Physical Functions and Lifestyle Behaviours in Post-COVID-19 Syndrome Based on Circadian Rhythms

Comparison of Respiratory Muscle Strength, Physical Activity Level, and Dietary Habits in Individuals With Post-COVID-19 Syndrome Having Different Circadian Rhythms

Post-COVID-19 syndrome is associated with persistent symptoms such as fatigue, reduced physical activity, and impaired respiratory function. Circadian rhythm differences (chronotype) may influence lifestyle behaviors including physical activity, nutrition, and sleep patterns.

This observational cross-sectional study aims to compare respiratory muscle strength, physical activity levels, and nutritional habits among individuals with post-COVID-19 syndrome according to their chronotype (morning, intermediate, and evening types).

Additionally, genetic analysis of the CLOCK gene polymorphism will be performed to support objective evaluation of circadian rhythm differences. The findings of this study may help to better understand the role of circadian rhythm in post-COVID-19 syndrome and contribute to the development of individualized rehabilitation and lifestyle interventions.

Study Overview

• Status: Recruiting
• Conditions: Post-COVID-19 Syndrome

Detailed Description

Post-COVID-19 syndrome is characterized by persistent symptoms such as fatigue, reduced exercise tolerance, and impaired respiratory function following acute SARS-CoV-2 infection. Emerging evidence suggests that circadian rhythm disruption may play a role in the pathophysiology of these symptoms by affecting metabolic regulation, hormonal balance, sleep quality, and physical performance.

Circadian rhythm varies between individuals and is commonly classified into chronotypes as morning, intermediate, and evening types. These chronotypes are associated with differences in daily activity patterns, nutritional behaviors, and physiological performance.

The aim of this observational cross-sectional study is to compare respiratory muscle strength, physical activity levels, nutritional habits, sleep quality, fatigue perception, and gastrointestinal symptoms in individuals with post-COVID-19 syndrome according to their chronotype.

Participants aged 18-65 years with a confirmed diagnosis of post-COVID-19 syndrome will be included. Chronotype will be assessed using the Munich Chronotype Questionnaire (MCTQ). Respiratory muscle strength will be evaluated using maximal inspiratory and expiratory pressures (MIP/MEP), and dynamic respiratory parameters will be assessed using a POWERbreathe device. Respiratory muscle endurance will be measured using threshold loading protocols.

Physical activity levels will be assessed using the International Physical Activity Questionnaire (IPAQ), while nutritional intake will be evaluated using 24-hour dietary recall. Sleep quality, fatigue severity, and gastrointestinal symptoms will be assessed using validated questionnaires.

In addition, blood samples will be collected for genetic analysis of the CLOCK gene polymorphism (rs1801260) using PCR-RFLP techniques to provide an objective assessment of circadian rhythm differences.

This study is expected to provide comprehensive insight into the relationship between circadian rhythm and functional, behavioral, and physiological outcomes in post-COVID-19 syndrome, and may contribute to the development of individualized rehabilitation strategies.

• Study Type: Observational
• Enrollment (Estimated): 50

Contacts and Locations

• Study Contact: Name: Ebru Çalık, Professor; Phone Number: +905442850087; Email: ecalik85@gmail.com

Study Locations

• Turkey (Türkiye)
  • Altindağ
    • Ankara, Altindağ, Turkey (Türkiye), 06100
      • Recruiting
      • Hacettepe University Faculty of Physical Therapy and Rehabilitation
      • Contact: EBRU ÇALIK, Professor; Phone Number: +905442850087; Email: ecalik85@gmail.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

The study population consists of post-COVID-19 syndrome patients aged 18-65 years who are referred to the Hacettepe University Cardiopulmonary Rehabilitation Unit. Participants will be classified into morning-type and evening-type chronotypes.

Description

Inclusion Criteria:

• Diagnosed with Post-COVID-19 Syndrome
• Aged between 18-65 years
• Able to read and understand Turkish
• Voluntary participation
• Classified as Post-Covid Functional Status Scale (PCFS) grade 2-3
• Clinically stable condition
• No uncontrolled comorbidities (e.g., hypertension, diabetes under control)
• No orthopedic or neurological conditions affecting exercise testing

Exclusion Criteria:

• Recent myocardial infarction or pulmonary embolism
• Severe uncontrolled chronic diseases
• Neurological or orthopedic conditions limiting mobility
• Psychiatric or neurological disorders affecting cooperation or test compliance
• Inability to complete assessments

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort
Morning Types (Larks); People who wake up early, feel most energetic in the morning, and reach their peak performance early in the day.
Evening Types (Owls); People who stay up late, struggle with early mornings, and reach their peak functional capacity in the late afternoon or evening.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Respiratory Muscle Strength	Maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP) values will be recorded with mouth pressure device.	Time Frame: Day 1
Dynamic respiratory muscle strength	Respiratory muscle strength index (S index) will be assessed using a portable POWERbreathe K5 device.	Time Frame: Day 1
Respiratory muscle endurance	Respiratory muscle endurance test at constant threshold load will be used.	Time Frame: Day 1

