Kirk L. English

Protecting muscle mass and function in older adults during bed rest

Purpose of reviewTo highlight the losses in muscle mass, strength, power, and functional capacity incurred in older adults during bed rest-mediated inactivity and to provide practical recommendations for both the prevention and rehabilitation of these losses. Recent findingsIn addition to sarcopenic muscle loss, older adults lose lean tissue more rapidly than the young during prolonged periods of physical inactivity. Amino acid or protein supplementation has the potential to maintain muscle protein synthesis and may reduce inactivity-induced muscle loss, but should ideally be part of an integrated countermeasure regimen consisting of nutrition, exercise, and, when appropriate, pharmacologic interventions. SummaryIn accordance with recent mechanistic advances, we recommend an applied, broad-based two-phase approach to limit inactivity-mediated losses of muscle mass and function in older adults: (i) Lifestyle: consume a moderate amount (25–30 g) of high-quality protein with each meal and incorporate habitual exercise in close temporal proximity to protein-containing meals; (ii) Crises: react aggressively to combat the accelerated loss of muscle mass and function during acute catabolic crises and periods of reduced physical activity. As a base strategy, this should include nutritional support such as targeted protein or amino acid supplementation and integrated physical therapy.

Dietary Protein Distribution Positively Influences 24-h Muscle Protein Synthesis in Healthy Adults

The RDA for protein describes the quantity that should be consumed daily to meet population needs and to prevent deficiency. Protein consumption in many countries exceeds the RDA; however, intake is often skewed toward the evening meal, whereas breakfast is typically carbohydrate rich and low in protein. We examined the effects of protein distribution on 24-h skeletal muscle protein synthesis in healthy adult men and women (n = 8; age: 36.9 ± 3.1 y; BMI: 25.7 ± 0.8 kg/m2). By using a 7-d crossover feeding design with a 30-d washout period, we measured changes in muscle protein synthesis in response to isoenergetic and isonitrogenous diets with protein at breakfast, lunch, and dinner distributed evenly (EVEN; 31.5 ± 1.3, 29.9 ± 1.6, and 32.7 ± 1.6 g protein, respectively) or skewed (SKEW; 10.7 ± 0.8, 16.0 ± 0.5, and 63.4 ± 3.7 g protein, respectively). Over 24-h periods on days 1 and 7, venous blood samples and vastus lateralis muscle biopsy samples were obtained during primed (2.0 μmol/kg) constant infusion [0.06 μmol/(kg⋅min)] of l-[ring-13C6]phenylalanine. The 24-h mixed muscle protein fractional synthesis rate was 25% higher in the EVEN (0.075 ± 0.006%/h) vs. the SKEW (0.056 ± 0.006%/h) protein distribution groups (P = 0.003). This pattern was maintained after 7 d of habituation to each diet (EVEN vs. SKEW: 0.077 ± 0.006 vs. 0.056 ± 0.006%/h; P = 0.001). The consumption of a moderate amount of protein at each meal stimulated 24-h muscle protein synthesis more effectively than skewing protein intake toward the evening meal.

Musculoskeletal adaptations to training with the advanced resistive exercise device.

