Short-term unilateral leg immobilization alters peripheral but not central arterial structure and function in healthy young humans.

Short-term leg immobilization is an acute model of inactivity, which induces vascular deconditioning. The present study was conducted to determine if short-term leg immobilization induced alterations in central and peripheral conduit artery structure (diameter and compliance), function (resting blood flow and mean wall shear rate), and peripheral flow-mediated dilation. Healthy participants (n = 7 women and n = 8 men) were studied before and after 12 days of unilateral leg immobilization. Carotid artery structure and function were unaltered with immobilization indicating that the unilateral immobilization did not have a detectable effect on this representative central artery. In contrast, peripheral measures of arterial structure at the common femoral and popliteal arteries showed significant reductions in both the immobilized and non-immobilized limbs but to a greater extent in the immobilized limbs. Specifically, femoral and popliteal artery compliance and femoral artery diameter were reduced in both the immobilized and the non-immobilized limb (p < 0.05) while popliteal artery diameter was reduced only in the immobilized leg. Popliteal artery flow-mediated dilation, an indicator of peripheral artery function, was increased in the immobilized limb, which parallels reports in paralyzed limbs of spinal-cord-injured individuals. The time course of vascular alterations with inactivity likely follows a sequence of adaptations in arterial structure and function reflecting differing initial flow patterns, and arterial wall composition, and diverse hemodynamic stimuli within different blood vessels.

Resistance exercise and appropriate nutrition to counteract muscle wasting and promote muscle hypertrophy.

PURPOSE OF REVIEW: Loss of skeletal muscle mass is a common feature of a number of clinical scenarios including limb casting, bed rest, and various disorders such as HIV-AIDS, sepsis, cancer cachexia, heart failure, and uremia. Commonly, muscle disuse (hypodynamia) is the sole reason, or a large part, of why muscle mass is lost. The reduction in strength, or dynapenia, that accompanies these conditions is also a function of the degree of hypodynamia and is related to muscle loss. RECENT FINDINGS: The major and consistent finding in a number of human-based models of muscle wasting is a decline in the synthesis of new muscle proteins both in the postabsorptive and fed states. Thus, countermeasures are best suited to those that augment muscle protein synthesis and not those that attempt to counteract proteolysis. Our main thesis is that retention of muscle mass in wasting conditions will be achieved to the greatest extent by focussing on increased muscle use with moderate-to-high resistance loads as the primary countermeasure with a secondary countermeasure being to provide adequate nutritional support. Either intervention alone will alleviate some part of hypodynamia-induced muscle mass loss and dynapenia; however, together nutrition and muscular contraction will result in greater mitigation of muscle loss. SUMMARY: Advances in our understanding of hypodynamia-induced muscle loss, a condition common to almost all syndromes of muscle wasting, has led to a focus on reduced basal and feeding-induced elevations in protein synthesis. Countermeasures for wasting should focus on stimulating anabolism rather than alleviating catabolism.

Low-volume resistance exercise attenuates the decline in strength and muscle mass associated with immobilization.

We determined the effectiveness of low-volume resistance exercise (EX) for the attenuation of loss of muscle mass and strength during leg immobilization. Men (N = 5) and women (N = 12, age 24 ± 5 years, body mass index 25.4 ± 3.6 kg/m(2)) were divided into two groups: exercise (EX; n = 12) and control (CON; n = 5). Subjects wore a knee brace on one leg that prevented weight bearing for 14 days. Resistance exercise (EX; 80% of maximal) was performed by the immobilized limb every other day. Immobilization induced a significant reduction (P < 0.05) in muscle fiber and thigh cross-sectional area (CSA), isometric knee extensor, and plantarflexor strength in the CON (P < 0.01) but not in the EX group. There were significant losses in triceps surae CSA in the CON and EX groups (P < 0.05), but the losses were greater in CON subjects (P < 0.01). A minimal volume (140 contractions in 14 days) of resistive exercise is an effective countermeasure against immobilization-induced atrophy of the quadriceps femoris but is only partially effective for the triceps surae.

A randomized trial of coenzyme Q10 in mitochondrial disorders.

Case reports and open-label studies suggest that coenzyme Q(10) (CoQ(10)) treatment may have beneficial effects in mitochondrial disease patients; however, controlled trials are warranted to clinically prove its effectiveness. Thirty patients with mitochondrial cytopathy received 1200 mg/day CoQ(10) for 60 days in a randomized, double-blind, cross-over trial. Blood lactate, urinary markers of oxidative stress, body composition, activities of daily living, quality of life, forearm handgrip strength and oxygen desaturation, cycle exercise cardiorespiratory variables, and brain metabolites were measured. CoQ(10) treatment attenuated the rise in lactate after cycle ergometry, increased (∽1.93 ml) VO(2)/kg lean mass after 5 minutes of cycling (P < 0.005), and decreased gray matter choline-containing compounds (P < 0.05). Sixty days of moderate- to high-dose CoQ(10) treatment had minor effects on cycle exercise aerobic capacity and post-exercise lactate but did not affect other clinically relevant variables such as strength or resting lactate.

