Average Work Rate Research Articles

Assessment of Physiological Profiles in Developing Norms for Cardiopulmonary Fitness for Sri Lankan Rowers

Measurement of maximum oxygen consumption at tissue level (VO2 max) using cardiopulmonary exercise testing (CPET) is considered the gold standard in evaluating physiological fitness of an athlete. No such testing had been conducted on Sri Lankan national level rowers up to date. With this background the aim of this study was to evaluate the physiological profile of national rowers of Sri Lanka to assess the state of their cardiopulmonary fitness. Anthropometrical and physiological profiles were created for 22 rowers (10 males and 11 females). The Shapiro-Wilcoxon test was used to check the normal distribution. Means and standard deviations of the parameters were calculated. A P value less than 0.05 was considered to be statistically significant. Twenty rowers achieved more than 90% of their predicted HR and one achieved a HR of more than 85% indicating a maximum effort by the entire group. The average work rate achieved by oarsmen were 231 W, which is an average of 82% of the predicted. The average HR achieved was 187 BPM, which corresponds to an achievement of 96% of the predicted. The average respiratory exchange ratio achieved by oarsmen were 0.96, an indication of anaerobic glycolysis at peak exercise. Oarswomen achieved a peak workload of 235 which is slightly more than oarsmen. This is an achievement of 81% of the predicted. The group average HR achieved by oarswomen was 95 BPM, which is an achievement of 95% of the predicted. The group average RER was 0.84 which indicates a mixture of aerobic and anaerobic glycolysis at peak exercise. The VO2 values obtained by Sri Lankan rowers are low compared to international standards. Despite the overall lower VO2 max obtained by male rowers, their VO2 at AT was at a higher percentage of their peak VO2, indicating better cardiovascular fitness. Cardiovascular exercise can be improved to achieve a higher VO2 with a lower HR through threshold training in order to improve performance and uplift the stranded of rowing in Sri Lanka.

MODELING OF FLAGELLUM BEHAVIOR AND TWO-DIMENSIONAL SPERM CELL MOTILITY WITHIN THE CONTEXT OF FLUID–SOLID INTERACTIONS

In this study, the flagellar motility of a swimmer microorganism as a model of a human sperm cell, inside a two-dimensional channel as a model of the female reproductive tract containing a viscous fluid, is numerically investigated. The Navier–Stokes equations governing the fluid are coupled with the equations governing the models flagellum via applying a fluid–solid interaction approach and then solved using the finite element method. To stimulate the flagellum to move, a prescribed sinusoidal waveform is applied to it. The strain induced by this waveform along the flagellum initiates a continuous interaction between the flagellum and the fluid. The simulations are validated using data available in the literature. A very good agreement is seen between them. The results show that by decreasing the Young modulus of the flagellum as well as increasing the fluid viscosity, the swimming velocity of the model significantly decreases. It is found that for lower Young modulus of the flagellum, the effect of the fluid viscosity on the flagellar deformation is stronger. It is also found that for higher amplitude of the waveform applied to stimulate the flagellum, both the swimming velocity of the model and the average work rate are greater. Moreover, it is found that in a channel with a smaller height, the model swims at a higher speed and with a higher average work rate.

Mean completion time for a randomly varying rate of work

The mean time to finish a project is studied where the rate of work varies randomly. It is proved that the mean time to finish is bounded below by the time taken to complete the project if the work is performed at a fixed average rate, specifically, at the average work rate of the corresponding unrestricted or non-exit problem. Several examples illustrate the usefulness of the result in a variety of areas including population dynamics, engineering, finance, and philosophy.

Continuous forearm cooling attenuates gastrointestinal temperature increase during cycling

