In this Issue
March 2017; volume 122, issue 3
EDITORIAL | Recovery from Exercise
REVIEWS | Recovery from Exercise
RESEARCH ARTICLE | Case Studies in Physiology
- Case Studies in Physiology: Maximal oxygen consumption and performance in a centenarian cyclist
This study shows, for the first time, that maximal oxygen consumption (+13%) and performance (+11%) can still be increased between 101 and 103 yr old with 2 yr of training and that a centenarian is able, at 103 yr old, to cover 26.9 km/h in 1 h.
RESEARCH ARTICLES | Recovery from Exercise
- Changes in muscle fiber contractility and extracellular matrix production during skeletal muscle hypertrophy
This study utilized a rat synergist ablation model to integrate changes in single muscle fiber contractility, extracellular matrix composition, activation of important signaling pathways in muscle adaption, and corresponding changes in the muscle transcriptome to provide novel insight into the basic biological mechanisms of muscle fiber hypertrophy.
- Intermittent hypobaric hypoxia combined with aerobic exercise improves muscle morphofunctional recovery after eccentric exercise to exhaustion in trained rats
Our study provides new insights into the use of intermittent hypobaric hypoxia combined with exercise as a strategy to recover muscle damage induced by eccentric exercise. We analyzed the effects of hypobaric exposure combined with aerobic exercise on histopathological features of muscle damage, fiber morphofunctionality, capillarization, angiogenesis, and the oxidative capacity of damaged soleus muscle. Most of these parameters were improved after a 2-wk protocol of intermittent hypobaric hypoxia combined with aerobic exercise.
- Suite of clinically relevant functional assays to address therapeutic efficacy and disease mechanism in the dystrophic mdx mouse
This study uses novel phenotypic assays which when applied to the mdx mouse resemble recently used primary end points for DMD clinical trials. A measurable distinction between dystrophic and control mice was seen at early time points in vivo compared with invasive muscle studies performed ex vivo. These assays shed light on normal and pathological responses to muscular exertion and have significant mechanistic and translational implications for the fields of basic myology and neuromuscular therapeutics.
- Mast cell degranulation and de novo histamine formation contribute to sustained postexercise vasodilation in humans
Blood flow to previously active skeletal muscle remains elevated following an acute bout of aerobic exercise and is dependent on activation of histamine H1 and H2 receptors. The intramuscular source of histamine that drives this response to exercise has not been identified. Using intramuscular microdialysis in exercising humans, we show both mast cell degranulation and formation of histamine by histidine decarboxylase contributes to the histamine-mediated vasodilation that occurs following a bout of aerobic exercise.
- Oxidative phosphorylation: unique regulatory mechanism and role in metabolic homeostasis
A model developed for oxidative phosphorylation in vivo is shown to predict behavior patterns that are both novel and consistent with experimental measurements of metabolism in working muscle and other cells. The dependence of the rate on ADP concentration shows a pronounced threshold with a steep, nearly linear increase above the threshold. The threshold determines the homeostatic set point, and the slope above threshold determines how much metabolism changes in response to varied energy demand.
- The impact of postexercise essential amino acid ingestion on the ubiquitin proteasome and autophagosomal-lysosomal systems in skeletal muscle of older men
The impact of postexercise leucine ingestion on processes of skeletal muscle breakdown in older adults is not well understood. Additional postexercise leucine ingestion appears to further reduce autophagy, but it does not interfere with the increase in ubiquitin proteasome system markers or the breakdown of intact proteins in skeletal muscle of older men. Postexercise leucine ingestion may promote a healthier protein pool and favorable muscle adaptations in older adults through greater accretion of myofibrillar proteins.
- The protective role of sex hormones in females and exercise prehabilitation in males on sternotomy-induced cranial hypoperfusion in aortic banded mini-swine
Our findings suggest a median sternotomy may predispose patients, possibly postmenopausal women and sedentary men, to perioperative cerebral ischemia, an increased risk of cardiac surgery-related stroke, and resulting neurocognitive impairments. Specifically, data from this common surgical procedure show: 1) median sternotomy independently decreases cranial perfusion; 2) female sex hormones improve cranial blood flow recovery following sternotomy, and 3) exercise prehabilitation prevents sternotomy-induced cranial hypoperfusion. Exercise prehabilitation before cardiac surgery may be advantageous for capable patients.
- Effects of different stresses on cardiac autonomic control and cardiovascular coupling
The study is the first to compare the time-variant pattern of autonomic nervous activities and cardiovascular coupling between the mental arithmetic task (MAT) and the cold pressor test (CPT). Our results demonstrated that MAT and CPT elicited different time-varying patterns of autonomic neural activities and cardiovascular synchronization. Both the amplitude and phase consistency of blood pressure and heart rate decreased in MAT. CPT may affect the harmonic frequency of the baroreflex loop.
