Long-term Adaptations of Skeletal Muscle After Hybrid Training.

Long-term Adaptations of Skeletal Muscle in Overweight and Obese Individuals 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.

Study Overview

• Status: Not yet recruiting
• Conditions: Obesity & Overweight
• Intervention / Treatment: Other: Exercise training; Other: Control group

Detailed Description

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.

• Study Type: Interventional
• Enrollment (Estimated): 30
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Ioannis G Fatouros, Professor; Phone Number: 0030 24310 47047; Email: ifatouros@pe.uth.gr

Study Locations

• Greece
  • Thessaly
    • Trikala, Thessaly, Greece, 42100
      • Department of Physical Education and Sport Science Trikala, University of Thessaly
      • Contact: Ioannis G Fatouros, Professor; Phone Number: +30 2431047047; Email: ifatouros@uth.gr
      • Contact: Athanasios Z Jamurtas, Professor; Phone Number: +30 2431047054; Email: ajamurt@uth.gr

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

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
• Fee 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

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Intervention group; Participants in this arm will participate in three hybrid-type HIIT sessions per week over a 6-month period while receiving a balanced diet	Other: Exercise training; 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.
Active Comparator: Control group; Participants in this arm will receive a balanced diet over the 6-month period but will not participate in exercise training	Other: Control group; Participants will receive a balanced diet but will not participate in any type of exercise training over a six month period.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in mitochondrial size	Mitochondrial size will be measured using transmission electron microscope	At baseline and at 6 months
Change in mitochondrial density	Mitochondrial density will be measured using transmission electron microscope	At baseline and at 6 months
Change in mitochondrial count	Mitochondrial count will be determined using transmission electron microscope	At baseline and at 6 months
Change in mitochondrial distribution	Mitochondrial distribution will be determined using transmission electron microscope	At baseline and at 6 months
Change in maximum oxygen consumption (VO2max)	Maximum oxygen consumption (VO2max) will be assessed during a cardiopulmonary exercise testing by using a portable indirect calorimetry system	At baseline and at 6 months
Change in muscle fiber cross-sectional area	Muscle fiber cross-sectional area (μm2) will be measured using immunohistochemical staining for myosin heavy chain	At baseline and at 6 months
Change in PAX7+ satellite cells count	PAX7+ satellite cells will be determined using immunohistochemistry techniques.	At baseline and at 6 months
Change in total protein content	Total protein content (total RNA) will be determined in skeletal muscle tissue using real time quantitative-Polymerase Chain Reaction (q-PCR) technique	At baseline and at 6 months
Change in myonuclei content	Myonuclei content will be determined in skeletal muscle tissue using immunohistochemistry techniques	At baseline and at 6 months
Change in peroxisome proliferator-activated receptor-gamma coactivator -1a (PGC-1a) expression	PGC-1a expression in skeletal muscle tissue will be assessed using immunoblotting techniques.	At baseline and at 6 months
Change in Krebs cycle (TCA cycle) enzymes activity	Krebs cycle enzymes activity will be determined using the Seahorse XF Analyzer	At baseline and at 6 months
Change in protein expression of respiratory chain complexes	Protein expression of respiratory chain complexes will be determined using immunoblotting techniques	At baseline and at 6 months
Change in cytochrome C oxidase amount and expression	Cytochrome C oxidase amount and expression will be assessed using immunohistochemistry and immunoblotting techniques	At baseline and at 6 months
Change in ATP synthase amount and expression	ATP synthase amount and expression will be assessed using immunohistochemistry and immunoblotting techniques	At baseline and at 6 months
Change in citrate synthase amount and expression	Citrate synthase amount and expression will be assessed using immunohistochemistry and immunoblotting techniques	At baseline and at 6 months
Change in succinate dehydrogenase amount and expression	Succinate dehydrogenase amount and expression will be assessed using immunohistochemistry and immunoblotting techniques	At baseline and at 6 months
Change in NADH dehydrogenase amount and expression	NADH dehydrogenase amount and expression will be assessed using immunohistochemistry and immunoblotting techniques	At baseline and at 6 months
Change in mitochondrial oxygen consumption rate	Mitochondrial oxygen consumption rate will be determined using the Seahorse XF Analyzer	At baseline and at 6 months
Change in spare respiratory capacity	Spare respiratory capacity will be determined using the Seahorse XF Analyzer	At baseline and at 6 months
Change in mitochondrial maximal respiration	Maximal mitochondrial respiration will be determined using the Seahorse XF Analyzer	At baseline and at 6 months
Change in mitochondrial basal respiration	Mitochondrial basal respiration will be determined using the Seahorse XF Analyzer	At baseline and at 6 months
Change in non-mitochondrial respiration	Non-mitochondrial respiration will be determined using the Seahorse XF Analyzer	At baseline and at 6 months
Change in body fat percentage	Body fat percentage will be assessed using dual energy x-ray absorptiometry (DEXA)	At baseline and at 6 months
Change in diastolic arterial pressure	Diastolic blood pressure will be measured using a sphygmomanometer	At baseline and at 6 months

