Orwik

Influence of Knowledge of Sprint Number on Pacing During Repeated-Sprint Exercise.

PURPOSE:: The anticipation of exercise-induced stress influences performance during continuous exercise. However, not all exercise is continuous. This study explores the influence of prior knowledge of sprint number on mechanical work, surface electr... expand abstractomyogram (EMG), and rating of perceived exertion (RPE) during repeated-sprint exercise (RSE). METHODS:: Fourteen athletes performed three RSE in random order. In one trial, subjects were informed that they would perform ten, 6-s cycle sprints (with 24 s of rest) and then completed ten sprints (control trial, CL). In a second trial, subjects were told to perform five sprints, but after the fifth sprint, they were asked to perform an additional five sprints (deception trial, DC). In a third trial, subjects were not told how many sprints they would be performing, but were stopped after 10 sprints (unknown trial, UN). Data were recorded for every sprint. RESULTS:: Both the initial-sprint work and work accumulated over the first five sprints were greater (6.5%, P < 0.05) in the DC than in the CL and UN trials. Furthermore, the work accumulated over the ten sprints was lower (4.0%, P < 0.05) in the UN trial than in the two other trials. The EMG was greater (P < 0.05) in the DC than in the CL and UN trials during the initial sprint (8.8%) and over the first five sprints (9.1%). The sprint-induced decrease in EMG and work occurred earlier in the UN trial compared with the CL and DC trials. The RPE profile was similar in all trials. CONCLUSIONS:: Results demonstrate that pacing occurs during short repeated-sprint efforts in anticipation of the number of sprints that are included in the trial. collapse abstract

Excessive skeletal muscle recruitment during strenuous exercise in McArdle patients.

We compared the cardiorespiratory response and muscle recruitment [as determined by electromyography (EMG)] of 37 McArdle patients [19 males, 37.4 +/- 2.8 years, body mass index (BMI): 25.1 +/- 4.7 kg m(-2)] and 33 healthy controls (18 males, 36.4 +/... expand abstract- 10.0 years, BMI: 25.7 +/- 3.8 kg m(-2)) during cycle-ergometer exercise (an incremental test to exhaustion and a 12-min submaximal constant workload test). We obtained cardiorespiratory [oxygen uptake and heart rate (HR)] and EMG data (rectus femoris and vastus lateralis muscles). During the incremental test, the patients exhibited the expected hyperkinetic cardiovascular response shown by a marked increase in the slope of the HR:Power relationship (p < 0.001). Throughout the incremental test and at the point of fatigue, the patients produced significantly less power than the controls (peak power output: 67 +/- 21 vs. 214 +/- 56 watts respectively, p < 0.001), yet they demonstrated significantly higher levels of muscle activity for a given absolute power. During the constant workload test, patients displayed higher levels of EMG activity than the controls during the second half of the test, despite a lower power production (34 +/- 13 vs. 94 +/- 29 watts respectively, p < 0.001). In conclusion, since the McArdle patients required more motor unit recruitment for a given power output, our data suggest that the state of contractility of their muscles is reduced compared with healthy people. Excessive muscle recruitment for a given load could be one of the mechanisms explaining the exercise intolerance of these patients. collapse abstract

Spinal cord injuries in South African Rugby Union (1980 - 2007).

Objectives and design. To address an apparent increase in the number of rugby-related spinal cord injuries (SCIs) in South Africa, a retrospective case-series study was conducted on injuries that occurred between 1980 and 2007. We aimed to identify p... expand abstractreventable causes to reduce the overall rate of SCIs in South African rugby. Methods. We identified 264 rugby-related SCIs. A structured questionnaire was used, and it was possible to obtain information on a total of 183 players, including 30 who had died. Results. SCIs increased in number in the 1980s and in 2006. Forwards sustained 76% of all SCIs, and club players 60%. Players aged 17 had the highest number of SCIs. In only 50% of cases were medical personnel present at the time of injury, and 49% of injured players waited longer than 6 hours for acute management. Of players with an SCI, 61% had a catastrophic outcome after 12 months, including 8% who died during that time; 65% received no financial compensation; and only 29% of players had medical aid or health insurance. Conclusion. A register of all rugby-related SCIs in South Africa is essential to monitor the magnitude of the problem, identify potential risk factors, and formulate appropriate preventive interventions. The lack of reliable denominator data limits calculation of incident rates. Players from previously disadvantaged communities in particular suffered the consequences of limited public health care resources and no financial compensation. collapse abstract

Afferent feedback from fatigued locomotor muscles is important, but not limiting, for endurance exercise performance.

