An interventional study of Progressive Muscle Training and Control Group in Hypothyroidism Primary, sponsored by Cyprus International University. Completed at 1 site in Turkey (Türkiye). Open to participants aged 18 Years and older, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-10-08.
Sponsored by Cyprus International University · Not applicable, Interventional, and Treatment
The goal of this randomized controlled study is to find out whether an eight-week respiratory muscle training program can improve breathing, respiratory muscle strength and endurance, physical capacity, body composition, fatigue, exercise-related beliefs and barriers, quality of life, and emotional well-being in adults aged 18 years or older with hypothyroidism who have been taking levothyroxine for at least three months. The study asks whether participants who complete progressive inspiratory muscle training show greater improvement in these areas than participants who train at the device's lowest resistance. Women and men will be randomly assigned to one of the two groups. Both groups will perform breathing exercises at home five days a week for eight weeks, with the training group gradually increasing the exercise resistance. Participants will be assessed before and after the program using breathing and lung-function tests, physical-capacity and muscle-strength tests, body-composition measurements, and questionnaires.
Hypothyroidism is characterized by systemic metabolic slowing that frequently leads to respiratory muscle weakness, impaired ventilatory responses to hypoxia and hypercapnia, diaphragmatic dysfunction, and skeletal muscle myopathy. These physiological impairments often manifest clinically as exertional dyspnea, heightened fatigue, reduced functional exercise tolerance, altered body composition, and psychological vulnerabilities such as anxiety and depressive symptoms. Despite the prevalence of cardiorespiratory and neuromuscular complications in patients with thyroid dysfunction, targeted rehabilitative interventions addressing respiratory muscle performance remain largely unexplored in this clinical population. This randomized controlled trial evaluates the physiological, physical, and psychological impacts of structured inspiratory muscle training (IMT) using a targeted threshold loading device (IMT/PEP, GH Innotek) in medically managed hypothyroid patients. Following baseline screening and stratified randomization, participants are allocated into either an active progressive IMT intervention group or a low-intensity sham-control group for an eight-week intervention period. The active intervention involves progressive inspiratory threshold loading conducted five days per week across two daily sessions of 30 breaths each, blending supervised clinical sessions with monitored home-based training. Loading intensity starts at 30% of maximal inspiratory pressure (MIP) during the initial week, advancing to 50% across weeks 2 to 5, and reaching 70% of MIP throughout weeks 6 to 8. The control arm performs breathing exercises with the same device set to its minimum fixed resistance without progression for an equivalent duration. Comprehensive multi-system evaluations are conducted at baseline and upon completion of the eight-week program at Eastern Mediterranean University, Faculty of Health Sciences, Cardiopulmonary Exercise Unit. Assessments encompass pulmonary mechanics via standard spirometric and lung volume determinations, respiratory muscle performance through maximal inspiratory/expiratory pressures and maximal voluntary ventilation, peripheral muscle strength via digital back/leg and handgrip dynamometry, functional exercise performance through the standardized six-minute walk test with continuous hemodynamic and desaturation monitoring, bioelectrical impedance-derived body composition metrics, and validated patient-reported outcome measures evaluating multidimensional fatigue, exercise barriers, health perceptions, and emotional status.
252 studies on the registry are indexed under Hypothyroidism; 57 are open to participants now.
This study's enrollment of 30 is below the median of 75 across 130 interventional studies indexed under Hypothyroidism.
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The training protocol was administered using the Philips Respironics®️ Threshold IMT device for both groups. The regimen was scheduled for seven days a week, consisting of one session per day (approximately 20 minutes). To enhance treatment adherence, three of the weekly sessions were supervised, while the remaining four were conducted as a home-based program monitored via telephone follow-ups. Each exercise session was structured as three sets of 30 repetitions, with one-minute rest intervals between the sets. In the study group, training intensity was set at 40% of the individual's maximal inspiratory pressure (PImax). To ensure progressive loading, this PImax value was re-evaluated and adjusted every two weeks throughout the entire training process.
Other: Progressive Muscle Training
To induce a placebo effect, the control group received sham training using the lowest possible resistance setting of the device (9 cmH₂O) for the full eight weeks, with no increments in training intensity.
Other: Control Group
At this point, the significance of specific rehabilitation approaches added to medical therapy, particularly structured inspiratory muscle training (IMT), becomes evident. Strong evidence in the literature demonstrates that IMT increases the proportion of Type 1 muscle fibers and induces structural hypertrophy in the diaphragm by improving oxidative capacity in other systemic diseases that increase respiratory workload, such as Chronic Obstructive Pulmonary Disease (COPD) and chronic heart failure. Considering that the diaphragmatic myopathy observed in hypothyroidism shares similar pathophysiological and cellular weaknesses, specific Respiratory Muscle Training (RMT) has a high potential to not only provide symptomatic relief but also improve mechanical function by triggering repair at the cellular level in this patient group.
To induce a placebo effect, the control group received sham training using the lowest possible resistance setting of the device (9 cmH₂O) for the full eight weeks, with no increments in training intensity.
