Enrollment goal not met in allotted recruitment period

It is recommended that individuals perform a combination of resistance exercise (RE) and endurance exercise. Lack of time is often cited as a reason for being unable to meet current exercise guidelines. Therefore, combining both forms in one session may be beneficial. However, research continues to elucidate whether interference of adaptive outcomes occurs when RE and endurance exercise are performed concurrently. A proposed interference effect suggests that concurrent training may dampen RE-induced adaptations (e.g., muscle strength and growth) compared to RE only.

The propose of this investigation is to determine the effects of concurrent RE and high-intensity interval training (HIIT), compared to RE only, on muscle health and cardiovascular risk in sedentary, middle-aged (40-65 years) who are overweight/obese with type 2 diabetes mellitus (T2DM). The investigators will measure the effects on muscle strength, muscle growth, cardiovascular fitness, glycaemic control and markers of cardiovascular risk before and after an 8-week training program. Data will be obtained through the analysis of skeletal muscle samples, blood samples, magnetic resonance imaging, questionnaires and exercise performance tests.It is hypothesized that concurrent RE + HIIT will amplify the exercise-induced muscle growth response, which will result in greater satellite cell content, compared to RE alone. As a result, this will lead to greater skeletal muscle mass and strength after RE + HIIT compared to RE in isolation.

A finding that concurrent resistance training and HIIT does not impede muscle adaptations could offer future strategies to minimize exercise time commitment whilst still maximizing the physiological benefits of both resistance and endurance exercise through a single training session. This may therefore provide an effective exercise strategy in the prevention and/or treatment of T2DM.

Data analysis will be performed using IBM SPSS statistical software (IBM Corp., Armonk, New York, USA). All data will be checked for normality and appropriate log transformations applied prior to analysis of variance (ANOVA) for primary and secondary outcomes. Satellite cell content will be compared using a two-way, mixed-model ANOVA with one within (2 levels; pre- and post-training) and one between factor (2 level; exercise group) with significance set at P < 0.05.

Based on a mixed ANOVA with between- and within-participant factors, and previously published data (Babcock et al. 2012), a sample size of 24 participants (12 per group) will provide a power of 84%. This sample size will allow detection of a mean change in satellite cell content of 2.35, assuming standard deviations of the change from pre- to post-training as 2.266 and 1.331 in the two exercise groups. Sample size calculation was performed with an alpha error of 0.05. SamplePower 2.0 (SPSS Inc., Chicago, Illinois, USA) software was used to determine sample size.

This study will combine data collected at the University of Birmingham with previously collected data from an identical study design performed by a co-investigator (Dr Pugh) in Rome, Italy. The previous study has collected data from 10 participants across both exercise groups (RE, N = 7; RE + HIIT, N = 3). Therefore, it is necessary for the present study to recruit a further 14 participants (RE, N = 5, RE + HIIT, N = 9) in order to achieve a sample size of 24 participants (12 per group). However, based on an assumption of a 25% drop-out rate, the total minimal sample necessary will be 19 participants (RE, N = 7; RE + HIIT, N = 12).

Inclusion Criteria:

• Male sex
• White British/European
• Aged between 40 and 65 years at the time of screening
• Have a body mass index (BMI; body weight/height in m2) between 27 and 40 kg/m2
• Sedentary/untrained for at least 1 year (based on physical activity self-reports of fewer than two sessions of structured exercise per week last <30 min)
• T2DM (American Diabetes Association 2014) for more than 1 year
• Central obesity (defined as waist circumference ≥94 cm for males)

Exclusion Criteria:

• Currently involved in research or have recently (<6 months) been involved in any research prior to recruitment
• Any condition limiting or contraindicating physical activity; including diabetic peripheral neuropathy, and coronary or peripheral artery disease
• Previous myocardial infarction, previous or current angina, shortness of breath, or other symptoms suggestive of heart failure
• Insulin medication
• HbA1c more than 75 mmol/mol (9%)
• Uncontrollable hypertension: systolic blood pressure ≥160 mmHg and diastolic blood pressure ≥100 mmHg
• Not weight stable for the last three months
• Smokers (within the last 12 months)
• Anticoagulant medication, such as warfarin or newer anticoagulant drugs. If participants are on aspirin medication, this would need to be stopped for 3 days prior to and during the day of any biopsy visit unless contraindicated (in which case participants would be excluded).