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in density and distribution of capillaries	Capillarization will be determined using immunohistochemistry techniques	At baseline and at 6 months
Change in skeletal muscle fiber typing	Fiber typing will be determined using immunohistochemistry techniques	At baseline and at 6 months
Change in GLUT-4 protein expression	GLUT-4 protein expression will be assessed using immunoblotting techniques	At baseline and at 6 months
Change reduced glutathione content in skeletal muscle cells	Reduced glutathione content will be determined spectrophotometrically	At baseline and at 6 months
Change in glutathione peroxidase activity in skeletal muscle cells	Glutathione peroxidase activity will be determined spectrophotometrically	At baseline and at 6 months
Change in glutathione reductase activity in skeletal muscle cells	Glutathione reductase activity will be determined spectrophotometrically	At baseline and at 6 months
Change in superoxide dismutase activity in skeletal muscle cells	Superoxide dismutase activity will be determined spectrophotometrically	At baseline and at 6 months
Change in fasting glucose levels	Fasting glucose levels will be measured on an automated clinical chemistry analyzer	At baseline and at 6 months
Change in fasting insulin levels	Fasting insulin levels will be measured on an automated clinical chemistry analyzer	At baseline and at 6 months
Change in glycosylated hemoglobin levels	Glycosylated hemoglobin levels will be measured on an automated clinical chemistry analyzer	At baseline and at 6 months
Change in high-density lipoprotein (HDL) levels	HDL will be measured on an automated clinical chemistry analyzer	At baseline and at 6 months
Change in low-density lipoprotein (LDL) levels	LDL will be measured on an automated clinical chemistry analyzer	At baseline and at 6 months
Change in total cholesterol levels	Total cholesterol will be measured on an automated clinical chemistry analyzer	At baseline and at 6 months
Change in triglyceride levels	Triglycerides will be measured on an automated clinical chemistry analyzer	At baseline and at 6 months
Change in general blood count	General blood count will be measured on a hematology analyzer	At baseline and at 6 months
Change in erythrocyte reduced glutathione (GSH) levels	Erythrocyte GSH levels will be determined spectrophotometrically	At baseline and at 6 months
Change in erythrocyte oxidized glutathione (GSSG) levels	Erythrocyte GSSG levels will be determined spectrophotometrically	At baseline and at 6 months
Change in myostatin expression	Myostatin expression will be assessed using immunoblotting techniques	At baseline and at 6 months
Change cortisol concentration	Blood cortisol concentration will be assessed using immunoassays (ELISA)	At baseline and at 6 months
Change in testosterone concentration	Blood testosterone concentration will be assessed using immunoassays (ELISA)	At baseline and at 6 months
Change in growth hormone concentration	Blood growth hormone concentration will be assessed using immunoassays (ELISA)	At baseline and at 6 months
Change in insulin-like growth factor-1 (IGF-1) concentration	Blood IGF-1 concentration will be assessed using immunoassays (ELISA)	At baseline and at 6 months
Change in body mass	Body mass will be measured on a beam scale	At baseline and at 6 months
Change in bone density	Bone density will be assessed using dual energy x-ray absorptiometry (DEXA)	At baseline and at 6 months
Change in fat-free mass	Fat-free mass will be assessed using dual energy x-ray absorptiometry (DEXA)	At baseline and at 6 months
Change in waist circumference	Waist circumference will be measured using a Gullick II tape	At baseline and at 6 months
Change in hip circumference	Hip circumference will be measured using a Gullick II tape	At baseline and at 6 months
Change in resting heart rate	Heart rate will be measured using a heart rate monitor	At baseline and at 6 months
Change in resting metabolic rate (RMR)	RMR will be measured using indirect calorimetry	At baseline and at 6 months
Change in systolic arterial pressure	Systolic blood pressure will be measured using a sphygmomanometer	At baseline and at 6 months

Collaborators and Investigators

• Sponsor: University of Thessaly

Study record dates

Study Major Dates

• Study Start (Estimated): January 8, 2026
• Primary Completion (Estimated): June 30, 2026
• Study Completion (Estimated): December 20, 2026

Study Registration Dates

• First Submitted: January 5, 2026
• First Submitted That Met QC Criteria: January 5, 2026
• First Posted (Actual): January 14, 2026

Study Record Updates

• Last Update Posted (Actual): January 14, 2026
• Last Update Submitted That Met QC Criteria: January 5, 2026
• Last Verified: October 1, 2025

More Information

Terms related to this study

• Keywords: obesity; overweight; skeletal muscle; high-intensity interval training
• Additional Relevant MeSH Terms: Nutrition Disorders; Overnutrition; Body Weight; Pathological Conditions, Signs and Symptoms; Nutritional and Metabolic Diseases; Signs and Symptoms; Overweight; Obesity; Motor Activity; Movement; Musculoskeletal Physiological Phenomena; Musculoskeletal and Neural Physiological Phenomena; Investigative Techniques; Epidemiologic Research Design; Epidemiologic Methods; Research Design; Methods; Exercise; Control Groups
• Other Study ID Numbers: 2482/4.12.2024

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED

Drug and device information, study documents

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