Clinical practice guideline for the management of paediatric Charcot-Marie-Tooth disease

BACKGROUND AND OBJECTIVES

Charcot-Marie-Tooth disease (CMT) is the most common inherited neuropathy and often presents during childhood. Guidelines for the optimal management of common problems experienced by individuals with CMT do not exist, for either children or adults. We formed the Paediatric CMT Best Practice Guidelines Consortium to develop evidence and consensus-based recommendations for the clinical management of children and adolescents with CMT, with the primary objective of promoting optimal, standardised care globally.

METHODS

Development of this clinical practice guideline involved a series of systematic reviews covering 10 clinical questions, modified Delphi methodology involving an international panel of clinicians to generate consensus where evidence did not exist, and application of the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach to evaluate the body of literature and formulate recommendations.

RESULTS

The final guideline includes three evidence-based and 31 consensus-based recommendations. They encompass the management of muscle weakness, balance and mobility impairment, sensory symptoms, muscle cramps, impaired upper limb function, respiratory impairment, maintenance of joint range of motion and non-surgical management of joint deformity. Consensus was not achieved in some management areas, reflecting differences in practice between clinicians and healthcare settings, and highlighting the need for further research.

CONCLUSIONS

This clinical practice guideline provides practical and implementable guidance on the management of common clinical problems experienced by children with CMT and advocates for improved access to multidisciplinary care. Successful dissemination and implementation of these recommendations will be critical in ensuring their application across multiple healthcare settings.

De novo pathogenic variant in SETX causes a rapidly progressive neurodegenerative disorder of early childhood-onset with severe axonal polyneuropathy

Pathogenic variants in SETX cause two distinct neurological diseases, a loss-of-function recessive disorder, ataxia with oculomotor apraxia type 2 (AOA2), and a dominant gain-of-function motor neuron disorder, amyotrophic lateral sclerosis type 4 (ALS4). We identified two unrelated patients with the same de novo c.23C > T (p.Thr8Met) variant in SETX presenting with an early-onset, severe polyneuropathy. As rare private gene variation is often difficult to link to genetic neurological disease by DNA sequence alone, we used transcriptional network analysis to functionally validate these patients with severe de novo SETX-related neurodegenerative disorder. Weighted gene co-expression network analysis (WGCNA) was used to identify disease-associated modules from two different ALS4 mouse models and compared to confirmed ALS4 patient data to derive an ALS4-specific transcriptional signature. WGCNA of whole blood RNA-sequencing data from a patient with the p.Thr8Met SETX variant was compared to ALS4 and control patients to determine if this signature could be used to identify affected patients. WGCNA identified overlapping disease-associated modules in ALS4 mouse model data and ALS4 patient data. Mouse ALS4 disease-associated modules were not associated with AOA2 disease modules, confirming distinct disease-specific signatures. The expression profile of a patient carrying the c.23C > T (p.Thr8Met) variant was significantly associated with the human and mouse ALS4 signature, confirming the relationship between this SETX variant and disease. The similar clinical presentations of the two unrelated patients with the same de novo p.Thr8Met variant and the functional data provide strong evidence that the p.Thr8Met variant is pathogenic. The distinct phenotype expands the clinical spectrum of SETX-related disorders.

Arm Numbness at 45 Degrees Abduction: A Case Report of Thoracic Outlet Syndrome After Brachial Neuritis

Objective

To describe a case of nerve kinking correlating with surgical findings in neurogenic thoracic outlet syndrome in a patient with history of brachial neuritis. Thoracic outlet syndrome and brachial neuritis are briefly reviewed.

Case report

A 32-year-old woman with a history of bilateral brachial neuritis presented with paraesthesias in her hand when abducting her shoulder to 45° or higher. A kink in the superior trunk of the brachial plexus, as well as asymmetrically narrowed costoclavicular space, was found on magnetic resonance imaging with the shoulder abducted. Conservative measures failed, leading to partial anterior scalenectomy and neurolysis, which led to improvement in her symptoms.

Conclusion

Anatomical variations in combination with biomechanical changes after brachial neuritis can be associated with neurogenic thoracic outlet syndrome.

Potato Protein Isolate Stimulates Muscle Protein Synthesis at Rest and with Resistance Exercise in Young Women

Skeletal muscle myofibrillar protein synthesis (MPS) increases in response to protein feeding and to resistance exercise (RE), where each stimuli acts synergistically when combined. The efficacy of plant proteins such as potato protein (PP) isolate to stimulate MPS is unknown. We aimed to determine the effects of PP ingestion on daily MPS with and without RE in healthy women. In a single blind, parallel-group design, 24 young women (21 ± 3 years, n = 12/group) consumed a weight-maintaining baseline diet containing 0.8 g/kg/d of protein before being randomized to consume either 25 g of PP twice daily (1.6 g/kg/d total protein) or a control diet (CON) (0.8 g/kg/d total protein) for 2 wks. Unilateral RE (~30% of maximal strength to failure) was performed thrice weekly with the opposite limb serving as a non-exercised control (Rest). MPS was measured by deuterated water ingestion at baseline, following supplementation (Rest), and following supplementation + RE (Exercise). Ingestion of PP stimulated MPS by 0.14 ± 0.09 %/d at Rest, and by 0.32 ± 0.14 %/d in the Exercise limb. MPS was significantly elevated by 0.20 ± 0.11 %/d in the Exercise limb in CON (p = 0.008). Consuming PP to increase protein intake to levels twice the recommended dietary allowance for protein augmented rates of MPS. Performance of RE stimulated MPS regardless of protein intake. PP is a high-quality, plant-based protein supplement that augments MPS at rest and following RE in healthy young women.

Whey protein but not collagen peptides stimulate acute and longer-term muscle protein synthesis with and without resistance exercise in healthy older women: a randomized controlled trial

BACKGROUND

Aging appears to attenuate the response of skeletal muscle protein synthesis (MPS) to anabolic stimuli such as protein ingestion (and the ensuing hyperaminoacidemia) and resistance exercise (RE).

OBJECTIVES

The purpose of this study was to determine the effects of protein quality on feeding- and feeding plus RE-induced increases of acute and longer-term MPS after ingestion of whey protein (WP) and collagen protein (CP).

METHODS

In a double-blind parallel-group design, 22 healthy older women (mean ± SD age: 69 ± 3 y, n = 11/group) were randomly assigned to consume a 30-g supplement of either WP or CP twice daily for 6 d. Participants performed unilateral RE twice during the 6-d period to determine the acute (via [13C6]-phenylalanine infusion) and longer-term (ingestion of deuterated water) MPS responses, the primary outcome measures.

RESULTS

Acutely, WP increased MPS by a mean ± SD 0.017 ± 0.008%/h in the feeding-only leg (Rest) and 0.032 ± 0.012%/h in the feeding plus exercise leg (Exercise) (both P < 0.01), whereas CP increased MPS only in Exercise (0.012 ± 0.013%/h) (P < 0.01) and MPS was greater in WP than CP in both the Rest and Exercise legs (P = 0.02). Longer-term MPS increased by 0.063 ± 0.059%/d in Rest and 0.173 ± 0.104%/d in Exercise (P < 0.0001) with WP; however, MPS was not significantly elevated above baseline in Rest (0.011 ± 0.042%/d) or Exercise (0.020 ± 0.034%/d) with CP. Longer-term MPS was greater in WP than in CP in both Rest and Exercise (P < 0.001).

CONCLUSIONS

Supplementation with WP elicited greater increases in both acute and longer-term MPS than CP supplementation, which is suggestive that WP is a more effective supplement to support skeletal muscle retention in older women than CP.This trial was registered at clinicaltrials.gov as NCT03281434.