UNLABELLED Resistance exercise has been used as a means to prevent the musculoskeletal losses associated with spaceflight. Therefore, the National Aeronautics and Space Administration designed the Advanced Resistive Exercise Device (ARED) to replace the initial device flown on the International Space Station. The ARED uses vacuum cylinders and inertial flywheels to simulate, in the absence of gravity, the constant mass and inertia, respectively, of free weight (FW) exercise. PURPOSE To compare the musculoskeletal effects of resistance exercise training using the ARED with the effects of training with FW. METHODS Previously untrained, ambulatory subjects exercised using one of two modalities: FW (6 men and 3 women) or ARED (8 men and 3 women). Subjects performed squat, heel raise, and dead lift exercises 3 d·wk(-1) for 16 wk. Squat, heel raise, and dead lift strength (one-repetition maximum; using FW and ARED), bone mineral density (via dual-energy x-ray absorptiometry), and vertical jump were assessed before, during, and after training. Muscle mass (via magnetic resonance imaging) and bone morphology (via quantitative computed tomography) were measured before and after training. Bone biomarkers and circulating hormones were measured before training and after 4, 8, and 16 wk. RESULTS Muscle strength, muscle volume, vertical jump height, and lumbar spine bone mineral density (via dual-energy x-ray absorptiometry and quantitative computed tomography) significantly increased (P ≤ 0.05) in both groups. There were no significant differences between groups in any of the dependent variables at any time. CONCLUSIONS After 16 wk of training, ARED exercise resulted in musculoskeletal effects that were not significantly different from the effects of training with FW. Because FW training mitigates bed rest-induced deconditioning, the ARED may be an effective countermeasure for spaceflight-induced deconditioning and should be validated during spaceflight.

Leucine partially protects muscle mass and function during bed rest in middle-aged adults

BACKGROUND Physical inactivity triggers a rapid loss of muscle mass and function in older adults. Middle-aged adults show few phenotypic signs of aging yet may be more susceptible to inactivity than younger adults. OBJECTIVE The aim was to determine whether leucine, a stimulator of translation initiation and skeletal muscle protein synthesis (MPS), can protect skeletal muscle health during bed rest. DESIGN We used a randomized, double-blind, placebo-controlled trial to assess changes in skeletal MPS, cellular signaling, body composition, and skeletal muscle function in middle-aged adults (n = 19; age ± SEM: 52 ± 1 y) in response to leucine supplementation (LEU group: 0.06 g ∙ kg(-1) ∙ meal(-1)) or an alanine control (CON group) during 14 d of bed rest. RESULTS Bed rest decreased postabsorptive MPS by 30% ± 9% (CON group) and by 10% ± 10% (LEU group) (main effect for time, P < 0.05), but no differences between groups with respect to pre-post changes (group × time interactions) were detected for MPS or cell signaling. Leucine protected knee extensor peak torque (CON compared with LEU group: -15% ± 2% and -7% ± 3%; group × time interaction, P < 0.05) and endurance (CON compared with LEU: -14% ± 3% and -2% ± 4%; group × time interaction, P < 0.05), prevented an increase in body fat percentage (group × time interaction, P < 0.05), and reduced whole-body lean mass loss after 7 d (CON compared with LEU: -1.5 ± 0.3 and -0.8 ± 0.3 kg; group × time interaction, P < 0.05) but not 14 d (CON compared with LEU: -1.5 ± 0.3 and -1.0 ± 0.3 kg) of bed rest. Leucine also maintained muscle quality (peak torque/kg leg lean mass) after 14 d of bed-rest inactivity (CON compared with LEU: -9% ± 2% and +1% ± 3%; group × time interaction, P < 0.05). CONCLUSIONS Bed rest has a profoundly negative effect on muscle metabolism, mass, and function in middle-aged adults. Leucine supplementation may partially protect muscle health during relatively brief periods of physical inactivity. This trial was registered at clinicaltrials.gov as NCT00968344.

Fourteen days of bed rest induces a decline in satellite cell content and robust atrophy of skeletal muscle fibers in middle-aged adults

