Energy cost of breathing at depth: effect of respiratory muscle training.

ABSTRACT

INTRODUCTION: Respiratory muscle training against resistance (RRMT) increases respiratory muscle strength and endurance as well as underwater swimming endurance. We hypothesized that the latter is a result of RRMT reducing the high energy cost of breathing at depth. METHODS: Eight subjects breathed air in a hyperbaric chamber at 55 fsw, both before and after RRMT. They rested for 10 minutes, cycled on an ergometer for 10 minutes (100 W), rested for 10 minutes, and then, while still at rest, they voluntarily mimicked the breathing pattern recorded during the exercise (isocapnic simulated exercise ventilation, ISEV). RESULTS: Post-RRMT values of V(E) at rest, exercise and ISEV were not different from those recorded pre-RRMT. Pre-RRMT minute-ventilation (V(E)) during ISEV was not different from the exercise ventilation (49.98 +/- 10.41 vs. 47.74 +/- 8.44 L/minute). The end-tidal PCO2 during ISEV and exercise were not different (44.26 +/- 2.54 vs. 44.49 +/- 4.49 mmHg) or affected by RRMT. Oxygen uptake (VO2) was 0.32 +/- 0.08 L/ minute at rest, 1.78 +/- 0.15 during exercise pre-RRMT, and not different post-RRMT. During ISEV, VO2 decreased significantly from pre-RRMT to post-RRMT (0.46 +/- 0.06 vs. 0.36 +/- 0.11 L/minute). Post-RRMT delta VO2/delta V(E) was significantly lower during ISEV than pre-RRMT (0.0094 +/- 0.0021 L/L vs. 0.0074 +/- 0.0023 L/L). CONCLUSION: RRMT significantly reduced the energy cost of ventilation, measured as delta VO2/delta V(E) during ISEV, at a depth of 55 fsw. Whether this change was due to reduced work of breathing and/or increased efficiency of the respiratory muscles remains to be determined.