Variations in exercise ventilation in hypoxia will affect oxygen uptake.

Reports of VO2 response differences between normoxia and hypoxia during incremental exercise do not agree. In this study VO2 and VE were obtained from 15-s averages at identical work rates during continuous incremental cycle exercise in 8 subjects under ambient pressure (633 mmHg ≈1,600 m) and during duplicate tests in acute hypobaric hypoxia (455 mmHg ≈4,350 m), ranging from 49 to 100% of VO2 peak in hypoxia and 42-87% of VO2 peak in normoxia. The average VO2 was 96 mL/min (619 mL) lower at 455 mmHg (n.s. P = 0.15) during ramp exercises. Individual response points were better described by polynomial than linear equations (mL/min/W). The VE was greater in hypoxia, with marked individual variation in the differences which correlated significantly and directly with the VO2 difference between 455 mmHg and 633 mmHg (P = 0.002), likely related to work of breathing (Wb). The greater VE at 455 mmHg resulted from a greater breathing frequency. When a subject's hypoxic ventilatory response is high, the extra work of breathing reduces mechanical efficiency (E). Mean ∆E calculated from individual linear slopes was 27.7 and 30.3% at 633 and 455 mmHg, respectively (n.s.). Gross efficiency (GE) calculated from mean VO2 and work rate and correcting for Wb from a VE-VO2 relationship reported previously, gave corresponding values of 20.6 and 21.8 (P = 0.05). Individual variation in VE among individuals overshadows average trends, as also apparent from other reports comparing hypoxia and normoxia during progressive exercise and must be considered in such studies.

The effect of aging on the autophagic and heat shock response in human peripheral blood mononuclear cells.

Autophagy is a lysosome degradation pathway through which damaged organelles and macromolecules are degraded within the cell. A decrease in activity of the autophagic process has been linked to several age-associated pathologies, including triglyceride accumulation, mitochondrial dysfunction, muscle degeneration, and cardiac malfunction. Here, we examined the differences in the autophagic response using autophagy-inducer rapamycin (Rapa) in peripheral blood mononuclear cells (PBMCs) from young (21.8 ± 1.9 years) and old (64.0 ± 3.7 years) individuals. Furthermore, we tested the interplay between the heat shock response and autophagy systems. Our results showed a significant increase in LC3-II protein expression in response to Rapa treatment in young but not in old individuals. This was associated with a decreased response in MAP1LC3B mRNA levels, but not SQSTM1/p62. Furthermore, HSPA1A mRNA was upregulated only in young individuals, despite no differences in HSP70 protein expression. The combined findings suggest a suppressed autophagic response following Rapa treatment in older individuals.

VESTPD as a measure of ventilatory acclimatization to hypobaric hypoxia.

This study compared the ventilation response to an incremental ergometer exercise at two altitudes: 633 mmHg (resident altitude = 1,600 m) and following acute decompression to 455 mmHg (≈4,350 m altitude) in eight male cyclists and runners. At 455 mmHg, the VESTPD at RER <1.0 was significantly lower and the VEBTPS was higher because of higher breathing frequency; at VO2max, both VESTPD and VEBTPS were not significantly different. As percent of VO2max, the VEBTPS was nearly identical and VESTPD was 30% lower throughout the exercise at 455 mmHg. The lower VESTPD at lower pressure differs from two classical studies of acclimatized subjects (Silver Hut and OEII), where VESTPD at submaximal workloads was maintained or increased above that at sea level. The lower VESTPD at 455 mmHg in unacclimatized subjects at submaximal workloads results from acute respiratory alkalosis due to the initial fall in HbO2 (≈0.17 pHa units), reduction in PACO2 (≈5 mmHg) and higher PAO2 throughout the exercise, which are partially pre-established during acclimatization. Regression equations from these studies predict VESTPD from VO2 and PB in unacclimatized and acclimatized subjects. The attainment of ventilatory acclimatization to altitude can be estimated from the measured vs. predicted difference in VESTPD at low workloads after arrival at altitude.

