Inspiratory loading and limb locomotor and respiratory muscle deoxygenation during cycling exercise

Abstract The aim of this study was to determine the effect of inspiratory loading on limb locomotor (LM) and respiratory muscle (RM) deoxygenation ([deoxy (Hb + Mb)]) using NIRS during constant-power cycling exercise. Sixteen, male cyclists completed three, 6-min trials. The intensity of the first 3-min of each trial was equivalent to ∼80% V ˙ O 2 max (EX 80% ); during the final 3-min, subjects received an intervention consisting of either moderate inspiratory loading (Load mod ), heavy inspiratory loading (Load heavy ), or maximal exercise (Load EX ). Load heavy significantly increased LM [deoxy(Hb + Mb)] from 12.2 ± 9.0 μm during EX 80% to 15.3 ± 11.7 μm, and RM [deoxy(Hb + Mb)] from 5.9 ± 3.6 μm to 9.5 ± 6.6 μm. LM and RM [deoxy(Hb + Mb)] were significantly increased from EX 80% to Load EX ; 12.8 ± 9.1 μm to 16.4 ± 10.3 μm and 5.9 ± 2.9 μm to 11.0 ± 6.4 μm, respectively. These data suggest an increase in respiratory muscle load increases muscle deoxy(Hb + Mb) and thus may indicate a reduction in oxygen delivery and/or increased oxygen extraction by the active muscles.