Towards Personalized Exercise: Identifying the Determinants of Individual Variation in Repeated Resistance Training (TraDeRe) and Examining Transferability of Responsiveness Between Resistance Training and Endurance Training

While the diverse health and performance benefits of resistance training (RT) are widely recognized, some individuals demonstrate notably divergent responses to RT intervention. This phenomenon is termed inter-individual response variation to RT. However, despite the prevalence of these research findings, the precise underlying mechanisms contributing to these differential RT responses remain ambiguous. Finally, it is currently unknown whether a responsiveness to RT predicts responsiveness to ET within the same set of participants, as this area of research is critically understudied.

Investigators aim to investigate the cellular, molecular, and neuromuscular mechanisms behind the plausible RT response variability intra- and inter-individually, using trial-to-trial, i.e. resistance training, detraining, and retraining design. Moreover, as the impact of diverse polygenic effects on RT responsiveness is yet to be determined, investigators will employ a multi-OMIC (genomic, epigenomic, transcriptomic, proteomic, and metabolomic) approach to unravel previously unknown denominators of RT responsiveness. Finally, numerous environmental factors, e.g. nutrition, stress, sleep, and physical activity are monitored during the study to assess the effects of non-physiological mechanisms on RT response variability.

In our study, 362 healthy male and female participants in total started in the study and were destined to undergo an RT period of 12 weeks in two separate periods (intervention I refers to NCT05874986). Then, a subset of the participants from intervention I will be reallocated into intervention II based on the magnitude increase of m. vastus lateralis (VL) cross-sectional area (CSA) assessed by ultrasound using extended-field-of-view mode. Similar to intervention I, intervention II will be performed in separate periods similarly to the data collection I and II of intervention I to first accumulate approximately 32 weeks of detraining for both cohorts, after which 12 weeks of RT is performed.

Moreover, a subset (n=30) of the participants aged 40-50 from intervention I not selected for intervention II have a chance to take part in a 10-week home training sub-study. These participants will be randomized to a non-training control group (n=15) and a home training group (n=15). The home training group will carry out a 10-week RT period utilizing muscle-strengthening activities in their home. This sub-study investigates how minimally supervised RT executed at home after supervised gym RT can maintain muscle strength and size compared to non-training. Home training is flexible, time-saving, and inexpensive. It is also done twice weekly using safe and effective training protocols and movements. Home-based training includes pistol squat, reverse nordic, push up, and bent-over row, and bicep curl exercises. To achieve progression, the total load will be increased by increasing the number of repetitions per set, and/or increasing the load by using a progression from easier to more difficult techniques and/or by adding resistance bands, which will be provided to participant's free of charge for the duration of the study. Participants will be contacted regularly to ensure motivation and adherence to home exercise. All the participants in this sub-study, as well as the other participants not selected for intervention II are offered a self-directed, non-supervised 7-week RT period with a similar design as in intervention I with access to our gym located in our Faculty's building. VL CSA, horizontal leg press 1 repetition maximum, and body composition will be assessed before and after home training and self-directed RT for each participant.

In intervention II, participants will be performing RT similarly to intervention I. However, for the last 5 weeks of the intervention, RT volume will be increased by 40 % for the lower body exercises to assess the impact of RT volume increment on RT responses. After 12 weeks of RT, an experimental RT session will be conducted to assess the acute physiological responses to resistance exercise. The experimental session will consist of five heavy sets of both horizontal leg press and leg extension exercises. During the last RT week, participants will engage in recovery measurements before and after the second-to-last and the last RT bout, and once during the days between these two bouts. After 12 weeks of RT, participants will be performing an additional acute resistance exercise session. All the participants NOT selected for intervention II are able to participate in a self-directed, 6-week RT period with measurements before and after this period. These measurements include body composition, muscle size (VL CSA and muscle thickness of elbow flexors) and muscle strength (dynamic 1RM of horizontal leg press and barbell scott curl) assessments. A subgroup of the participants (n=10) will engage in a control period of 6 weeks in duration, before the onset of RT.