Time course of supine and standing shifts in total body, intracellular and extracellular water for a sample of healthy adults.

BACKGROUND/OBJECTIVES: Traditional tetrapolar bioimpedance spectroscopy (BIS) is performed with the participant supine for 10 min. New vertical analyzers are penetrating clinical, home and fitness markets, but have body water values that differ from supine reference measures. The minimum time standing prior to assessment does not appear in the literature. We investigated the time course of body water shifts in healthy adults undergoing 30-min assessments in supine and vertical positions. SUBJECTS/METHODS: While seated, participants were prepped for standard tetrapolar electrode placement. Starting position was counterbalanced and body water measurements were taken every 5 min for 30 min in both positions. Participants sat for 2 min prior to switching positions. Of the 64 participants, three were unable to stand for 30 min; their data were excluded. Body size differences were minimized via computation of relative (%) change between time intervals for total body water (TBW), extracellular water (ECW) and intracellular water (ICW). RESULTS: ECW and ICW shifted in opposite directions while participants were supine; as ECW decreased at each time point, ICW increased (P<0.0125). Likewise, when participants stood, ECW increased incrementally (P<0.0125), but the decreases in ICW were not significant. At each time interval, the changes in supine ECW and ICW differed from the standing values (P<0.05). No postural or time differences were found for %change TBW. CONCLUSIONS: For TBW, 5 min appears sufficient for fluid stabilization in either position. Supine ECW and ICW stabilization require more than 30 min as does standing ECW.

Does heat acclimation improve exercise capacity at altitude? A cross-tolerance model.

New approaches to inducing altitude acclimation in a relatively short timeframe are needed, as it is not practical for many soldiers and athletes to gain access to specialized training facilities. Acclimation to one environmental stressor could enhance adaptation to various other stressors in animals and humans. This phenomenon has been described as cross-tolerance and involves the activation of common protective pathways. The purpose of this review is to discuss possible mechanisms involved in the cross-tolerance between heat and hypoxia. Future data could potentially support the use of a cross-tolerance model as a means for military personnel to prepare for deployment to high-altitude environments, as well as for athletes competing at high altitude.

Characterization of the metabolic effects of irisin on skeletal muscle in vitro.

AIMS: This work explored the effects of irisin on metabolism, gene expression and mitochondrial content in cultured myocytes. METHODS: C2C12 myocytes were treated with various concentrations of irisin for various durations. Glycolysis and oxidative metabolism were quantified by measurement of extracellular acidification and oxygen consumption, respectively. Metabolic gene expression was measured by quantitative real-time polymerase chain reaction (qRT-PCR) and mitochondrial content was assessed by flow cytometry and confocal microscopy. RESULTS: Cells treated with irisin exhibited significantly increased oxidative metabolism. Irisin treatment also significantly increased mitochondrial uncoupling at various doses and durations. Lastly, treatment with irisin also significantly elevated metabolic gene expression including peroxisome proliferator-activated receptor γ coactivator-1 alpha (PGC-1α), nuclear respiratory factor 1 (NRF1), mitochondrial transcription factor A (TFAM), irisin, glucose transporter 4 (GLUT4) and mitochondrial uncoupling protein 3 (UCP3) leading to increased mitochondrial biogenesis. CONCLUSIONS: Our observations are the first to document increased metabolism in myocytes through irisin-mediated induction of mitochondrial biogenesis and uncoupling with corresponding gene expression. These observations support the need for further investigation into the therapeutic and pharmacological effects of irisin, as well as development of irisin-based therapy.

Physiological and anthropometric determinants of sport climbing performance.