ABSTRACT Hot environmental conditions can challenge thermoregulation resulting in exacerbated heat strain. This study evaluated the influence of continuous inner forearm cooling on gastrointestinal temperature (TGI) and physiological responses to exercise in hot (30°C) and humid (relative humidity: 70%) conditions. Eleven trained cyclists (seven male age: 37±12 years; four female age: 41±15 years; mean±standard deviation) performed two experimental trials, cycling at 66% of their self-reported functional threshold power (average work rate over an hour of maximum effort cycling; 175±34W) for 45 minutes in an environmental chamber. One trial employed continuous inner forearm cooling (COOL) with 5°C water passing through aluminum heat exchangers, while the other had no cooling (CONTROL). Heat was removed from the body at an average rate of 30.3±6.6W during the COOL trial resulting in an attenuation of TGI rise (CONTROL: 2.46±0.70, COOL: 2.03±0.63°C·h−1; p=0.002). The change in heart rate from the 10th minute to the end of exercise, as an indicator of cardiovascular drift, was reduced (CONTROL: 20±7, COOL: 17±6beats·min−1; p=0.050) and end-exercise thermal comfort was improved in the COOL trial with a trend for reduced rating of perceived exertion (p=0.055). Findings suggest that continuous cooling of the inner forearms can attenuate the rise of TGI and help mitigate the risk of heat injury during exercise in hot and humid conditions.

Submaximal Exercise Does Not Increase Brain-Derived Neurotrophic Factor (BDNF) In People With Spinal Cord Injury

Brain-derived neurotrophic factor (BDNF) has been implicated in repair and regeneration of peripheral neurons, and is important for brain health. Acute exercise (EX) increases circulating BDNF in an intensity dependent manner in able-bodied individuals. However, the response of BDNF to EX in people with spinal cord injury (SCI) is poorly understood. PURPOSE: to investigate the hypothesis that submaximal EX will increase serum and plasma BDNF in people with SCI. METHODS: Nine adults with SCI participated (M age = 39.2 ± 11.0 years; M years post-injury = 16.5 ± 9.2). After completing a maximal exercise test on an electromagnetically braked arm-crank ergometer to determine peak power output (PPO), participants completed two visits in randomized order: 1) submaximal EX (30 minutes maintaining 55-65 rpm @ 60% PPO); and 2) seated control (CTL). Ratings of perceived exertion (RPE) were measured during EX using the 6-20 visual Borg RPE scale. Heart rate (HR) and blood pressure (BP) were measured pre- and post-EX. BDNF was measured via ELISA in both serum and plasma from venous blood sampled at pre-, post-, and 90 min post-EX. For the CTL visit, participants rested quietly for 120 min and blood was sampled at equivalent time points to EX. A 2-factor repeated measures ANOVA was computed to assess BDNF responses by time and condition. Paired t-tests were computed to assess HR and BP responses to EX. Pearson correlations were computed to explore relationships between BDNF and physiological responses to EX and work rate. RESULTS: The average EX work rate was 47 ± 17 W and RPE was 13 ± 1. HR increased by 26 ± 33 bpm (+41%; p=0.059), whereas systolic and diastolic BP remained unchanged after EX. Contrary to our hypotheses, EX had no effect on serum (Pre vs. Post-EX = 22447.9 ± 9071.1 pg/mL vs. 26552.8 ± 6563.4 pg/mL; F(1,12) = 0.51, p=0.53) or plasma (Pre vs. Post-EX = 1802.7 ± 1031.1 vs. 1662.7 ± 1390.0 pg/mL; F(1,10) = 0.77, p=0.45) BDNF. Exploratory correlational analyses showed no relationships between changes in BDNF and the outlined parameters. CONCLUSIONS: Submaximal EX did not increase BDNF in people with SCI. Future studies should systematically investigate BDNF responses to higher EX intensities given the intensity-dependent response in able-bodied people. FUNDING: Rick Hansen Foundation through the Blusson Integrated Cures Partnership.

Greater exercise tolerance in COPD during acute interval, compared to equivalent constant-load, cycle exercise: physiological mechanisms.

