Effects of inspiratory muscle training on thoracoabdominal muscle kinematics during exercise in older adults

Background: Reduced inspiratory muscle strength is characteristic of the healthy ageing process. Methods: 24 healthy adults (mean age: 68.3±2.5 years) were evenly randomised into an inspiratory muscle training (IMT) or sham group. Participants in the IMT group performed 30 breaths, twice daily, for 8 weeks, at an initial intensity corresponding to ~50% maximal inspiratory pressure (PImax) and <15% PImax for the sham group. Pre- and 8-week measurements included PImax, six-minute walk distance (6MWD), and assessment of thoracoabdominal volumes via optoelectronic plethysmography during cycling at 75% of predicted peak work rate. Within group changes were assessed by paired t-tests. Results: PImax significantly increased (by 20.0±11.9cmH2O; p=0.001) in the IMT group but did not change in the control group (by 2.4±9.3 cmH2O). 6MWD increased by 18.8±28.4m (p=0.042) in the IMT group with no change (-0.4±29.0m) in the control group. Post-IMT at a given level of minute ventilation during cycling, there was a significant (p=0.04) increase in the contribution of the pulmonary and abdominal rib cage compartments (reflecting intercostal and diaphragm muscle activity, respectively) to tidal volume (V_T) expansion relative to that of the abdomen compartment (reflecting abdominal muscle activity). In contrast, in the sham group there was greater (p=0.001) contribution of the abdomen compartment to V_T expansion relative to that of the pulmonary and abdominal rib cage compartments. Conclusions: IMT is associated with increased 6MWD and PImax. Improved PImax translates into greater contribution of the rib cage muscles and the diaphragm to V_T expansion during sub-maximal exercise.