Author(s): APICELLA, M., JAMESON, T., ABDELRAHMAN, D., MURTON, A., ALAMDARI, N., DIRKS, M., WALL, B., STEPHENS, F., Institution: UNIVERSITY OF EXETER, Country: UNITED KINGDOM, Abstract-ID: 1165

INTRODUCTION:
Optimal adaptation to resistance exercise likely requires a maximal rate of myofibrillar protein synthesis (MyoPS), which is thought to be achieved by the post exercise consumption of >20g of protein or ~2g of the essential amino acid (EAA) leucine. Recent work has challenged this centrality of leucine and suggested that such responses may also vary in females due to typically lower body mass and differing hormonal profiles. However, limited data is available on the role of naturally fluctuating oestrogen (O) concentrations during the menstrual cycle (MC) in regulating postprandial post-exercise MyoPS. This study aims to investigate the effect of post-exercise ingestion of low and moderate compared to an optimal dose of leucine on MyoPS, and determine if post-exercise MyoPS and expression of 46 genes involved in the regulation of muscle mass are different during the early follicular (EF, low O) and late follicular (LF, high O) phases of the MC, when progesterone (Pg) is low.
METHODS:
Twenty-eight healthy, eumenorrheic females (age: 27±8 y; BMI: 24±3 kg/m2) completed one of three parallel experimental trials in a randomised double-blind manner during EF (4±1d following menses; O 183±78 pmol/l, Pg 1.1±0.7 nmol/l). A subset of 17 participants completed a second trial during LF (2±2 d before luteinising hormone surge; O 855±571 pmol/l, Pg 4.0±5.1 nmol/l), in a randomised order. On each visit, participants received a primed continuous infusion of L-[ring-2H5]phenylalanine for 7.5h. Following a bout of resistance exercise, participants ingested one of three drinks containing 1.5g EAA (n=10) or 15g (n=10) and 20g (n=8) whey protein, equating to 0.6, 1.5, and 2.0g leucine, respectively. Muscle biopsies were collected before and during the 4h post-exercise postprandial period to assess MyoPS and gene expression. Two-way ANOVAs were performed to detect changes across drinks and MC phases. Data are expressed as means±SD.
RESULTS:
Post-exercise drink ingestion increased MyoPS above postabsorptive values after 2h by 0.058±0.038, 0.035±0.050 and 0.064±0.036%⋅h-1 (P<0.0001) and after 2-4h by 0.050±0.035, 0.011±0.040, and 0.031±0.063%⋅h-1 (P=0.009) for 0.6g, 1.5g, and 2.0g drinks, respectively, with no interactions observed. MyoPS increased by 0.050±0.056 and 0.048±0.081%⋅h-1 after 2h (P<0.001), but not 2-4h (P=0.522) for EF and LF, respectively, with no differences between MC phase at either timepoint. Muscle mRNA expression of several genes involved in oestrogen signalling, protein synthesis, and inflammation were increased in LF vs EF, and to a greater extent 4h post-exercise, whereas protein breakdown genes were decreased.
CONCLUSION:
Ingestion of 0.6g (1.5g EAA) or 1.5g leucine (15g protein) increases post-exercise MyoPS to a comparable extent as 2g leucine (20g protein) in females. This increase in MyoPS does not appear to be affected by increased O during the LF phase of the MC, despite a gene expression profile in LF consistent with muscle growth.