Dose Adjustment of Subcutaneous IgG in Chronic Inflammatory Demyelinating Polyneuropathy

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is an immune-mediated neuropathy that is characterized by a slowly progressive sensory and motor involvement lasting at least 2 months. We present a CIDP patient on subcutaneous Ig (SCIg). Upon fine-tuning his dose from 24 to 28 g/week, this showed a dramatic improvement in both hand grip (13-25%) and dorsiflexion (73-278%). Follow-up nerve conduction studies also demonstrated significant improvements in latencies, motor amplitudes, and conduction velocities. Ongoing surveillance of CIDP patients receiving SCIg therapy is therefore necessary to ensure therapeutic optimization.

Lactalbumin, Not Collagen, Augments Muscle Protein Synthesis with Aerobic Exercise

INTRODUCTION

Protein ingestion and the ensuing hyperaminoacidemia stimulates skeletal muscle protein synthesis in the postexercise period. This response facilitates muscle remodeling, which is important during intensified training. The aim of this study was to determine whether supplementation with α-lactalbumin (LA), with high leucine and tryptophan contents, would improve responses to short periods of intensified aerobic training compared with supplementation with an isonitrogenous quantity of collagen peptides (CP).

METHODS

Endurance-trained participants (5 male, 6 female, 24 ± 4 yr, V˙O2 = 53.2 ± 9.1 mL·kg·min, peak power output = 320 ± 48 W; means ± SD) consumed a controlled diet (1.0 g·kg·d protein) and refrained from habitual training for 11 d while taking part in this double-blind randomized, crossover trial. The two intervention phases, which consisted of brief intensified training (4 × 4-min cycling intervals at 70% of peak power output on 3 consecutive days) combined with the ingestion of LA or CP supplements after exercise (20 g) and before sleep (40 g), were separated by 4 d of washout without protein supplementation (i.e., the control phase). In response to each phase, myofibrillar (MyoPS), sarcoplasmic protein synthesis (SarcPS) rates (via H2O ingestion) and parameters of sleep quality were measured.

RESULTS

LA ingestion increased plasma leucine (P < 0.001) and tryptophan concentrations (P < 0.001) relative to CP. Intensified training increased MyoPS and SarcPS above the washout phase in LA- and CP-supplemented phases (P < 0.01), with increases being 13% ± 5% and 5% ± 7% greater with LA than CP for MyoPS (P < 0.01) and SarcPS, respectively (P < 0.01).

CONCLUSIONS

Despite an isonitrogenous diet, protein synthesis was enhanced to a greater extent when trained participants consumed LA compared with CP during intensified aerobic training, suggesting that protein quality is an important consideration for endurance-trained athletes aiming to augment adaption to exercise training.

Failed Recovery of Glycemic Control and Myofibrillar Protein Synthesis With 2 wk of Physical Inactivity in Overweight, Prediabetic Older Adults

Background

Physical inactivity impairs insulin sensitivity, which is exacerbated with aging. We examined the impact of 2 wk of acute inactivity and recovery on glycemic control, and integrated rates of muscle protein synthesis in older men and women.

Methods

Twenty-two overweight, prediabetic older adults (12 men, 10 women, 69 ± 4 y) undertook 7 d of habitual activity (baseline; BL), step reduction (SR; <1,000 steps.d-1 for 14 d), followed by 14 d of recovery (RC). An oral glucose tolerance test was used to assess glycemic control and deuterated water ingestion to measure integrated rates of muscle protein synthesis.

Results

Daily step count was reduced (all p < .05) from BL at SR (7362 ± 3294 to 991 ± 97) and returned to BL levels at RC (7117 ± 3819). Homeostasis model assessment-insulin resistance increased from BL to SR and Matsuda insulin sensitivity index decreased and did not return to BL in RC. Glucose and insulin area under the curve were elevated from BL to SR and did not recover in RC. Integrated muscle protein synthesis was reduced during SR and did not return to BL in RC.

Conclusions

Our findings demonstrate that 2 wk of SR leads to lowered rates of muscle protein synthesis and a worsening of glycemic control that unlike younger adults is not recovered during return to normal activity in overweight, prediabetic elderly humans.

Clinical Trials Registration

ClinicalTrials.gov identifier: NCT03039556.

A randomized controlled trial of the impact of protein supplementation on leg lean mass and integrated muscle protein synthesis during inactivity and energy restriction in older persons

Background

In older persons, muscle loss is accelerated during physical inactivity and hypoenergetic states, both of which are features of hospitalization. Protein supplementation may represent a strategy to offset the loss of muscle during inactivity, and enhance recovery on resumption of activity.

Objective

We aimed to determine if protein supplementation, with proteins of substantially different quality, would alleviate the loss of lean mass by augmenting muscle protein synthesis (MPS) while inactive during a hypoenergetic state.

Design

Participants (16 men, mean ± SD age: 69 ± 3 y; 15 women, mean ± SD age: 68 ± 4 y) consumed a diet containing 1.6 g protein · kg-1 · d-1, with 55% ± 9% of protein from foods and 45% ± 9% from supplements, namely, whey protein (WP) or collagen peptides (CP): 30 g each, consumed 2 times/d. Participants were in energy balance (EB) for 1 wk, then began a period of energy restriction (ER; -500 kcal/d) for 1 wk, followed by ER with step reduction (ER + SR; <750 steps/d) for 2 wk, before a return to habitual activity in recovery (RC) for 1 wk.

Results

There were significant reductions in leg lean mass (LLM) from EB to ER, and from ER to ER + SR in both groups (P < 0.001) with no differences between WP and CP or when comparing the change from phase to phase. During RC, LLM increased from ER + SR, but in the WP group only. Rates of integrated muscle protein synthesis decreased during ER and ER + SR in both groups (P < 0.01), but increased during RC only in the WP group (P = 0.05).

Conclusions

Protein supplementation did not confer a benefit in protecting LLM, but only supplemental WP augmented LLM and muscle protein synthesis during recovery from inactivity and a hypoenergetic state. This trial was registered at http://www.clinicaltrials.gov as NCT03285737.

Leucine, Not Total Protein, Content of a Supplement Is the Primary Determinant of Muscle Protein Anabolic Responses in Healthy Older Women

Background

Older adults show a blunted muscle protein synthesis (MPS) response to postprandial hyperaminoacidemia relative to younger adults. Evidence suggests that this anabolic resistance can be overcome by consuming greater quantities of leucine.

Objective

The purpose of this trial was to determine whether the addition of leucine to a smaller dose (10 g) of milk proteins would, when compared with a larger dose (25 g) of whey protein isolate (WPI), result in similar increases in acute (hourly) and integrated (daily) myofibrillar protein synthesis (myoPS).

Methods

Healthy older (mean ± SD age: 69 ± 1 y) women (n = 11/group) were randomly assigned with the use of a single-blind, parallel-group design to twice-daily consumption of either WPI [25 g WPI (3 g l-leucine)] or leucine (LEU; 10 g milk protein with 3 g total l-leucine) for 6 d. Participants performed unilateral resistance exercise to allow assessment of the impact of the supplement alone and with resistance exercise. We determined acute (13C6-phenylanine) and integrated [using deuterated water (D2O)] rates of myoPS in the fasting (acute), basal (integrated), nonexercised, and exercised states.

Results

Acute myoPS increased in both legs in response to LEU (fed: 45%; fed+exercise: 71%; P < 0.001) and WPI (fed: 29%; fed+exercise: 47%; P < 0.001) compared with fasting; the increase was greater with LEU than with WPI in the exercised leg (46%; P = 0.04) but not in the rested leg (P = 0.07). The acute myoPS response was greater in the exercised leg than in the rested leg for both WPI (63%) and LEU (58%) (P < 0.001). Integrated myoPS increased with WPI and LEU in the exercised leg (both 9%; P < 0.001) during supplementation, and with WPI (3%; P = 0.02) but not LEU (2%, P = 0.1) in the rested leg compared with the basal state.