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Physical Activity Level	Physical activity levels will be assessed using the International Physical Activity Questionnaire Short Form (IPAQ-SF), expressed as MET-min/week. The total weekly IPAQ score (MET-min/week) were then used to classify participants into three categories: Low PA (individuals who did not meet criteria for moderate or high categories); Moderate PA (≥3 days of vigorous-intensity activity of at least 20 min per day; ≥5 days of moderate-intensity activity and/or walking of at least 30 min per day; or 3-5 or more days of any combination of walking, moderate-intensity or vigorous intensity activities achieving a minimum total PA of at least 600 MET-min/week); high PA (vigorous activity on at least 3 days with a minimum total PA of at least 1500 MET-min/week or 7 days of any combination of walking and moderate or vigorous activities with a minimum total PA of 3000 MET-min/week).	Time Frame: Day 1
Dietary Intake	Dietary intake will be assessed using 24-hour dietary recall records analyzed for macro and micronutrient intake.	Time Frame: Day 1
Chronotype Classification	Chronotype will be determined using the Munich Chronotype Questionnaire (MCTQ), categorizing participants into morning-type and evening-type groups.Total MCTQ scores can range from 16 to 86, with the lowest values representing extreme-late chronotypes.	Time Frame: Day 1
Fatigue Severity	Fatigue will be assessed using the Fatigue Severity Scale (FSS). Total FSS score ranges between 0-7. Total FSS score 4 and more indicates severe fatigue.	Time Frame: Day 1
Gastrointestinal Symptoms	Gastrointestinal symptoms will be evaluated using the Gastrointestinal Symptom Rating Scale (GSRS).The total GSRS score ranges from 15 to 105, with higher scores indicating more severe gastrointestinal symptoms.	Time Frame: Day 1
Sleep Quality	Sleep quality will be evaluated using the Pittsburgh Sleep Quality Index (PSQI). Total PSQI score ranges from 0 to 21, with higher scores indicating poorer sleep quality. A total score greater than 5 is widely used as the cutoff, suggesting poor sleep quality.	Time Frame: Day 1
Classificationof human faeces forms	Classification of human faeces forms will be evaluated using the Bristol Stool Scale.The seven types of stool are recorded by this scale. Type 1: Separate hard lumps, like nuts (difficult to pass) Type 2: Sausage-shaped, but lumpy Type 3: Like a sausage but with cracks on its surface Type 4: Like a sausage or snake, smooth and soft (average stool) Type 5: Soft blobs with clear cut edges Type 6: Fluffy pieces with ragged edges, a mushy stool (diarrhea) Type 7: Watery, no solid pieces, entirely liquid (diarrhea)	Time Frame: Day 1

Collaborators and Investigators

• Sponsor: Hacettepe University

Publications and helpful links

General Publications

• 2. Suwazono Y, Dochi M, Sakata K, Okubo Y, Oishi M, Tanaka K, et al. A longitudinal study on the effect of shift work on weight gain in male Japanese workers. Obesity (Silver Spring). 2008;16(8):1887-93.
• 1. Voigt RM, Forsyth CB, Green SJ, Engen PA, Keshavarzian A. Circadian Rhythm and the Gut Microbiome. Int Rev Neurobiol. 2016;131:193-205.

Study record dates

Study Major Dates

• Study Start (Actual): May 22, 2025
• Primary Completion (Estimated): August 22, 2026
• Study Completion (Estimated): May 22, 2027

Study Registration Dates

• First Submitted: April 14, 2026
• First Submitted That Met QC Criteria: April 21, 2026
• First Posted (Actual): April 22, 2026

Study Record Updates

• Last Update Posted (Actual): April 22, 2026
• Last Update Submitted That Met QC Criteria: April 21, 2026
• Last Verified: April 1, 2026

More Information

Terms related to this study

• Keywords: Physical Activity; Nutrition; Circadian Rhythm; Long COVID; Genetic Polymorphism; Post-COVID; Chronotype; Respiratory Muscle Strength; CLOCK Gene
• Additional Relevant MeSH Terms: Post-Infectious Disorders; COVID-19; Pathologic Processes; Chronic Disease; Disease Attributes; Respiratory Tract Infections; Infections; RNA Virus Infections; Virus Diseases; Respiratory Tract Diseases; Lung Diseases; Pneumonia, Viral; Pneumonia; Coronavirus Infections; Coronaviridae Infections; Nidovirales Infections; Pathological Conditions, Signs and Symptoms; Behavior; Post-Acute COVID-19 Syndrome; Motor Activity
• Other Study ID Numbers: FTREK25/33

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No