Muscle oxygenation maintained during repeated sprints despite inspiratory muscle loading

A high work of breathing can compromise limb oxygen delivery during sustained high-intensity exercise. However, it is unclear if the same is true for intermittent sprint exercise. This project examined the addition of an inspiratory load on locomotor muscle tissue reoxygenation during repeated-sprint exercise. Ten healthy males completed three experimental sessions of ten 10 s sprints, separated by 30 s of passive rest on a cycle ergometer. The first two sessions were "all-out efforts performed without (CTRL) or with inspiratory loading (INSP) in a randomised and counterbalanced order. The third experimental session (MATCH) consisted of ten 10 s work-matched intervals. Tissue saturation index (TSI) and deoxy-haemoglobin (HHb) of the vastus lateralis and sixth intercostal space was monitored with near-infrared spectroscopy. Vastus lateralis reoxygenation ({Delta}Reoxy) was calculated as the difference from peak HHb (sprint) to nadir HHb (recovery). Total mechanical work completed was similar between INSP and CTRL (effect size: -0.18, 90% confidence limit {+/-}0.43), and differences in vastus lateralis TSI during the sprint (-0.01, {+/-}0.33) and recovery (-0.08, {+/-}0.50) phases were unclear. There was also no meaningful difference in {Delta}Reoxy (0.21, {+/-}0.37). Intercostal HHb was higher in the INSP session compared to CTRL (0.42, {+/-}0.34), whilst the difference was unclear for TSI (-0.01, {+/-}0.33). During MATCH exercise, differences in vastus lateralis TSI were unclear compared to INSP for both sprint (0.10, {+/-}0.30) and recovery (-0.09, {+/-}0.48) phases, and there was no meaningful difference in {Delta}Reoxy (-0.25, {+/-}0.55). Intercostal TSI was higher during MATCH compared to INSP (0.95, {+/-}0.53), whereas HHb was lower (-1.09, {+/-}0.33). The lack of difference in {Delta}Reoxy between INSP and CTRL suggests that for intermittent sprint exercise, the metabolic O2 demands of both the respiratory and locomotor muscles can be met. Additionally, the similarity of the MATCH suggests that {Delta}Reoxy was maximal in all exercise conditions.