Conclusions

A lower-protein (10 compared with 25 g/dose), leucine-matched beverage induced similar increases in acute and integrated myoPS in healthy older women. Lower-protein supplements with added leucine may represent an advantageous approach in older adults to maintain skeletal muscle anabolic sensitivity and attenuate muscle loss; however, further work is needed using longer-term interventions to substantiate these findings. This trial was registered at www.clinicaltrials.gov as NCT02282566.

Microvascular adaptations to resistance training are independent of load in resistance-trained young men

Resistance training promotes microvasculature expansion; however, it remains unknown how different resistance training programs contribute to angiogenesis. Thus, we recruited experienced resistance-trained participants and determined the effect of 12 wk of either high-repetition/low-load or low-repetition/high-load resistance training performed to volitional fatigue on muscle microvasculature. Twenty men performed either a high-repetition [20-25 repetitions, 30-50% of 1-repetition maximum (1RM); n = 10] or a low-repetition (8-12 repetitions, 75-90% of 1RM; n = 10) resistance training program. Muscle biopsies were taken before and after resistance training, and immunohistochemistry was used to assess fiber type (I and II)-specific microvascular variables. High-repetition/low-load and low-repetition/high-load groups were not different in any variable before resistance training. Both protocols resulted in an increase in capillarization. Specifically, after resistance training, the capillary-to-fiber ratio, capillary contacts, and capillary-to-fiber perimeter exchange index were elevated, and sharing factor was reduced. These data demonstrate that resistance training performed to volitional failure, using either high repetition/low load or low repetition/high load, induced similar microvascular adaptations in recreationally resistance-trained young men.

Protein leucine content is a determinant of shorter- and longer-term muscle protein synthetic responses at rest and following resistance exercise in healthy older women: a randomized, controlled trial

Background

Older women may not be consuming enough protein to maintain muscle mass. Augmentation of protein intake with leucine may enhance the muscle protein synthetic response in older women to aid in maintaining muscle mass.

Objective

We measured the acute (hourly) and integrated (daily) myofibrillar protein synthesis (myoPS) response to consumption of a high-quality mixed protein beverage compared with an isonitrogenous protein beverage with added leucine.

Design

In a parallel design, free-living, healthy older women (aged 65-75 y, n = 11/group) consumed a fixed, weight-maintaining diet with protein at 1.0 g · kg-1 · d-1 and were randomly assigned to twice-daily consumption of either 15 g milk protein beverage containing 4.2 g leucine (LEU) or 15 g mixed protein (milk and soy) beverage containing 1.3 g leucine (CON). Unilateral leg resistance exercise allowed a determination of acute ([13C6]-phenylalanine infusion, hourly rate) and integrated (deuterated water ingestion, daily rate) exercised and rested myoPS responses.

Results

Acute myoPS increased in response to feeding in the rested (CON: 13% ± 4%; LEU: 53% ± 5%) and exercised (CON: 30% ± 4%; LEU: 87% ± 7%) leg in both groups, but the increase was greater in LEU (P < 0.001). Integrated myoPS increased during the supplementation period in both legs (rested: 9% ±1%; exercised: 17% ± 2%; P < 0.001) in LEU, but in the exercised leg only (7% ± 2%; P < 0.001) in CON.

Conclusions

A 15-g protein-containing beverage with ∼4 g leucine induced greater increases in acute and integrated myoPS than did an isonitrogenous, isoenergetic mixed-protein beverage. Declines in muscle mass in older women may be attenuated with habitual twice-daily consumption of a protein beverage providing 15 g protein and higher (4.2 g/serving) amounts of leucine. This trial was registered at clinicaltrials.gov as NCT02282566.

Pronounced energy restriction with elevated protein intake results in no change in proteolysis and reductions in skeletal muscle protein synthesis that are mitigated by resistance exercise

Preservation of lean body mass (LBM) may be important during dietary energy restriction (ER) and requires equal rates of muscle protein synthesis (MPS) and muscle protein breakdown (MPB). Currently, the relative contribution of MPS and MPB to the loss of LBM during ER in humans is unknown. We aimed to determine the impact of dietary protein intake and resistance exercise on MPS and MPB during a controlled short-term energy deficit. Adult men (body mass index, 28.6 ± 0.6 kg/m²; age 22 ± 1 yr) underwent 10 d of 40%-reduced energy intake while performing unilateral resistance exercise and consuming lower protein (1.2 g/kg/d, n = 12) or higher protein (2.4 g/kg/d, n = 12). Pre- and postintervention testing included dual-energy X-ray absorptiometry, primed constant infusion of ring-[¹³C₆]phenylalanine, and ¹⁵[N]phenylalanine to measure acute postabsorptive MPS and MPB; D₂O to measure integrated MPS; and gene and protein expression. There was a decrease in acute MPS after ER (higher protein, 0.059 ± 0.006 to 0.051 ± 0.009%/h; lower protein, 0.061 ± 0.005 to 0.045 ± 0.006%/h; P < 0.05) that was attenuated with resistance exercise (higher protein, 0.067 ± 0.01%/h; lower protein, 0.061 ± 0.006%/h), and integrated MPS followed a similar pattern. There was no change in MPB (energy balance, 0.080 ± 0.01%/hr; ER rested legs, 0.078 ± 0.008%/hr; ER exercised legs, 0.079 ± 0.006%/hr). We conclude that a reduction in MPS is the main mechanism that underpins LBM loss early in ER in adult men.-Hector, A. J., McGlory, C., Damas, F., Mazara, N., Baker, S. K., Phillips, S. M. Pronounced energy restriction with elevated protein intake results in no change in proteolysis and reductions in skeletal muscle protein synthesis that are mitigated by resistance exercise.

Leucine supplementation enhances integrative myofibrillar protein synthesis in free-living older men consuming lower- and higher-protein diets: a parallel-group crossover study

BACKGROUND

Leucine co-ingestion with lower-protein (LP)-containing meals may overcome the blunted muscle protein synthetic response to food intake in the elderly but may be effective only in individuals who consume LP diets.

OBJECTIVE

We examined the impact of leucine co-ingestion with mixed macronutrient meals on integrated 3-d rates of myofibrillar protein synthesis (MyoPS) in free-living older men who consumed higher protein (HP) (1.2 g · kg^-1 · d^-1) or LP (0.8 g · kg^-1 · d^-1) in rested and resistance exercise (REX) conditions.

DESIGN

In a crossover design, 20 healthy older men [aged 65-85 y] were randomly assigned to receive LP or HP diets while ingesting a placebo (days 0-2) and Leu supplement (5 g leucine/meal; days 3-5) with their 3 main daily meals. A bout of unilateral REX was performed during the placebo and Leu treatments. Ingested ²H₂O and skeletal muscle biopsies were used to measure the 3-d integrated rate of MyoPS during the placebo and Leu treatments in the rested and REX legs.

RESULTS

Leucinemia was higher with Leu treatment than with placebo treatment (P < 0.001). MyoPS was similar in LP and HP during both treatments (P = 0.39) but was higher with Leu treatment than with placebo treatment in the rested (pooled mean ± SD: Leu, 1.57% ± 0.11%/d; placebo, 1.48% ± 0.08%/d; main effect of treatment: P < 0.001) and REX (pooled mean: Leu, 1.87% ± 0.09%/d; placebo, 1.71 ± 0.10%/d; main effect of treatment: P < 0.001) legs.

CONCLUSIONS

Leu co-ingestion with daily meals enhances integrated MyoPS in free-living older men in rested and REX conditions and is equally effective in older men who consume daily protein intakes greater than or equal to the RDA. This trial was registered at clinicaltrials.gov as NCT02371278.

