The effect of pedaling rate on the work of breathing

It is generally accepted that the rate of oxygen consumption (VO 2) increases with contraction frequency in exercising muscle; however, the contribution of respiratory muscle work to VO2 is often neglected. The purpose of this study was to investigate if pedaling rate influences the contribution of the work of breathing (WB) to VO2 and if the elevated recruitment of respiratory muscles restricts locomotor muscle VO2 (VO2LM) during incremental and constant-load cycling. Subjects (n=10) performed two maximal incremental tests (MIT) and two constant-load tests (CLRCP); power output that induced respiratory compensation) until exhaustion; one of each, at 100 rpm and at 70 rpm. During the MIT, VO 2, VE, WB, and VO2RM were all higher when pedaling at 100 compared to 70 rpm regardless of power output (p<0.05). Direct measurements of local muscle VO2 showed increased changes in deoxygenated hemoglobin (ΔHHb) and total hemoglobin (ΔTHb) counts in the respiratory muscle when pedaling at the faster cadence, without compromising VO2LM. During the CLRCP, no significant differences were seen in respiratory variables between pedaling rates. Locomotor muscle ΔTHb was significantly higher when pedaling at 100 rpm compared to 70 rpm, however, there was no difference in ΔHHb when comparing the two cadences. Interestingly, there was no significant difference in local ΔHHb or ΔTHb in the respiratory muscle during the CLRCP. These results show that pedaling rate influences WB and the contribution of respiratory muscles to whole-body VO 2 regardless of power output during MIT but not during CLRCP. Furthermore, this data provides pertinent information regarding the ongoing battle for oxygen delivery between central and peripheral mechanisms and on cardiopulmonary regulation during exercise.