Christian Doria

Improved V̇O2 uptake kinetics and shift in muscle fiber type in high-altitude trekkers

The study investigated the effect of prolonged hypoxia on central [i.e., cardiovascular oxygen delivery (Q(a)O(2))] and peripheral (i.e., O(2) utilization) determinants of oxidative metabolism response during exercise in humans. To this aim, seven male mountaineers were examined before and immediately after the Himalayan Expedition Interamnia 8000-Manaslu 2008, lasting 43 days, among which, 23 days were above 5,000 m. The subjects showed a decrease in body weight (P < 0.05) and of power output during a Wingate Anaerobic test (P < 0.05) and an increase of thigh cross-sectional area (P < 0.05). Absolute maximal O(2) uptake (VO(2max)) did not change. The mean response time of VO(2) kinetics at the onset of step submaximal cycling exercise was reduced significantly from 53.8 s ± 10.9 to 39.8 s ± 10.9 (P < 0.05), whereas that of Q(a)O(2) was not. Analysis of single fibers dissected from vastus lateralis biopsies revealed that the expression of slow isoforms of both heavy and light myosin subunits increased, whereas that of fast isoforms decreased. Unloaded shortening velocity of fibers was decreased significantly. In summary, independent findings converge in indicating that adaptation to chronic hypoxia brings about a fast-to-slow transition of muscle fibers, resulting in a faster activation of the mitochondrial oxidative metabolism. These results indicate that a prolonged and active sojourn in hypoxia may induce muscular ultrastructural and functional changes similar to those observed after aerobic training.

Tiny percutaneous needle biopsy: An efficient method for studying cellular and molecular aspects of skeletal muscle in humans

Needle biopsy is widely used to obtain specimens for physiological, anatomical and biochemical studies of skeletal muscle (SM). We optimized a procedure which we termed tiny percutaneous needle biopsy (TPNB), to efficiently gather good numbers of human satellite cells and single dissociated fibers for the functional study of skeletal muscle; these samples permit isolation of high-quality RNA and sufficient amounts of proteins to allow molecular analysis. Moreover, TPNB showed a clear advantage in that the technique was easier than other procedures used on healthy volunteers in human trials. TPNB is a very safe minor surgical procedure. It is less traumatic than needle aspiration biopsy, and significant complications are improbable. TPNB should become established as an important tool in the investigation of SM and may be employed to study various physiological aspects of SM in human subjects. We suggest that TPNB should also be used in the study of muscle diseases and disorders including muscular dystrophy, congenital myopathy, and metabolic defects.

Effect of in-water oxygen prebreathing at different depths on decompression-induced bubble formation and platelet activation

Effect of in-water oxygen prebreathing at different depths on decompression-induced bubble formation and platelet activation in scuba divers was evaluated. Six volunteers participated in four diving protocols, with 2 wk of recovery between dives. On dive 1, before diving, all divers breathed normally for 20 min at the surface of the sea (Air). On dive 2, before diving, all divers breathed 100% oxygen for 20 min at the surface of the sea [normobaric oxygenation (NBO)]. On dive 3, before diving, all divers breathed 100% O2 for 20 min at 6 m of seawater [msw; hyperbaric oxygenation (HBO) 1.6 atmospheres absolute (ATA)]. On dive 4, before diving, all divers breathed 100% O2 for 20 min at 12 msw (HBO 2.2 ATA). Then they dove to 30 msw (4 ATA) for 20 min breathing air from scuba. After each dive, blood samples were collected as soon as the divers surfaced. Bubbles were measured at 20 and 50 min after decompression and converted to bubble count estimate (BCE) and numeric bubble grade (NBG). BCE and NBG were significantly lower in NBO than in Air [0.142+/-0.034 vs. 0.191+/-0.066 (P<0.05) and 1.61+/-0.25 vs. 1.89+/-0.31 (P<0.05), respectively] at 20 min, but not at 50 min. HBO at 1.6 ATA and 2.2 ATA has a similar significant effect of reducing BCE and NBG. BCE was 0.067+/-0.026 and 0.040+/-0.018 at 20 min and 0.030+/-0.022 and 0.020+/-0.020 at 50 min. NBG was 1.11+/-0.17 and 0.92+/-0.16 at 20 min and 0.83+/-0.18 and 0.75+/-0.16 at 50 min. Prebreathing NBO and HBO significantly alleviated decompression-induced platelet activation. Activation of CD62p was 3.0+/-0.4, 13.5+/-1.3, 10.7+/-0.9, 4.5+/-0.7, and 7.6+/-0.8% for baseline, Air, NBO, HBO at 1.6 ATA, and HBO at 2.2 ATA, respectively. The data show that prebreathing oxygen, more effective with HBO than NBO, decreases air bubbles and platelet activation and, therefore, may be beneficial in reducing the development of decompression sickness.