Skeletal muscle satellite cells are located at a closer proximity to capillaries in healthy young compared with older men

BACKGROUND

Skeletal muscle satellite cells (SC) are instrumental in maintenance of muscle fibres, the adaptive responses to exercise, and there is an age-related decline in SC. A spatial relationship exists between SC and muscle fibre capillaries. In the present study, we aimed to investigate whether chronologic age has an impact on the spatial relationship between SC and muscle fibre capillaries. Secondly, we determined whether this spatial relationship changes in response to a single session of resistance exercise.

METHODS

Muscle biopsies were obtained from the vastus lateralis of previously untrained young men (YM, 24 ± 3 years; n = 23) and older men (OM, 67 ± 4 years; n = 22) at rest. A subset of YM (n = 9) performed a single bout of resistance exercise, where additional muscle biopsies taken at 24 and 72 h post-exercise recovery. Skeletal muscle fibre capillarization, SC content, and activation status were assessed using immunofluorescent microscopy of muscle cross sections.

RESULTS

Type II muscle fibre SC and capillary content was significantly lower in the YM compared with OM (P < 0.05). Furthermore, type II muscle fibre SC were located at a greater distance from the nearest capillary in OM compared with YM (21.6 ± 1.3 vs. 17.0 ± 0.8 µm, respectively; P < 0.05). In response to a single bout of exercise, we observed a significant increase in SC number and activation status (P < 0.05). In addition, activated vs. quiescent SC were situated closer (P < 0.05) to capillaries.

CONCLUSIONS

We demonstrate that there is a greater distance between capillaries and type II fibre-associated SC in OM as compared with YM. Furthermore, quiescent SC are located significantly further away from capillaries than active SC after single bout of exercise. Our data have implications for how muscle adapts to exercise and how aging may affect such adaptations.

Altered muscle satellite cell activation following 16 wk of resistance training in young men

Skeletal muscle satellite cells (SC) play an important role in muscle adaptation. In untrained individuals, SC content and activation status have been observed to increase in response to a single bout of exercise. Muscle fiber characteristics change considerably when resistance exercise is performed chronically, but whether training status affects the activity of SC in response to a single bout of exercise remains unknown. We examined the changes in SC content and activation status following a single bout of resistance exercise, before and following a 16-wk progressive resistance training (RT) program in 14 young (25 ± 3 yr) men. Before and after RT, percutaneous biopsies from the vastus lateralis muscle were taken before a single bout of resistance exercise and after 24 and 72 h of postexercise recovery. Muscle fiber size, capillarization, and SC response were determined by immunohistochemistry. Following RT, there was a greater activation of SC after 24 h in response to a single bout of resistance exercise (Pre, 1.4 ± 0.3; 24 h, 3.1 ± 0.3 Pax7⁺/MyoD⁺ cells per 100 fibers) compared with before RT (Pre, 1.4 ± 0.3; 24 h, 2.2 ± 0.3 Pax7⁺/MyoD⁺ cells per 100 fibers, P < 0.05); no difference was observed 72 h postexercise. Following 16 wk of RT, MyoD mRNA expression increased from basal to 24 h after the single bout of exercise (P < 0.05); this change was not observed before training. Individual capillary-to-fiber ratio (C/Fi) increased in both type I (1.8 ± 0.3 to 2.0 ± 0.3 C/Fi, P < 0.05) and type II (1.7 ± 0.3 to 2.2 ± 0.3 C/Fi, P < 0.05) fibers in response to RT. After RT, enhanced activation of SC in response to resistance exercise is accompanied by increases in muscle fiber capillarization.

Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men

We reported, using a unilateral resistance training (RT) model, that training with high or low loads (mass per repetition) resulted in similar muscle hypertrophy and strength improvements in RT-naïve subjects. Here we aimed to determine whether the same was true in men with previous RT experience using a whole-body RT program and whether postexercise systemic hormone concentrations were related to changes in hypertrophy and strength. Forty-nine resistance-trained men (23 ± 1 yr, mean ± SE) performed 12 wk of whole-body RT. Subjects were randomly allocated into a higher-repetition (HR) group who lifted loads of ∼30-50% of their maximal strength (1RM) for 20-25 repetitions/set (n = 24) or a lower-repetition (LR) group (∼75-90% 1RM, 8-12 repetitions/set, n = 25), with all sets being performed to volitional failure. Skeletal muscle biopsies, strength testing, dual-energy X-ray absorptiometry scans, and acute changes in systemic hormone concentrations were examined pretraining and posttraining. In response to RT, 1RM strength increased for all exercises in both groups (P < 0.01), with only the change in bench press being significantly different between groups (HR, 9 ± 1, vs. LR, 14 ± 1 kg, P = 0.012). Fat- and bone-free (lean) body mass and type I and type II muscle fiber cross-sectional area increased following training (P < 0.01) with no significant differences between groups. No significant correlations between the acute postexercise rise in any purported anabolic hormone and the change in strength or hypertrophy were found. In congruence with our previous work, acute postexercise systemic hormonal rises are not related to or in any way indicative of RT-mediated gains in muscle mass or strength. Our data show that in resistance-trained individuals, load, when exercises are performed to volitional failure, does not dictate hypertrophy or, for the most part, strength gains.

Phenotypic variability of CMT4C in a French-Canadian kindred

INTRODUCTION

Charcot-Marie-Tooth type 4C (CMT4C) is an autosomal recessive dysmyelinating neuropathy characterized by precocious and rapidly progressive scoliosis.

METHODS

Patients in a French-Canadian kindred were evaluated with clinical examination, electrophysiologic study, and genomic DNA extraction.

RESULTS

Six of 10 siblings were clinically symptomatic with supportive electrophysiologic features. The proband presented with regional side-to-side sensorimotor asymmetry, typical pes cavus without obvious scoliosis, and unremarkable plain films of the spine. Affected siblings all share symptoms of foot deformity but have variable onset of neuropathic symptoms, degree of extremity weakness, progression of symptoms, and, most notably, evidence of scoliosis. DNA sequence analysis revealed a novel combination of 2 known recessive mutations, p.R904X and p.R954X, in the SH3TC2 gene.

CONCLUSIONS

A broad spectrum of phenotypes should be considered in the possible diagnosis of CMT4C. The absence of scoliosis or late-onset symptoms should not exclude SH3TC2 from the list of candidate genes under consideration. Age of onset and clinical features were variable and suggest that polygenic factors contribute to the final phenotype.

Whey protein supplementation preserves postprandial myofibrillar protein synthesis during short-term energy restriction in overweight and obese adults

BACKGROUND

Higher dietary energy as protein during weight loss results in a greater loss of fat mass and retention of muscle mass; however, the impact of protein quality on the rates of myofibrillar protein synthesis (MPS) and lipolysis, processes that are important in the maintenance of muscle and loss of fat, respectively, are unknown.

OBJECTIVE

We aimed to determine how the consumption of different sources of proteins (soy or whey) during a controlled short-term (14-d) hypoenergetic diet affected MPS and lipolysis.

METHODS

Men (n = 19) and women (n = 21) (age 35-65 y; body mass index 28-50 kg/m(2)) completed a 14-d controlled hypoenergetic diet (-750 kcal/d). Participants were randomly assigned, double blind, to receive twice-daily supplements of isolated whey (27 g/supplement) or soy (26 g/supplement), providing a total protein intake of 1.3 ± 0.1 g/(kg · d), or isoenergetic carbohydrate (25 g maltodextrin/supplement) resulting in a total protein intake of 0.7 ± 0.1 g/(kg · d). Before and after the dietary intervention, primed continuous infusions of L-[ring-(13)C6] phenylalanine and [(2)H5]-glycerol were used to measure postabsorptive and postprandial rates of MPS and lipolysis.

