The primary objective of this study was to investigate the effects of a 4-week respiratory muscle endurance training (eRMT) program on the physiological and psychological aspects of central fatigue using, respectively, near-infrared spectroscopy (NIRS) and quantification of effort perceptions during maximal exercise. A secondary objective was to assess any impact of eRMT on respiratory health and exercise performance. This study compared pre- and post-eRMT data from the same group of healthy adults. The results indicated that eRMT did not have any effect on respiratory function, exercise time to exhaustion, or physiological responses to exercise but significantly decreased ratings of perceived exertion (RPE) during exercise. An increase in the concentrations of oxygenated hemoglobin [O2Hb], deoxygenated hemoglobin [HHb], and total hemoglobin [tHb] during exercise was observed post-eRMT compared to pre-eRMT, and this increase differed by hemisphere. Based on these preliminary findings, we suggest an eRMTinduced left-to-right hemodynamic shift during exercise, consistent with the change from a novel to a learned task.
People have been traveling to high altitude for centuries where they are faced with adverse environmental conditions. As one ascends to elevation, the barometric pressure is reduced and the air gets thinner. These changes affect the partial pressure of gases in the ambient air. The decreased partial pressures of oxygen affects physiological processes, such as increased ventilation (hyperventilation), vascular tone and the decreased capacity for cellular metabolism. These changes have serious implications on exercise capacity and overall safety of individuals exposed to these conditions as well as their health. Prior studies have shown voluntary isocapnic hyperpnea training (VIHT) to eliminate the hyperventilatory response associated with exercise at sea level. Since high altitude provokes hyperventilation at rest, and the addition of higher intensity exercise exacerbates this response, the respiratory muscles have a higher propensity to fatigue, further limiting exercise capacity. High ventilation rates, especially at altitude, cause significant decreases in the arterial partial pressure of carbon dioxide (PaCO2) leading to the constriction of blood vessels. The constriction has potential detrimental effects on cerebral oxygenation and therefore central fatigue. These factors, taken together, produce severe limitations on exercise capacity at altitude. This study was designed to measure the effects of VIHT three days per week for four weeks on exercise performance at 10,000ft simulated altitude. Ten healthy non-smoking moderately active men were recruited, five of which completed the study. The subjects performed Pre- and Post-VIHT exercise endurance trials cycling at 60rpm against 75% of their predetermined maximal workload (determined at sea level) on an electrically break cycle ergometer in a hypobaric (decompression) chamber. Prior to the start of exercise and during exercise physiological responses were measured and recorded during exercise at altitude. Heart rate, arterial oxygen saturation (SaO2), cerebral blood flow velocity (CBFv), diffused cerebral tissue oxygen saturation, end tidal CO2 and mixed expiratory gases were measured as well as ventilatory characteristics such as minute ventilation, respiratory rate and tidal volumes were recorded. All subjects training minute ventilation rates improved over the twelve training sessions, 37% on average. At rest, subjects SaO2 decreased 6. 6% on average from sea level to simulated altitude while heart rates subsequently increased on average from 73 to 86 bpm.^During exercise at altitude there was marked hyperventilation in both Pre- and Post-VIHT endurance trials, and more so in the post-VIHT trials, lowering end tidal CO2 throughout the trial. Corresponding to the hyperventilation, CBFv also decreased while cerebral oxygen saturation remained constant. Exercise endurance times improved 64% on average from Pre- to Post VIHT trials. These results suggest that VIHT reduces respiratory muscle fatigue, allowing subjects to breathe at higher ventilation rates for extended periods of time, which improves exercise endurance at altitude. Key Words:Altitude, respiratory muscle training, exercise, cerebral blood flow velocity.
In the past, ‘traditional’ moderate-intensity continuous training (60-75% peak heart rate) was the type of physical activity most frequently recommended for both athletes and clinical populations (cf. American College of Sports Medicine guidelines). However, growing evidence indicates that high-intensity interval training (80-100% peak heart rate) could actually be associated with larger cardiorespiratory fitness and metabolic function benefits and, thereby, physical performance gains for athletes. Similarly, recent data in obese and hypertensive individuals indicate that various mechanisms – further improvement in endothelial function, reductions in sympathetic neural activity, or in arterial stiffness – might be involved in the larger cardiovascular protective effects associated with training at high exercise intensities. Concerning hypoxic training, similar trends have been observed from ‘traditional’ prolonged altitude sojourns (‘Live High Train High’ or ‘Live High Train Low’), which result in increased hemoglobin mass and blood carrying capacity. Recent innovative ‘Live Low Train High’ methods (‘Resistance Training in Hypoxia’ or ‘Repeated Sprint Training in Hypoxia’) have resulted in peripheral adaptations, such as hypertrophy or delay in muscle fatigue. Other interventions inducing peripheral hypoxia, such as vascular occlusion during endurance/resistance training or remote ischemic preconditioning (i.e. succession of ischemia/reperfusion episodes), have been proposed as methods for improving subsequent exercise performance or altitude tolerance (e.g. reduced severity of acute-mountain sickness symptoms). Postulated mechanisms behind these metabolic, neuro-humoral, hemodynamics, and systemic adaptations include stimulation of nitric oxide synthase, increase in anti-oxidant enzymes, and down-regulation of pro-inflammatory cytokines, although the amount of evidence is not yet significant enough. Improved O2 delivery/utilization conferred by hypoxic training interventions might also be effective in preventing and treating cardiovascular diseases, as well as contributing to improve exercise tolerance and health status of patients. For example, in obese subjects, combining exercise with hypoxic exposure enhances the negative energy balance, which further reduces weight and improves cardio-metabolic health. In hypertensive patients, the larger lowering of blood pressure through the endothelial nitric oxide synthase pathway and the associated compensatory vasodilation is taken to reflect the superiority of exercising in hypoxia compared to normoxia. A hypoxic stimulus, in addition to exercise at high vs. moderate intensity, has the potential to further ameliorate various aspects of the vascular function, as observed in healthy populations. This may have clinical implications for the reduction of cardiovascular risks. Key open questions are therefore of interest for patients suffering from chronic vascular or cellular hypoxia (e.g. work-rest or ischemia/reperfusion intermittent pattern; exercise intensity; hypoxic severity and exposure duration; type of hypoxia (normobaric vs. hypobaric); health risks; magnitude and maintenance of the benefits). Outside any potential beneficial effects of exercising in O2-deprived environments, there may also be long-term adverse consequences of chronic intermittent severe hypoxia. Sleep apnea syndrome, for instance, leads to oxidative stress and the production of reactive oxygen species, and ultimately systemic inflammation. Postulated pathophysiological changes associated with intermittent hypoxic exposure include alteration in baroreflex activity, increase in pulmonary arterial pressure and hematocrit, changes in heart structure and function, and an alteration in endothelial-dependent vasodilation in cerebral and muscular arteries. There is a need to explore the combination of exercising in hypoxia and association of hypertension, developmental defects, neuro-pathological and neuro-cognitive deficits, enhanced susceptibility to oxidative injury, and possibly increased myocardial and cerebral infarction in individuals sensitive to hypoxic stress. The aim of this Research Topic is to shed more light on the transcriptional, vascular, hemodynamics, neuro-humoral, and systemic consequences of training at high intensities under various hypoxic conditions.
