The research project is aiming to examine the muscular adaptations to resistance training (RT), detraining (DT) and repeated RT (i.e. retraining). The research project will also examine differences in muscular adaptations between 20 weeks of continuous RT and 20 weeks of intermittent RT including a 10-week DT period in the middle of the training intervention. This is randomized controlled trial in which the research participants will be randomized into discontinuous and continuous groups (both n=~20). Both will be doing a 2-3-week familiarization and control period at the start. Then in the former there will be an initial strength training period (10-wks), a DT period (10-wks), and a second strength training (retraining) period (10-wks). The second group includes a 10-wk non-training control period (10-wks) followed by a RT period (20-wks). Participants will be young, healthy men and women (age 18-35, which 50% are females) with no systematic RT experience during the last 6 months. Measurements will be completed before and after each study period. Body composition will be measured via bioelectrical impedance analysis (BIA) and 3D body scans. Dynamic leg press and elbow flexion one repetition-maximum (1RM) will be used to test maximal strength. Anaerobic performance and strength endurance will be tested in elbow flexion and dynamic leg press using RM tests. Vastus lateralis (VL) and biceps brachii muscle cross-sectional area (CSA) will be assessed via ultrasound. Muscle biopsies of the VL muscle will be obtained to assess changes in muscle fiber morphology and factors regulating and associated with the hypertrophic processes and metabolism. Blood samples will be collected to analyze changes in metabolism and physiology. A rating of perceived exertion (RPE) during training will be collected after every exercise to ensure proper training intensity. Finally, nutrition and habitual physical activity will be assessed with 4-day diet diaries and physical activity questionnaires before the intervention and during each 10-week period.

It is well known that RT increases skeletal muscle size and strength. However, there seems to be a difference in increases in muscle size (termed hypertrophy) and strength in upper and lower limb musculature in untrained population after RT. Moreover, there is large inter-individual variation in the adaptations gained through RT. Also at the moment, the responses to de- and retraining are not well known, and new research designs for investigating possible muscle memory are needed. Muscle mass and strength, once achieved with RT, can be obtained faster with subsequent retraining if the initial adaptations were lost due to inactivity. RT causes many molecular and cellular changes in myofibers that aid in hypertrophic processes, yet their adaptations to DT and contribution to muscle memory are still marginally researched. It is, therefore, essential to widen our knowledge about the permanence of physiological adaptations in skeletal muscle to periods of DT and repeated exposure to RT.

The primary objectives to achieve by this project are:

1. to determine the magnitude of 10-week RT period on upper and lower limb maximal dynamic strength and muscle size compared to the non-training control group
2. to determine whether the responses to 20-week continuous RT differs in adaptations in maximal strength and muscle hypertrophy from two 10-week RT periods separated by a 10-week detraining period
3. to identify molecular and cellular biomarkers explaining responses to RT, detraining and retraining

Inclusion Criteria:

• No regular resistance training history
• BMI within range 18.5-30 kg/m2
• Participants must be 18-40 years old
• No history in systematic endurance-type training (> 2 endurance exercise sessions lasting > 30 minutes per week for the last six months)
• non-smoker
• not currently consuming any anti-inflammatory drug(s)

Exclusion Criteria:

• history of medication that could affect exercise responses
• use of nutritional supplements aside from those that are protein- or carbohydrate-based (ex. creatine) or basic minerals, vitamins, or fish oil products
• any acute or chronic illness affecting cardiovascular, respiratory, musculoskeletal and/or endocrine function
• any other condition that may limit the ability to perform resistance training and testing (ex. uncontrolled hypertension, diabetes, arthritic conditions, neuromuscular complications)