Immobilization induces anabolic resistance in human myofibrillar protein synthesis with low and high dose amino acid infusion.

We tested the hypothesis that increasing blood amino acid (AA) availability would counter the physical inactivity-induced reduction in muscle protein synthesis. We determined how 14 days of unilateral knee immobilization affected quadriceps myofibrillar protein synthesis (MPS) in young healthy subjects (10 men, 2 women, 21 +/- 1 years; 80.2 +/- 4.0 kg, mean +/- S.E.M.) in the post-absorptive state and after infusing AA (10% Primene) at low or high doses (43 and 261 mg kg(-1) h(-1)). Muscle cross-sectional area (MRI) and peak isometric torque declined in the immobilized leg (-5.0 +/- 1.2% and -25 +/- 3%, respectively, both P < 0.005), but were unchanged (all P > 0.6) in the non-immobilized leg. Immobilization induced a 27% decline in the rate of post-absorptive MPS (immobilized, 0.027 +/- 0.003: non-immobilized, 0.037 +/- 0.003% h(-1); P < 0.001). Regardless of dose, AA infusion stimulated a greater rise in MPS in the non-immobilized legs; at 4 h MPS was greater by +54 +/- 12% with low dose and +68 +/- 17% with high dose AA infusion (both P < 0.001). There was some evidence of delayed responsiveness of phosphorylation of Akt to high doses of AA and p70S6k at both doses but no marked differences in that of mTOR, GSK3beta or eEF2. Phosphorylation of focal adhesion kinase (Tyr(576/577)) was reduced (P < 0.05) with immobilization. We observed no change in polyubiquitinated protein content after immobilization. We confirm that 14 days of immobilization reduces MPS in the post-absorptive state and this diminution is reduced but not abolished by increased provision of AA, even at high rates. The immobilization-induced decline in post-absorptive MPS with the 'anabolic resistance' to amino acids can account for much of immobilization-induced muscle atrophy.

Dietary intake is independently associated with the maximal capacity for fat oxidation during exercise.

Background: Substantial interindividual variability exists in the maximal rate of fat oxidation (MFO) during exercise with potential implications for metabolic health. Although the diet can affect the metabolic response to exercise, the contribution of a self-selected diet to the interindividual variability in the MFO requires further clarification.Objective: We sought to identify whether recent, self-selected dietary intake independently predicts the MFO in healthy men and women.Design: The MFO and maximal oxygen uptake ([Formula: see text]O2 max) were determined with the use of indirect calorimetry in 305 healthy volunteers [150 men and 155 women; mean ± SD age: 25 ± 6 y; body mass index (BMI; in kg/m2): 23 ± 2]. Dual-energy X-ray absorptiometry was used to assess body composition with the self-reported physical activity level (SRPAL) and dietary intake determined in the 4 d before exercise testing. To minimize potential confounding with typically observed sex-related differences (e.g., body composition), predictor variables were mean-centered by sex. In the analyses, hierarchical multiple linear regressions were used to quantify each variable's influence on the MFO.Results: The mean absolute MFO was 0.55 ± 0.19 g/min (range: 0.19-1.13 g/min). A total of 44.4% of the interindividual variability in the MFO was explained by the [Formula: see text]O2 max, sex, and SRPAL with dietary carbohydrate (carbohydrate; negative association with the MFO) and fat intake (positive association) associated with an additional 3.2% of the variance. When expressed relative to fat-free mass (FFM), the MFO was 10.8 ± 3.2 mg · kg FFM-1 · min-1 (range: 3.5-20.7 mg · kg FFM-1 · min-1) with 16.6% of the variability explained by the [Formula: see text]O2 max, sex, and SRPAL; dietary carbohydrate and fat intakes together explained an additional 2.6% of the variability. Biological sex was an independent determinant of the MFO with women showing a higher MFO [men: 10.3 ± 3.1 mg · kg FFM-1 · min-1 (3.5-19.9 mg · kg FFM-1 · min-1); women: 11.2 ± 3.3 mg · kg FFM-1 · min-1 (4.6-20.7 mg · kg FFM-1 · min-1); P < 0.05].Conclusion: Considered alongside other robust determinants, dietary carbohydrate and fat intake make modest but independent contributions to the interindividual variability in the capacity to oxidize fat during exercise. This trial was registered at clinicaltrials.gov as NCT02070055.

