To explore the simultaneous contraction pattern of the diaphragm and sternocleidomastoid (SCM) muscles at various inspiratory pressure resistance loads, in people after stroke.
Patients diagnosed with stroke were invited to perform in random order sets of 10 breaths at 30%, 40%, 50%, 60%, 70% and 80% maximum inspiratory pressure (MIP) with 15 minutes between sets. Bilateral muscle activity of the SCM and diaphragm thickness were recorded simultaneously using surface electromyography (sEMG) and ultrasonography, respectively.
Thirty-six people diagnosed with stroke, with a mean duration of 3.6 ± 2.9 months, participated in this study. Diaphragmatic thickness on the hemiplegic side was significantly lower than on the non-affected side at all inspiratory loads. There was however no difference in the calculated diaphragmatic thickening fraction (DTf) for both hemi diaphragms. DTf for both hemi diaphragms increased with increased inspiratory load, peaked at 50% of MIP, and then decreased with further increases in inspiratory load. Muscle recruitment of the SCM on both sides elevated with increasing inspiratory load and reached a maximum value at 80% MIP, but the activity of SCM muscle on the hemiplegic side was significantly higher compared to the non-affected side with all inspiratory loads.
An inspiratory pressure of 50%MIP elicited the highest diaphragmatic contraction bilaterally in people after stroke. Increasing the inspiratory load beyond this intensity did not further enhance diaphragmatic contraction but increased recruitment of the sternocleidomastoid muscle, particularly on the stroke-affected side.
These findings suggest that an inspiratory load of 50% MIP may be the optimal intensity for maximizing diaphragmatic contraction in stroke patients without over-recruiting accessory muscles like the sternocleidomastoid. This has significant implications for the design of inspiratory muscle training programs, indicating that intensities above 50% MIP might not further enhance diaphragmatic strengthening and could lead to an increased reliance on accessory muscles.
stroke
diaphragm
