Author(s): HAMARSLAND, H., ELLEFSEN, S., HAMMARSTRÖM, D., Institution: INLAND UNIVERSITY OF APPLIED SCIENCES, Country: NORWAY, Abstract-ID: 2486

INTRODUCTION:
Obesity has been linked to decreased fasted muscle protein synthesis and anabolic resistance in response to feeding and exercise (summarised in 1). Although not a consistent finding, it may be of great clinical relevance if excess fat mass indeed drives anabolic resistance and hampers adaptations to exercise in obesity.
METHODS:
To investigate the effects of obesity on long-term adaptations of muscle hypertrophy and strength, we recruited 95 healthy inactive individuals (♂: 46, ♀: 49, age: 47.9 ± 7.2 years, fat % range: 21.3-57.4) to 13 weeks of bi-weekly sessions of supervised progressive heavy resistance exercise. Exercises were leg press, knee extension, knee flexion, bench press and dumbell row. Upper body exercises were performed to failure with three sets of 10RM. The leg training was unilateral, with each leg randomly assigned to three sets of 10RM or three sets of 30RM to failure. Dual-energy X-ray absorptiometry and ultrasound of the thigh were completed at baseline and after the intervention to measure total lean body mass and vastus lateralis thickness, respectively. After a familiarisation session, leg press 1RM was performed before and after the intervention. Linear models explaining post-intervention vastus lateralis thickness, lean mass, and 1RM by baseline values, sex, relative fat mass at baseline and condition (1RM and vastus lateralis thickness) were fitted. Data are reported as mean ± SE.
RESULTS:
The intervention effectively increased vastus lateralis muscle thickness by ~ 14%, total lean mass by ~ 2.5% and leg press 1RM strength by ~ 15 %. For every percentage point difference in baseline fat mass, lean body mass increased by 3 ± 13 grams (p = 0.824), vastus lateralis thickness decreased by 0.02 ± 0.039 millimetres (p = 0.436), and 1RM leg press increased by 0.05 ± 0.25 kg (p = 0.841). The different RM conditions induced no difference in vastus lateralis growth (30RM: +0.97 ± 1.02 (p = 0.366)). In leg press strength, 30RM improved 10.8 ± 4.94 % (p = 0.032) less than 10RM.
CONCLUSION:
In conclusion, relative fat mass does not interfere with muscle hypertrophy or strength adaptations in healthy middle-aged individuals in response to 13 weeks of heavy progressive resistance training.

1. Freitas, E. D. S. & Katsanos, C. S. (Dys)regulation of Protein Metabolism in Skeletal Muscle of Humans With Obesity. Front. Physiol._13, 843087 (2022).