- Muscle metabolic and neuromuscular determinants of fatigue during cycling in different exercise intensity domains
The gas exchange threshold and the critical power demarcate discrete exercise intensity domains. For the first time, we show that the limit of tolerance during whole body exercise within these domains is characterized by distinct metabolic and neuromuscular responses. Fatigue development during exercise greater than critical power is associated with the attainment of consistent “limiting” values of muscle metabolites, whereas substrate availability and limitations to muscle activation may constrain performance at lower intensities.
- Are there sex differences in the capillary blood volume and diffusing capacity response to exercise?
Women demonstrate lower diffusing capacity-to-cardiac output ratio (DlCO/Q̇), pulmonary capillary blood volume (Vc), and membrane diffusing capacity (Dm) compared with height-matched men during exercise. However, these differences disappear after correction for lung size. The drop in DlCO/Q̇ was proportionally less in women, and pulmonary transit time did not drop below 0.3 s in either group. After differences in lung volume are accounted for, there is no intrinsic sex difference in DlCO, Vc, or Dm response to exercise.
- Altered nuclear dynamics in MDX myofibers
Microtubules provide means for nuclear movement but show altered organization in the muscular dystrophy mouse model (MDX) (dystrophin-null) muscle. Here, MDX myofibers show increased nuclear movement, altered transcriptional activity, and altered linkers of nucleoskeleton and cytoskeleton complex expression compared with healthy myofibers. Microtubule architecture was incorporated in finite element modeling of passive stretch, revealing a role of fiber malformation, commonly found in MDX muscle. The results suggest that alterations in microtubule architecture in MDX muscle affect nuclear movement, which is essential for muscle function.
- Velopharyngeal mucosal surface topography in healthy subjects and subjects with obstructive sleep apnea
A new methodology was used to model the upper airway mucosal surface topography from magnetic resonance images of patients with obstructive sleep apnea and healthy adults. Curvature analysis was used to analyze the topography of the models, and a new metric was derived to describe the mucosal surface roughness. Increased roughness was found in the obstructive sleep apnea vs. healthy group, but further research is required to determine the functional effects of the measured difference on upper airway airflow mechanics.
- The effects of voluntary exercise and prazosin on capillary rarefaction and metabolism in streptozotocin-induced diabetic male rats
It is currently well established that poorly controlled diabetes reduces both skeletal muscle mass and muscle capillarization. These muscle-specific features of diabetes may, in turn, compromise insulin sensitivity and glucose control. Using a model of streptozotocin-induced diabetes, we show the vascular complications linked with disease and how chronic exposure to exercise and prazosin (an α1-adrenergic antagonist) can reduce these complications and improve glycemic control.
- Assessment of airway response distribution and paradoxical airway dilation in mice during methacholine challenge
Information on the distribution of airway diameters during bronchoconstriction in situ is critical for understanding the regional response of the lungs. We have developed an imaging method to quantify and compare the size of hundreds of airways in vivo during bronchoconstriction in mice. The results demonstrate large heterogeneity with both constriction and paradoxical dilation of airways, confirming the importance of considering the lung as an interconnected system rather than a collection of independent units.
- Esmolol infusion versus propranolol infusion: effects on heart rate and blood pressure in healthy volunteers
We used cycle ergometry exercise and infusions of isoproterenol and epinephrine to test the heart rate-lowering effect of esmolol compared with propranolol and saline in healthy humans. Collectively, our data indicate that infusion of ~160 mg of esmolol (range 110-200 mg in the 5 min before exercise) acutely and selectively blocks β1-adrenergic receptors. These infusion parameters can be used in future experiments to evaluate β1- vs. β2-receptor control of the circulation in humans.
- Sarcomeric protein modification during adrenergic stress enhances cross-bridge kinetics and cardiac output
Posttranslational modifications to sarcomeric regulatory proteins provide a mechanism to modulate cardiac function in response to stress. In this study, we demonstrate that neurohormonal stress produces modifications to myosin-binding protein C and troponin I, including a reduction in protein expression within the sarcomere and increased phosphorylation of the remaining protein, which serve to enhance cross-bridge kinetics and increase cardiac output. These findings highlight the importance of sarcomeric regulatory protein modifications in modulating ventricular function during cardiac stress.
- Influence of dietary nitrate supplementation on physiological and muscle metabolic adaptations to sprint interval training
We investigated the influence of nitrate-rich and nitrate-depleted beetroot juice on the muscle metabolic and physiological adaptations to 4 wk of sprint interval training. Compared with placebo, dietary nitrate supplementation reduced the O2 cost of submaximal exercise, resulted in greater improvement in incremental (but not severe-intensity) exercise performance, and augmented some muscle metabolic adaptations to training. Nitrate supplementation may facilitate some of the physiological responses to sprint interval training.