RESULTS

Preintervention, MPS was stimulated more (P < 0.05) with ingestion of whey than with soy or carbohydrate. Postintervention, postabsorptive MPS decreased similarly in all groups (all P < 0.05). Postprandial MPS was reduced by 9 ± 1% in the whey group, which was less (P < 0.05) than the reduction in soy and carbohydrate groups (28 ± 5% and 31 ± 5%, respectively; both P < 0.05) after the intervention. Lipolysis was suppressed during the postprandial period (P < 0.05), but more so with ingestion of carbohydrate (P < 0.05) than soy or whey.

CONCLUSION

We conclude that whey protein supplementation attenuated the decline in postprandial rates of MPS after weight loss, which may be of importance in the preservation of lean mass during longer-term weight loss interventions. This trial was registered at clinicaltrials.gov as NCT01530646.

An assessment by the Statin Muscle Safety Task Force: 2014 update

The National Lipid Association's Muscle Safety Expert Panel was charged with the duty of examining the definitions for statin-associated muscle adverse events, development of a clinical index to assess myalgia, and the use of diagnostic neuromuscular studies to investigate muscle adverse events. We provide guidance as to when a patient should be considered for referral to neuromuscular specialists and indications for the performance of a skeletal muscle biopsy. Based on this review of evidence, we developed an algorithm for the evaluation and treatment of patients who may be intolerant to statins as the result of adverse muscle events. The panel was composed of clinical cardiologists, clinical lipidologists, an exercise physiologist, and a neuromuscular specialist.

Pseudoephedrine-induced Hemorrhage Associated with a Cerebral Vascular Malformation

Background:

Sympathomimetic-related intracerebral hemorrhage is well-documented. Most cases are associated with phenylpropanolamine use.

Case Report:

We report a case of intracerebral hemorrhage occurring in a middle-aged man who suffered from chronic sinusitis and had been ingesting pseudoephedrine daily for one year. This patient was previously well with no known cardiovascular risk factors. Clinical examination revealed no evidence of vasculitis nor coagulopathy and initial neuroimaging (i.e., computed tomography, angiography, magnetic resonance imaging) demonstrated no features consistent with aneurysm, arteriovenous malformation (AVM), cavernoma, nor cerebral metastases. A follow-up cerebral angiogram demonstrated a small AVM arising off a branch of the pericallosal artery and a small arteriovenous fistula arising off the costal marginal branch. The AVM was embolized without incident, however, the AVF was not accessible.

Conclusions:

Sympathomimetics have long been associated with intracerebral hemorrhage. Since 1979, over 30 published case reports have documented the relationship between phenylpropanolamine and stroke. Only one report links phenylpropanolamine consumption to an intracerebral hemorrhage in a patient with an AVM. There is a paucity of literature etiologically inculpating other ephedra alkaloids in the causation of intracerebral hemorrhage. This is a case of pseudoephedrine-induced intracerebral hemorrhage in a patient with an underlying vascular malformation.

Citrulline does not enhance blood flow, microvascular circulation, or myofibrillar protein synthesis in elderly men at rest or following exercise

Aging is associated with anabolic resistance, a reduced sensitivity of myofibrillar protein synthesis (MPS) to postprandial hyperaminoacidemia, particularly with low protein doses. Impairments in postprandial skeletal muscle blood flow and/or microvascular perfusion with hyperaminoacidemia and hyperinsulinemia may contribute to anabolic resistance. We examined whether providing citrulline, a precursor for arginine and nitric oxide synthesis, would increase arterial blood flow, skeletal muscle microvascular perfusion, MPS, and signaling through mTORC1. Twenty-one elderly males (65-80 yr) completed acute unilateral resistance exercise prior to being assigned to ingest a high dose (45 g) of whey protein (WHEY) or a low dose (15 g) of whey protein with 10 g of citrulline (WHEY + CIT) or with 10 g of nonessential amino acids (WHEY + NEAA). A primed, continuous infusion of L-[ring-(13)C6] phenylalanine with serial muscle biopsies was used to measure MPS and protein phosphorylation, whereas ultrasound was used to measure microvascular circulation under basal and postprandial conditions in both a rested (FED) and exercised (EX-FED) leg. Argininemia was greater in WHEY + CIT vs. WHEY and WHEY + NEAA from 30 to 300 min postexercise (P < 0.001), but there were no treatment differences in blood flow or microvascular perfusion (all P > 0.05). Phosphorylation of p70S6K-Thr(389) was greater in WHEY vs. WHEY + NEAA (P = 0.02). Postprandial MPS was greater in WHEY vs. WHEY + CIT and WHEY + NEAA under both FED (WHEY: ~128%; WHEY + CIT: ~56%; WHEY + NEAA: ~38%) and EX-FED (WHEY: ~251%; WHEY + CIT: ~124%; WHEY + NEAA: ~108%) conditions (P = 0.003). Citrulline coingestion with a low quantity of protein was ineffective in augmenting the anabolic properties of protein compared with nonessential amino acids.

Influence of aerobic exercise intensity on myofibrillar and mitochondrial protein synthesis in young men during early and late postexercise recovery

Aerobic exercise is typically associated with expansion of the mitochondrial protein pool and improvements in muscle oxidative capacity. The impact of aerobic exercise intensity on the synthesis of specific skeletal muscle protein subfractions is not known. We aimed to study the effect of aerobic exercise intensity on rates of myofibrillar (MyoPS) and mitochondrial (MitoPS) protein synthesis over an early (0.5-4.5 h) and late (24-28 h) period during postexercise recovery. Using a within-subject crossover design, eight males (21 ± 1 yr, Vo2peak 46.7 ± 2.0 ml·kg(-1)·min(-1)) performed two work-matched cycle ergometry exercise trials (LOW: 60 min at 30% Wmax; HIGH: 30 min at 60% Wmax) in the fasted state while undergoing a primed constant infusion of l-[ring-(13)C6]phenylalanine. Muscle biopsies were obtained at rest and 0.5, 4.5, 24, and 28 h postexercise to determine both the "early" and "late" response of MyoPS and MitoPS and the phosphorylation status of selected proteins within both the Akt/mTOR and MAPK pathways. Over 24-28 h postexercise, MitoPS was significantly greater after the HIGH vs. LOW exercise trial (P < 0.05). Rates of MyoPS were increased equivalently over 0.5-4.5 h postexercise recovery (P < 0.05) but remained elevated at 24-28 h postexercise only following the HIGH trial. In conclusion, an acute bout of high- but not low-intensity aerobic exercise in the fasted state resulted in a sustained elevation of both MitoPS and MyoPS at 24-28 h postexercise recovery.

Acute post-exercise myofibrillar protein synthesis is not correlated with resistance training-induced muscle hypertrophy in young men

Muscle hypertrophy following resistance training (RT) involves activation of myofibrillar protein synthesis (MPS) to expand the myofibrillar protein pool. The degree of hypertrophy following RT is, however, highly variable and thus we sought to determine the relationship between the acute activation of MPS and RT-induced hypertrophy. We measured MPS and signalling protein activation after the first session of resistance exercise (RE) in untrained men (n = 23) and then examined the relation between MPS with magnetic resonance image determined hypertrophy. To measure MPS, young men (24±1 yr; body mass index  = 26.4±0.9 kg•m²) underwent a primed constant infusion of L-[ring-¹³C₆] phenylalanine to measure MPS at rest, and acutely following their first bout of RE prior to 16 wk of RT. Rates of MPS were increased 235±38% (P<0.001) above rest 60–180 min post-exercise and 184±28% (P = 0.037) 180–360 min post exercise. Quadriceps volume increased 7.9±1.6% (−1.9–24.7%) (P<0.001) after training. There was no correlation between changes in quadriceps muscle volume and acute rates of MPS measured over 1–3 h (r = 0.02), 3–6 h (r = 0.16) or the aggregate 1–6 h post-exercise period (r = 0.10). Hypertrophy after chronic RT was correlated (r = 0.42, P = 0.05) with phosphorylation of 4E-BP1^Thr37/46 at 1 hour post RE. We conclude that acute measures of MPS following an initial exposure to RE in novices are not correlated with muscle hypertrophy following chronic RT.

