Oxygen uptake (VO₂) kinetics during moderate constant-workrate (WR) exercise (>lactate-threshold (θL)) are well described as exponential. AboveθL, these kinetics are more complex, consequent to the development of a delayed slow component (VO₂sc), whose aetiology remains controversial. To assess the extent of the contribution to the VO₂sc from arm muscles involved in postural stability during cycling, six healthy subjects completed an incremental cycle-ergometer test to the tolerable limit for estimation of θL and determination of peak VO₂. They then completed two constant-WR tests at 90% of θL and two at 80% of ∆ (difference between θL and VO_2peak). Gas exchange variables were derived breath-by-breath. Local oxygenation profiles of the vastus lateralis and biceps brachii muscles were assessed by near-infrared spectroscopy, with maximal voluntary contractions (MVC) of the relevant muscles being performed post-exercise to provide a frame of reference for normalising the exercise-related oxygenation responses across subjects. Above supra-θL, VO₂ rose in an exponential-like fashion ("phase 2), with a delayed VO₂sc subsequently developing. This was accompanied by an increase in [reduced haemoglobin] relative to baseline (∆[Hb]), which attained 79 ± 13 % (mean, SD) of MVC maximum in vastus lateralis at end-exercise and 52 ± 27 % in biceps brachii. Biceps brachii ∆[Hb] was significantly correlated with VO₂ throughout the slow phase. In contrast, for sub- L exercise, VO₂ rose exponentially to reach a steady state with a more modest increase in vastus lateralis ∆[Hb] (30 ± 11 %); biceps brachii ∆[Hb] was minimally affected (8 ± 2 %). That the intramuscular O₂ desaturation profile in biceps brachii was proportional to that for VO₂sc during supra-θL cycle ergometry is consistent with additional stabilizing arm work contributing to the VO₂sc.

• The source(s) of the "slow component" component of pulmonary oxygen uptake kinetics (VOsc) associated with high-intensity exercise remains the source of debate.

• Noninvasive interrogation techniques of the biceps brachii muscle during cycle ergometry suggest that "resting" muscles, such as those of the arms and shoulder girdle, may contribute to the VOsc, through stabilising actions (e.g. more forceful pulling on the ergometer handlebars).

• The quantitative contribution of such extra "resting"-muscle work awaits precise determination.