Exercise intolerance is common in chronic obstructive pulmonary disease (COPD) patients. In patients with COPD, we compared an interval exercise (IE) protocol (alternating 30s at 100% peak work rate (WRpeak ) with 30s at 50% WRpeak ) with moderate-intensity constant-load exercise (CLE) at 75% WRpeak , which yielded the same work rate. Exercise endurance time and total work output were almost twice as high for IE than CLE. At exercise isotime (when work completed was the same between IE and CLE), IE was associated with less dynamic hyperinflation, lower blood lactate concentration, and greater respiratory and locomotor muscle oxygenation, but there were no differences in ventilation or cardiac output. However, at the limit of tolerance for each modality, dynamic hyperinflation was not different between IE and CLE, while blood lactate remained lower and muscle oxygenation higher with IE. Taken together, these findings suggest that dynamic hyperinflation and not muscle-based factors dictate the limits of tolerance in these COPD patients. The relative importance of ventilatory, circulatory and peripheral muscle factors in determining tolerance to exercise in patients with chronic obstructive pulmonary disease (COPD) is not known. In 12 COPD patients (forced expiratory volume in one second: 58±17%pred.) we measured ventilation, cardiac output, dynamic hyperinflation, local muscle oxygenation, blood lactate and time to exhaustion during (a) interval exercise (IE) consisting of 30s at 100% peak work rate alternating with 30s at 50%, and (b) constant-load exercise (CLE) at 75% peak work rate, designed to produce the same average work rate. Exercise time was substantially longer during IE than CLE (19.5±4.8 versus 11.4±2.1min, p=0.0001). Total work output was therefore greater during IE than CLE (81.3±27.7 versus 48.9±23.8kJ, p=0.0001). Dynamic hyperinflation (assessed by changes from baseline in inspiratory capacity, ΔIC) was less during IE than CLE at CLE exhaustion time (isotime, p=0.009), but was similar at exhaustion (ΔICCLE : -0.38±0.10 versus ΔICIE : -0.33±0.12l, p=0.102). In contrast, at isotime, minute ventilation, cardiac output and systemic oxygen delivery did not differ between protocols (P>0.05). At exhaustion in both protocols, the vastus lateralis and intercostal muscle oxygen saturation were higher in IE than CLE (p=0.014 and p=0.0002, respectively) and blood lactate concentrations were lower (4.9±2.4mmoll-1 versus 6.4±2.2mmoll-1 , p=0.039). These results suggest that (1) exercise tolerance with COPD is limited by dynamic hyperinflation; and (2) cyclically lower (50%) effort intervals in IE help to preserve muscle oxygenation and reduce metabolic acidosis compared with CLE at the same average work rate; but these factors do not appear to determine time to exhaustion.

Analisa Perbandingan Percepatan Penyelesaian Proyek Dengan Metode (Studi Kasus : Proyek Mercu Suar,Yogyakarta)

Time constraints are often a problem in construction projects. Project scheduling and consistent evaluation are needed so that the project is completed on time. Evaluation is applied using performance intensity methods and Microsoft Project. Performance Intensity is a calculation carried out to determine the pace of project work. Performance intensity provides information on how quickly an activity can be completed. For the calculation of Performance Intensity use PPI, API and CPI. To control work in the field using CCS and CCP.
 Evaluation to find out the time performance applied to the Yogyakarta Lighthouse project. The project is planned to be completed on December 14, 2014 with a duration of 266 days. Evaluation is carried out for 35 periods. The results of this evaluation are differences in the analysis of the final day between the method of Performance Intensity and Microsoft project. The final day analysis of Performance Intensity at week 35 for 279 days, while analysis of Microsoft Project for 280 days. Differences in the range of predictions for the day-to-day analysis of a project are caused by the Performance Intensity method using the average cumulative work rate as a benchmark that changes every period. To pursue delays, the project acceleration method is used, namely Schedule. The time needed for the Schedule is 80 days.

The effect of time trial position on physiological variables in elite cycling.

Introduction Improving time trial performance can be achieved by cycling with an optimized aerodynamic position 1 . However, although reducing the cyclist’s frontal area will reduce the air resistance that must be overcome, a time trial position has significant flexibility requirements and some positions can potentially impair the ability to produce external power 2 . Physiological effects of using an aerodynamic position compared to an upright one, such as increased oxygen cost, have been shown in recreational cyclists 2 . In competitive cyclists, on the other hand, no difference between using the drops compared to an upright position has been shown 3 . However, less is known about the effect of these position changes in cyclists at the highest level, as well as the effect of using a too low position. Therefore, the purpose of the present pilot study was to investigate the effect of different time trial positions on physiological variables in elite competitive cyclists. Methods Three male junior elite cyclists participated in the study. All participants were competitive at the national level and participated in the national championships. Three positions on the bike were used: a high and low time trial position and an upright position with straight arms holding on the base bars. Each bout lasted 5 minutes, was separated by 4 minutes of rest and the work rate was set relative to the individual level of each cyclist, at ~90% of their 20-min peak power. All cycling was done at freely chosen cadences on a time trial specific bike mounted on a trainer (Computrainer Lab TM , Race Mate, Seattle, WA, USA). Results Average work rate during the cycling bouts was 339±16W (4.7±0.2 W/kg). The physiological response of cycling in the three positions is presented in Figure 1. The lowest time trial position resulted in higher blood lactate levels, higher oxygen consumption and lower gross efficiency compared to the high time trial position. For the upright position, oxygen consumption and gross efficiency were comparable to the lowest time trial position. However, blood lactate during the upright position was the lowest measured across all conditions. Discussion The main finding of the present study was that using a very low time trial position led to decreased gross efficiency and increased oxygen consumption and blood lactate compared to the high time trial position. The upright position led to an increased oxygen consumption compared to the time trial positions, but blood lactate was lower, which could indicate an increased energetic cost of maintaining an upright position with the arms. The reduced gross efficiency and increased blood lactate further indicate that in elite level junior cyclists, having a too low time trial position may be physiologically unfavourable.