Leucine supplementation of a low-protein mixed macronutrient beverage enhances myofibrillar protein synthesis in young men: a double-blind, randomized trial

BACKGROUND

Leucine is a key amino acid involved in the regulation of skeletal muscle protein synthesis.

OBJECTIVE

We assessed the effect of the supplementation of a lower-protein mixed macronutrient beverage with varying doses of leucine or a mixture of branched chain amino acids (BCAAs) on myofibrillar protein synthesis (MPS) at rest and after exercise.

DESIGN

In a parallel group design, 40 men (21 ± 1 y) completed unilateral knee-extensor resistance exercise before the ingestion of 25 g whey protein (W25) (3.0 g leucine), 6.25 g whey protein (W6) (0.75g leucine), 6.25 g whey protein supplemented with leucine to 3.0 g total leucine (W6+Low-Leu), 6.25 g whey protein supplemented with leucine to 5.0 g total leucine (W6+High-Leu), or 6.25 g whey protein supplemented with leucine, isoleucine, and valine to 5.0 g total leucine. A primed continuous infusion of l-[ring-(13)C6] phenylalanine with serial muscle biopsies was used to measure MPS under baseline fasted and postprandial conditions in both a rested (response to feeding) and exercised (response to combined feeding and resistance exercise) leg.

RESULTS

The area under the blood leucine curve was greatest for the W6+High-Leu group compared with the W6 and W6+Low-Leu groups (P < 0.001). In the postprandial period, rates of MPS were increased above baseline over 0-1.5 h in all treatments. Over 1.5-4.5 h, MPS remained increased above baseline after all treatments but was greatest after W25 (∼267%) and W6+High-Leu (∼220%) treatments (P = 0.002).

CONCLUSIONS

A low-protein (6.25 g) mixed macronutrient beverage can be as effective as a high-protein dose (25 g) at stimulating increased MPS rates when supplemented with a high (5.0 g total leucine) amount of leucine. These results have important implications for formulations of protein beverages designed to enhance muscle anabolism. This trial was registered at clinicaltrials.gov as NCT 1530646.

Muscular and systemic correlates of resistance training-induced muscle hypertrophy

Purpose

To determine relationships between post-exercise changes in systemic [testosterone, growth hormone (GH), insulin like grow factor 1 (IGF-1) and interleukin 6 (IL-6)], or intramuscular [skeletal muscle androgen receptor (AR) protein content and p70S6K phosphorylation status] factors in a moderately-sized cohort of young men exhibiting divergent resistance training-mediated muscle hypertrophy.

Methods

Twenty three adult males completed 4 sessions•wk^-1 of resistance training for 16 wk. Muscle biopsies were obtained before and after the training period and acutely 1 and 5 h after the first training session. Serum hormones and cytokines were measured immediately, 15, 30 and 60 minutes following the first and last training sessions of the study.

Results

Mean fiber area increased by 20% (range: -7 to 80%; P<0.001). Protein content of the AR was unchanged with training (fold change = 1.17 ± 0.61; P=0.19); however, there was a significant correlation between the changes in AR content and fiber area (r=0.60, P=0.023). Phosphorylation of p70S6K was elevated 5 hours following exercise, which was correlated with gains in mean fiber area (r=0.54, P=0.007). There was no relationship between the magnitude of the pre- or post-training exercise-induced changes in free testosterone, GH, or IGF-1 concentration and muscle fiber hypertrophy; however, the magnitude of the post exercise IL-6 response was correlated with muscle hypertrophy (r=0.48, P=0.019).

Conclusion

Post-exercise increases in circulating hormones are not related to hypertrophy following training. Exercise-induced changes in IL-6 correlated with hypertrophy, but the mechanism for the role of IL-6 in hypertrophy is not known. Acute increases, in p70S6K phosphorylation and changes in muscle AR protein content correlated with muscle hypertrophy implicating intramuscular rather than systemic processes in mediating hypertrophy.

Dose-dependent responses of myofibrillar protein synthesis with beef ingestion are enhanced with resistance exercise in middle-aged men

Aging impairs the sensitivity of skeletal muscle to anabolic stimuli, such as amino acids and resistance exercise. Beef is a nutrient-rich source of dietary protein capable of stimulating muscle protein synthesis (MPS) rates in older men at rest. To date, the dose-response of myofibrillar protein synthesis to graded ingestion of protein-rich foods, such as beef, has not been determined. We aimed to determine the dose-response of MPS with and without resistance exercise to graded doses of beef ingestion. Thirty-five middle-aged men (59 ± 2 years) ingested 0 g, 57 g (2 oz; 12 g protein), 113 g (4 oz; 24 g protein), or 170 g (6 oz; 36 g protein) of (15% fat) ground beef (n = 7 per group). Subjects performed a bout of unilateral resistance exercise to allow measurement of the fed state and the fed plus resistance exercise state within each dose. A primed constant infusion of l-[1-(13)C]leucine was initiated to measure leucine oxidation and of l-[ring-(13)C(6)]phenylalanine was initiated to measure myofibrillar MPS. Myofibrillar MPS was increased with ingestion of 170 g of beef to a greater extent than all other doses at rest and after resistance exercise. There was more leucine oxidation with ingestion of 113 g of beef than with 0 g and 57 g, and it increased further after ingestion of 170 g of beef (all p < 0.05). Ingestion of 170 g of beef protein is required to stimulate a rise in myofibrillar MPS over and above that seen with lower doses. An isolated bout of resistance exercise was potent in stimulating myofibrillar MPS, and acted additively with feeding.

Sex-based comparisons of myofibrillar protein synthesis after resistance exercise in the fed state

We made sex-based comparisons of rates of myofibrillar protein synthesis (MPS) and anabolic signaling after a single bout of high-intensity resistance exercise. Eight men (20 ± 10 yr, BMI = 24.3 ± 2.4) and eight women (22 ± 1.8 yr, BMI = 23.0 ± 1.9) underwent primed constant infusions of l-[ ring-13C6]phenylalanine on consecutive days with serial muscle biopsies. Biopsies were taken from the vastus lateralis at rest and 1, 3, 5, 24, 26, and 28 h after exercise. Twenty-five grams of whey protein was ingested immediately and 26 h after exercise. We also measured exercise-induced serum testosterone because it is purported to contribute to increases in myofibrillar protein synthesis (MPS) postexercise and its absence has been hypothesized to attenuate adaptative responses to resistance exercise in women. The exercise-induced area under the testosterone curve was 45-fold greater in men than women in the early (1 h) recovery period following exercise ( P < 0.001). MPS was elevated similarly in men and women (2.3- and 2.7-fold, respectively) 1–5 h postexercise and after protein ingestion following 24 h recovery. Phosphorylation of mTORSer2448 was elevated to a greater extent in men than women acutely after exercise ( P = 0.003), whereas increased phosphorylation of p70S6K1Thr389 was not different between sexes. Androgen receptor content was greater in men (main effect for sex, P = 0.049). Atrogin-1 mRNA abundance was decreased after 5 h recovery in both men and women ( P < 0.001), and MuRF-1 expression was elevated in men after protein ingestion following 24 h recovery ( P = 0.003). These results demonstrate minor sex-based differences in signaling responses and no difference in the MPS response to resistance exercise in the fed state. Interestingly, our data demonstrate that exercise-induced increases in MPS are dissociated from postexercise testosteronemia and that stimulation of MPS occurs effectively with low systemic testosterone concentrations in women.

