UBC Theses and Dissertations
Effects of cycling cadence on respiratory and haemodynamic responses in trained cyclists Mitchell, Reid Andrew
The physiological consequences of cycling cadence selection are poorly understood. Purpose: To determine the impact of cadence on cardiorespiratory and metabolic parameters; perceptual responses; power of breathing (Pb); electromyography of the diaphragm (EMGdi) and leg muscles; and microvascular leg blood flow. Methods: Eleven trained cyclists (10M:1F; age=27±6yrs; V̇O2max=60.8±3.7ml·kg-¹·min-¹) completed four 6-min constant-load cycling trials at 10% below their gas exchange threshold (63±5% peak power) while pedaling at 60rpm, 90rpm, 120rpm, and a freely chosen cadence (FCC, 94.3±6.9 rpm), in randomized order, on an electromagnetically braked cycle ergometer. Ventilatory and metabolic parameters were measured using a commercially available metabolic cart. An oesophageal electrode balloon catheter was used to assess Pb and EMGdi. Surface EMG was placed on four leg muscles predominant in cycling. Blood flow index (BFI) was determined on the same muscles of the contralateral limb using near-infrared spectroscopy and indocyanine green. Perceptual responses were measured using the modified 0-10 category ratio Borg scale. Results: With each increase in cadence there was a corresponding increase in V̇O2 (all pairwise comparisons p<0.05). Pb and EMGdi was significantly greater at 120rpm compared to all other conditions (p<0.05). There were no differences in leg EMG across cadences except for the gastrocnemius, which was significantly higher at 90rpm, FCC, and 120rpm versus 60rpm (all p<0.05). A significant main effect was observed for BFI in three out of the four muscles tested, where 120rpm was higher than 60rpm and 90rpm in the vastus medialis (9.1±3.8 vs. 7.1±1.8 and 6.8±2.5µmol·s-¹, respectively, both p<0.05) and semitendinosus (4.8±3.1 vs. 3.4±1.5 and 3.2±1.4µmol·s-¹, respectively, both p<0.05). The gastrocnemius was higher at 120rpm compared to 60rpm, 90rpm and FCC (8.1±2.0 vs. 4.1±1.5, 5.4±2.1 and 5.9±2.0 µmol·s-¹ respectively, all p<0.01). No difference in BFI was found in the vastus lateralis (p=0.06). There was no effect of cadence on breathing or leg discomfort ratings (p>0.05). Conclusion: Relative blood flow appears to be closely linked with metabolic activity of the muscle, which was significantly elevated during the highest cadence condition. In combination with the substantial rise in respiratory variables and the Pb, cadence may represent the balance between peripheral and central stressors.
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