In this Issue
August 2016; volume 121, issue 2
- Lifelong strength training mitigates the age-related decline in efferent drive
This cross-sectional study shows that efferent drive to contracting muscle is compromised with age. Furthermore, it shows that old subjects involved in long-term strength training mitigate this decline in efferent drive. In contrast, no difference in efferent drive was observed between recreationally active and sedentary old subjects. This indicates that strength training in particular may be beneficial for counteracting the age-related loss of efferent drive.
- Faster and stronger manifestation of mitochondrial diseases in skeletal muscle than in heart related to cytosolic inorganic phosphate (Pi) accumulation
A novel mechanism contributing to a faster (at lower OXPHOS deficiencies) and stronger manifestation of mitochondrial diseases in skeletal muscle than in heart, namely a much higher cytosolic inorganic phosphate (Pi) accumulation that causes muscle fatigue even at low/moderate exercise intensity, is proposed.
- The effects of a roundtrip trans-American jet travel on physiological stress, neuromuscular performance, and recovery
This study demonstrated trans-American jet travel going from east to west to participate in a rigorous simulated sport competition had dramatic effects on hormonal responses, sleep quality, and neuromuscular performances. Return travel to the east after the simulated sport competition resulted in muscle tissue damage and delays in neuromuscular and muscle tissue recovery upon return home. The use of extended wear whole body compression garments reduced the recovery times upon the homebound arrival.
- Qualitative dimensions of exertional dyspnea in adults with cystic fibrosis
This is the first study to characterize the evolution of the qualitative descriptors of exertional dyspnea in cystic fibrosis (CF). Adults with CF experience greater ventilatory constraints, have an earlier onset of unsatisfied inspiration, and are more likely to report chest tightness during exercise relative to controls. This study provides new insight into the qualitative dimensions of dyspnea in CF and may aid clinicians in tailoring therapies to manage dyspnea during physical activity.
- Antiapoptotic effect of exercise training on ovariectomized rat hearts
Cardiac widely dispersed apoptosis was found after ovariectomy. Exercise training on treadmill could prevent ovariectomy-induced cardiac widely dispersed apoptosis in Fas receptor-dependent apoptotic pathway (TNF-α, TNFR1, Fas-L, Fas, activated caspase-8, and activated caspase-3) and mitochondria-dependent apoptotic pathway (t-Bid, Bad, Bak, Bax, cytosolic cytochrome c, activated caspase-9, and activated caspase-3). Exercise training has antiapoptotic effects on ovariectomized rat hearts via both Fas receptor-dependent and mitochondria-dependent apoptotic pathways.
- Regional activation within the vastus medialis in stimulated and voluntary contractions
This study showed, for the first time, that regional activation induced by intramuscular stimulation in vastus medialis is relatively unaffected by changes in knee angle. When examined in voluntary dynamic contractions, there were shifts in regional activation that were not attributable to anatomic factors. The difference in EMG amplitude distribution between concentric and eccentric contractions provides preliminary evidence that regions within the VM can be preferentially recruited according to the mechanical demands of the task.
- Rate modulation of human anconeus motor units during high-intensity dynamic elbow extensions
We recorded single MUFRs during a high-intensity fatiguing dynamic elbow extension task. Because of unique features, the anconeus muscle (an accessory elbow extensor) facilitates tracking of units during rapid maximal effort concentric contractions at a moderately high load. Despite baseline dynamic rates being higher than those recorded during isometric maximum contractions, there was a decrease in MUFRs over the ∼80-s fatiguing protocol, indicating rate reduction is a common feature to both isometric and dynamic high-intensity fatiguing tasks.
- Effect of 23-day muscle disuse on sarcoplasmic reticulum Ca2+ properties and contractility in human type I and type II skeletal muscle fibers
This study identified for the first time a number of important cellular adaptations in human skeletal muscle fibers following 23 days of disuse, such as 1) a lower sarcoplasmic reticulum (SR) Ca2+ content in both fiber types and 2) an early upregulation of SR Ca2+ handling proteins, in particular an increase in SERCA1 and calsequestrin content, which precedes any transition in myosin heavy chain isoforms from slow to fast.
- The slow component of pulmonary O2 uptake accompanies peripheral muscle fatigue during high-intensity exercise
Quadriceps muscle torque production in response to electrically stimulated contractions (a measure of peripheral muscle fatigue) progressively decreases with greater durations of high-intensity constant-load cycling, and the time course and magnitude of this response mirrors that of the pulmonary oxygen uptake (V̇o2p) slow component. The quantitative and temporal association between the V̇o2p slow component and peripheral muscle fatigue suggests that mechanisms contributing to muscle fatigue also contribute to an increased O2 cost of exercise.