Deficits in exercise endurance and cognitive function have been observed at altitude for hundreds of years. Respiratory muscle training (RMT) has been demonstrated as an effective means of improving exercise performance in divers as well as in sea-level experiments. It has also been shown to decrease the work of breathing and improve the mechanical efficiency of breathing. It is however, unknown if respiratory muscle training is effective during exercise at altitude. Furthermore, the changes in breathing pattern imposed by respiratory muscle training and how they relate to cognitive function during exercise at altitude, have not been elucidated. Cognitive function of five male subjects (21. 2 & plusmn 1. 3 years) was tested at an altitude of 10,000 feet during exercise at 75% of their VO2 peak. Three different tests were used: the Digit-Span Forward test, Stroop Color Word test, and Symbol Digit Modalities test (SDMT). Cerebral blood flow velocity and oxygenation were measured with transcranial Doppler and cerebral oximeter, respectively, due to the role of cerebral oxygenation and blood flow in altered cognitive function. Exercise testing at altitude revealed a significant improvement in time to exhaustion in all subjects (Pre-RMT 17. 28 & plusmn 4. 25 vs. Post-RMT 24. 11 & plusmn 2. 19; p = 0. 01). Measures of cerebral oxygenation and blood flow velocity revealed no significant changes. There was a significant improvement in Stroop Color Word test scores (Pre-RMT 53. 4 & plusmn 8. 79 vs. Post-RMT 62. 6 & plusmn 7. 96; p = 0. 007). No significant changes were observed in the Digit Span Forward test and SDMT. These results suggest four weeks of RMT may improve cognitive function during exercise at altitude.
"Maximal heart rate (HR), cardiac output (Qc), oxygen uptake (Vo2) and minute ventilation (V) were measured in; 1. four hockeyists before and again at the end of a four-month season, 2. eleven other athletes (four swimmers, four skiers and three wrestlers) in the trained state only. Subjects exercised upright on a bicycle ergometer. HR was measured by ECG chest electrodes, Qc by the N20 method, V02 by collection of mixed expired air and V by a dry gas meter. Results were; 1. work capacity increased by 10% or more in the hockeyists, but maximal HR, Qc, V02 and V were not increased, 2. these parameters were remarkably constant among all athlete groups in the trained state, except that skiers had a higher V02 which may be a prerequisite for excellence at this sport rather than a training effect. Findings at submaximal work loads provided an explanation for the increased work capacity following seasonal training. Thus, a decreased HR, Qc and V at any given submaximal work load characterized the trained state. Since work after training causes less stress on cardio-respiratory function than it did before training, a higher maximal work capacity is possible with no increase in maximal cardiorespiratory dimensions."--
The 14th volume in the series will focus on cutting edge research at the interface of hypoxia and exercise. The work will cover the range from molecular mechanisms of muscle fatigue and muscle wasting to whole body exercise on the world’s highest mountains. State of the art papers on training at high altitude for low altitude athletic performance will also be featured.
The activities of the Food and Nutrition Board's Committee on Military Nutrition Research (CMNR, the committee) have been supported since 1994 by grant DAMD17-94-J-4046 from the U.S. Army Medical Research and Materiel Command (USAMRMC). This report fulfills the final reporting requirement of the grant, and presents a summary of activities for the grant period from December 1, 1994 through May 31, 1999. During this grant period, the CMNR has met from three to six times each year in response to issues that are brought to the committee through the Military Nutrition and Biochemistry Division of the U.S. Army Research Institute of Environmental Medicine at Natick, Massachusetts, and the Military Operational Medicine Program of USAMRMC at Fort Detrick, Maryland. The CMNR has submitted five workshop reports (plus two preliminary reports), including one that is a joint project with the Subcommittee on Body Composition, Nutrition, and Health of Military Women; three letter reports, and one brief report, all with recommendations, to the Commander, U.S. Army Medical Research and Materiel Command, since September 1995 and has a brief report currently in preparation. These reports are summarized in the following activity report with synopses of additional topics for which reports were deferred pending completion of military research in progress. This activity report includes as appendixes the conclusions and recommendations from the nine reports and has been prepared in a fashion to allow rapid access to committee recommendations on the topics covered over the time period.
