Protein Requirements Are Increased in Endurance-Trained Athletes but Similar between Females and Males during Postexercise Recovery.

PURPOSE: This study aimed to determine the daily protein requirements of female and male endurance athletes in a home-based setting using noninvasive stable isotope methodology (i.e., indicator amino acid oxidation). METHODS: Eight males (30 ± 3 yr; 78.6 ± 10.5 kg; 75.6 ± 7.5 mL·kgFFM-1·min-1; mean ± SD) and seven females (30 ± 4 yr; 57.7 ± 5.0 kg; 77.5 ± 7.1 mL·kgFFM-1·min-1) during the midluteal phase were studied. After 2 d of controlled diet (1.4 gprotein·kg-1·d-1) and training (10 and 5 km run·d-1, respectively), participants completed a 20-km run before an at-home indicator amino acid oxidation trial testing a suboptimal, a moderate, and an excess (i.e., 0.2, 1.2, and 2.0 g·kg-1·d-1, respectively) protein intake. Protein was consumed as a crystalline amino acid mixture containing [1-13C]phenylalanine to examine whole-body phenylalanine flux and phenylalanine oxidation (PheOx; the reciprocal of whole-body protein synthesis) through breath and urine sample collection. A modified biphasic linear regression determined the breakpoint in PheOx for each participant to generate an estimated average intake that would maximize whole-body protein synthesis for each sex. RESULTS: PheOx was different (P < 0.01) between all protein intakes with no effect of sex (P = 0.63). Using a modified three-point curve resulted in a breakpoint that was not different (P = 0.94) between males and females (1.60 and 1.61 g·kg-1·d-1, respectively). The recommended intake (i.e., upper 95% confidence interval) was estimated to be 1.81 and 1.89 g·kg-1·d-1 for males and females, respectively. CONCLUSIONS: Our findings indicate that endurance athletes consuming a daily protein intake toward the upper end of current consensus recommendations (~1.85 g·kg-1·d-1) will maximize whole-body protein synthesis during postexercise recovery regardless of sex.

Ankle flexor torque, size and density are differential determinants of distal tibia trabecular plate-rod morphometry and bone strength: The Ankle Quality Study.

HYPOTHESIS: Greater peak torque and higher myotendinous density at the ankle are associated with a more plate-like architecture at the distal tibia. METHODS: In this cross-sectional study, women and men ≥ 50 years old with no metal implants, reconstructive surgery, muscular dystrophies, or tendinopathies in any leg were recruited by convenience. Isometric ankle dorsi-plantar flexion and inversion-eversion peak torques were measured using dynamometry. HR-pQCT distal tibia scans were completed. Both assessments were completed on the same day on the non-dominant leg. Integral and trabecular vBMD were derived from standard analyses, failure load (FL) was obtained from finite element analysis, plate-specific parameters were computed from individual trabecula segmentation (ITS) analysis, myotendinous density (MyD) and volume fraction (MyV/TV) were computed from soft tissue analysis. pQCT scans of the 66 % mid-leg were performed (500 µm at 15 mm/s) to obtain muscle density (MD) and muscle cross-sectional area (MCSA). STATISTICAL ANALYSIS: General linear models estimated how ankle muscle group torque and muscle size and density differentially related, both separately and together, to whole-bone properties (integral vBMD, FL) and trabecular morphometry (ITS plate parameters). Models were adjusted for age, sex, BMI, use of glucocorticoids, current osteoarthritis, and participation in moderate to vigorous recreational or sport activities. RESULTS: Among 105 participants (77 % female, mean age: 63 (10) years, BMI: 25.8 (5.4) kg/m2, 25 % with OA, 17 % fracture history, 42 % falls history), all torque measures, particularly ankle dorsiflexion and eversion, were correlates of plate-plate/rod junction density and failure load. However, muscle size and density measures were further associated with vBMD. The effect of greater ankle flexor-extensor torque on more connected bone was stronger when MyD was higher (interaction p < 0.001). CONCLUSION: Strength of muscles around the ankle are correlates of plate-like trabeculae at the distal tibia, while leaner muscle and myotendinous tissues facilitates better quality bone for stronger ankle muscle torque.

