Resistance Training, Detraining, and Retraining Study 2024 (TraDeRe2024)

The goals of our research project are to identify factors explaining inter-individual variation in responses to resistance training (RT) and the baseline determinants underlying an individual's sensitivity to respond to RT. Moreover, investigators aim to assess whether a responsiveness to RT predicts responsiveness to endurance training (ET). Thus, investigators aim to gain a deeper understanding of exercise adaptation processes. The main questions investigators aim to answer are: * Can the physiological responses of one RT intervention be extrapolated to a subsequent RT intervention? * If so, what are the mechanisms underlying differing skeletal muscle growth responses in low, and high responders of skeletal muscle hypertrophy? * If so, do the low responders of skeletal muscle growth respond more favourably when the amount of RT is increased? * Are the high, moderate, and low responders of RT also the highest, moderate, and lowest responders to ET? To examine these main research questions, high (n=30), low (n=30), and moderate (n=30) responders of skeletal muscle growth in response to RT (intervention I, NCT05874986) are reallocated into a subsequent 12-week RT intervention (intervention II) after a detraining period. A subgroup of these participants (n=10) will engage in a 6-week control period before starting the second RT period. Additionally, after intervention II, participants will participate in an ET intervention, lasting 6 weeks. In this intervention II, reallocated participants will be: * Resistance training with supervision for 12 weeks * Consuming deuterium oxide for the assessment of muscle protein synthesis * Consuming D3-3-methylhistidine for the assessment of acute muscle protein breakdown * Consuming D3-creatine for the examination of whole-body skeletal muscle mass * Providing a spot urine sample six (6) times, and urine collection for 24 hours performed twice * Providing saliva samples (30-32 in total) for the assessment of body water enrichment of deuterium * Providing a muscle biopsy four or five (4-5) times during the study * Providing a blood sample fourteen (14) times during the study * Assessed for body composition and body volume four or five times (4-5) during the study * Participating in muscle size, maximal dynamic strength and TMS measurements four or five (4-5) times during the study * Asked to answer questionnaires related to e.g. stress, physical activity, sleep, perceived exertion, and diet * Participating in recovery measurements before and after the second-to-last and the last RT bout, and once in the days between these RT bouts, consisting of six (6) body volume measurements and six (6) maximal voluntary isometric contraction (kg) tests using horizontal leg press for the assessment of neuromuscular recovery * Participating in an acute resistance exercise (RE) after the 12-week RT intervention. Furthermore, in the ET intervention, participants will be: * Participating in a familiarization session and resting electrocardiograph measurements before the intervention * Participating in endurance testing consisting of body composition, movement economy, and incremental RAMP testing before and after ET intervention * Endurance training with supervision for 6 weeks, three times a week.