Effects of essential amino acid supplementation on muscular adaptations to 3 weeks of combined unilateral glenohumeral & radiohumeral joints immobilisation

Background: Short-term immobilisation results in a decrease in muscle size and strength. Ingestion of essential amino-acids (EAAs) stimulates net protein synthesis and supplementation is shown to improve lean body mass, strength and physical function, even without exercise. This study set out to determine whether EAA supplementation would attenuate immobilisation-induced changes in muscle characteristics. Methods: In n=16 healthy, habitually active participants from a mixed gender (n=10 females, 5 males) population aged 21 ± 3.1 years, the non-dominant arm was immobilised in a sling for 9 waking hours a day over 3 continuous weeks. Participants were randomly assigned to one of two groups: EAA or placebo treatment. The nutritional supplement treatment was consumed throughout the immobilisation period. Measures of muscle thickness (via b-mode ultrasonography), upper and lower arm girth (anthropometry), isometric torque (dynamometry), muscle activation (electromyography), and serum interleukin-6 (ELISA) were taken immediately before immobilisation (PRE) and immediately on removal of the sling (POST). Results: The decrease relative to baseline in arm girths was significantly greater with the placebo (-1.75% and -1.48%) than with the EAA supplement (-0.31% and -0.55%) in both the upper (p=0.01) and lower (p=0.045) arm. The direction of change in biceps sub-cutaneous adipose thickness differed significantly between the placebo and EAA supplements (-3.3% and 19.6%, respectively, p=0.03). Torque normalised by muscle thickness in the biceps decreased less in the EAA compared with the placebo group (-6% vs. -20%, P<0.05). Similarly, normalised torque in the triceps also changed differently in the EAA compared with the placebo group (+15% vs. -23%, P