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NCT Number: NCT07341711

Long-term Adaptations of Skeletal Muscle After Hybrid Training

Obesity is a major challenge for public health and renders it imperative to reduce its prevalence. High intensity interval training (HIIT) is a form of exercise training that can efficiently induce weight loss in adults with overweight or obesity, even in the absence of dietary intake manipulation. Hybrid type training represents a form of HIIT, that incorporates both cardiorespiratory and musculoskeletal stimuli, by combining multiple types of exercise into a circuit-type, interval style workout. Recent evidence suggests that long-term participation in hybrid HIIT results in significant health-related benefits. However, the molecular mechanisms driving the chronic effects of hybrid HIIT on cardiometabolic and musculoskeletal health remains to be elucidated.

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Key information

Conditions

Obesity & Overweight Body Weight Nutrition Disorders Nutritional and Metabolic Diseases Obesity Overnutrition Overweight Pathological Conditions, Signs and Symptoms Signs and Symptoms

Age range

30 year–50 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

About this study

A total number of 30 adults (both males and females) aged 30-50, meeting the inclusion criteria, will be enrolled in this study. Participants will be randomly assigned to either (i) a Control group or (ii) an Intervention group. The Intervention group will participate in three hybrid-type HIIT sessions per week over a 6-month period while receiving a balanced diet. The Control group will receive a balanced diet over the 6-month period but will not participate in exercise training. At baseline and 6 months, both groups will undergo assessment of their anthropometric profile, body composition, resting metabolic rate, muscle strength and cardiorespiratory capacity and provide resting blood and skeletal muscle samples.

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • BMI: >25 kg/m2 and <40 kg/m2
  • Untrained individuals (abstain >1 year from exercise training)
  • No dietary intervention over the last 6 months preceding the study
  • Low cardiorespiratory fitness level (VO2max: <45 ml/kg/min)
  • No use of any medication, dietary supplements
  • Low risk for cardiovascular disease
  • A weight loss <10% over the last 6 months preceding the study
  • Free of non-communicable diseases (excluding metabolic syndrome)

Exclusion criteria

  • Low participation rate (<80% completion of the exercise training sessions)
  • Unbalanced diet
  • Participation in additional exercise training regimes
  • Cosumption of anti-inflammatory of pain relief medication

Treatment and study plan

Exercise training

Other

Participants will perform a six-month hybrid training program while receiving a balanced diet. The periodization of hybrid training intervention will consist of three 2-month phases of gradually increased exercise intensity and volume. In every training will participate 5-8 individuals. The training will contain 6-12 different exercises (stations), depending on the phase of the intervention, which will be executed in a circuit for a total of 2-3 rounds, with 2-3 minutes of rest period between sets (depending on the phase). The exercise execution will last 20-45 seconds, and the rest between them will last 30-60 seconds (depending on the phase), while the exercise intensity will range from 75 to 85% of maximal heart rate. The stations of hybrid training will contain multi-joint exercises or neuromuscular activation exercises using either body weight resistance or portable equipment.

Control Group

Other

Participants will receive a balanced diet but will not participate in any type of exercise training over a six month period.

Primary outcomes

  1. Change in mitochondrial size

    Time frame: At baseline and at 6 months

    Mitochondrial size will be measured using transmission electron microscope

  2. Change in mitochondrial density

    Time frame: At baseline and at 6 months

    Mitochondrial density will be measured using transmission electron microscope

  3. Change in mitochondrial count

    Time frame: At baseline and at 6 months

    Mitochondrial count will be determined using transmission electron microscope

  4. Change in mitochondrial distribution

    Time frame: At baseline and at 6 months

    Mitochondrial distribution will be determined using transmission electron microscope

  5. Change in maximum oxygen consumption (VO2max)

    Time frame: At baseline and at 6 months

    Maximum oxygen consumption (VO2max) will be assessed during a cardiopulmonary exercise testing by using a portable indirect calorimetry system

  6. Change in muscle fiber cross-sectional area

    Time frame: At baseline and at 6 months

    Muscle fiber cross-sectional area (μm2) will be measured using immunohistochemical staining for myosin heavy chain

  7. Change in PAX7+ satellite cells count

    Time frame: At baseline and at 6 months

    PAX7+ satellite cells will be determined using immunohistochemistry techniques.