Low Intensity Exercise Training Improves Skeletal Muscle Regeneration Potential

Purpose: The aim of this study was to determine whether 12 days of low-to-moderate exercise training at low altitude (598 m a.s.l.) improves skeletal muscle regeneration in sedentary adult women. Methods: Satellite cells were obtained from the vastus lateralis skeletal muscle of seven women before and after this exercise training at low altitude. They were investigated for differentiation aspects, superoxide anion production, antioxidant enzymes, mitochondrial potential variation after a depolarizing insult, intracellular Ca2+ concentrations, and micro (mi)RNA expression (miR-1, miR-133, miR-206). Results: In these myogenic populations of adult stem cells, those obtained after exercise training, showed increased Fusion Index and intracellular Ca2+ concentrations. This exercise training also generally reduced superoxide anion production in cells (by 12–67%), although not in two women, where there was an increase of ~15% along with a reduced superoxide dismutase activity. miRNA expression showed an exercise-induced epigenetic transcription profile that was specific according to the reduced or increased superoxide anion production of the cells. Conclusions: The present study shows that low-to-moderate exercise training at low altitude improves the regenerative capacity of skeletal muscle in adult women. The differentiation of cells was favored by increased intracellular calcium concentration and increased the fusion index. This low-to-moderate training at low altitude also depicted the epigenetic signature of cells.

Neuromuscular electrical stimulation improves skeletal muscle regeneration through satellite cell fusion with myofibers in healthy elderly subjects

The aim of this study was to determine whether neuromuscular electrical stimulation (NMES) affects skeletal muscle regeneration through a reduction of oxidative status in satellite cells of healthy elderly subjects. Satellite cells from the vastus lateralis skeletal muscle of 12 healthy elderly subjects before and after 8 wk of NMES were allowed to proliferate to provide myogenic populations of adult stem cells [myogenic precursor cells (MPCs)]. These MPCs were then investigated in terms of their proliferation, their basal cytoplasmic free Ca2+ concentrations, and their expression of myogenic regulatory factors (PAX3, PAX7, MYF5, MYOD, and MYOG) and micro-RNAs (miR-1, miR-133a/b, and miR-206). The oxidative status of these MPCs was evaluated through superoxide anion production and superoxide dismutase and glutathione peroxidase activities. On dissected single skeletal myofibers, the nuclei were counted to determine the myonuclear density, the fiber phenotype, cross-sectional area, and tension developed. The MPCs obtained after NMES showed increased proliferation rates along with increased cytoplasmic free Ca2+ concentrations and gene expression of MYOD and MYOG on MPCs. Muscle-specific miR-1, miR-133a/b, and miR-206 were upregulated. This NMES significantly reduced superoxide anion production, along with a trend to reduction of superoxide dismutase activity. The NMES-dependent stimulation of muscle regeneration enhanced satellite cell fusion with mature skeletal fibers. NMES improved the regenerative capacity of skeletal muscle in elderly subjects. Accordingly, the skeletal muscle strength and mobility of NMES-stimulated elderly subjects significantly improved. NMES may thus be further considered for clinical or ageing populations.NEW & NOTEWORTHY The neuromuscular electrical stimulation (NMES) effect on skeletal muscle regeneration was assessed in healthy elderly subjects for the first time. NMES improved the regenerative capacity of skeletal muscle through increased myogenic precursor cell proliferation and fusion with mature myofibers. The increased cytoplasmic free Ca2+ concentration along with MYOD, MYOG, and micro-RNA upregulation could be related to reduced O2·- production, which, in turn, favors myogenic regeneration. Accordingly, the skeletal muscle strength of NMES-stimulated lower limbs of healthy elderly subjects improved along with their mobility.

Determination of Blood Lactate Training Zone Boundaries With Rating of Perceived Exertion in Runners

Abstract Dantas, JL, Doria, C, Rossi, H, Rosa, G, Pietrangelo, T, Fanò-Illic, G, and Nakamura, FY. Determination of blood lactate training zone boundaries with rating of perceived exertion in runners. J Strength Cond Res 29(2): 315–320, 2015—This study aimed to determine the rating of perceived exertion (RPE) values corresponding to the blood lactate concentration (BLC) training zone boundaries (2 and 4 mmol·L−1) in moderately trained runners using the Borg CR-10 scale. Moderately trained runners (n = 95) performed a submaximal incremental test on a treadmill, recording BLC and RPE at every stage. Simple linear regression analysis was used to determine the RPE values corresponding to the BLC training zone boundaries, which revealed that RPE was significantly and strongly correlated with BLC (r = 0.821, p < 0.001, R 2 = 0.675, adjusted R 2 = 0.674, standard error of estimate = 1.18). The prediction equation (RPE = 1.092 × BLC + 2.143) was obtained, and RPE values at the BLC training zone boundaries of 2 and 4 mmol·L−1 were calculated as 4.3 (95% confidence interval [CI], 3.9–4.7) and 6.5 (95% CI, 6.0–7.1), respectively. In conclusion, the RPE values at the BLC training zone boundaries of 2 mmol·L−1 (4.3) and 4 mmol·L−1 (6.5) were adequately predicted. Rating of perceived exertion (4.3 and 6.5) can be used as an affordable tool for controlling intensity to maintain the athletes in prescribed zones during training sessions.

