ECSS Paris 2023: OP-PN23
INTRODUCTION: locomotor muscles such as the knee extensors and the plantar flexors. Prolonged bed rest can lead to a reduction in muscle mass of up to 30%. However, the onset of muscle atrophy is rapid, with measurable changes occurring within a few days of disuse. A 3% reduction in the cross-sectional area of the thigh muscle has been observed after only 5 days of full leg casting 1. Although the full leg cast model is frequently used for studies investigating the initial mechanisms of muscle atrophy, it has some serious drawbacks. The angle of fixation can influence the number of serial sarcomeres. Fixation also makes it difficult to adapt the model outside of clinical investigations, for example in studies investigating atrophy induced by spaceflight, as the joint is fixed in an unnatural position. One option to overcome these limitations is the unilateral lower limb suspension (ULLS) model, in which the intervention limb is unloaded by lifting the contralateral limb with a plateau shoe. This allows the unloaded limb to assume a straight position and move passively and freely around the hip, which is closer to the situation of an astronaut in weightlessness. To date, there have been no studies investigating whether the ULLS model results in comparable changes in muscle volume to those reported for short periods of bed rest and full leg casting. Therefore, this study aimed to investigate the changes in muscle volume induced by 5 days of ULLS. METHODS: At the time of abstract submission, a total of 11 subjects have completed the 5-day ULLS protocol, 8 men and 3 women. At the congress we will have data from 20 participants, equally divided between the sexes. The volume of the quadriceps muscle was measured by MRI before and after the five-day unloading. All subjects wore a thermometer patch on the gastrocnemius muscle on both legs, which recorded the skin temperature every minute during the unloading phase. RESULTS: The intervention resulted in a significant decrease (2.35 ± 1.45%) in m. quadriceps in the unloaded leg (894.7 ± 323.8 cm3 vs 873.7 ± 319.5 cm3, p < 0.05). The control leg was unaffected (917.5 ± 323.5 cm3 vs 920.0 ± 327.1 cm3, p > 0.05). The magnitude of muscle loss was similar between the sexes (females; -2.35 ± 1.57%, men; -2.36 ± 1.52%). The skin temperature in the unloaded leg was on average 4.2 ± 1.3 °C lower than in the control leg during daily activities. CONCLUSION: Our preliminary data shows that short-term ULLS produces similar changes in m. quadriceps to those previously reported for bed rest and full leg casting protocols of the same length. This means that the method is suitable for interventions aiming to investigate the early responses of muscle atrophy. We also show that men and women respond similarly, and that continuous temperature monitoring can serve as a tool for protocol compliance. 1 Wall, BT et al. (2014). Acta Physiol. 210, 600–611
Read CV Mirko MandicECSS Paris 2023: OP-PN23
INTRODUCTION: Skeletal muscle loss occurs during short-term muscle disuse, e.g. immobilisation following injury. Muscle disuse is accompanied by a decrease in muscle protein synthesis (MPS) rates and branched-chain amino acid (BCAA) accumulation. However, the relevance of BCAAs in disuse atrophy remains unclear. Thus, we aimed to manipulate muscle BCAA availability via a BCAA restricted diet to assess its impact on MPS and amino acid kinetics during forearm immobilisation. METHODS: Twenty healthy participants (15/5 M/F; 22±1 yrs, BMI 22.7±0.5 kg·m-2) attended two metabolic test days before (PRE) and after (POST) 48 h forearm immobilisation, during which they were randomly allocated to a control (CON; n=10) or BCAA restricted diet (BCAA-; n=9). During immobilisation, CON consumed a fully controlled diet (50-55 en% carbohydrates, 25-30 en% fat, and 1.5 g·kg-1·day-1 protein [15-20 en%]) containing 20.0±0.7 g·d⁻¹ BCAA), whilst BCAA- consumed the same macronutrient matched diet but with 0.9±0.1 g·d⁻¹ BCAA. An intravenous infusion of L-[ring-2H5]phenylalanine with repeated arterialised-venous forearm balance samples and m. brachioradialis forearm muscle biopsies in fasted and clamped (hyperinsulinaemic [50 mU·m-2·min-1]-hyperaminoacidaemic [0.11 g·kg-1·h-1]-euglycaemic [5.0 mmol·L-1]) conditions was used to explore the flux of amino acids between 3-pools (arterialised, venous, and intracellular [IC] pools) and mixed muscle fractional synthesis rate (FSR). Data (mean±SEM) were analysed via a 3-way repeated