  8. Change in total protein content

    Time frame: At baseline and at 6 months

    Total protein content (total RNA) will be determined in skeletal muscle tissue using real time quantitative-Polymerase Chain Reaction (q-PCR) technique

  9. Change in myonuclei content

    Time frame: At baseline and at 6 months

    Myonuclei content will be determined in skeletal muscle tissue using immunohistochemistry techniques

  10. Change in peroxisome proliferator-activated receptor-gamma coactivator -1a (PGC-1a) expression

    Time frame: At baseline and at 6 months

    PGC-1a expression in skeletal muscle tissue will be assessed using immunoblotting techniques.

  11. Change in Krebs cycle (TCA cycle) enzymes activity

    Time frame: At baseline and at 6 months

    Krebs cycle enzymes activity will be determined using the Seahorse XF Analyzer

  12. Change in protein expression of respiratory chain complexes

    Time frame: At baseline and at 6 months

    Protein expression of respiratory chain complexes will be determined using immunoblotting techniques

  13. Change in cytochrome C oxidase amount and expression

    Time frame: At baseline and at 6 months

    Cytochrome C oxidase amount and expression will be assessed using immunohistochemistry and immunoblotting techniques

  14. Change in ATP synthase amount and expression

    Time frame: At baseline and at 6 months

    ATP synthase amount and expression will be assessed using immunohistochemistry and immunoblotting techniques

  15. Change in citrate synthase amount and expression

    Time frame: At baseline and at 6 months

    Citrate synthase amount and expression will be assessed using immunohistochemistry and immunoblotting techniques

  16. Change in succinate dehydrogenase amount and expression

    Time frame: At baseline and at 6 months

    Succinate dehydrogenase amount and expression will be assessed using immunohistochemistry and immunoblotting techniques

  17. Change in NADH dehydrogenase amount and expression

    Time frame: At baseline and at 6 months

    NADH dehydrogenase amount and expression will be assessed using immunohistochemistry and immunoblotting techniques

  18. Change in mitochondrial oxygen consumption rate

    Time frame: At baseline and at 6 months

    Mitochondrial oxygen consumption rate will be determined using the Seahorse XF Analyzer

  19. Change in spare respiratory capacity

    Time frame: At baseline and at 6 months

    Spare respiratory capacity will be determined using the Seahorse XF Analyzer

  20. Change in mitochondrial maximal respiration

    Time frame: At baseline and at 6 months

    Maximal mitochondrial respiration will be determined using the Seahorse XF Analyzer

  21. Change in mitochondrial basal respiration

    Time frame: At baseline and at 6 months

    Mitochondrial basal respiration will be determined using the Seahorse XF Analyzer

  22. Change in non-mitochondrial respiration

    Time frame: At baseline and at 6 months

    Non-mitochondrial respiration will be determined using the Seahorse XF Analyzer

  23. Change in body fat percentage

    Time frame: At baseline and at 6 months

    Body fat percentage will be assessed using dual energy x-ray absorptiometry (DEXA)

  24. Change in diastolic arterial pressure

    Time frame: At baseline and at 6 months

    Diastolic blood pressure will be measured using a sphygmomanometer

Secondary outcomes

  1. Change in density and distribution of capillaries

    Time frame: At baseline and at 6 months

    Capillarization will be determined using immunohistochemistry techniques

  2. Change in skeletal muscle fiber typing

    Time frame: At baseline and at 6 months

    Fiber typing will be determined using immunohistochemistry techniques

  3. Change in GLUT-4 protein expression

    Time frame: At baseline and at 6 months

    GLUT-4 protein expression will be assessed using immunoblotting techniques

  4. Change reduced glutathione content in skeletal muscle cells

    Time frame: At baseline and at 6 months

    Reduced glutathione content will be determined spectrophotometrically

  5. Change in glutathione peroxidase activity in skeletal muscle cells

    Time frame: At baseline and at 6 months

    Glutathione peroxidase activity will be determined spectrophotometrically

  6. Change in glutathione reductase activity in skeletal muscle cells

    Time frame: At baseline and at 6 months

    Glutathione reductase activity will be determined spectrophotometrically

  7. Change in superoxide dismutase activity in skeletal muscle cells

    Time frame: At baseline and at 6 months

    Superoxide dismutase activity will be determined spectrophotometrically

  8. Change in fasting glucose levels

    Time frame: At baseline and at 6 months

    Fasting glucose levels will be measured on an automated clinical chemistry analyzer

