Inspiratory and Trunk Muscle Activity During Inspiratory Muscle Training on Stable and Unstable Surfaces in People After Stroke
Conditions: Stroke, Inspiratory Muscle Training, Diaphragm, Sternocleidomastoid Muscles, Trunk Muscle Activity
Sponsor: Hong Kong Metropolitan University

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Study proposal 
 
 
Inspiratory and trunk muscle activity during inspiratory 
muscle training on stable and unstable surfaces in people 
after stroke  
 
 
Objectives 
This study aims to investigate the differences in muscle recruitment of the diaphragm (assessed 
using ultrasound), the sternocleidomastoid (SCM) and trunk muscles (both measured via 
surface electromyography (sEMG)), during loaded breathing training performed on both stable 
and unstable surfaces. The goal is to understand the interaction between the inspiratory and 
trunk muscles during inspiratory muscle training (IMT) across these two surface conditions.  
 
Materials and methods 
This cross-sectional observational study has been approved by the Institutional Review Board 
of Hong Kong Metropolitan University (Ethics approval number: HE-OT2023/13) and 
Shenzhen Second People’s Hospital (Ethics approval number: 2023-274-01PJ).  
 
Participants 
Sample size calculation 
The sample size was calculated using G*Power 3.1.9.7. Repeated-measures analysis of 
variance (ANOVA) will be the primary statistical method for comparing changes in 
diaphragmatic thickness between different loaded inspiratory training protocols. Based on an 
estimated effect size of 0.25, an alpha level of 0.05, and a power of 0.80, the required sample 
size is 24.  
 
Inclusion criteria  
(1) Age ≥ 40 years and < 80 years; (2) breathing spontaneously; (3) clinically diagnosed with 
ischemic and/or hemorrhagic stroke; (4) duration of stroke from onset falls within 1 month to 
12 months after diagnosis; (5) no thoracic or abdominal surgery within the last 6 months; (6) 

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no cognitive impairment (Montreal Cognitive Assessment (MoCA) score ≥ 26); (7) able to 
understand and follow verbal instructions; (8) no facial palsy, or mild facial palsy without 
limitation of labial occlusion; (9) able to complete all loaded breath tests on stable and unstable 
included in this study. 
 
Exclusion criteria 
(1) Acute myocardial infarction or acute heart failure; (2) acute pain in any part of the body; 
(3) the history of chronic respiratory illness or positive clinical signs of impaired respiratory 
function (such as shortness of breath, hypoxemia, chronic cough, and sputum retention); (4) 
patients with a nasal feeding tube, tracheal tube, or any condition that prevents the measurement 
or implementation of the study procedures. 
 
Procedures  
Participants will be instructed to perform 10 loaded breaths via a threshold inspiratory load 
device (POWERbreathe KH2, UK) on both a stable surface (sitting on a chair, Protocol 1) and 
an unstable surface (sitting on a soft pad, Protocol 2) in random order. The inspiratory 
load/resistance will be set at 50% of the MIP, an intensity previously shown to elicit maximal 
diaphragm contraction. During all breathing protocols, participants' feet will be supported on 
the ground, and a nose clip will be employed to prevent air leakage. Bilateral muscle activity 
of the diaphragm (measured by ultrasonography), as well as the SCM and trunk muscles—
including the rectus abdominis (RA), external oblique (EO), internal oblique/transversus 
abdominis (IO/TrA), and erector spinae (ES)—will be simultaneously recorded using sEMG 
during all breathing protocol tests. Self-perceived exertion levels after each loaded breath 
protocol will also be recorded using the modified Borg Rating Scale of Perceived Exertion.  
 
Outcome Measurements 
Diaphragm contraction 
 
The magnitude of diaphragmatic contraction will be reflected by the diaphragm thickening 
fraction (DTf). The DTf will be calculated by the difference between the mean diaphragmatic 
thickness at the end of each loaded breathing protocol and the mean diaphragmatic thickness 
at the end of tidal expiration, then divided by the diaphragmatic thickness at the end of tidal 
expiration. 
 

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Two identical ultrasound machines (Mindray M9, Shenzhen, China) will be used for 
measurement of diaphragmatic thickness of both hemi-diaphragms.  Tidal inspiration and 
expiration diaphragmatic thickness will be measured before the loaded inspiratory protocol, 
and three images will be captured for each phase and averaged for subsequent data analysis. 
The diaphragm thickness at the end of each loaded breath (from a total of 10 breaths) will be 
recorded, and the average will be calculated to determine the DTf for each loaded inspiratory 
protocol. 
 
Recruitment of SCM muscles and trunk muscles 
A Noraxon Ultium wireless surface EMG system (Noraxon USA, Inc., Scottsdale, AZ, USA) 
will be used to measure bilateral muscle activity in SCM and trunk muscles simultaneously 
during all breathing protocol tests. 
 
Self-perceived exertion level 
Self-perceived exertion level at the end of each 10-breath set at each protocol, will be also 
recorded using the Borg’s scale of Rate of Perceived Exertion. 
 
 
Statistical analysis  
All data were analyzed using the IBM SPSS Statistics for Windows, Version 25.0 (Armonk, 
NY: IBM Corp).  
 
Changes in DTf, SCM muscle activity, and trunk muscle activity will be analyzed using 
repeated-measures ANOVA, comparing the hemiplegic and non-affected sides within each 
protocol, and between the different inspiratory protocols.  
 
Perceived exertion levels will be compared between the two protocols using the Wilcoxon 
signed-rank test.