Estimation of carbon-oxide emissions of tractors during operation and correlation with the not-to-exceed zone

The continuing rise in fossil fuel use significantly aggravates global warming problems because of carbon dioxide (CO2) emissions. This article shows a procedure to indirectly obtain data concerning the environmental pollution of a tractor by starting from direct data. The research confirms that qualitative indicators of a tractor's work for an operational period could be identified from a database compiled from engine processors. The average work rate of tractors measured under field conditions, together with the operating time in an engine's work mode, fuel consumption, and CO2 and CO emissions, have been measured. Correlations between CO2 and CO emissions and the NTE (not-to-exceed) zones during a tractor's operational period have also been determined. The study showed that the tractors worked, on average, 51% of the operational period with the engine working modes within the NTE zone. While working in these modes, the tractors consumed approximately 73.4% of the fuel used for the whole operational period, and emitted into the environment approximately 76% of the CO2 and 9.7% of the CO of the emissions of the whole operational period. It was found that there are possibilities to reduce fuel consumption and CO2 and CO emissions during tractor operational periods by improving the tractor's operation by choosing engine work modes in a more rational way.

Nonadiabatic quantum state engineering driven by fast quench dynamics

There are a number of tasks in quantum information science that exploit non-transitional adiabatic dynamics. Such a dynamics is bounded by the adiabatic theorem, which naturally imposes a speed limit in the evolution of quantum systems. Here, we investigate an approach for quantum state engineering exploiting a shortcut to the adiabatic evolution, which is based on rapid quenches in a continuous-time Hamiltonian evolution. In particular, this procedure is able to provide state preparation faster than the adiabatic brachistochrone. Remarkably, the evolution time in this approach is shown to be ultimately limited by its "thermodynamical cost,"provided in terms of the average work rate (average power) of the quench process. We illustrate this result in a scenario that can be experimentally implemented in a nuclear magnetic resonance setup.

The Physiologic Effects of an Acute Bout of Supramaximal High-Intensity Interval Training Compared with a Continuous Exercise Bout in Patients with COPD

This study compared physiological responses and work performed during a supramaximal high-intensity interval exercise training session (HIIT) and a constant work rate (CWR) exercise session. Fourteen patients with COPD (mean FEV1 53±13% predicted (±SD)) completed an incremental cardiopulmonary exercise test (CPET) and a steep ramp anaerobic test (SRAT) and then two exercise bouts to symptom limitation on separate days, in random order: (1) a CWR trial at 80% of CPET peak work rate (mean 63±15 W) and (2) a HIIT trial using repeats of 30 s at 70% of SRAT peak work rate (mean 112±29 W) followed by 90 s at 20% of CPET peak work rate. Subjects ceased exercise primarily due to dyspnea for both HIIT and CWR (64% vs. 57%, resp.). End-exercise VE, HR, dyspnea, and leg fatigue were similar between the two exercise protocols. Average work rate was lower in HIIT than CWR (32 vs. 63 W, P<0.05); however, subjects performed HIIT longer (542 vs. 202 s, P<0.05) and for greater total work (23.3 vs. 12.0 kJ, P<0.05). The supramaximal HIIT protocol was well tolerated and demonstrated similar maximal physiologic responses to constant work rate exercise, but with greater leg muscle work performed and greater peak exercise intensity.

Analyses of the redistribution of work following cardiac resynchronisation therapy in a patient specific model.