Respiratory Muscle Strength
Respiratory muscle strength was evaluated using an electronic mouth pressure meter (MicroMPM, Micro Medical Ltd., UK). Measurements were performed in accordance with the American Thoracic Society (ATS) and European Respiratory Society (ERS) criteria. Maximal inspiratory pressure (PImax) was assessed following a maximal expiration to residual volume, whereupon the airway was occluded by a valve, and the participant performed a rapid, maximal inspiratory effort (Müller maneuver) sustained for 1-3 seconds. Conversely, maximal expiratory pressure (PEmax) was measured following a maximal inspiration to total lung capacity, where the participant performed a rapid, maximal expiratory effort (Valsalva maneuver) against an occluded airway for 1-3 seconds. Three measurements were obtained for each maneuver, and the highest value was recorded in cmH₂O.
Time frame: From enrollment to the end of treatment at 8 weeks
Respiratory Muscle Endurance
Maximum voluntary ventilation (MVV) was measured using the direct method to assess respiratory muscle endurance. Participants were instructed to breathe as deeply and rapidly as possible for 15 seconds, and the recorded volume was subsequently multiplied by four to extrapolate the value to one minute. The normative values for MVV are typically 140-180 L/min for healthy individuals, and 80-120 L/min for females. Additionally, the predicted values calculated based on the variables of age, gender, and height were documented.
Time frame: From enrollment to the end of treatment at 8 weeks
Pulmonary Function Parameters
Pulmonary functions were evaluated via spirometry. Spirometric measurements were conducted in a seated position using a nose clip, strictly adhering to ERS guidelines. Forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and inspiratory capacity (IC) were measured using a spirometer (SensorMedics™️ Vmax spectra 229, Bilthoven, The Netherlands). Participants performed three acceptable maneuvers, ensuring a variation of less than 5% between the efforts, and the highest values were recorded as the final result. The ERS reference equations were used to determine the predicted values.
Time frame: From enrollment to the end of treatment at 8 weeks
Functional Capacity
Functional capacity will be assessed using the 6-Minute Walk Test (6MWT). Participants will be instructed to walk as far as possible for six minutes along a flat corridor at least 30 meters long. The total distance walked will be recorded in meters.
Time frame: From enrollment to the end of treatment at 8 weeks
Dyspnea and Fatigue Assessment
Dyspnea and fatigue will be assessed immediately before and after the 6MWT using the modified Borg scale. Changes in dyspnea and fatigue scores from pre-test to post-test will be recorded separately.
Time frame: From enrollment to the end of treatment at 8 weeks
Depression
Participants' depressive symptoms will be assessed using the Beck Depression Inventory, a self-report questionnaire designed to measure the severity of depressive symptoms in adults. Higher scores indicate greater symptom severity.
Time frame: From enrollment to the end of treatment at 8 weeks
Anxiety
Participants' anxiety symptoms will be assessed using the Beck Anxiety Inventory, a 21-item self-report questionnaire. Each item is scored from 0 to 3, with higher total scores indicating greater anxiety symptom severity.
Time frame: From enrollment to the end of treatment at 8 weeks
Exercise Beliefs
Participants' exercise beliefs will be assessed using a 33-item questionnaire with three subscales: perceived advantages, affected individuals, and perceived disadvantages. Items are rated on a 6-point scale from 1 ("strongly disagree") to 6 ("strongly agree"). Higher scores indicate more positive exercise beliefs.
Time frame: From enrollment to the end of treatment at 8 weeks
Fatigue
Fatigue will be assessed using the Fatigue Impact Scale, a 40-item questionnaire covering the physical, cognitive, and social effects of fatigue. Each item is scored from 1 to 4, with total scores ranging from 40 to 160; higher scores indicate a greater impact of fatigue.
Time frame: From enrollment to the end of treatment at 8 weeks
Sleep Quality
Sleep quality will be assessed using the Pittsburgh Sleep Quality Index (PSQI), which evaluates seven components: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleep medication, and daytime dysfunction. The total score ranges from 0 to 21, with higher scores indicating poorer sleep quality; scores above 5 indicate poor sleep quality.
Time frame: From enrollment to the end of treatment at 8 weeks
Quality of Life
Quality of life will be assessed using the Short Form-36 (SF-36), a 36-item questionnaire covering eight domains: physical functioning, role limitations due to physical health, role limitations due to emotional problems, bodily pain, vitality, social functioning, mental health, and general health. Each domain is scored from 0 to 100, with higher scores indicating better quality of life.
Time frame: From enrollment to the end of treatment at 8 weeks
Plan to share: Yes — Individual participant data that underlie the results reported in this study-including de-identified sociodemographic and clinical characteristics, body composition metrics, and pre- and post-intervention scores for respiratory parameters (spirometry and lung volumes), respiratory and peripheral muscle strength, respiratory muscle endurance, functional exercise capacity (6MWT), fatigue (FIS), psychological status (BDI, BAI), and exercise beliefs-will be shared.
Supporting information: Study protocol, Statistical analysis plan
Time frame: Data and supporting documents will be made available beginning immediately following publication and will remain accessible for a period of three years.
Access criteria: IPD and supporting documents will be shared with researchers who provide a methodologically sound proposal to achieve the aims of the approved proposal. Proposals should be directed to the corresponding author (aysevolkan11@gmail.com). To gain access, data requestors will be required to sign a data access agreement.
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Cyprus International University