Sex-based differences in skeletal muscle function and morphology with short-term limb immobilization.

The purpose of this study was to determine the effects of short-term (14-day) unilateral leg immobilization using a simple knee brace (60 degree flexion)- or crutch-mediated model on muscle function and morphology in men (M, n = 13) and women (W, n = 14). Isometric and isokinetic (concentric-slow, 0.52 rad/s and fast, 5.24 rad/s) knee extensor peak torque was determined at three time points (Pre, Day-2, and Day-14). At the same time points, magnetic resonance imaging was used to measure the cross-sectional area of the quadriceps femoris and dual-energy X-ray absorptiometry scanning was used to calculate leg lean mass. Muscle biopsies were taken from vastus lateralis at Pre and Day-14 for myosin ATPase and myosin heavy chain analysis. Women showed greater decreases (Pre vs. Day-14) compared with men in specific strength (N/cm2) for isometric [M = 3.1 +/- 13.3, W = 17.1 +/- 15.9%; P = 0.055 (mean +/- SD)] and concentric-slow (M = 4.7 +/- 11.3, W = 16.6 +/- 18.4%; P < 0.05) contractions. There were no immobilization-induced sex-specific differences in the decrease in quadriceps femoris cross-sectional area (M = 5.7 +/- 5.0, W = 5.9 +/- 5.2%) or leg lean mass (M = 3.7 +/- 4.2, W = 2.7 +/- 2.8%). There were no fiber-type transformations, and the decreases in type I (M = 4.8 +/- 5.0, W = 5.9 +/- 3.4%), IIa (M = 7.9 +/- 9.9, W = 8.8 +/- 8.0%), and IIx (M = 10.7 +/- 10.8, W = 10.8 +/- 12.1%) fiber areas were similar between sexes. These findings indicate that immobilization-induced loss of knee extensor muscle strength is greater in women compared with men despite a similar extent of atrophy at the myofiber and whole muscle levels after 14 days of unilateral leg immobilization. Furthermore, we have described an effective and safe knee immobilization method that results in reductions in quadriceps muscle strength and size.

Little change in markers of protein breakdown and oxidative stress in humans in immobilization-induced skeletal muscle atrophy.

A number of studies in rodents suggest that disuse atrophy results from a large increase in proteolysis affected by, or accompanying, increased oxidative stress. Little information is available, however, about the effects of immobilization on markers of muscle protein breakdown and oxidative stress in humans. Therefore, the purpose of this investigation was to measure markers of breakdown or oxidative stress in subjects who underwent 14 days of knee-brace-mediated immobilization. Vastus lateralis samples taken from 21 young subjects before, and 2 days and 14 days after, single leg immobilization were measured for ubiquitin-protein conjugates, caspase 3/7 activity, the 14-kDa caspase-3 cleaved actin fragment, 4-hydroxy-2-nonenal (4-HNE) adducts, and protein carbonyls. Quadriceps cross-sectional area decreased by 5.7% +/- 1.1% (p < 0.0001) following immobilization. Ubiquitin-protein conjugates were elevated at 2 days of immobilization (12%, p < 0.05) but were not different from baseline at 14 days. Levels of the 14-kDa actin fragment and caspase 3/7 activity did not change over the immobilization period. The oxidative stress markers, 4-HNE adducts and protein carbonyls, did not change at any time point. These static measures of breakdown and oxidative modification suggest that a small increase in protein ubiquitination occurs early (2 days), but elevations in ubiquitinated or oxidatively modified proteins are not sustained during the later phase (14 days) of uncomplicated disuse atrophy in humans, suggesting that these pathways are not playing a major role in simple disuse-induced atrophic loss of protein mass.

Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men.

BACKGROUND: The anabolic effect of resistance exercise is enhanced by the provision of dietary protein. OBJECTIVES: We aimed to determine the ingested protein dose response of muscle (MPS) and albumin protein synthesis (APS) after resistance exercise. In addition, we measured the phosphorylation of candidate signaling proteins thought to regulate acute changes in MPS. DESIGN: Six healthy young men reported to the laboratory on 5 separate occasions to perform an intense bout of leg-based resistance exercise. After exercise, participants consumed, in a randomized order, drinks containing 0, 5, 10, 20, or 40 g whole egg protein. Protein synthesis and whole-body leucine oxidation were measured over 4 h after exercise by a primed constant infusion of [1-(13)C]leucine. RESULTS: MPS displayed a dose response to dietary protein ingestion and was maximally stimulated at 20 g. The phosphorylation of ribosomal protein S6 kinase (Thr(389)), ribosomal protein S6 (Ser(240/244)), and the epsilon-subunit of eukaryotic initiation factor 2B (Ser(539)) were unaffected by protein ingestion. APS increased in a dose-dependent manner and also reached a plateau at 20 g ingested protein. Leucine oxidation was significantly increased after 20 and 40 g protein were ingested. CONCLUSIONS: Ingestion of 20 g intact protein is sufficient to maximally stimulate MPS and APS after resistance exercise. Phosphorylation of candidate signaling proteins was not enhanced with any dose of protein ingested, which suggested that the stimulation of MPS after resistance exercise may be related to amino acid availability. Finally, dietary protein consumed after exercise in excess of the rate at which it can be incorporated into tissue protein stimulates irreversible oxidation.