Regulation of regional work is essential for efficient cardiac function. In patients with heart failure and electrical dysfunction such as left branch bundle block regional work is often depressed in the septum. Following cardiac resynchronisation therapy (CRT) this heterogeneous distribution of work can be rebalanced by altering the pattern of electrical activation. To investigate the changes in regional work in these patients and the mechanisms underpinning the improved function following CRT we have developed a personalised computational model. Simulations of electromechanical cardiac function in the model estimate the regional stress, strain and work pre- and post-CRT. These simulations predict that the increase in observed work performed by the septum following CRT is not due to an increase in the volume of myocardial tissue recruited during contraction but rather that the volume of recruited myocardium remains the same and the average peak work rate per unit volume increases. These increases in the peak average rate of work is is attributed to slower and more effective contraction in the septum, as opposed to a change in active tension. Model results predict that this improved septal work rate following CRT is a result of resistance to septal contraction provided by the LV free wall. This resistance results in septal shortening over a longer period which, in turn, allows the septum to contract while generating higher levels of active tension to produce a higher work rate.

Determining the running-related injury risk factors in long distance runners

BackgroundIncreased popularity in long-distance running over the last 30–40 years has induced an increase in the incidence of running-related injuries (RRI). Among others, running experience could be a determining factor...

Numerical Modeling of Wear Damage in Seals of a Wave Energy Converter with Hydraulic Power Take-Off under Random Loads

Understanding and managing the safety and reliability issues of ocean energy converters is a key factor in the development of viable technologies. The present article deals with wear in the high-pressure hydraulic power take-off machinery in a heaving-buoy wave energy converter. In this study, an abrasive wear model for such machinery is developed for the steady-state operation by considering the effects of sealed pressure, relative velocity, material properties, time-varying environmental conditions, and lubrication, with a focus on the piston ring. In particular, the dependence of the wear damage on the sea state condition is investigated. The dynamic parameter named instantaneous wear work rate (Load × Velocity) is numerically calculated in the time domain. An estimate of the average wear work rate in each sea state is computed on the basis of a wave scatter table (significant wave heights versus peak period). Long-term wear damage can then be accounted for by summing up the short-term wear damage multiplied with the occurrence probability of each sea state. Finally, the relative contribution of wear damage from different sea states is obtained.

Mechanics and energetics of step-to-step transitions isolated from human walking

We isolated step-to-step transitions from other contributors to walking mechanics using a cyclical rocking task and then examined the contribution of individual joints to the total work required to redirect the velocity of the center of mass (COM). Nine participants were instructed to rock backward and forward in the sagittal plane, eliminating the need to swing the legs and progress forward. To systematically increase the required work, we increased step length from 60 to 100% of leg length, keeping rocking frequency constant. The individual limbs method quantified the COM work and the joint power method apportioned the COM work among its various sources. As predicted by a physics-based model, we found that work in rocking was performed mainly during the step-to-step transitions and increased strongly with step length. We also found that increases in the average COM work rate exacted a proportional metabolic cost. The similar patterns of COM work and COM work rate during rocking and walking support the use of rocking to isolate the mechanics of step-to-step transitions. We found that the ankle was the main joint contributing to the positive work required to redirect the COM velocity during forward rocking. At the longest length, it accounted for 88% of the work performed by the trailing leg joints. Interestingly, the summed contribution of ankle, knee and hip joint work accounted for only 39% of the front leg negative COM work during the forward transition, suggesting that most of the collision work is performed by passive tissue.

