During heavy training blocks, it can be difficult to meet the demands of training on back-to-back days. This may be due to a variety of reasons, such as heavy legs, tiredness or fatigue, but most of the time it shouldn’t stop us from training the next day in preparation for an event. One strategy to continue training the next day could be to reduce the intensity (i.e., a slower velocity or lower power output). However, this may lead to intervals being carried out in the wrong target zone (i.e., lower heart rate than planned) and smaller-than-planned adaptations may occur. In essence, the training stimulus may not be sufficient.

It is well-known that training in hypoxia is generally harder than normoxia. Typically for the same velocity or power output, your heart rate will be considerably higher. Therefore, it would be expected that working at a lower intensity in hypoxia would lead to a similar training intensity in normoxia.

We recently investigated this in a group of trained runners. During this study, they carried out a high-intensity interval session (4 x 4-min running, 3-min resting) in hypoxia (15% O2) and normoxia. During running, it was down to the runners to ensure that the intensity felt ‘hard’ to ‘very hard’ – they could do so by running faster, slower or maintaining the velocity. The results showed that the velocity selected in hypoxia was slower (-7%) than normoxia across the intervals. Interestingly this led to the same heart rate and muscle oxygenation changes between conditions throughout the intervals. However, even though the intensity was lower, perceptual responses (recovery, motivation, breathlessness, limb discomfort and pleasure) were negatively impacted more so in hypoxia than normoxia.

Overall, lower self-paced intensities in hypoxia than normoxia lead to similar levels of physiological stress during high-intensity interval training. This may be advantageous for ‘bad days’ where the legs don’t feel as good as they should do. Essentially, still carrying out the interval session in hypoxia will allow you to run slower but still achieve the same amount of gains if you were to do the session in normoxia. Be aware that perceptually, the session will still feel tough – but you knew that anyway!

Now it’s time to head into the chamber for your next HypoxicHIIT, the rest day can wait!

Hobbins, L., Gaoua, N., Hunter, S., & Girard, O. (2019). Psycho-physiological responses to perceptually-regulated interval runs in hypoxia and normoxia. Physiology & Behavior, 112611.