Limb immobilization induces a coordinate down-regulation of mitochondrial and other metabolic pathways in men and women.

Advancements in animal models and cell culture techniques have been invaluable in the elucidation of the molecular mechanisms that regulate muscle atrophy. However, few studies have examined muscle atrophy in humans using modern experimental techniques. The purpose of this study was to examine changes in global gene transcription during immobilization-induced muscle atrophy in humans and then explore the effects of the most prominent transcriptional alterations on protein expression and function. Healthy men and women (N = 24) were subjected to two weeks of unilateral limb immobilization, with muscle biopsies obtained before, after 48 hours (48 H) and 14 days (14 D) of immobilization. Muscle cross sectional area (approximately 5%) and strength (10-20%) were significantly reduced in men and women (approximately 5% and 10-20%, respectively) after 14 D of immobilization. Micro-array analyses of total RNA extracted from biopsy samples at 48 H and 14 D uncovered 575 and 3,128 probes, respectively, which were significantly altered during immobilization. As a group, genes involved in mitochondrial bioenergetics and carbohydrate metabolism were predominant features at both 48 H and 14 D, with genes involved in protein synthesis and degradation significantly down-regulated and up-regulated, respectively, at 14 D of muscle atrophy. There was also a significant decrease in the protein content of mitochondrial cytochrome c oxidase, and the enzyme activity of cytochrome c oxidase and citrate synthase after 14 D of immobilization. Furthermore, protein ubiquitination was significantly increased at 48 H but not 14 D of immobilization. These results suggest that transcriptional and post-transcriptional suppression of mitochondrial processes is sustained throughout 14 D of immobilization, while protein ubiquitination plays an early but transient role in muscle atrophy following short-term immobilization in humans.

Resistance exercise decreases eIF2Bepsilon phosphorylation and potentiates the feeding-induced stimulation of p70S6K1 and rpS6 in young men.

We investigated the effect of resistance exercise and feeding on the activation of signaling proteins involved in translation initiation. Nine young men (23.7+/-0.41 yr; BMI=25.5+/-1.0 kg/m2; means+/-SE) were tested twice after they performed a strenuous bout of unilateral resistance exercise, such that their contralateral leg acted as a nonexercised comparator, in either the fasted and fed [1,000 kJ, each 90 min (3 doses): 10 g protein, 41 g carbohydrate, 4 g fat] states. Muscle biopsies were obtained 6 h postexercise from both legs, resulting in four experimental conditions: rest-fasted, rest-fed, exercise-fasted, and exercise-fed. Feeding increased PKB/Akt (Ser473) phosphorylation (P<0.05), while exercise increased the phosphorylation of Akt and the downstream 70 kDa S6 protein kinase (p70S6K1, Thr389) and ribosomal protein S6 (rpS6, Ser235/236, Ser240/244; all P<0.05). The combination of resistance exercise and feeding increased the phosphorylation of p70S6K1 (Thr389) and rpS6 (Ser240/244) above exercise alone (P<0.05). Exercise also reduced phosphorylation of the catalytic epsilon subunit of eukaryotic initiation factor 2B (eIF2Bepsilon, Ser540; P<0.05). Mammalian target of rapamycin (mTOR, Ser2448), glycogen synthase kinase-3beta (GSK-3beta, Ser9), and focal adhesion kinase (FAK, Tyr576/577) phosphorylation were unaffected by either feeding or resistance exercise (all P>0.14). In summary, feeding resulted in phosphorylation of Akt, while resistance exercise stimulated phosphorylation of Akt, p70S6K1, rpS6, and dephosphorylation eIF2Bepsilon with a synergistic effect of feeding and exercise on p70(S6K1) and its downstream target rpS6. We conclude that resistance exercise potentiates the effect of feeding on the phosphorylation and presumably activation of critical proteins involved in the regulation of muscle protein synthesis in young men.