Distribution of Power Output During Cycling

We aim to summarise the impact and mechanisms of work-rate pacing during individual cycling time trials (TTs). Unlike time-to-exhaustion tests, a TT provides an externally valid model for examining how an initial work rate is chosen and maintained by an athlete during self-selected exercise. The selection and distribution of work rate is one of many factors that influence cycling speed. Mathematical models are available to predict the impact of factors such as gradient and wind velocity on cycling speed, but only a few researchers have examined the inter-relationships between these factors and work-rate distribution within a TT. When environmental conditions are relatively stable (e.g. in a velodrome) and the TT is >10 minutes, then an even distribution of work rate is optimal. For a shorter TT (< or = 10 minutes), work rate should be increased during the starting effort because this proportion of total race time is significant. For a very short TT (< or = 2 minutes), the starting effort should be maximal, since the time saved during the starting phase is predicted to outweigh any time lost during the final metres because of fatigue. A similar 'time saving' rationale underpins the advice that work rate should vary in parallel with any changes in gradient or wind speed during a road TT. Increasing work rate in headwind and uphill sections, and vice versa, decreases the variability in speed and, therefore, the total race time. It seems that even experienced cyclists naturally select a supraoptimal work rate at the start of a longer TT. Whether such a start can be 'blunted' through coaching or the monitoring of psychophysiological variables is unknown. Similarly, the extent to which cyclists can vary and monitor work rate during a TT is unclear. There is evidence that sub-elite cyclists can vary work rate by +/-5% the average for a TT lasting 25-60 minutes, but such variability might be difficult with high-performance cyclists whose average work rate during a TT is already extremely high (>350 watts). During a TT, pacing strategy is regulated in a complex anticipatory system that monitors afferent feedback from various physiological systems, and then regulates the work rate so that potentially limiting changes do not occur before the endpoint of exercise is reached. It is critical that the endpoint of exercise is known by the cyclist so that adjustments to exercise work rate can be made within the context of an estimated finish time. Pacing strategies are thus the consequence of complex regulation and serve a dual role: they are both the result of homeostatic regulation by the brain, as well as being the means by which such regulation is achieved. The pacing strategy 'algorithm' is sited in the brain and would need afferent input from interoceptors, such as heart rate and respiratory rate, as well as exteroceptors providing information on local environmental conditions. Such inputs have been shown to induce activity in the thalamus, hypothalamus and the parietal somatosensory cortex. Knowledge of time, modulated by the cerebellum, basal ganglia and primary somatosensory cortex, would also input to the pacing algorithm as would information stored in memory about previous similar exercise bouts. How all this information is assimilated by the different regions of the brain is not known at present.

Salivary IgA Response to Intermittent and Continuous Exercise

Current evidence would support a view that intense exercise increases whereas moderate exercise reduces the susceptibility to illness, predominately upper respiratory tract infections. Concentrations of IgA and cortisol in saliva may be used to reflect changes in immune function. The aim of this study was to determine if the type of exercise (soccer-specific intermittent or continuous exercise at the same average work-rate and duration) affects salivary IgA (s-IgA) and cortisol responses. In a randomized, counterbalanced design, eight healthy males completed two trials one week apart at the same time of day on a motorized treadmill. One session entailed soccer-specific intermittent exercise, the other involved continuous exercise at the same overall work-rate. Diet and activity were standardized for 48 hours prior to and following each trial. Unstimulated saliva samples were collected via passive expectoration during the week prior to commencement of exercise, before, at half-time, immediately post-exercise, and 6 hours, 24 hours, and 48 hours post-exercise. No significant difference was observed in heart rate between the two exercise conditions (Intermittent: 142 +/- 14; Continuous: 141 +/- 16 beats x min (-1)). Average rating of perceived exertion was higher (p < 0.05) in intermittent exercise (11.9 +/- 0.8) than during continuous exercise (10.8 +/- 1.2). The pattern of change in salivary responses, including solute secretion rate, IgA concentration, IgA secretion rate, IgA to osmolality ratio, cortisol, and cortisol secretion rate did not differ between the two trials (p > 0.05). Concentrations of s-IgA for the intermittent and continuous protocols were 131.6 +/- 61.2 vs. 146.4 +/- 107.6 before, 148.4 +/- 82.5 vs. 229.2 +/- 159.6 after, and 125 +/- 78.7 vs. 131.1 +/- 80.7 48 h post-exercise, respectively. Saliva flow rate decreased and osmolality increased significantly across all time points (p < 0.05). In conclusion, soccer-specific intermittent exercise did not suppress the salivary IgA response or alter cortisol secretion compared to continuous exercise performed at the same overall work-rate.