Resistance exercise load does not determine training-mediated hypertrophic gains in young men

We have reported that the acute postexercise increases in muscle protein synthesis rates, with differing nutritional support, are predictive of longer-term training-induced muscle hypertrophy. Here, we aimed to test whether the same was true with acute exercise-mediated changes in muscle protein synthesis. Eighteen men (21 ± 1 yr, 22.6 ± 2.1 kg/m(2); means ± SE) had their legs randomly assigned to two of three training conditions that differed in contraction intensity [% of maximal strength (1 repetition maximum)] or contraction volume (1 or 3 sets of repetitions): 30%-3, 80%-1, and 80%-3. Subjects trained each leg with their assigned regime for a period of 10 wk, 3 times/wk. We made pre- and posttraining measures of strength, muscle volume by magnetic resonance (MR) scans, as well as pre- and posttraining biopsies of the vastus lateralis, and a single postexercise (1 h) biopsy following the first bout of exercise, to measure signaling proteins. Training-induced increases in MR-measured muscle volume were significant (P < 0.01), with no difference between groups: 30%-3 = 6.8 ± 1.8%, 80%-1 = 3.2 ± 0.8%, and 80%-3= 7.2 ± 1.9%, P = 0.18. Isotonic maximal strength gains were not different between 80%-1 and 80%-3, but were greater than 30%-3 (P = 0.04), whereas training-induced isometric strength gains were significant but not different between conditions (P = 0.92). Biopsies taken 1 h following the initial resistance exercise bout showed increased phosphorylation (P < 0.05) of p70S6K only in the 80%-1 and 80%-3 conditions. There was no correlation between phosphorylation of any signaling protein and hypertrophy. In accordance with our previous acute measurements of muscle protein synthetic rates a lower load lifted to failure resulted in similar hypertrophy as a heavy load lifted to failure.

Supplementation of a suboptimal protein dose with leucine or essential amino acids: effects on myofibrillar protein synthesis at rest and following resistance exercise in men

Leucine is a nutrient regulator of muscle protein synthesis by activating mTOR and possibly other proteins in this pathway. The purpose of this study was to examine the role of leucine in the regulation of human myofibrillar protein synthesis (MPS). Twenty-four males completed an acute bout of unilateral resistance exercise prior to consuming either: a dose (25 g) of whey protein (WHEY); 6.25 g whey protein with total leucine equivalent to WHEY (LEU); or 6.25 g whey protein with total essential amino acids (EAAs) equivalent to WHEY for all EAAs except leucine (EAA-LEU). Measures of MPS, signalling through mTOR, and amino acid transporter (AAT) mRNA abundance were made while fasted (FAST), and following feeding under rested (FED) and post-exercise (EX-FED) conditions. Leucinaemia was equivalent between WHEY and LEU and elevated compared to EAA-LEU (P=0.001). MPS was increased above FAST at 1–3 h post-exercise in both FED (P <0.001) and EX-FED (P <0.001) conditions with no treatment effect.At 3–5 h, only WHEY remained significantly elevated above FAST in EX-FED(WHEY 184% vs. LEU 55% and EAA-LEU 35%; P =0.036). AAT mRNA abundance was increased above FAST after feeding and exercise with no effect of leucinaemia. In summary, a low dose of whey protein supplemented with leucine or all other essential amino acids was as effective as a complete protein (WHEY) in stimulating postprandial MPS; however only WHEY was able to sustain increased rates of MPS post-exercise and may therefore be most suited to increase exercise-induced muscle protein accretion.

Muscle time under tension during resistance exercise stimulates differential muscle protein sub-fractional synthetic responses in men

We aimed to determine if the time that muscle is under loaded tension during low intensity resistance exercise affects the synthesis of specific muscle protein fractions or phosphorylation of anabolic signalling proteins. Eight men (24 ± 1 years (sem), BMI = 26.5 ± 1.0 kg m(-2)) performed three sets of unilateral knee extension exercise at 30% of one-repetition maximum strength involving concentric and eccentric actions that were 6 s in duration to failure (SLOW) or a work-matched bout that consisted of concentric and eccentric actions that were 1 s in duration (CTL). Participants ingested 20 g of whey protein immediately after exercise and again at 24 h recovery. Needle biopsies (vastus lateralis) were obtained while fasted at rest and after 6, 24 and 30 h post-exercise in the fed-state following a primed, constant infusion of l-[ring-(13)C(6)]phenylalanine. Myofibrillar protein synthetic rate was higher in the SLOW condition versus CTL after 24-30 h recovery (P < 0.001) and correlated to p70S6K phosphorylation (r = 0.42, P = 0.02). Exercise-induced rates of mitochondrial and sarcoplasmic protein synthesis were elevated by 114% and 77%, respectively, above rest at 0-6 h post-exercise only in the SLOW condition (both P < 0.05). Mitochondrial protein synthesis rates were elevated above rest during 24-30 h recovery in the SLOW (175%) and CTL (126%) conditions (both P < 0.05). Lastly, muscle PGC-1α expression was increased at 6 h post-exercise compared to rest with no difference between conditions (main effect for time, P < 0.001). These data show that greater muscle time under tension increased the acute amplitude of mitochondrial and sarcoplasmic protein synthesis and also resulted in a robust, but delayed stimulation of myofibrillar protein synthesis 24-30 h after resistance exercise.

Sonographic features in hereditary neuropathy with liability to pressure palsies

INTRODUCTION

Diagnostic nerve ultrasound is becoming more commonly used by both radiologists and clinicians. The features of different neuromuscular conditions must be described to broaden our understanding and ability to interpret findings.

METHODS

Our study examines the sonographic features of 7 subjects with hereditary neuropathy with liability to pressure palsies (HNPP) in comparison to 32 controls by measuring the nerve cross-sectional area (CSA) of the median, ulnar and tibial nerves.

RESULTS

Significant differences (P < 0.05) in nerve size were found. The HNPP group had a larger CSA for the median nerve at the wrist and ulnar nerve at the elbow (entrapment sites), but not the forearms. The tibial nerve at the ankle was also larger in the HNPP group, suggesting possible concomitant tibial neuropathy at the ankle.

CONCLUSION

These results will help shape imaging protocols to better detect conditions with non-uniform nerve enlargements.

Carbohydrate does not augment exercise-induced protein accretion versus protein alone

PURPOSE

We tested the thesis that CHO and protein coingestion would augment muscle protein synthesis (MPS) and inhibit muscle protein breakdown (MPB) at rest and after resistance exercise.

METHODS

Nine men (age=23.0±1.9 yr, body mass index=24.2±2.1 kg·m) performed two unilateral knee extension trials (four sets×8-12 repetitions to failure) followed by consumption of 25 g of whey protein (PRO) or 25 g of whey protein plus 50 g of maltodextrin (PRO+CARB). Muscle biopsies and stable isotope methodology were used to measure MPS and MPB.

RESULTS

The areas under the glucose and insulin curves were 17.5-fold (P<0.05) and 5-fold (P<0.05) greater, respectively, for PRO+CARB than for PRO. Exercise increased MPS and MPB (both P<0.05), but there were no differences between PRO and PRO+CARB in the rested or exercised legs. Phosphorylation of Akt was greater in the PRO+CARB than in the PRO trial (P<0.05); phosphorylations of Akt (P=0.05) and acetyl coA carboxylase-β (P<0.05) were greater after exercise than at rest. The concurrent ingestion of 50 g of CHO with 25 g of protein did not stimulate mixed MPS or inhibit MPB more than 25 g of protein alone either at rest or after resistance exercise.

CONCLUSIONS

Our data suggest that insulin is not additive or synergistic to rates of MPS or MPB when CHO is coingested with a dose of protein that maximally stimulates rates of MPS.

Rapid aminoacidemia enhances myofibrillar protein synthesis and anabolic intramuscular signaling responses after resistance exercise

BACKGROUND

Ingestion of whey or casein yields divergent patterns of aminoacidemia that influence whole-body and skeletal muscle myofibrillar protein synthesis (MPS) after exercise. Direct comparisons of the effects of contrasting absorption rates exhibited by these proteins are confounded by their differing amino acid contents.

