Endurance training of respiratory muscles improves cycling performance in fit young cyclists

Abstract

Background: Whether or not isolated endurance training of the respiratory muscles improves whole-body endurance exercise performance is controversial, with some studies reporting enhancements of 50% or more, and others reporting no change. Twenty fit (VO2 max 56.0 ml/kg/min), experienced cyclists were randomly assigned to three groups. The experimental group (n = 10) trained their respiratory muscles via 20, 45 min sessions of hyperpnea. The placebo group (n = 4) underwent "sham" training (20, 5 min sessions), and the control group (n = 6) did no training.

Results: After training, the experimental group increased their respiratory muscle endurance capacity by 12%. Performance on a bicycle time trial test designed to last about 40 min improved by 4.7% (9 of 10 subjects showed improvement). There were no test-re-test improvements in either respiratory muscle or bicycle exercise endurance performance in the placebo group, nor in the control group. After training, the experimental group had significantly higher ventilatory output and VO2, and lower PCO2, during constant work-rate exercise; the placebo and control groups did not show these changes. The perceived respiratory effort was unchanged in spite of the higher ventilation rate after training.

Conclusions: The results suggest that respiratory muscle endurance training improves cycling performance in fit, experienced cyclists. The relative hyperventilation with no change in respiratory effort sensations suggest that respiratory muscle training allows subjects to tolerate the higher exercise ventilatory response without more dyspnea. Whether or not this can explain the enhanced performance is unknown.

Figure 1

Test-re-test reproducibility in the control/placebo group subjects during the time trial test and the constant work-rate exercise (CWE) test, before (Pre) and after (Post) the intervention period. Control and placebo group subjects are depicted with different symbols. Identity lines drawn in both graphs. Note that the time trial test is significantly more reproducible than the CWE test, consistent with the findings of others [13,14]. See text for numerical analysis.

Figure 2

Sustainable ventilatory capacity before the training phase (Pre), after two weeks of training (Mid) and immediately after (Post) the training phase in the three subject groups. The RMET group had a higher sustainable ventilatory capacity after training (see text for detailed explanation of this test).

Figure 3

Identity plots comparing time trial performance before (Pre) and after (Post) the intervention period in the RMET group (top panel) and in the control (bottom panel, open squares) and placebo (bottom panel, filled triangles) groups. Note that all but one subject in the RMET group improved their performance time, and that only three subjects in the control and placebo groups improved (two controls, one placebo), and then only marginally.

Figure 4

Changes in pulmonary ventilation rate (V_E) as a function of the % endurance time during the constant work-rate exercise test. The RMET group showed a significant increase in V_E after training; there were no significant pre-post differences in the control/placebo group. Bracket, P < 0.01, by ANOVA, for pre vs. post-training comparison.

Figure 5

Changes in the partial pressure of end-tidal CO₂ (P_ETCO₂) as a function of the % endurance time during the constant work-rate exercise test, before and after training. There were no significant changes in either group, although the RMET group showed a trend towards a decrease after training (P = 0.18). Note that P_ETCO₂ did decline markedly as a function of time during exercise in both groups, both before and after training, consistent with the upward drift in ventilation.

Figure 6

Changes in VO₂ as a function of the % endurance time during the constant work-rate exercise test. The RMET group showed an increase after training (Bracket, P < 0.027, by ANOVA, for pre vs. post-training comparison); no significant changes were observed in the control/placebo group.

Figure 7

Changes in VO₂ (left-hand panels) and ventilation (V_E, right-hand panels) as a function of performance time during the time trial test, before and after either RMET (top two panels) or a period of no training (control group, C, bottom two panels), in two representative subjects. The filled circles represent data obtained before the period of training, and the shaded triangles are the post-training values. The subject in the RMET group showed an increase in V_E and VO₂ after training, mirroring the changes observed with constant work-rate exercise. The control subject showed no changes between the first and second test. See text for a more detailed explanation, and Table 3 for the average data.

Figure 8

Correlation between the change in performance time and the change in V_E with RMET. Values were computed as the difference between the values obtained on the pre-training test and the post-training test in the RMET group, and in the control and placebo group subjects. The correlation was statistically significant (r = -0.522, P = 0.0183), suggesting that the subjects that breathed more during exercise also had better performance, as reflected as faster times (negative % change) on the time trial test.