The human endurance athlete: heterogeneity and adaptability of selected exercise and skeletal muscle characteristics

In human subjects, large variations between individuals (up to 3-fold) exist in the capacity for endurance exercise performance. In a heterogeneous population, endurance performance is strongly related to whole body maximal oxygen uptake (VO2 max). This is in part genotype dependent (~25%) but is adaptable with training. However, this relationship does not hold within a homogeneous group of well-trained runners. Other phySiOlogical characteristics must contribute to endurance performance and these may include specific advantageous skeletal muscle phenotypes. Muscle fibre type distribution is also heterogeneous, although less adaptable. In contrast, muscle oxidative enzyme capacity is highly adaptable with training. The genetic influences on these muscle characteristics have been indirectly investigated by comparing African endurance athletes, who dominate world-class events, to Caucasian endurance athletes. We have established that African runners have greater resistance to fatigue than Caucasians (p < 0.01) and 50% greater oxidative enzyme activity in vastus lateralis samples (p < 0.05), despite somewhat lower Type I fibre proportion. These differences were not inherently present in a group of sedentary Africans, suggesting that the genotypic influence on athletic performance may be a superior adaptation to training, rather than a baseline genetic effect. Combined physiological and genetic studies are likely to elucidate a polygenetic basis for superior endurance performance

The human endurance athlete: Heterogeneity and adaptability of selected exercise and skeletal muscle characteristics

In human subjects, large variations between individuals (up to 3-fold) exist in the capacity for endurance exercise performance. In a heterogeneous population, endurance performance is strongly related to whole body maximal oxygen uptake (VO2max). This is in part genotype dependent (∼25%) but is adaptable with training. However, this relationship does not hold within a homogeneous group of well-trained runners. Other physiological characteristics must contribute to endurance performance and these may include specific advantageous skeletal muscle phenotypes. Muscle fibre type distribution is also heterogeneous, although less adaptable. In contrast, muscle oxidative enzyme capacity is highly adaptable with training. The genetic influences on these muscle characteristics have been indirectly investigated by comparing African endurance athletes, who dominate world-class events, to Caucasian endurance athletes. We have established that African runners have greater resistance to fatigue than Caucasians (p < 0.01) and 50% greater oxidative enzyme activity in vastus lateralis samples (p < 0.05), despite somewhat lower Type I fibre proportion. These differences were not inherently present in a group of sedentary Africans, suggesting that the genotypic influence on athletic performance may be a superior adaptation to training, rather than a baseline genetic effect. Combined physiological and genetic studies are likely to elucidate a polygenetic basis for superior endurance performance.Articl

Myostatin levels in skeletal muscle of hibernating ground squirrels

Myostatin, a negative regulator of muscle mass, is elevated during disuse and starvation. Mammalian hibernation presents a unique scenario, where animals are hypocaloric and in torpor, but the extent of muscle protein loss is minimized. We hypothesized that myostatin expression, which is usually increased early in disuse and under hypocaloric conditions, could be suppressed in this unique model. Skeletal muscle was collected from thirteen-lined ground squirrels, Spermophilus tridecemlineatus, at six time points during hibernation: control euthermic (CON); entrance into hibernation (ENT), body temperature (Tb) falling; early hibernation (EHib), stable Tb in torpor for 24h; late hibernation (LHib), stable Tb in torpor for 3days; early arousal (EAr), Tb rising; and arousal (AR), T b restored to 34-37°C for about 18h. There was no significant increase of myostatin during ENT, EHib or LHib. Unexpectedly, there were approximately sixfold increases in myostatin protein levels as squirrels arose from torpor. The elevation during EAr remained high in AR, which represented an interbout time period. Mechanisms that could release the suppression or promote increased levels of myostatin were assessed. SMAD2 and phosphorylated SMAD2 were increased during EHib, but only the phosphorylated SMAD2 during AR mirrored increases in myostatin. Follistatin, a negative regulator of myostatin, did not follow the same time course as myostatin or its signaling pathway, indicating more control of myostatin at the signaling level. However, SMAD7, an inhibitory SMAD, did not appear to play a significant role during deep hibernation. Hibernation is an excellent natural model to study factors involved in the endogenous intracellular mechanisms controlling myostatin. © 2011. Published by The Company of Biologists Ltd.Articl