Measuring submaximal performance parameters to monitor fatigue and predict cycling performance: a case study of a world-class cyclo-cross cyclist.

Recently a novel submaximal test, known as the Lamberts and Lambert submaximal cycle test (LSCT), has been developed with the purpose of monitoring and predicting changes in cycling performance. Although this test has been shown to be reliable and ab... expand abstractle to predict cycling performance, it is not known whether it can measure changes in training status. Therefore, the aim of this study was to determine whether the LSCT is able to track changes in performance parameters, and objective and subjective markers of well-being. A world class cyclo-cross athlete (31 years) volunteered to participate in a 10-week observational study. Before and after the study, a peak power output (PPO) test with respiratory gas analysis (VO(2max)) and a 40-km time trial (40-km TT) test were performed. Training data were recorded in a training logbook with a daily assessment of well-being, while a weekly LSCT was performed. After the training period all performance parameters had improved by a meaningful amount (PPO +5.2%; 40-km TT time -2.5%; VO(2max) +1.4%). Increased training loads during weeks 2 and 6 and the subsequent training-induced fatigue was reflected in the increased well-being scores. Changes during the LSCT were most clearly notable in (1) increased power during the first minute of third stage, (2) increased rating of perceived exertion during second and third stages, and (3) a faster heart rate recovery after the third stage. In conclusion, these data suggest that the LSCT is able to track changes in training status and detect the consequences of sharp increases in training loads which seem to be associated with accumulating fatigue. collapse abstract

Peripheral arterial disease and intermittent claudication: efficacy of short-term upper body strength training, dynamic exercise training, and advice to exercise at home.

OBJECTIVE: To compare the effect of two training programmes and advice to exercise at home on physiological adaptations in patients with peripheral arterial disease (PAD). DESIGN: 30 patients with a typical history of PAD and intermittent claudicatio... expand abstractn were randomised to either an upper body strength training programme (UBST), a dynamic (walking, cycling, circuit) conventional exercise rehabilitation programme (CER), or advice to 'walk as much as possible at home' (CONT). Before and after intervention groups performed a standard graded treadmill exercise test (GTET) and a 6-minute walk test (SMWT) to determine peak physiological parameters and walking distances. Maximal walking distance (MWD), pain-free walking distance (PFWD), peak oxygen uptake (VO2) , heart rate and perceived pain were measured. RESULTS: MWD on the GTET increased significantly in the CER group compared with the CONT and UBST groups (93.9 +/- 79% v. 7.0 +/- 19.8% v. 7.3 +/- 46%; CER v. UBST v. CONT p = 0.003). Similarly, peak VO2 increased with CER compared with the CONT and UBST groups (28.4 +/- 20 v. -6.2 +/- 15 v. -1.0 +/- 21%; CER v. UBST v. CONT p = 0.004). During the SMWT the CER and UBST groups improved in PFWD compared with the CONT group (37 +/- 47% v. 27 +/- 71% v. -30 +/- 29%; CER v. UBST v. CONT p = 0.03), and perceived pain decreased in the CER group compared with the UBST group (-24 +/- 39% v. 27 +/- 48%; CER v. UBST p = 0.01). CONCLUSION: CER improves physiological parameters and walking distances more than UBST does. CER is effective within 6 weeks. Verbal encouragement to exercise is an ineffective form of management. collapse abstract

Cold fluids improve exercise performance in the heat by slowing the rate of heat gain.

Dehydration: cause of fatigue or sign of pacing in elite soccer?

Numerous studies have suggested that dehydration is a causal factor to fatigue across a range of sports such as soccer; however, empirical evidence is equivocal on this point. It is also possible that exercise-induced moderate dehydration is purely a... expand abstractn outcome of significant metabolic activity during a game. The diverse yet sustained physical activities in soccer undoubtedly threaten homeostasis, but research suggests that under most environmental conditions, match-play fluid loss is minimal ( approximately 1-2% loss of body mass), metabolite accumulation remains fairly constant, and core temperatures do not reach levels considered sufficiently critical to require the immediate cessation of exercise. A complex (central) metabolic control system which ensures that no one (peripheral) physiological system is maximally utilized may explain the diversity of research findings concerning the impact of individual factors such as dehydration on elite soccer performance. In consideration of the existing literature, we propose a new interpretative pacing model to explain the self-regulation of elite soccer performance and, in which, players behaviourally modulate efforts according to a subconscious strategy. This strategy is based on both pre-match (intrinsic and extrinsic factors) and dynamic considerations during the game (such as skin temperature, thirst, accumulation of metabolites in the muscles, plasma osmolality and substrate availability), which enables players to avoid total failure of any single peripheral physiological system either prematurely or at the conclusion of a match. In summary, we suggest that dehydration is only an outcome of complex physiological control (operating a pacing plan) and no single metabolic factor is causal of fatigue in elite soccer. collapse abstract

Changes in heart rate recovery after high-intensity training in well-trained cyclists.

