Exploring the influence of resistance training volume, intensity, and diet on skeletal muscle adaptations

Abstract

Background and Aims. Progressive resistance training programs continue to stand out as the cornerstone for enhancing both maximal strength and muscle mass in individuals. The varied muscle adaptations observed in individuals undergoing resistance training highlight the nuanced impact of training variables and the influence of biological predisposition shaping these adaptations. As a result, the degree to which individuals strength gains and muscle growth respond to training variables, such as number of sets (volume), varies. In some environments, particularly the military, maximal strength and power are increasingly recognized as important components of military performance. However, given the exposure of military personnel to various stressors in their daily routines, including field exercises that may compromise muscular adaptations, it is important to implement optimal training strategies aiming to enhance and sustain muscle strength while mitigating unfavorable changes in body composition.

Study I aimed to explore the effects of low and moderate resistance-training volume on muscle strength and hypertrophy and its association with individual biological characteristics using untrained individuals (Paper I). In Study II, the aim was to explore the temporal patterns of markers associated with ribosomal biogenesis in response to resistance training and to examining how variations in training volume may induce differences in these markers (Paper II). In Study III, we aimed to compare various resistance-intensty strategies incorporated as a part of the soldiers regular training regimen on muscle strength, hypertrophy, and performance in moderately trained soldiers (Paper III). Furthermore, as a part of soldiers regular training regime, we investigated in Study IV whether protein supplementation could mitigate losses of muscle mass and muscular performance during a strenuous military field exercise undergoing severe energy deficit and whether the soldiers could fully recover within a week following the exercise (Paper IV).

Methods. In Study I, 34 individuals (avg. age: 22) underwent 12 weeks of contralateral low (1-SET) and moderate (3-SET) volume resistance training in three lower body exercises. Muscle cross-sectional area (CSA) and maximal strength were measured at baseline and 12 weeks, along with muscle biopsy sampling (m. vastus lateralis), which was also sampled pre- and post-fifth training session in Week 2. In Study II, eleven individuals (avg. age: 24) performed 12 sessions of unilateral knee extension, performing either a variation in training volume or constant volume. Muscle biopsies were taken bilaterally before and 48 hours after the first (baseline), fourth, fifth, eighth, ninth, and twelfth sessions and after eight days of de-training. A nontraining control group (n=11) had biopsies at baseline, 48 hours, and 3-5 weeks later. Muscle strength, lean mass, and muscle thickness were measured at baseline, after 12 training sessions, and following the de-training period. In Study III, 27 cadets (avg. age: 20) performed a prolonged 22-week whole-body resistance-training program (7 exercises), performing either 10 repetitions maximum (RM) or 30RM. Muscle strength and mass (DXA) and performance were assessed at baseline and week 22 for the upper and lower limbs, in addition to a mid-intervention assessment at week 10. Biopsy sampling (m.vastus lateralis) was also conducted at the three time points. In Study IV, 38 cadets (ave. age: 21) were recruited and randomly allocated to ingest 1 or 2 g kg-1 d-1 protein in an isocaloric manner (∼ 15 kcal kg-1 d-1) resulting in a severe energy deficit during the 10-day field exercise. Outcome measures of hormone levels, muscle strength, and performance were assessed before and following the 10-day exercise as well as after seven days of recovery. Changes in muscle mass (DXA) were assessed at baseline and directly after the 10-day exercise.

Results. The thesis demonstrates a resistance training volume-dose relationship with muscle growth and strength. It further emphasizes the determinant role of ribosomal biogenesis in resistance training-associated adaptation. The initial accumulation of ribosomal biogenesis serves as a predictive factor for long-term training adaptations, with the benefit of 3-SET training compared to 1-SET training. Moreover, RNA abundance reaches peak values within eight resistance training sessions with a relatively high training volume, and ribosomal biogenesis is sensitive to training cessation.

The thesis further underscores the impact of long-term systematic resistance training in a military training environment. Twenty-two weeks with 10RM training stand out as the preferred resistance training modality in moderately trained cadets, achieving in general superior gains in muscle strength, growth, and performance compared to 30RM training. Furthermore, the ingestion of either a higher protein intake of 2 g kg-1 d-1 or a lower protein intake of 1 g kg-1 d-1 in the cadets diets during the demanding field exercise with severe energy deficit did not result in differences between supplementation groups in muscle performance or in body mass composition.