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Inspiratory muscle training attenuates the human respiratory muscle metaboreflex Witt, Jonathan Derek

Abstract

PURPOSE: High-resistance inspiratory muscle work results in inspiratory muscle fatigue and sympathetically mediated increases in heart rate (HR) and mean arterial pressure (MAP). We hypothesized that 5 wks of inspiratory muscle training (IMT) would attenuate such a response. METHODS: An experimental group (EXP, n = 8) performed IMT 6 days/wk for 5-wks at 50% of maximal inspiratory pressure (MIP), while a mock training group (SHAM, n = 8) performed IMT at 10% MIP. Pre- and post- training, subjects underwent a eucapnic resistive breathing protocol (RBT) at a resistance of approx. 50% MIP (breathing frequency = 15 breaths/min, duty cycle = 0.70) while HR and MAP were continuously monitored. RBT duration was matched within each subject pre and post. MIP was assessed weekly. RESULTS: MIP increased significantly (p < 0.05) in the EXP group (-125.0 ± 28.4 to - 145.5 ± 33.3 cm H₂0, mean ± SD) but not in the SHAM group (-141.2 ± 31.8 to -147.5 ± 32.0 cm H₂0) . Mean RBT duration was significantly shorter in the SHAM group (392 ± 93.7 sec vs. 677 ± 197 sec). Prior to IMT, the RBT resulted in significant, rises in HR (SHAM: 58.7 ± 5.2 to 82.9 ± 11.6 beats/min; EXP : 61.7 ± 9.3 to 82.7 ± 12.1 beats/min) and MAP (SHAM: 88.1 ± 4.6 to 106.2 ± 7.3 mmHg; EXP : 84.5 ± 4.0 to 99.2 ± 8.1 mmHg) in both groups. The SHAM group responded similarly to the RBT post-training (HR: 56.9 ± 6.2 to 76.8 ± 8.5 beats/min; MAP : 89.3 ± 9.0 to 102.5 ± 8.0 mmHg). Following IMT in the EXP group, the RBT failed to increase HR and MAP to the same extent as before training (HR: 58.6 ± 8.7 to 73.8 ± 7.1 beats/min; MAP : 84.5 ± 3.3 to 88.7 ± 6.1 mmHg). MIP measured before and after the RBT did not change in either group pre or post training. CONCLUSIONS: IMT reduces the HR and MAP response to resistive inspiratory muscle work. This may indicate a reduction in sympatho-excitation due to either reduced accumulation of, or reduced responsiveness to, metabolites within the inspiratory muscles.

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