude Hypoxia Training in Swimmers: Role of Blood Perfusion to Skeletal Muscles. Chinese Journal of Physiology. 2013 [Epub ahead of print]
G. John Mullen received his Doctorate in Physical Therapy from the University of Southern California and a Bachelor of Science of Health from Purdue University. He is the founder of the Center of Optimal Restoration, head strength coach at Santa Clara Swim Club, creator of the Swimmer's Shoulder System, and chief editor of the Swimming Science Research Review.