- Adjustments with running speed reveal neuromuscular adaptations during landing associated with high mileage running training
Although neuromuscular factors play a key role during running, the influence of high mileage training on neuromuscular function has been poorly studied, especially in relation to running speed. This study is the first to demonstrate changes in neuromuscular conditioning with high mileage training, mainly characterized by lower thigh muscle activation after touch down, higher initial knee stiffness, and greater estimates of energy return, with adaptations being increasingly evident at faster running speeds.
- Alterations to mitochondrial fatty-acid use in skeletal muscle after chronic exposure to hypoxia depend on metabolic phenotype
Affinity for low concentrations of long-chain fatty acids (LCFA) in mitochondria skeletal muscles increases after chronic hypoxia. Combined with a lower respiratory exchange ratio, this suggests facility for fatty acid utilization at rest. This fuel preference is related to caloric restriction in oxidative muscle and to hypoxia in glycolytic one. In contrast, maximal oxidation for LCFA is decreased by chronic hypoxia in glycolytic muscle and can explain glucose dependence at exercise.
- Kinetics of circulating progenitor cell mobilization during submaximal exercise
Using a comprehensive evaluation of circulating progenitor cells (CPCs), we show that CPC mobilization during exercise is related to tissue damage, and not plasma concentrations of CXC chemokine ligand 12 and stem cell factor. These data have implications for the use of exercise interventions as adjuvant therapy for CPC mobilization in the context of hematopoietic stem cell transplant and also support the role of mobilized progenitor cells as cellular mediators of systemic adaptations to exercise.
- Heat induces interleukin-6 in skeletal muscle cells via TRPV1/PKC/CREB pathways
Heat increases the release of interleukin-6 (IL-6) from skeletal muscle cells. IL-6 has been shown to serve immune responses and metabolic functions in muscle. It can be anti-inflammatory as well as proinflammatory. However, the mechanism that induces release of IL-6 from skeletal muscle cells remains unknown. Here we show that heat increases IL-6 in skeletal muscle cells through the transient receptor potential vannilloid 1, PKC, and cAMP response element-binding protein signal transduction pathway.
- A new method to evaluate macaque health using exhaled breath: A case study of M. tuberculosis in a BSL-3 setting
To the best of our knowledge, this is the first time the volatile molecule content of macaque breath has been comprehensively sampled and analyzed. We do so here in a Biosafety Level 3 setting in the context of M. tuberculosis lung infection. The breath of nonhuman primates represents a novel fluid that could provide insight into disease pathogenesis.
- Commentaries on Viewpoint: Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning?COMMENTARY ON VIEWPOINT: COULD SMALL-DIAMETER MUSCLE AFFERENTS BE RESPONSIBLE FOR THE ERGOGENIC EFFECT OF LIMB ISCHEMIC PRECONDITIONING?COMMENTARY ON VIEWPOINT: COULD SMALL-DIAMETER MUSCLE AFFERENTS BE RESPONSIBLE FOR THE ERGOGENIC EFFECT OF LIMB ISCHEMIC PRECONDITIONING?SMALL-DIAMETER MUSCLE AFFERENTS MAY NOT BE THE PREDOMINANT FACTOR RESPONSIBLE FOR THE ERGOGENIC EFFECT ASSOCIATED WITH ISCHEMIC PRECONDITIONINGCOMMENTARY ON VIEWPOINT: COULD SMALL-DIAMETER MUSCLE AFFERENTS BE RESPONSIBLE FOR THE ERGOGENIC EFFECT OF LIMB ISCHEMIC PRECONDITIONING?COMMENTARY ON VIEWPOINT: COULD SMALL-DIAMETER MUSCLE AFFERENTS BE RESPONSIBLE FOR THE ERGOGENIC EFFECT OF LIMB ISCHEMIC PRECONDITIONING?COMMENTARY ON VIEWPOINT: COULD SMALL-DIAMETER MUSCLE AFFERENTS BE RESPONSIBLE FOR THE ERGOGENIC EFFECT OF LIMB ISCHEMIC PRECONDITIONING?COMMENTARY ON VIEWPOINT: COULD SMALL-DIAMETER MUSCLE AFFERENTS BE RESPONSIBLE FOR THE ERGOGENIC EFFECT OF LIMB ISCHEMIC PRECONDITIONING?COMMENTARY ON VIEWPOINT: COULD SMALL-DIAMETER MUSCLE AFFERENTS BE RESPONSIBLE FOR THE ERGOGENIC EFFECT OF LIMB ISCHEMIC PRECONDITIONING?COMMENTARY ON VIEWPOINT: COULD SMALL-DIAMETER MUSCLE AFFERENTS BE RESPONSIBLE FOR THE ERGOGENIC EFFECT OF LIMB ISCHEMIC PRECONDITIONING?ROS-INDUCED ADAPTATIONS IN LIMP ISCHEMIC PRECONDITIONING