Cross, T. J., Winters, C., Constantini, N., & Sabapathy, S. (2013). The work of breathing and the slow-component of O2 uptake kinetics during strenuous exercise. Medicine & Science in Sports & Exercise, 45(5), Supplement abstract number 2477.

"The slow-component of oxygen uptake kinetics represents a progressive decline in work efficiency during strenuous constant-load exercise. The majority of the slow-component of oxygen uptake kinetics is explained by factors intrinsic to the working muscles (~86%). The remainder of the slow-component of oxygen uptake kinetics is likely due to the rising work of breathing associated with the hyperventilatory response to strenuous activity. To date, no study has quantified the work of breathing (and its components) with respect to the slow-component of oxygen uptake kinetics during strenuous exercise."

This study quantified the work of breathing during strenuous constant-load exercise, and examined the relationship between the resistive and elastic components of the work of breathing and the amplitude of the slow-component of oxygen uptake kinetics. Ss (N = 11) performed two separate, 6-minute bouts of heavy and severe-intensity cycling exercise. Gas-exchange and oesophageal manometry were used to quantify the amplitude of the slow-component of oxygen uptake kinetics and work of breathing parameters. The slow-component of oxygen uptake kinetics was determined as the difference in oxygen uptake between the third and sixth minute of constant-load exercise. Work of breathing parameters were quantified over the same period.

The amplitude of the slow-component of oxygen uptake kinetics was significantly greater during severe-intensity exercise compared with heavy trials. The relative increase in total work of breathing over the slow-component of oxygen uptake kinetics period was significantly greater during severe-intensity than for heavy exercise. There was no relationship between the work of breathing and the slow-component of oxygen uptake kinetics for heavy trials. Conversely, the slow-component of oxygen uptake kinetics was positively correlated with the increase in inspiratory elastic work of breathing (R2 = 71%), inspiratory resistive work of breathing (R2 = 86%), and expiratory resistive work of breathing (R2 = 87%) between the third and sixth minute of severe-intensity exercise.

Implication. The resistive and elastic work of breathing significantly influences the development of the slow-component of oxygen uptake kinetics during strenuous exercise, particularly in the severe-intensity domain.

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