Essential Amino Acid Ingestion Facilitates Leucine Retention and Attenuates Myofibrillar Protein Breakdown following Bodyweight Resistance Exercise in Young Adults in a Home-Based Setting.

Home-based resistance exercise (RE) has become increasingly prevalent, but its effects on protein metabolism are understudied. We tested the effect of an essential amino acid formulation (EAA+: 9 g EAAs, 3 g leucine) and branched-chain amino acids (BCAAs: 6 g BCAAs, 3 g leucine), relative to a carbohydrate (CHO) placebo, on exogenous leucine retention and myofibrillar protein breakdown following dynamic bodyweight RE in a home-based setting. Twelve recreationally active adults (nine male, three female) participated in a double-blind, placebo-controlled, crossover study with four trial conditions: (i) RE and EAA+ (EX-EAA+); (ii) RE and BCAAs (EX-BCAA); (iii) RE and CHO placebo (EX-CHO); and (iv) rest and CHO placebo (REST-CHO). Total exogenous leucine oxidation and retention (estimates of whole-body anabolism) and urinary 3-methylhistidine:creatinine ratio (3MH:Cr; estimate of muscle catabolism) were assessed over 5 h post-supplement. Total exogenous leucine oxidation and retention in EX-EAA+ and EX-BCAA did not significantly differ (p = 0.116) but were greater than EX-CHO (p < 0.01). There was a main effect of condition on urinary 3MH:Cr (p = 0.034), with post hoc analysis revealing a trend (p = 0.096) for reduced urinary 3MH:Cr with EX-EAA+ (32%) compared to EX-CHO. By direct comparison, urinary 3MH:Cr was significantly lower (23%) in EX-EAA+ than EX-BCAA (p = 0.026). In summary, the ingestion of EAA+ or BCAA provided leucine that was ~60% retained for protein synthesis following home-based bodyweight RE, but EAA+ most effectively attenuated myofibrillar protein breakdown.

Validation of High-Resolution peripheral Quantitative Computed Tomography-Derived Achilles Tendon Properties Against Diagnostic Ultrasound.

OBJECTIVES: 1) To assess the precision of high resolution peripheral quantitative computed tomography (HR-pQCT)-derived Achilles tendon (AT) cross-sectional area (HR AT-CSA) and density, and 2) to validate HR AT-CSA against ultrasound-derived AT-CSA (US AT-CSA). METHODS: Women and men (≥50 years) had HR-pQCT (0.082mm isotropic) and US scans (B-mode) performed on the non-dominant ankle. Linear regression and Bland-Altman analyses assessed systematic differences between HR-pQCT and US-derived AT-CSA. Precision measured by % root mean square coefficients of variation (%RMSCV) and agreement by type 2,1 intraclass correlation coefficients (ICC2,1), were determined for test-retest US AT-CSA scans, and analysis-reanalysis of 30 HR-pQCT and US images. RESULTS: Among 44 participants, HR and US AT-CSA were strongly correlated (R2=0.84, p<0.01, B=1.05[0.90-1.19]), with no differences between modalities (p=0.37). Bland-Altman analysis revealed minimal systematic bias (-0.7mm2[-10.7-9.3]; 1.3%) between HR-pQCT and US-derived AT-CSA with smaller AT-CSA values showing larger inter-modality differences (R2=0.098, B=-0.137 [-0.268--0.008], p=0.039). US AT-CSA demonstrated excellent test-retest precision (ICC2,1=0.998, %RMSCV=1.04%). Analysis-reanalysis of HR-pQCT AT-density and both HR-pQCT and US AT-CSA displayed ICC2,1 above 0.95 and %RMSCV within 3%. CONCLUSION: HR-pQCT can examine AT-morphometry with acceptable analytical precision. Future studies should explore these metrics' association with functional outcomes and ankle-bone structural and mechanical properties.

