Editor,—I read with interest the leader by Veronique Billat entitled “V̇o₂ slow component and performance in endurance sports”.¹ Oxygen uptake kinetics in general, and the aetiology of the V̇o₂ slow component phenomenon in particular, are certainly topics of great conceptual and practical importance. However, there were several points of contention within Dr Billat's article that should be brought to the attention of readers so that an informed and balanced debate can take place.

Dr Billat states that “A high range of work (rates) can be identified at which there is a sustained increase in blood lactate . . .with time. These responses decline back towards a baseline value.” These two sentences, which are applied to a description of the physiological responses to moderate intensity exercise, are clearly inconsistent. It is also stated that during moderate exercise “oxygen uptake stabilises at about 80% in high level marathon runners”. This suggests that V̇o₂ will reach a steady state close to 80% V̇o₂max irrespective of the absolute work rate within the moderate exercise intensity domain. However, it should be remembered that moderate intensity exercise is, by definition, any exercise that is performed below the lactate threshold. Therefore constant load moderate exercise can lead to the attainment of a steady …