VASCULAR ENDOTHELIAL REACTIVITY MEDIATED BY [HbO2] THE EFFECTS OF EXERCISE TRAINING ON SEDENTARY SUBJECTS

Mounting evidence is linking decreased endothelial reactivity as mediated by the concentration of oxygen bound to hemoglobin ([HbO2]) to a sedentary lifestyle. Previously, a cross sectional study revealed that subjects with a sedentary lifestyle showed an attenuated increase in skeletal muscle blood flow (MBF) resulting from a decrease in [HbO2] when compared with recreationally physically active subjects. PURPOSE: To perform a longitudinal study to determine the effects of exercise on endothelial reactivity as mediated by [HbO2]. METHODS: As a surrogate measure of endothelial function, the thermal dilution technique was used to measure quadriceps MBF and thereby assess changes in endothelial reactivity. Submaximal MBF was measured in 5 sedentary males (18.4 ± 0.3 yrs) prior to and after completion of an 8 week knee- extensor ergometer exercise training protocol in which subjects exercised for 1 hour 3 times a week. Subjects were studied during two graded exercise tests, the first under normoxic (N) conditions followed by conditions of decreased [HbO2] which was attained by the administration carbon monoxide (CO) + hyperoxia. RESULTS: At the onset of the investigation, the subjects attained an average maximal normoxic work rate of 25 ± 2 Watts, which increased to an average normoxic work rate of 37 ± 1 Watts post training. In the pre-training study, MBF at 50% of maximal effort increased from 2737 ± 167 ml/min with an average [HbO2] of 19 ± 0.3 to 2954 ± 148 ml/min with an average [HbO2] of 15.4 ± 0.2, an increase of ∼216 ml/min resulting from a drop in [HbO2] of ∼3.6 mL/dL. After completion of the eight week training protocol there was a much larger increase MBF from 2317 ml/min at 50% of maximum work rate with an average [HbO2] of 19.1 ± 0.2 mL/dL to 2973.0 ml/min at an average of 15.2 ± 0.1 mL/dL, an increase of ∼650 ml/min for a similar drop in [HbO2] of ∼3.9 mL/dL. CONCLUSION: The enhanced MBF response to changes in [HbO2] with regular exercise is suggestive of an endothelial dependent vasodilatory mechanism and may ultimately assist in the understanding of MBF control. Support: HL-17731

Energy demands in competitive soccer

In elite outfield players, the average work rate during a soccer match, as estimated from variables such as heart rate, is approximately 70% of maximal oxygen uptake (VO2 max). This corresponds to an energy production of approximately 5700 kJ (1360 kcal) for a person weighing 75 kg with a VO2 max of 60 ml kg-1 min-1. Aerobic energy production appears to account for more than 90% of total energy consumption. Nevertheless, anaerobic energy production plays an essential role during soccer matches. During intensive exercise periods of a game, creatine phosphate, and to a lesser extent the stored adenosine triphosphate, are utilized. Both compounds are partly restored during a subsequent prolonged rest period. In blood samples taken after top-class soccer matches, the lactate concentration averages 3-9 mM, and individual values frequently exceed 10 mM during match-play. Furthermore, the adenosine diphosphate degradation products--ammonia/ammonium, hypoxanthine and uric acid--are elevated in the blood during soccer matches. Thus, the anaerobic energy systems are heavily taxes during periods of match-play. Glycogen in the working muscle seems to be the most important substrate for energy production during soccer matches. However, muscle triglycerides, blood free fatty acids and glucose are also used as substrates for oxidative metabolism in the muscles.

Optimal ventilatory patterns in periodic breathing.

The goal of this study was to determine whether periodic breathing (PB), which is highly prevalent during sleep at high altitudes, imposes physiological penalties on the respiratory system in the absence of any accompanying disease. Using a computer model of respiratory gas exchange, we compared the effects of a variety of PB patterns on the chemical and mechanical costs of breathing to those resulting from regular tidal breathing. Although PB produced considerable fluctuation in arterial blood gas tensions, for the same cycle-averaged ventilation, higher arterial oxygen saturation and lower arterial carbon dioxide levels were achieved. This result can be explained by the fact that the combination of large breaths and apnea in PB leads to a substantial reduction in dead space ventilation. At the same time, the savings in mechanical cost achieved by the respiratory muscles during apnea partially offset the increase during the breathing phase. Consequently, the "pressure cost," a criterion based on mean inspiratory pressure, was elevated only slightly, although the average work rate of breathing increased significantly. We found that, at extreme altitudes, PB patterns with clusters of 2 to 4 large breaths that alternate with apnea produce the highest arterial oxygenation levels and lowest pressure costs. The common occurrence of PB patterns with closely similar features has been reported in sleeping healthy sojourners at extreme altitudes. Taken together, these findings suggest that PB favors a reduction in the oxygen demands of the respiratory muscles and therefore may not be as detrimental as it is generally believed to be.