Challenges of rapamycin repurposing as a potential therapeutic candidate for COVID-19: implications for skeletal muscle metabolic health in older persons.

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged as the causative agent of the ongoing coronavirus disease 2019 (COVID-19) pandemic that has spread worldwide, resulting in over 6 million deaths as of March 2022. Older people have been disproportionately affected by the disease, as they have a greater risk of hospitalization, are more vulnerable to severe infection, and have higher mortality than younger patients. Although effective vaccines have been rapidly developed and administered globally, several clinical trials are ongoing to repurpose existing drugs to combat severe infection. One such drug, rapamycin, is currently under study for this purpose, given its immunosuppressant effects that are mediated by its inhibition of the mechanistic target of rapamycin (mTOR), a master regulator of cell growth. Consistent with this premise, acute rapamycin administration in young healthy humans blocks or attenuates mTOR and its downstream effectors, leading to the inhibition of muscle protein synthesis (MPS). Skeletal muscle mass declines when MPS is chronically lower than muscle protein breakdown. This is consequential for older people who are more susceptible to anabolic resistance (i.e., the blunting of MPS) due to reduced activity, sedentariness, or bed rest such as that associated with COVID-19 hospitalization, and who have also demonstrated a delayed or blunted ability to regain inactivity-induced muscle loss. The lack of studies investigating rapamycin administration on skeletal muscle in older people, and the emergence of effective antiviral medications against severe infection, may indicate the reduced relevance of drug repurposing for present or future pandemics.

Low-Carbohydrate Training Increases Protein Requirements of Endurance Athletes.

INTRODUCTION: Training with low-carbohydrate (CHO) availability enhances markers of aerobic adaptation and has become popular to periodize throughout an endurance-training program. However, exercise-induced amino acid oxidation is increased with low muscle glycogen, which may limit substrate availability for postexercise protein synthesis. We aimed to determine the impact of training with low-CHO availability on estimates of dietary protein requirements. METHODS: Eight endurance-trained males (27 ± 4 yr, 75 ± 10 kg, 67 ± 10 mL·kg body mass·min) completed two trials matched for energy and macronutrient composition but with differing CHO periodization. In the low-CHO availability trial (LOW), participants consumed 7.8 g CHO·kg before evening high-intensity interval training (10 × 5 min at 10-km race pace, 1 min rest) and subsequently withheld CHO postexercise (0.2 g·kg). In the high-CHO availability trial (HIGH), participants consumed 3 g CHO·kg during the day before high-intensity interval training, and consumed 5 g CHO·kg that evening to promote muscle glycogen resynthesis. A 10-km run (~80% HRmax) was performed the following morning, fasted (LOW) or 1 h after consuming 1.2 g CHO·kg (HIGH). Whole-body phenylalanine flux and oxidation were determined over 8 h of recovery via oral [C]phenylalanine ingestion, according to standard indicator amino acid oxidation methodology, while consuming sufficient energy, 7.8 g CHO·kg·d, and suboptimal protein (0.93 g·kg·d). RESULTS: Fat oxidation (indirect calorimetry) during the 10-km run was higher in LOW compared with HIGH (0.99 ± 0.35 g·min vs 0.60 ± 0.26 g·min, P < 0.05). phenylalanine flux during recovery was not different between trials (P > 0.05) whereas phenylalanine oxidation (reciprocal of protein synthesis) was higher in LOW compared with HIGH (8.8 ± 2.7 µmol·kg·h vs 7.9 ± 2.4 µmol·kg·h, P < 0.05), suggesting a greater amino acid requirement to support rates of whole-body protein synthesis. CONCLUSIONS: Our findings suggest that performing endurance exercise with low-CHO availability increases protein requirements of endurance athletes.