Accelerated skeletal muscle recovery after in vivo polyphenol administration

Acute skeletal muscle damage results in fiber disruption, oxidative stress and inflammation. We investigated cell-specific contributions to the regeneration process after contusion-induced damage (rat gastrocnemius muscle) with or without chronic grape seed-derived proanthocyanidolic oligomer (PCO) administration. In this placebo-controlled study, male Wistar rats were subjected to PCO administration for 2 weeks, after which they were subjected to a standardised contusion injury. Supplementation was continued after injury. Immune and satellite cell responses were assessed, as well as oxygen radical absorption capacity and muscle regeneration. PCO administration resulted in a rapid satellite cell response with an earlier peak in activation (Pax7 +, CD56 +, at 4 h post-contusion) vs. placebo groups (PLA) (P<.001: CD56 + on Day 5 and Pax7 + on Day 7). Specific immune-cell responses in PLA followed expected time courses (neutrophil elevation on Day 1; sustained macrophage elevation from Days 3 to 5). PCO dramatically decreased neutrophil elevation to nonsignificant, while macrophage responses were normal in extent, but significantly earlier (peak between Days 1 and 3) and completely resolved by Day 5. Anti-inflammatory cytokine, IL-10, increased significantly only in PCO (Day 3). Muscle fiber regeneration (MHC f content and central nuclei) started earlier and was complete by Day 14 in PCO, but not in PLA. Thus, responses by three crucial cell types involved in muscle recovery were affected by in vivo administration of a specific purified polyphenol in magnitude (neutrophil), time course (macrophages), or time course and activation state (satellite cell), explaining faster effective regeneration in the presence of proanthocyanidolic oligomers. © 2011 Elsevier Inc. All rights reserved

Specific muscle adaptations in type II fibers after high-intensity interval training of well-trained runners

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Characteristics of impala (Aepyceros melampus) skeletal muscles

The aim of this study was to determine citrate synthase (CS), phosphofructokinase (PFK) activities and myosin heavy chain (MHC) isoform contents in four muscle groups (semimembranosus (S), deltoideus (D), longissimus lumborum (LL), and psoas major (PM)) of impala (n = 6). All four muscle groups expressed predominantly MHC Ha (means of 55 ± 22-93 ± 12%). MHC IIx was only expressed in D. In D, positive correlations were found between MHC I and age (r = 0.93; P < 0.05) and the weight of the animals (r = 0.94; P < 0.01). PFK (means of 175 ± 179-374 ± 181), CS (means of 100 ± 23-126 ± 38 μmol/min/g dw) and MHC content indicated that energy provision in the impala is produced to a large extent via oxidative pathways and fibre types vary with animal characteristics. © 2004 Published by Elsevier Ltd.Articl

The acute hypoxic ventilatory response: Testing the adaptive significance in human populations

The acute Hypoxic Ventilatory Response (HVR) is an important component of human hypoxia tolerance, hence presumably physiological adaptation to high altitude. We measured the isocapnic HVR (L min¯¹ %¯¹) in two genetically divergent low altitude southern African populations. The HVR does not differ between African Xhosas (X) and Caucasians (C) (X:-0.34±0.36; C:-0.42±0.33; P>0.34), but breathing patterns do. Among all Xhosa subjects, size-independent tidal volume was smaller (X: 0.75±0.20; C: 1.11±0.32 L; P<0.01), breathing frequency higher (X: 22.2±5.7; C: 14.3±4.2 breaths min¯¹; P<0.01) and hypoxic oxygen saturation lower than among Caucasians (X: 78.4±4.7%; C: 81.7±4.7%; P<0.05). The results remained significant if subjects from Xhosa and Caucasian groups were matched for gender, body mass index and menstrual cycle phase in the case of females. The latter also employed distinct breathing patterns between populations in normoxia. High repeatability (intra-class correlation coefficient) of the HVR in both populations (0.77–0.87)demonstrates that one of the prerequisites for natural selection, consistent between-individual variation, is met. Finally, we explore possible relationships between inter-population genetic distances and HVR differences among Xhosa, European, Aymara Amerindians, Tibetan and Chinese populations. Inter-population differences in the HVR are not attributable to genetic distance (Mantel Z-test, P=0.59). The results of this study add novel support for the hypothesis that differences in the HVR, should they be found between other human populations, may reflect adaptation to hypoxia rather than genetic divergence through time.Centre of Excellence for Invasion Biolog