OBJECTIVE: To identify the physiological and anthropometric determinants of sport climbing performance. METHODS: Forty four climbers (24 men, 20 women) of various skill levels (self reported rating 5.6-5.13c on the Yosemite decimal scale) and years of experience (0.10-44 years) served as subjects. They climbed two routes on separate days to assess climbing performance. The routes (11 and 30 m in distance) were set on two artificial climbing walls and were designed to become progressively more difficult from start to finish. Performance was scored according to the system used in sport climbing competitions where each successive handhold increases by one in point value. Results from each route were combined for a total climbing performance score. Measured variables for each subject included anthropometric (height, weight, leg length, arm span, % body fat), demographic (self reported climbing rating, years of climbing experience, weekly hours of training), and physiological (knee and shoulder extension, knee flexion, grip, and finger pincer strength, bent arm hang, grip endurance, hip and shoulder flexibility, and upper and lower body anaerobic power). These variables were combined into components using a principal components analysis procedure. These components were then used in a simultaneous multiple regression procedure to determine which components best explain the variance in sport rock climbing performance. RESULTS: The principal components analysis procedure extracted three components. These were labelled training, anthropometric, and flexibility on the basis of the measured variables that were the most influential in forming each component. The results of the multiple regression procedure indicated that the training component uniquely explained 58.9% of the total variance in climbing performance. The anthropometric and flexibility components explained 0.3% and 1.8% of the total variance in climbing performance respectively. CONCLUSIONS: The variance in climbing performance can be explained by a component consisting of trainable variables. More importantly, the findings do not support the belief that a climber must necessarily possess specific anthropometric characteristics to excel in sport rock climbing.

Energy expenditure and physiological responses during indoor rock climbing.

OBJECTIVES: To report the physiological responses of indoor rock climbing. METHODS: Fourteen experienced climbers (nine men, five women) performed three climbing trials on an indoor climbing wall. Subjects performed three trials of increasing difficulty: (a) an easy 90 degrees vertical wall, (b) a moderately difficult negatively angled wall (106 degrees), and (c) a difficult horizontal overhang (151 degrees). At least 15 minutes separated each trial. Expired air was collected in a Douglas bag after four minutes of climbing and heart rate (HR) was recorded continuously using a telemetry unit. Arterialised blood samples were obtained from a hyperaemised ear lobe at rest and one or two minutes after each trial for measurement of blood lactate. RESULTS: Significant differences were found between trials for HR, lactate, oxygen consumption (VO2), and energy expenditure, but not for respiratory exchange ratio. Analysis of the HR and VO2 responses indicated that rock climbing does not elicit the traditional linear HR-VO2 relationship characteristic of treadmill and cycle ergometry exercise. During the three trials, HR increased to 74-85% of predicted maximal values and energy expenditure was similar to that reported for running at a moderate pace (8-11 minutes per mile). CONCLUSIONS: These data indicate that indoor rock climbing is a good activity to increase cardiorespiratory fitness and muscular endurance. In addition, the traditional HR-VO2 relationship should not be used in the analysis of this sport, or for prescribing exercise intensity for climbing.

Oronasal distribution of ventilation at different ages.

The route of breathing, oral or nasal, is a determinant of the doses of inhaled pollutants delivered to target sites in the upper and lower respiratory tracts. We measured partitioning of ventilation, using a divided oronasal mask during a submaximal exercise test, in 37 male and female subjects who ranged in age from 7 to 72 y. The following four patterns of breathing were evident during exercise: (1) nasal only (13.5%), nasal shifting to oronasal (40.5%), oronasal only (40.5%), and oral only (5.4%). Children (i.e., 7-16 y of age) displayed more variability than adults with respect to their patterns of ventilation with exercise. Young adults (i.e., 17-30 y of age) who initially breathed nasally with exercise switched to oral ventilation at a lower percentage of the previously measured maximum ventilation (10.8%) than older subjects (31.8%). The partitioning of ventilation between the nasal and oral routes follows complex patterns that cannot be predicted readily by the age, gender, or nasal airway resistance of the subject.

Sources of variability in posterior rhinomanometry.