Heart rate recovery (HRR) after submaximal exercise improves after training. However, it is unknown if this also occurs in already well-trained cyclists. Therefore, 14 well-trained cyclists (VO(2max) 60.3 +/- 7.2 ml kg(-1) min(-1); relative peak powe... expand abstractr output 5.2 +/- 0.6 W kg(-1)) participated in a high-intensity training programme (eight sessions in 4 weeks). Before and after high-intensity training, performance was assessed with a peak power output test including respiratory gas analysis (VO(2max)) and a 40-km time trial. HRR was measured after every high-intensity training session and 40-km time trial. After the training period peak power output, expressed as W kg(-1), improved by 4.7% (P = 0.000010) and 40-km time trial improved by 2.2% (P = 0.000007), whereas there was no change in VO(2max) (P = 0.066571). Both HRR after the high intensity training sessions (7 +/- 6 beats; P = 0.001302) and HRR after the 40-km time trials (6 +/- 3 beats; P = 0.023101) improved significantly after the training period. Good relationships were found between improvements in HRR(40-km) and improvements in peak power output (r = 0.73; P < 0.0001) and 40-km time trial time (r = 0.96; P < 0.0001). In conclusion, HRR is a sensitive marker which tracks changes in training status in already well-trained cyclists and has the potential to have an important role in monitoring and prescribing training. collapse abstract

Skeletal muscle monocarboxylate transporter content is not different between black and white runners.

The superior performance of black African runners has been associated with lower plasma lactate concentrations at sub-maximal intensities compared to white runners. The aim was to investigate the monocarboxylate transporters 1 (MCT1) and MCT4 content... expand abstract in skeletal muscle of black and white runners. Although black runners exhibited lower plasma lactate concentrations after maximum exercise (8.8 +/- 2.0 vs. 12.3 +/- 2.7 mmol l(-1), P < 0.05) and a tendency to be lower at 16 km h(-1) (2.4 +/- 0.7 vs. 3.8 +/- 2.4 mmol l(-1), P = 0.07) than the white runners, there were no differences in MCT1 or MCT4 levels between the two groups. For black and white runners together, MCT4 content correlated significantly with 10 km personal best time (r = -0.74, P < 0.01) and peak treadmill speed (r = 0.88, P < 0.001), but MCT1 content did not. Although whole homogenate MCT content was not different between the groups, more research is required to explain the lower plasma lactate concentrations in black runners. collapse abstract

Acute changes in endocrine and fluid balance markers during high-intensity, steady-state, and prolonged endurance running: unexpected increases in oxytocin and brain natriuretic peptide during exercise.

Maintenance of fluid homeostasis during periods of heightened physical stress can be best evaluated in humans using exercise as a model. Although it is well established that arginine vasopressin (AVP), aldosterone and atrial natriuretic peptide (ANP)... expand abstract are the principle hormones regulating fluid balance at rest, the potential contributions of other related endocrine factors, such as oxytocin (OT) and brain natriuretic peptide (BNP), have not been well described during exercise. Seven endurance-trained runners completed three separate running trials: a maximal test to exhaustion (high intensity), a 60-min treadmill run (steady state), and a 56 km ultramarathon (prolonged endurance exercise). Statistically significant pre- to post-run increases were found only following the ultramarathon in [AVP](p) (1.9 vs 6.7 pg/ml; P<0.05), [OT](p) (1.5 vs 3.5 pg/ml; P<0.05), [NT-proBNP](p) (23.6 vs 117.9 pg/ml; P<0.01), [interleukin 6](p) (4.0 vs 59.6 pg/ml; P<0.05), [cortisol](p) (14.6 vs 32.6 microg/ml; P<0.01), [corticosterone](p) (652.8 vs 3491.4 ng/ml; P<0.05) and [11-deoxycortisol](p) (0.1 vs 0.5 microg/ml; P<0.05) while a significant post-run increase in [aldosterone](p) was documented after high-intensity (4.9 vs 12.5 ng/ml; P<0.05), steady-state (6.1 vs 16.9 ng/ml; P<0.05) and prolonged endurance running (2.6 vs 19.7 ng/ml; P<0.05). Similarly, changes in fluid balance parameters were significantly different between the ultramarathon versus high-intensity and steady-state running with regard to plasma volume contraction (less % contraction), body weight loss (increased % weight loss), plasma [Na(+)] Delta (decreased from baseline), and urine osmolality Delta (increase from baseline). Hypothetically driven relationships between [OT](p) and [AVP](p) (r=0.69; P<0.01) and between [NT-proBNP](p) Delta and plasma [Na(+)] Delta (r=-0.79; P<0.001)--combined with the significant and unexpected pre- to post-race increases after prolonged endurance exercise--allows for possible speculation that OT and BNP may assist their better known companion hormones (AVP and ANP) in the regulation of fluid balance during conditions of extreme physical stress. collapse abstract

