Exercising with Intermittent Hypoxia
Recently, shorter applications of hypoxia (intermittent hypoxia) at rest or exercise during daytime have been suggested for improvement of sea-level performance. This modality allows the application of a stronger hypoxic stimulus, equivalent to an altitude about 16000 feet (5000 m), which is in generally well tolerated by healthy individuals when applied for some minutes at a time. The rationale for this is to induce acclimatization to hypoxia in a shorter time with a stronger stimulus. Two modalities exist: persistent exposure at rest to altitudes (or normobaric hypoxia) of 16000 feet for up to 3 hours, or intermittent hypoxic exposure, which consists of six to nine consecutive cycles of breathing hypoxic air for 6 minutes followed by room air for 4 minutes. The level of hypoxia (concentration of oxygen) is usually about 12%. The machine needed to produce normobaric hypoxia is called an altitude generator or hypoxia machine. Also, a well-sealed dual valve mask (see photo) must be used as to limit the entrainment of room air.
When applying normobaric hypoxia, one needs to consider that the altitude at which nitrogen-enriched air is applied has a large eﬀect on the resulting partial pressure of oxygen, and thus on the ‘‘treatment altitude’’ for a given level of oxygen concentration or FiO2 (Fraction of Inspired Oxygen). This is particularly important for low levels of FiO2: 10% O2 will result in a PO2 equivalent to 19,000 feet (5800 m). A further modality of using hypoxia with the intention to achieve greater improvement of performance compared with living and training at low altitude is to train in hypoxia and live in normoxia. Various levels of hypoxia ranging from 6500 to 18000 feet (2000 to 5500 m) are often used with this approach. Keep in mind that hypoxia decreases maximum aerobic performance and that training with equal workloads in hypoxia versus normoxia therefore means training at a higher relative workload in hypoxia. In this case, it will not be possible to distinguish between eﬀects by hypoxia and those by increased workload. If the question is whether training in hypoxia has greater eﬀects than training in normoxia, it is important to train at the same relative workload. Finally, the athlete needs to monitor for signs of overtraining (discussed in the first blog).
Johnathan Edwards is a medical doctor with 30 years of sport medicine experience. A former professional athlete in the sport of motocross and a Category 1 bicycle racer, Johnathan understands human performance. He obtained a complete Physiology degree from UC Davis, medical school in Norfolk, VA, Internal medicine in Las Vegas, Sports medicine in Utah, and Anesthesiology in Florida. Today he is a performance coach, clinical instructor, team doctor for many cycling teams, UFC, motocross and Olympic athletes. Husband and father, he aspires to live part time in France and the United States, and riding his bike. Full Disclosure – Johnathan is a consultant for Masimo and the Mighty Sat.