Characterisation of L-Type Amino Acid Transporter 1 (LAT1) Expression in Human Skeletal Muscle by Immunofluorescent Microscopy.

The branch chain amino acid leucine is a potent stimulator of protein synthesis in skeletal muscle. Leucine rapidly enters the cell via the L-Type Amino Acid Transporter 1 (LAT1); however, little is known regarding the localisation and distribution of this transporter in human skeletal muscle. Therefore, we applied immunofluorescence staining approaches to visualise LAT1 in wild type (WT) and LAT1 muscle-specific knockout (mKO) mice, in addition to basal human skeletal muscle samples. LAT1 positive staining was visually greater in WT muscles compared to mKO muscle. In human skeletal muscle, positive LAT1 staining was noted close to the sarcolemmal membrane (dystrophin positive staining), with a greater staining intensity for LAT1 observed in the sarcoplasmic regions of type II fibres (those not stained positively for myosin heavy-chain 1, Type II-25.07 ± 5.93, Type I-13.71 ± 1.98, p < 0.01), suggesting a greater abundance of this protein in these fibres. Finally, we observed association with LAT1 and endothelial nitric oxide synthase (eNOS), suggesting LAT1 association close to the microvasculature. This is the first study to visualise the distribution and localisation of LAT1 in human skeletal muscle. As such, this approach provides a validated experimental platform to study the role and regulation of LAT1 in human skeletal muscle in response to various physiological and pathophysiological models.

The role of amino acids in skeletal muscle adaptation to exercise.

The synthesis of new protein is necessary for both strength and endurance adaptations. While the proteins that are made might differ, myofibrillar proteins following resistance exercise and mitochondrial proteins and metabolic enzymes following endurance exercise, the basic premise of shifting to a positive protein balance after training is thought to be the same. What is less clear is the contribution of nutrition to the adaptive process. Following resistance exercise, proteins rich in the amino acid leucine increase the activation of mTOR, the rate of muscle protein synthesis (MPS), and the rate of muscle mass and strength gains. However, an effect of protein consumption during acute post-exercise recovery on mitochondrial protein synthesis has yet to be demonstrated. Protein ingestion following endurance exercise does facilitate an increase in skeletal MPS, supporting muscle repair, growth and remodeling. However, whether this results in improved performance has yet to be demonstrated. The current literature suggests that a strength athlete will experience an increased sensitivity to protein feeding for at least 24 h after exercise, but immediate consumption of 0.25 g/kg bodyweight of rapidly absorbed protein will enhance MPS rates and drive the skeletal muscle hypertrophic response. At rest, ∼0.25 g/kg bodyweight of dietary protein should be consumed every 4-5 h and another 0.25-0.5 g/kg bodyweight prior to sleep to facilitate the postprandial muscle protein synthetic response. In this way, consuming dietary protein can complement intense exercise training and facilitate the skeletal muscle adaptive response.

Optimal elastic cord assistance for sprinting in collegiate women soccer players.

Overspeed exercises are commonly integrated into a training program to help athletes perform at a speed greater than what they are accustomed to when unassisted. However, the optimal assistance for maximal sprinting has not been determined. The purpose of this study was to determine the optimal elastic cord assistance for sprinting performance. Eighteen collegiate women soccer players completed 3 testing sessions, which consisted of a 5-minute warm-up, followed by 5 randomized experimental conditions of 0, 10, 20, 30, and 40% body weight assistance (BWA). In all BWA sessions, subjects wore a belt while attached to 2 elastic cords and performed 2 maximal sprints under each condition. Five minutes of rest was given between each sprint attempt and between conditions. Split times (0-5, 5-10, 10-15, 15-20, and 0-20 yd) for each condition were used for analysis. Results for 0-20 yd demonstrated a significant main effect for condition. Post hoc comparisons revealed that as BWA increased, sprint times decreased up to 30% BWA (0%: 3.20 ± 0.12 seconds; 10%: 3.07 ± 0.09 seconds; 20%: 2.96 ± 0.07 seconds; 30%: 2.81 ± 0.08 seconds; 40%: 2.77 ± 0.10 seconds); there was no difference between 30 and 40% BWA. There was also a main effect for condition when examining split times. Post hoc comparisons revealed that as BWA increased, sprint times decreased up to 30% BWA for distances up to 15 yd. These results demonstrate that 30% of BWA with elastic cords appears optimal in decreasing sprint times in collegiate women soccer players for distances up to 15 yd.