measures ANOVA with clamp, immobilisation and diet as factors. RESULTS: BCAA- reduced fasted arterialised plasma leucine concentrations (PRE: 125.1±6.5 to POST: 108.6±8.1 µmol·L-1; P<0.05), resulting in lower concentrations POST compared to CON (135.6±6.4 µmol·L-1; P<0.05). Fasted IC pool phenylalanine and leucine concentrations increased by 26±9% and 24±9% POST in CON, respectively (both P<0.05), but remained unchanged in BCAA- (P>0.05). Phenylalanine net balance (NB) decreased by 56±6% (fasted) and 67±6% (clamp) from PRE to POST (P<0.05), with no effect of diet (P>0.05). Three-pool amino acid fluxes increased after clamp (P<0.05) but were not affected by immobilisation or diet (P>0.05). Forearm FSR increased from PRE to POST (P<0.05) but was not affected by diet (PRE: CON 0.052±0.008, BCAA- 0.041±0.007%·h-1; POST: CON 0.103±0.027, BCAA- 0.058±0.015%·h-1; P>0.05). CONCLUSION: Dietary BCAA- decreases plasma leucine concentrations and suppresses intracellular amino acid accumulation but does not affect three-pool amino acid kinetics or MPS during short-term immobilisation. Forearm immobilisation decreases forearm phenylalanine NB, indicating early muscle protein loss, but does not affect 3-pool modelled amino acid fluxes. The rise in MPS after immobilisation may be attributed to intracellular amino acid accumulation, providing leads for future research on the role of extra- and intracellular amino acid availability in muscle disuse atrophy.
Read CV Samuel OakleyECSS Paris 2023: OP-PN23
INTRODUCTION: Periods of muscle disuse occur across the lifespan due to illness, injury, and hospitalisation, suppressing muscle protein synthesis (MPS) rates and leading to muscle atrophy and a reduction in physical performance and quality of life. To date, no studies have investigated use of a combined exercise and nutrition prehabilitation regimen to mitigate declines in MPS or muscle mass during a period of disuse. This study aims to investigate the effect of beta-lactoglobulin (BLG), a leucine rich protein, supplementation combined with resistance exercise training before 5-days of unilateral limb immobilisation on muscle mass, strength, and MPS rates. METHODS: We conducted a randomised, placebo-controlled trial whereby healthy young adults (n=11) ingested a BLG supplement or a dextrose monohydrate placebo (PLA) thrice daily for 1-wk prior to, and during, 5-d of unilateral limb immobilisation. Participants completed four sessions of resistance training during the week prior to immobilisation. Deuterium oxide tracer methodology was used to measure free-living MPS rates in response to prehabilitation and muscle disuse. Measurements of thigh lean mass by dual energy x-ray absorptiometry and muscle strength by isokinetic dynamometry were conducted at baseline, pre-immobilisation (post-exercise training), and post-immobilisation. RESULTS: Thigh lean mass remained unchanged for BLG (3.1±12.9% pre-immobilisation, 1.7±12.5% post-immobilisation) and PLA (2.2±5.4% pre-immobilisation, 0.4±6.6% post-immobilisation) in response to prehabilitation and muscle disuse. Isometric strength increased in BLG (12.7±16.9%) and PLA (12.6±13.9%) with exercise training, but declined to below baseline in BLG (-3.0±17.4%) and baseline levels in PLA (0.6±16.2%) following immobilisation. Isokinetic strength appeared to decline to a greater extent in BLG than PLA (BLG: -4.7±19.0% pre-immobilisation, -19.5±22.8% post-immobilisation, PLA: 25.7±9.9% pre-immobilisation, -1.5±13.2% post-immobilisation). However, the decline in MPS in response to disuse was attenuated in BLG compared with PLA (change pre- to post-immobilisation, BLG: -23.7±7.4%, PLA: -41.2±12.7%). Protein expression of muscle protein breakdown (MPB) markers indicated a pre-post immobilisation increase in MuRF1 (BLG: 60.7±51.3%, PLA: 57.1±39.5%) and Atrogin-1 (BLG: 55.9±26.6%, PLA: 43.8±31.4%) in both groups. CONCLUSION: To conclude, BLG supplementation combined with resistance exercise as a prehabilitation strategy may attenuate the decline in MPS following 5-d of immobilisation. However, the improvements in MPS in BLG did not appear to translate to the better preservation of muscle mass and strength compared with PLA, of which the PLA group achieved better outcomes. An increased expression of MPB markers in both groups may be explained by the novel resistance exercise training stimulus, although immobilisation also elicited elevations in MuRF1 and Atrogin-1 levels above baseline.
Read CV Alix HughesECSS Paris 2023: OP-PN23