- Intermuscular adipose tissue and thigh muscle area dynamics during an 18-month randomized weight loss trial
This 18-mo randomized controlled trial among 273 sedentary adults considered yet to be addressed questions on the long-term effects of different lifestyle intervention strategies on the dynamics of both intermuscular adipose tissue and thigh muscle area, and their associations with cardiometabolic risk factors and abdominal subdepots. We found that intermuscular adipose tissue largely reflects body weight change per se, whereas moderate weight loss induced a significant decrease in thigh muscle area.
- The effect of 1 year of Alagebrium and moderate-intensity exercise training on left ventricular function during exercise in seniors: a randomized controlled trial
Exercise for 1 yr improved stroke volume and effective arterial elastance during exercise in previously sedentary seniors; however, these adaptations were not enhanced by the advanced glycation end-product cross-link breaker Alagebrium. Exercise plus Alagebrium for 1 yr failed to restore exercising left ventricular function to levels associated with lifelong exercise, despite a similar exercise frequency.
- Elevation of iron storage in humans attenuates the pulmonary vascular response to hypoxia
This study shows that a single dose of intravenous iron reduces the effects of hypoxia on the pulmonary circulation in a manner that persists for at least several weeks. This is long after the foreign iron-sugar complex has been cleared from the blood. It raises the possibility that manipulating iron stores, even in people who are not initially iron deficient, could be used for therapeutic gain in some forms of pulmonary hypertension.
- Intermittent hypoxia promotes recovery of respiratory motor function in spinal cord-injured mice depleted of serotonin in the central nervous system
In the present investigation we showed that exposure to intermittent hypoxia promotes the recovery of respiratory motor function in a spinal cord-injured mouse model. Moreover, we demonstrated that the recovery of respiratory motor function after spinal cord injury can occur despite the depletion of serotonin in the central nervous system.
- A possible carbon monoxide shuttle in the lung
This study provides evidence regarding a physiological mechanism that determines the lung mean capillary PCO that drives pulmonary CO excretion and functions as “back pressure” during CO uptake. Relevant to findings that CO is an intracellular signaling molecule and that there are clinical trials under way evaluating CO therapy, the goal of this study was to obtain a better understanding of the physiology of pulmonary CO exchanges that determine the body CO stores and intracellular PCO values.
- A methodological approach for quantifying and characterizing the stability of agitated saline contrast: implications for quantifying intrapulmonary shunt
Indicator dilution theory can quantify agitated saline contrast and be used to characterize the stability of agitated saline contrast. Agitated saline contrast is unstable suggesting that any measure of blood flow through intrapulmonary arteriovenous anastomoses (Q̇IPAVA) should consider transpulmonary transit time. Gases with high density and low blood solubility sufficiently stabilize saline contrast. Because of contrast instability, Q̇IPAVA is likely underestimated at rest.
- Correcting the dynamic response of a commercial esophageal balloon-catheter
Measurement of esophageal pressure affords calculation of many insightful and clinically important parameters of respiratory mechanics. It is recommended that an esophageal balloon-catheter possess an adequate frequency response up to 15 Hz. In this report we show that when this requirement is not met, it is possible to digitally compensate for the dynamic response of an esophageal balloon-catheter using an exponential model correction, or Wiener deconvolution (whereby superior results are obtained via the latter method).
- Predicting metabolic rate during level and uphill outdoor walking using a low-cost GPS receiver
This is the first study to characterize the direct relationship between global positioning system (GPS) speed and grade and the metabolic rate while walking outdoors under different controlled speed and grade conditions. Using GPS speed and grade yields accurate metabolic rate predictions during level and uphill outdoor walking, particularly when GPS grade is corrected. Moreover, when using GPS parameters with published speed/grade-based equations, the metabolic rate predictions were close to those obtained using actual speed and grade values.
Highlighted Topic | Hypoxia 2015
- Commentaries on Viewpoint: Could lobar flow sequencing account for convection-dependent ventilation heterogeneity in normal humans?Commentaries on Viewpoint: Could lobar flow sequencing account for convection-dependent ventilation heterogeneity in normal humans?Commentaries on Viewpoint: Could lobar flow sequencing account for convection-dependent ventilation heterogeneity in normal humans?
- Commentaries on Viewpoint: The rigorous study of exercise adaptations: Why mRNA might not be enoughCommentaries on Viewpoint: The rigorous study of exercise adaptations: Why mRNA might not be enoughCommentaries on Viewpoint: The rigorous study of exercise adaptations: Why mRNA might not be enoughCommentaries on Viewpoint: The rigorous study of exercise adaptations: Why mRNA might not be enoughCommentaries on Viewpoint: The rigorous study of exercise adaptations: Why mRNA might not be enoughCommentaries on Viewpoint: The rigorous study of exercise adaptations: Why mRNA might not be enoughCommentaries on Viewpoint: The rigorous study of exercise adaptations: Why mRNA might not be enoughCommentaries on Viewpoint: The rigorous study of exercise adaptations: Why mRNA might not be enough