  9. Change in fasting insulin levels

    Time frame: At baseline and at 6 months

    Fasting insulin levels will be measured on an automated clinical chemistry analyzer

  10. Change in glycosylated hemoglobin levels

    Time frame: At baseline and at 6 months

    Glycosylated hemoglobin levels will be measured on an automated clinical chemistry analyzer

  11. Change in high-density lipoprotein (HDL) levels

    Time frame: At baseline and at 6 months

    HDL will be measured on an automated clinical chemistry analyzer

  12. Change in low-density lipoprotein (LDL) levels

    Time frame: At baseline and at 6 months

    LDL will be measured on an automated clinical chemistry analyzer

  13. Change in total cholesterol levels

    Time frame: At baseline and at 6 months

    Total cholesterol will be measured on an automated clinical chemistry analyzer

  14. Change in triglyceride levels

    Time frame: At baseline and at 6 months

    Triglycerides will be measured on an automated clinical chemistry analyzer

  15. Change in general blood count

    Time frame: At baseline and at 6 months

    General blood count will be measured on a hematology analyzer

  16. Change in erythrocyte reduced glutathione (GSH) levels

    Time frame: At baseline and at 6 months

    Erythrocyte GSH levels will be determined spectrophotometrically

  17. Change in erythrocyte oxidized glutathione (GSSG) levels

    Time frame: At baseline and at 6 months

    Erythrocyte GSSG levels will be determined spectrophotometrically

  18. Change in myostatin expression

    Time frame: At baseline and at 6 months

    Myostatin expression will be assessed using immunoblotting techniques

  19. Change cortisol concentration

    Time frame: At baseline and at 6 months

    Blood cortisol concentration will be assessed using immunoassays (ELISA)

  20. Change in testosterone concentration

    Time frame: At baseline and at 6 months

    Blood testosterone concentration will be assessed using immunoassays (ELISA)

  21. Change in growth hormone concentration

    Time frame: At baseline and at 6 months

    Blood growth hormone concentration will be assessed using immunoassays (ELISA)

  22. Change in insulin-like growth factor-1 (IGF-1) concentration

    Time frame: At baseline and at 6 months

    Blood IGF-1 concentration will be assessed using immunoassays (ELISA)

  23. Change in body mass

    Time frame: At baseline and at 6 months

    Body mass will be measured on a beam scale

  24. Change in bone density

    Time frame: At baseline and at 6 months

    Bone density will be assessed using dual energy x-ray absorptiometry (DEXA)

  25. Change in fat-free mass

    Time frame: At baseline and at 6 months

    Fat-free mass will be assessed using dual energy x-ray absorptiometry (DEXA)

  26. Change in waist circumference

    Time frame: At baseline and at 6 months

    Waist circumference will be measured using a Gullick II tape

  27. Change in hip circumference

    Time frame: At baseline and at 6 months

    Hip circumference will be measured using a Gullick II tape

  28. Change in resting heart rate

    Time frame: At baseline and at 6 months

    Heart rate will be measured using a heart rate monitor

  29. Change in resting metabolic rate (RMR)

    Time frame: At baseline and at 6 months

    RMR will be measured using indirect calorimetry

  30. Change in systolic arterial pressure

    Time frame: At baseline and at 6 months

    Systolic blood pressure will be measured using a sphygmomanometer

Study contacts

Contact information is provided by the study sponsor or research team.

Ioannis G Fatouros, Professor

CONTACT

[email protected]

24310 47047 ext. 0030

Sponsors and collaborators

Lead sponsor

University of Thessaly

Other

Registry information

Official study title

Long-term Adaptations of Skeletal Muscle in Overweight and Obese Individuals After Hybrid Training

Important dates

Study start
2026
Primary completion
2026
Study completion
2026
First posted
Jan 14, 2026
Registry last updated
Jun 12, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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