Sources of variability in nasal airway resistance measured by posterior rhinomanometry were studied in 5 subjects tested on 5 different days and 56 subjects tested on 2 different days. On each day, a questionnaire on upper airway health and nasal symptoms was completed. The mean individual difference in nasal airway resistance between the 2 test days in the group of 56 subjects was 5.3% (SD 52.7%). Between-subject variability accounted for 74.9% and 72.5% of the total variability in the group of 5 and the group of 56 subjects, respectively. For the 5 subjects, by accounting for a change in upper airway symptoms or upper respiratory tract infection that occurred over the 5 test days, there was a significant decrease in the between-subject variability. The difference in sources of variation due to a change in upper airway symptoms was not seen in the group of 56 subjects. We conclude that the largest source of variability in nasal airway resistance is due to between-subject differences.

Evaluation of the relationship between heart rate and ventilation for epidemiologic studies.

Estimation of pulmonary exposure and dose in air pollution epidemiology has been impaired by the lack of methods for directly measuring ventilation in ambulatory subjects. Heart-rate monitoring offers an approach to estimate ventilation by using ventilation-on-heart-rate (VE-HR) regressions established during exercise testing to estimate ventilation in the field. Conventional methods and protocols for testing were used to evaluate the relationship between VE and HR during three tasks: (1) exercising on a cycle ergometer, (2) lifting, and (3) vacuuming. The relationship between VE and HR was curvilinear and was best fit with linear regression models, using a natural log transformation of VE. Considerable interindividual variability in slopes and intercepts was observed across all types of exercise tests. The variability about the fitted regression lines for individual subjects was minimal; for example, individual R2 values for the maximum exercise test on 15 men ranged from 0.90 to 0.99 (mean = 0.97). The regression slopes established during upper-body exercise were greater by approximately 30%, relative to those derived in lower-body exercise (paired t test, p < .001). However, VE-HR regression slopes derived from tests in which progressively increasing workloads were used were comparable to those obtained during variable and nonprogressive protocols. These findings indicate that predictive accuracy is maximized by deriving VE-HR regressions for individual subjects and for both lower- and upper-body activities.

Assessment of heart rate as a predictor of ventilation.

The rate of ventilation and route of breathing (i.e., nasal versus oronasal) are potential determinants of pollutant doses to target sites in the lung. However, the lack of accurate methods for ambulatory measurement of ventilation has hindered estimation of exposure and dose in freely ranging individuals, complicating the interpretation of the relationships among exposure, dose, and response in epidemiological studies. The goal of this project was to develop and validate a method of monitoring ventilation for large-scale epidemiologic investigations. We estimated ventilation for individual subjects from ambulatory heart rate monitoring, using the relationship between ventilation and heart rate that had been obtained during exercise testing. Fifty-eight subjects participated in the study, which included healthy adults and children, and subjects with lung and heart disease. Subjects performed cycle exercise and tasks involving lifting and vacuuming. Work loads of progressive and variable order were used in the testing. Conventional methods were used to measure heart rate and total ventilation, and a sampling mask was developed to measure the partitioning of breathing between oral and nasal routes. The minute ventilation-heart rate relation was evaluated under steady-state and varying work loads. In a second phase, subjects wore wristwatch monitors that recorded their heart rates, minute by minute, throughout the day. Subjects recorded activities, locations, and levels of exertion. Two 16-hour monitoring periods were obtained from each subject. The laboratory findings documented considerable intersubject variability in the minute ventilation-heart rate relation with a two- to five-fold range in the coefficients describing the change in ventilation relative to heart rate. This variation implies that individual testing is required to derive accurate predictive equations. Minute ventilation-heart rate regressions for the maximal progressive exercise test and for the test with a nonprogressive submaximal work load sequence were comparable, indicating that varying the sequence of work loads does not substantially affect the minute ventilation-to-heart rate ratio. During upper body work (e.g., lifting), the minute ventilation-to-heart rate ratio was one-third greater than during lower body exercise. Diverse patterns of partitioning breathing between oral and nasal routes were observed with increasing oral ventilation in most subjects as work load increased. In the field, heart rate and activity patterns were monitored successfully in adults and children with low rates of instrument failure and noncompliance.(ABSTRACT TRUNCATED AT 400 WORDS)