Bed rest, a ground-based spaceflight analog, induces robust atrophy of skeletal muscle, an effect that is exacerbated with increasing age. We examined the effect of 14 days of bed rest on skeletal muscle satellite cell content and fiber type atrophy in middle-aged adults, an understudied age demographic with few overt signs of muscle aging that is representative of astronauts who perform long-duration spaceflight. Muscle biopsies were obtained from the vastus lateralis of healthy middle-aged adults [n= 7 (4 male, 3 female); age: 51 ± 1 yr] before (Pre-BR) and after (Post-BR) 14 days of bed rest. Immunohistochemical analyses were used to quantify myosin heavy chain (MyHC) isoform expression, cross-sectional area (CSA), satellite cell and myonuclear content, and capillary density. Peak oxygen consumption, knee extensor strength, and body composition were also measured Pre-BR and Post-BR. Post-BR MyHC type 2a fiber percentage was reduced, and mean CSA decreased in all fiber types (-24 ± 5%;P< 0.05). Satellite cell content was also reduced Post-BR (-39 ± 9%;P< 0.05), and the change in satellite cell content was significantly correlated with the change in mean fiber CSA (r(2)= 0.60;P< 0.05). A decline in capillary density was observed Post-BR (-23 ± 6%;P< 0.05), and Post-BR capillary content was significantly associated with Post-BR peak aerobic capacity (r(2)= 0.59;P< 0.05). A subtle decline in myonuclear content occurred during bed rest (-5 ± 1%;P< 0.05). The rapid maladaptation of skeletal muscle to 14 days of mechanical unloading in middle-aged adults emphasizes the need for robust countermeasures to preserve muscle function in astronauts.

Nullius in verba: a call for the incorporation of evidence-based practice into the discipline of exercise science.

Evidence-based practice (EBP) is a concept that was popularized in the early 1990s by several physicians who recognized that medical practice should be based on the best and most current available evidence. Although this concept seems self-evident, much of medical practice was based on outdated textbooks and oral tradition passed down in medical school. Currently, exercise science is in a similar situation. Due to a lack of regulation within the exercise community, the discipline of exercise science is particularly prone to bias and misinformation, as evidenced by the plethora of available programmes with efficacy supported by anecdote alone. In this review, we provide a description of the five steps in EBP: (i) develop a question; (ii) find evidence; (iii) evaluate the evidence; (iv) incorporate evidence into practice; and (v) re-evaluate the evidence. Although objections have been raised to the EBP process, we believe that its incorporation into exercise science will improve the credibility of our discipline and will keep exercise practitioners and academics on the cutting edge of the most current research findings.

Isokinetic Strength Changes Following Long-Duration Spaceflight on the ISS.

INTRODUCTION Long-duration spaceflight results in a loss of muscle strength that poses both operational and medical risks, particularly during emergency egress, upon return to Earth, and during future extraterrestrial exploration. Isokinetic testing of the knee, ankle, and trunk quantifies movement-specific strength changes following spaceflight and offers insight into the effectiveness of in-flight exercise countermeasures. METHODS We retrospectively evaluated changes in isokinetic strength for 37 ISS crewmembers (Expeditions 1-25) following 163 ± 38 d (mean ± SD) of spaceflight. Gender, in-flight resistance exercise hardware, and preflight strength were examined as potential modifiers of spaceflight-induced strength changes. RESULTS Mean isokinetic strength declined 8-17% following spaceflight. One month after return to Earth, strength had improved, but small deficits of 1-9% persisted. Spaceflight-induced strength losses were not different between men and women. Mean strength losses were as much as 7% less in crewmembers who flew after the Advanced Resistive Exercise Device (ARED) replaced the interim Resistive Exercise Device (iRED) as the primary in-flight resistance exercise hardware, although these differences were not statistically significant. Absolute and relative preflight strength were moderately correlated (r = -0.47 and -0.54, respectively) with postflight strength changes. DISCUSSION In-flight resistance exercise did not prevent decreased isokinetic strength after long-duration spaceflight. However, continued utilization of ARED, a more robust resistance exercise device providing higher loads than iRED, may result in greater benefits as exercise prescriptions are optimized. With reconditioning upon return to Earth, strength is largely recovered within 30 d.