Endurance and resistance training modifies the transcriptional profile of the vastus lateralis skeletal muscle in healthy elderly subjects

Ageing in humans is associated with physiological loss of strength and skeletal muscle fibres, known as sarcopenia. This results in loss of mobility and independence in the elderly, and is a major socioeconomic and public health issue. Progression of sarcopenia can be influenced by a range of concomitant factors. In our ongoing investigations into the effects on skeletal muscle of specific and intensity-graduated endurance and resistance training, we investigated the associated muscle adaptation at the molecular level through transcription profile analysis. Although the 12-week training programmes appeared to have little benefit, with increases in muscle strength of 1–2%, the transcriptional profiles obtained from tiny percutaneous needle biopsies of the vastus lateralis muscle demonstrated that the training was specific and efficient. This classification of the transcriptome in terms of the functional groupings of the gene expression profiles associated with the endurance and resistance training programmes provides a signature of the muscle responsiveness to the specific training. Therefore, such analyses could provide a useful tool to personalize specific skeletal muscle training, and they indicate that both endurance and resistance training should indeed be incorporated into weekly scheduled exercise in elderly subjects.

The influence of altitude hypoxia on uroflowmetry parameters in women.

There is scientific evidence to suggest a correlation between hypoxia and the physiology of micturition. During a Himalayan Scientific and Mountaineering Expedition, we performed tests to investigate the functional interactions between altitude hypoxia and uroflowmetry parameters in women. The tests were carried out in seven women (36.3 ± 7.1 yr) from normoxic [1,340 meters above sea level (m a.s.l.)] to hypoxic conditions (up to 5,050 m a.s.l.) and during the return descent. The following measures were determined: uroflowmetry parameters and saturation of peripheral oxygen (SpO2 ). As expected, SpO2 decreased from 97.7 to 77.8% with increasing altitude. Micturition flow time, flow volume, and voiding time increased with altitude (P < 0.04 for all), indicating a negative correlation with SpO2 In conclusion, in young adult women, micturition physiological parameters were affected during adaptation to hypoxia; the correlation with SpO2 strongly suggests a role of hypoxia in these changes. These data could help to support the design of new strategies for both prevention and medical treatment. An example of the latter might be hyperbaric oxygen therapy, which in some studies has proved able to reduce the symptoms in patients with hypoxic bladder.

Detection of the Lactate Threshold in Runners: What is the Ideal Speed to Start an Incremental Test?

Abstract Incremental tests on a treadmill are used to evaluate endurance athletes; however, no criterion exists to determine the intensity at which to start the test, potentially causing the loss of the first lactate threshold. This study aimed to determine the ideal speed for runners to start incremental treadmill tests. The study consisted of 94 runners who self-reported the average speed from their last competitive race (10-42.195 km) and performed an incremental test on a treadmill. The speeds used during the first three test stages were normalised in percentages of average competition speed and blood lactate concentration was analysed at the end of each stage. The relationship between speed in each stage and blood lactate concentration was analysed. In the first stage, at an intensity corresponding to 70% of the reported average race speed, only one volunteer had blood lactate concentration equal to 2 mmol·L-1, and in the third stage (90% of the average race speed) the majority of the volunteers had blood lactate concentration ≥2 mmol·L-1. Our results demonstrated that 70% of the average speed from the subject’s last competitive race - from 10 to 42.195 km - was the best option for obtaining blood lactate concentration <2 mmol·L-1 in the first stage, however, 80% of the average speed in marathons may be a possibility. Evaluators can use 70% of the average speed in competitive races as a strategy to ensure that the aerobic threshold intensity is not achieved during the first stage of incremental treadmill tests.

Physiological effects of high‐altitude trekking on gonadal, thyroid hormones and macrophage migration inhibitory factor (MIF) responses in young lowlander women

Altitude hypoxia is often associated with impairment of human reproduction. In this study, hormones and macrophage migration inhibitory factor (MIF, a proinflammatory cytokine with key roles in human reproduction) were determined in seven regularly menstruating, lowlander native women living at sea level participating in 14 days of trekking at moderate and high altitude. Blood and saliva samples were collected from each subject at high altitude (5050 m a.s.l. [above sea level]), and at sea level before and after the expedition. Testosterone level was lowered by high altitude and was restored after the end of the expedition, while progesterone decreased significantly in all participants at the end of the expedition, although most of the participants were in the luteal phase. The salivary concentration of MIF decreased greatly at altitude, but its levels were completely restored after the return to sea level. Our findings showed high sensitivity and rapid changes in the determined parameters in response to the high‐altitude hypoxic environment, particularly MIF.