The Mexico 1968 Olympic Games represented a turning point in altitude training. Due to the dominance of athletes acclimatised to the altitude during the  Games (they were held at an altitude of 2,340 m),¹ in the 1970s, the implications of training or living in hypoxic conditions to improve performance started to be studied.

Given that oxygen is essential for our cellular metabolism, the body has a control mechanism to maintain oxygen concentration balanced. This mechanism depends greatly on haemoglobin, a protein found in red blood cells, which increases hypoxic conditions to counteract the oxygen reduction. Altitude training seeks to increase the haematocrit (amount of red blood cells in blood), as hypoxia causes a decrease in oxygen saturation in the body which results in a compensatory response by increasing the haemoglobin mass in the body. This increase improves the maximal oxygen uptake, one of the main markers for performance in endurance sports.² Moreover, although it was suggested that these improvements were only observed in individuals with low haemoglobin levels, increases of 3-4 % were also seen among athletes with high baseline levels (>14 g/kg) during training camps where they lived “high” (2,200-3,000 m) and trained “low”.²

Controlling the respiratory frequency to simulate Hypoxic conditions

Recently, researchers such as Xavier Woorons and Grégoire P. Millet have been studying if reducing the respiratory frequency or doing apnoea during high-intensity training sessions can produce physiological effects similar to those which take place during hypoxic training. As an example, a study ³ that compared the effect of hypoventilation under normoxic conditions (inhaling every 4 seconds when in normal conditions it is done every 1 second) with a normal respiratory pattern in hypoxic conditions, showed that the hypoxic state is similar to the one observed at an altitude of approximately 2,400 m. In other words, reducing the respiratory frequency to as low as 25 % (breathing 15 times instead of 60) resulted in a decrease in oxygen saturation, the same way it would happen at 2,400 m (Figure 1). Thus, voluntary hypoventilation could induce arterial oxygen desaturation⁴ that results in muscle⁴ or cerebral⁵ deoxygenation, producing a series of cardiovascular and metabolic responses to counteract the decrease in oxygen.

Holding your breath can improve the ability to perform repeated high-intensity efforts

The same researchers have also studied the effects of holding the breath (breathing out and holding the breath) in short sprints. For example, a study ⁶ performed with swimmers showed that, after 6 apneic sprint sessions (2 series, 16×15 m and resting 30 seconds between repetitions), increased the ability to do repeated sprints (from 7 to 9). On the other hand, those who trained with a normal breathing pattern did not improve. Similarly, a study carried out by the same research group⁷ with rugby players showed how after 4-week training (2-3 series of 8×40 m sprint) those who did apneic sprints increased the number of repeated sprints by 64 %. They went from being able to do 9 sprints to 15.

A recent published article⁸ analysed the impact of 6 sprint training sessions on a bicycle for team sports athletes’ ability to repeat sprints. During three weeks, 20 men who compete in different team sports (basketball, football, handball, rugby and hockey) performed 3 sets of 8 series of 8 seconds to 150 % of maximal power, resting 16 seconds in between repetitions. After this period, those who did the series in apnoea improved different aspects related to the ability to make repeated efforts of maximal intensity in running: they increased the distance covered in the Yo-Yo test (pre: 1111 m v. post: 1468 m) and the fatigue decreased during repeated sprints (pre: 5.8 % v. post: 7.72%). On the other hand, those who maintained a normal breathing pattern did not improve.

A possible explanation to the increase in the ability to do sprints can be related to an increase in the anaerobic metabolism, as in the case of the swimmers who did apnoea training, they accomplished a rise in the production of lactate (pre 7.9 v. post 11.5 mmol/L).⁶ Besides these adaptations associated with an increase of the glycolytic metabolism, cardiovascular adaptations also take place to increase the blood flow to the tissues. When performing apneic sprints or longer series up to 5 minutes reducing respiratory frequency to 25 %, an increase in the systolic volume takes place which counteract the oxygen saturation drop.^3,9

Conclusions

Adjusting the respiratory frequency can produce physiological changes similar to those produced in altitude. Cardiovascular and metabolic adaptations resulting from high-intensity training holding the breath, can improve significant parameters in different sports such as swimming, cycling, or team sports. In team sports, where the ability to perform actions at maximum speed becomes especially relevant as in football (most goals are preceded by sprints),¹⁰ these results suggest the fact that “playing” with the respiratory frequency can help improve the ability to do sprints by increasing heart function and glycolytic metabolism.

Adrián Castillo

References:

1. Millet, G. P., Girard, O., Beard, A. & Brocherie, F. Repeated sprint training in hypoxia–an innovative method. Dtsch. Z. Sportmed. 2019, 115–122 (2019).
2. Hauser, A. et al. Do male athletes with already high initial haemoglobin mass benefit from ‘live high–train low’ altitude training? Exp. Physiol. 103, 68–76 (2018).
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10. Faude, O., Koch, T. & Meyer, T. Straight sprinting is the most frequent action in goal situations in professional football. J. Sports Sci. 30, 625–631 (2012).