Baseline Determinants Of Resistance Training Response Heterogeneity In Muscle Strength And Size

Multiple genomic and non-genomic factors may influence inter-individual variation in muscle strength and size responses to chronic resistance training (RT). PURPOSE: This study examined the role of age, body composition, health status, stress, sleep, nutrition, physical activity, and psychological factors on 12-week RT responses in maximal muscle strength and size. METHODS: Healthy men and women (19-46 years, n = 165) with no systematic RT background volunteered in the 12-week supervised RT period with two whole-body training sessions per week. For lower limbs, four sets of leg presses and four sets of knee extensions of 8-10 repetitions were performed per training session. RT-induced changes were measured in one repetition maximum (1RM) in leg press and vastus lateralis cross-sectional area (VL CSA) by ultrasound. When entering the study, questionnaires were used to survey age, perceived health status, stress (Perceived Stress Scale, PSS), sleep (average sleeping time per night), sport and exercise history, nutrition (eating frequency of protein-rich food such as meat, chicken, fish, eggs, and milk products), physical activity (Global Physical Activity Questionnaire, GPAC), mood (The Profile of Mood States, POMS), and self-efficacy, social support and motivation to exercise. Weight and body fat percentage were measured by Bioimpedance, and body mass index (BMI) was calculated. RESULTS: RT-induced change in 1RM leg press correlated with age (r = -.269, p < .001), sport and exercise history (r = -.271, p < .001), and perceived health status at baseline (r = -.167, p = .033). RT-induced change in VL CSA correlated with BMI (r = -.178, p = .022) and Fat% (r = -.211, p = .006). Linear regression analysis showed that the change in 1RM leg press was associated with age (p = .009) and sport and exercise history (p = .008). CONCLUSIONS: This preliminary study suggests that especially participants' higher age and previous activity in sports and exercise can negatively affect RT responsiveness in maximal strength. It should be noted, however, that this study did not include older adults, which could affect the generalizability of the present finding. Although these determinants appeared to have a minor role in RT responses, they should be considered in predicting muscle responses achieved by systematic RT over time.