Myostatin levels in skeletal muscle of hibernating ground squirrels

Myostatin, a negative regulator of muscle mass, is elevated during disuse and starvation. Mammalian hibernation presents a unique scenario, where animals are hypocaloric and in torpor, but the extent of muscle protein loss is minimized. We hypothesized that myostatin expression, which is usually increased early in disuse and under hypocaloric conditions, could be suppressed in this unique model. Skeletal muscle was collected from thirteen-lined ground squirrels, Spermophilus tridecemlineatus, at six time points during hibernation: control euthermic (CON); entrance into hibernation (ENT), body temperature (Tb) falling; early hibernation (EHib), stable Tb in torpor for 24 h; late hibernation (LHib), stable Tb in torpor for 3 days; early arousal (EAr), Tb rising; and arousal (AR), Tb restored to 34–37°C for about 18 h. There was no significant increase of myostatin during ENT, EHib or LHib. Unexpectedly, there were approximately sixfold increases in myostatin protein levels as squirrels arose from torpor. The elevation during EAr remained high in AR, which represented an interbout time period. Mechanisms that could release the suppression or promote increased levels of myostatin were assessed. SMAD2 and phosphorylated SMAD2 were increased during EHib, but only the phosphorylated SMAD2 during AR mirrored increases in myostatin. Follistatin, a negative regulator of myostatin, did not follow the same time course as myostatin or its signaling pathway, indicating more control of myostatin at the signaling level. However, SMAD7, an inhibitory SMAD, did not appear to play a significant role during deep hibernation. Hibernation is an excellent natural model to study factors involved in the endogenous intracellular mechanisms controlling myostatin

Muscle satellite cells increase during hibernation in ground squirrels

Skeletal muscle satellite cells (SCs) are involved in muscle growth and repair. However, clarification of their behavior in hibernating mammals is lacking. The aim of this study was to quantify SCs and total myonuclei in hibernator muscle during different phases of the torpor-arousal cycle. Skeletal muscle was collected from thirteen-lined ground squirrels, Ictidomys tridecemlineatus, at five timepoints during hibernation: control euthermic [CON, stable body temperature (Tb)], early torpor (ET, within 24h), late torpor (LT, 5+ consecutive days), early arousal (EA, increased respiratory rate >60 breaths/min, Tb 9-12°C) and interbout arousal (IA, euthermic Tb). Protein levels of p21, Myf5, Wnt4, and β-catenin were determined by western blotting. SCs (Pax7+) and myonuclei were identified using immunohistochemistry. Over the torpor-arousal cycle, myonuclei/fiber remained unchanged. However, the percentage of SCs increased significantly during ET (7.35±1.04% vs. control: 4.18±0.58%; p<0.05) and returned to control levels during LT. This coincided with a 224% increase in p21 protein during ET. Protein levels of Wnt4 did not change throughout, whereas Myf5 was lower during EA (p<0.08) and IA (p<0.05). Compared to torpor, β-catenin increased by 247% and 279% during EA and IA, respectively (p<0.05). In conclusion, SCs were not dormant during hibernation and increased numbers of SC during ET corresponded with elevated amounts of p21 suggesting that cell cycle control may explain the SC return to baseline levels during late torpor. Despite relatively low Tb during early arousal, active control of quiescence by Myf5 is reduced

Skeletal muscle atrophy: disease-induced mechanisms may mask disuse atrophy

Disuse atrophy is the loss of skeletal muscle mass due to inactivity or lower than ‘normal’ use. It is not only a furtive component of the ‘modern’ sedentary lifestyle but also a part of numerous pathologies, where muscle loss is linked to disease specific and/or other toxicity factors, eventually leading to wasting (cachexia). Whether disuse-or-disease induced, muscle loss leads to weakness and metabolic comorbidities with a high societal and financial cost. This review discusses the intricate network of interacting signalling pathways including Atrogin-1/MAFbx, IGF1-Akt, myostatin, glucocorticoids, NF-kB, MAPKs and caspases that seem to regulate disuse atrophy but also share common activation patterns in other states of muscle loss such as sarcopenia or cachexia. Reactive oxygen species are also important regulators of cell signalling pathways that can accelerate proteolysis and depress protein synthesis. Exercise is an effective countermeasure and antioxidants may show some benefit. We discuss how the experimental model used can crucially affect the outcome and hence our understanding of atrophy. Timing of sampling is crucial as some signalling mechanisms reach their peak early during the atrophy process to rapidly decline thereafter, while other present high levels even weeks and months after study initiation. The importance of such differences lays in future consideration of appropriate treatment targets. Apart from attempting to correct defective genes or negate their effects, technological advances in new rational ways should aim to regulate specific gene expression at precise time points for the treatment of muscle atrophy in therapeutic protocols depending on the origin of atrophy induction. © 2015, Springer International Publishing Switzerland