OBJECTIVE

Our objective was to determine the effect of divergent aminoacidemia by manipulating ingestion patterns of whey protein alone on MPS and anabolic signaling after resistance exercise.

DESIGN

In separate trials, 8 healthy men consumed whey protein either as a single bolus (BOLUS; 25-g dose) or as repeated, small, "pulsed" drinks (PULSE; ten 2.5-g drinks every 20 min) to mimic a more slowly digested protein. MPS and phosphorylation of signaling proteins involved in protein synthesis were measured at rest and after resistance exercise.

RESULTS

BOLUS increased blood essential amino acid (EAA) concentrations above those of PULSE (162% compared with 53%, P < 0.001) 60 min after exercise, whereas PULSE resulted in a smaller but sustained increase in aminoacidemia that remained elevated above BOLUS amounts later (180-220 min after exercise, P < 0.05). Despite an identical net area under the EAA curve, MPS was elevated to a greater extent after BOLUS than after PULSE early (1-3 h: 95% compared with 42%) and later (3-5 h: 193% compared with 121%) (both P < 0.05). There were greater changes in the phosphorylation of the Akt-mammalian target of rapamycin pathway after BOLUS than after PULSE.

CONCLUSIONS

Rapid aminoacidemia in the postexercise period enhances MPS and anabolic signaling to a greater extent than an identical amount of protein fed in small pulses that mimic a more slowly digested protein. A pronounced peak aminoacidemia after exercise enhances protein synthesis. This trial was registered at clinicaltrials.gov as NCT01319513.

17β-estradiol attenuates exercise-induced neutrophil infiltration in men

17β-estradiol (E2) attenuates exercise-induced muscle damage and inflammation in some models. Eighteen men completed 150 eccentric contractions after random assignment to placebo (Control group) or E2 supplementation (Experimental group). Muscle biopsies and blood samples were collected at baseline, following 8-day supplementation and 3 h and 48 h after exercise. Blood samples were analyzed for sex hormone concentration, creatine kinase (CK) activity and total antioxidant capacity. The mRNA content of genes involved in lipid and cholesterol homeostasis [forkhead box O1 (FOXO1), caveolin 1, and sterol regulatory element binding protein-2 (SREBP2)] and antioxidant defense (SOD1 and -2) were measured by RT-PCR. Immunohistochemistry was used to quantify muscle neutrophil (myeloperoxidase) and macrophage (CD68) content. Serum E2 concentration increased 2.5-fold with supplementation ( P < 0.001), attenuating neutrophil infiltration at 3 h ( P < 0.05) and 48 h ( P < 0.001), and the induction of SOD1 at 48 h ( P = 0.02). Macrophage density at 48 h ( P < 0.05) and SOD2 mRNA at 3 h ( P = 0.01) increased but were not affected by E2. Serum CK activity was higher at 48 h for both groups ( P < 0.05). FOXO1, caveolin 1 and SREBP2 expression were 2.8-fold ( P < 0.05), 1.4-fold ( P < 0.05), and 1.5-fold ( P < 0.001) and higher at 3 h after exercise with no effect of E2. This suggests that E2 attenuates neutrophil infiltration; however, the mechanism does not appear to be lesser oxidative stress or membrane damage and may indicate lesser neutrophil/endothelial interaction.

Enhanced amino acid sensitivity of myofibrillar protein synthesis persists for up to 24 h after resistance exercise in young men

We aimed to determine whether an exercise-mediated enhancement of muscle protein synthesis to feeding persisted 24 h after resistance exercise. We also determined the impact of different exercise intensities (90% or 30% maximal strength) or contraction volume (work-matched or to failure) on the response at 24 h of recovery. Fifteen men (21 ± 1 y, BMI = 24.1 ± 0.8 kg · m(-2)) received a primed, constant infusion of l-[ring-(13)C(6)]phenylalanine to measure muscle protein synthesis after protein feeding at rest (FED; 15 g whey protein) and 24 h after resistance exercise (EX-FED). Participants performed unilateral leg exercises: 1) 4 sets at 90% of maximal strength to failure (90FAIL); 2) 30% work-matched to 90FAIL (30WM); or 3) 30% to failure (30FAIL). Regardless of condition, rates of mixed muscle protein and sarcoplasmic protein synthesis were similarly stimulated at FED and EX-FED. In contrast, protein ingestion stimulated rates of myofibrillar protein synthesis above fasting rates by 0.016 ± 0.002%/h and the response was enhanced 24 h after resistance exercise, but only in the 90FAIL and 30FAIL conditions, by 0.038 ± 0.012 and 0.041 ± 0.010, respectively. Phosphorylation of protein kinase B on Ser473 was greater than FED at EX-FED only in 90FAIL, whereas phosphorylation of mammalian target of rapamycin on Ser2448 was significantly increased at EX-FED above FED only in the 30FAIL condition. Our results suggest that resistance exercise performed until failure confers a sensitizing effect on human skeletal muscle for at least 24 h that is specific to the myofibrillar protein fraction.

Molecular diagnosis of myopathies

Neuromuscular diseases (NMD) constitute a group of phenotypically and genetically heterogeneous disorders, characterized by (progressive) weakness and atrophy of proximal and/or distal muscles. The objective of molecular testing is to confirm the pathogenicity of a relevant sequence variation by correlating an individual's phenotype with what is expected in a given condition. Within the last two decades the application of molecular genetic strategies has led to a delineation of subgroups of clinically indistinguishable NMDs and has disclosed marked disease overlap. The expanding number of molecular defined NMDs requires new strategies to classify overlapping and clinical indistinguishable phenotypes.

Validation of a single biopsy approach and bolus protein feeding to determine myofibrillar protein synthesis in stable isotope tracer studies in humans

Background

Minimizing the number of muscle biopsies has important methodological implications and minimizes subject discomfort during a stable isotope amino acid infusion. We aimed to determine the reliability of obtaining a single muscle biopsy for the calculation of muscle protein fractional synthetic rate (FSR) as well as the amount of incorporation time necessary to obtain that biopsy after initiating a stable isotope infusion (Study 1). The calculation of muscle protein FSR requires tracer steady-state during the stable isotope infusion. Therefore, a second aim was to examine if steady-state conditions are compromised in the precursor pools (plasma free or muscle intracellular [IC]) after ingestion of a tracer enriched protein drink and after resistance exercise (Study 2).

Methods

Sixteen men (23 ± 3 years; BMI = 23.8 ± 2.2 kg/m², means ± SD) were randomized to perform Study 1 or Study 2 (n = 8, per study). Subjects received a primed, constant infusion of L-[ring-¹³C₆]phenylalanine coupled with muscle biopsies of the vastus lateralis to measure rates of myofibrillar protein synthesis (MPS). Subjects in Study 2 were fed 25 g of whey protein immediately after an acute bout of unilateral resistance exercise.

Results

There was no difference (P = 0.3) in rates of MPS determined using the steady-state precursor-product equation and determination of tracer incorporation between sequential biopsies 150 min apart or using plasma protein as the baseline enrichment, provided the infusion length was sufficient (230 ± 0.3 min). We also found that adding a modest amount of tracer (4% enriched), calculated based on the measured phenylalanine content of the protein (3.5%) in the drink, did not compromise steady-state conditions (slope of the enrichment curve not different from zero) in the plasma free or, more importantly, the IC pool (both P > 0.05).

Conclusions

These data demonstrate that the single biopsy approach yields comparable rates of muscle protein synthesis, provided a longer incorporation time is utilized, to that seen with a traditional two biopsy approach. In addition, we demonstrate that enriching protein-containing drinks with tracer does not disturb isotopic steady-state and thus both are reliable techniques to determine rates of MPS in humans.