The Astronaut-Athlete: Optimizing Human Performance in Space

Abstract Hackney, KJ, Scott, JM, Hanson, AM, English, KL, Downs, ME, and Ploutz-Snyder, LL. The astronaut-athlete: optimizing human performance in space. J Strength Cond Res 29(12): 3531–3545, 2015—It is well known that long-duration spaceflight results in deconditioning of neuromuscular and cardiovascular systems, leading to a decline in physical fitness. On reloading in gravitational environments, reduced fitness (e.g., aerobic capacity, muscular strength, and endurance) could impair human performance, mission success, and crew safety. The level of fitness necessary for the performance of routine and off-nominal terrestrial mission tasks remains an unanswered and pressing question for scientists and flight physicians. To mitigate fitness loss during spaceflight, resistance and aerobic exercise are the most effective countermeasure available to astronauts. Currently, 2.5 h·d−1, 6–7 d·wk−1 is allotted in crew schedules for exercise to be performed on highly specialized hardware on the International Space Station (ISS). Exercise hardware provides up to 273 kg of loading capability for resistance exercise, treadmill speeds between 0.44 and 5.5 m·s−1, and cycle workloads from 0 and 350 W. Compared to ISS missions, future missions beyond low earth orbit will likely be accomplished with less vehicle volume and power allocated for exercise hardware. Concomitant factors, such as diet and age, will also affect the physiologic responses to exercise training (e.g., anabolic resistance) in the space environment. Research into the potential optimization of exercise countermeasures through use of dietary supplementation, and pharmaceuticals may assist in reducing physiological deconditioning during long-duration spaceflight and have the potential to enhance performance of occupationally related astronaut tasks (e.g., extravehicular activity, habitat construction, equipment repairs, planetary exploration, and emergency response).

Protein and Essential Amino Acids to Protect Musculoskeletal Health during Spaceflight: Evidence of a Paradox?

Long-duration spaceflight results in muscle atrophy and a loss of bone mineral density. In skeletal muscle tissue, acute exercise and protein (e.g., essential amino acids) stimulate anabolic pathways (e.g., muscle protein synthesis) both independently and synergistically to maintain neutral or positive net muscle protein balance. Protein intake in space is recommended to be 12%–15% of total energy intake (≤1.4 g∙kg−1∙day−1) and spaceflight is associated with reduced energy intake (~20%), which enhances muscle catabolism. Increasing protein intake to 1.5–2.0 g∙kg−1∙day−1 may be beneficial for skeletal muscle tissue and could be accomplished with essential amino acid supplementation. However, increased consumption of sulfur-containing amino acids is associated with increased bone resorption, which creates a dilemma for musculoskeletal countermeasures, whereby optimizing skeletal muscle parameters via essential amino acid supplementation may worsen bone outcomes. To protect both muscle and bone health, future unloading studies should evaluate increased protein intake via non-sulfur containing essential amino acids or leucine in combination with exercise countermeasures and the concomitant influence of reduced energy intake.

What is “Evidence-Based” Strength and Conditioning?

SUMMARY THE TERM “EVIDENCE-BASED” HAS BEGUN APPEARING IN THE FIELD OF STRENGTH AND CONDITIONING. HOWEVER, THIS TERM HAS YET TO BE FORMALLY INTRODUCED TO THE STRENGTH AND CONDITIONING COMMUNITY. FAR FROM BEING A MERE BUZZWORD, EVIDENCE-BASED PRACTICE (EBP) IS A DEFINED PROCESS BY WHICH PRACTITIONERS (IN THIS INSTANCE, STRENGTH AND CONDITIONING PROFESSIONALS) INCORPORATE THE “BEST” AVAILABLE EVIDENCE INTO THE EVERYDAY TRAINING OF ATHLETES AND CLIENTS. INCORPORATION OF EBP INTO THE STRENGTH AND CONDITIONING FIELD WILL IMPROVE THE QUALITY OF TRAINING PROGRAMS PROVIDED FOR ATHLETES AND CLIENTS AND INCREASE THE PRESTIGE AND STANDING OF OUR DISCIPLINE.