The comparative incidence of reported concussions presenting for follow-up management in South African Rugby Union.

OBJECTIVE: The objective of this study was to compare the seasonal concussion incidence for school, university, club and provincial level Rugby Union players in South Africa. DESIGN: The study presents a retrospective statistical analysis of the numb... expand abstracter of reported concussions documented annually for groups of Rugby Union players as a proportion of those who received preseason neurocognitive assessment. SETTING: Between 2002 and 2006, concussion management programs using computerized neuropsychological assessment were implemented for clinical and research purposes by psychologists in selected South African institutions involved in Rugby Union from school through to the professional level. PARTICIPANTS: The incidence figures were based on 175 concussive episodes reported for 165 athletes who were referred for neurocognitive assessment from a population of 1366 athletes who received preseason baseline testing. INTERVENTIONS: Concussion management routines varied according to the protocols adopted by the different psychologists and rugby organizations. MAIN OUTCOME MEASUREMENTS: It was expected that the incidence of concussion would vary significantly due to level of play and different management protocols. RESULT: There was wide disparity in the manner in which concussion follow-up was managed by the various organizations. Within broadly comparable cohorts, tighter control was associated with a relatively higher concussion incidence for athletes per rugby playing season, with average institutional figures ranging from 4% to 14% at school level and 3% to 23% at adult level. CONCLUSIONS: This analysis suggests that concussion goes unrecognized and therefore incorrectly managed in a number of instances. Recommendations for optimal identification of concussed athletes for follow-up management are presented. collapse abstract

Changes in plasma arginine vasopressin concentrations in cyclists participating in a 109-km cycle race.

Objective To evaluate the osmotic and non-osmotic regulation of arginine vasopressin (AVP) during endurance cycling. Design Observational study. Setting 109 km cycle race. Participants 33 Cyclists. Interventions None. Main outcome measurements Plasma... expand abstract sodium concentration ([Na(+)]), plasma volume (PV) and plasma arginine vasopressin (AVP) concentration ([AVP](p)). Results A fourfold increase in [AVP](p) occurred despite a 2-mmol l(-1) decrease in plasma [Na(+)] combined with only modest (5%) PV contraction. A significant inverse correlation was noted between [AVP](p) Delta and urine osmolality Delta (r = -0.41, p<0.05), whereas non-significant inverse correlations were noted between [AVP](p) and both plasma [Na(+)] Delta and % PV Delta. Four cyclists finished the race with asymptomatic hyponatraemia. The only significant difference between the entire cohort with this subset of athletes was postrace plasma [Na(+)] (137.7 vs 133.5 mmol l(-1), p<0.001) and plasma [Na(+)] Delta (-1.9 vs -5.1 mmol l(-1), p<0.05). The mean prerace [AVP](p) of these four cyclists was just below the minimum detectable limit (0.3 pg ml(-1)) and increased marginally (0.4 pg ml(-1)) despite the decline in plasma [Na(+)]. Conclusions The osmotic regulation of [AVP](p) during competitive cycling was overshadowed by non-osmotic AVP secretion. The modest decrease in PV was not the primary non-osmotic stimulus to AVP. Partial suppression of AVP occurred in four (12%) cyclists who developed hyponatraemia during 5 h of riding. Therefore, these results confirm that non-osmotic AVP secretion and exercise-associated hyponatraemia does, in fact, occur in cyclists participating in a 109 km cycle race. However, the stimuli to AVP is likely different between cycling and running. collapse abstract

Chronic disease risk factors, healthy days and medical claims in South African employees presenting for health risk screening.

BACKGROUND: Non-communicable diseases (NCD) accounts for more than a third (37%) of all deaths in South Africa. However, this burden of disease can be reduced by addressing risk factors. The aim of this study was to determine the health and risk prof... expand abstractile of South African employees presenting for health risk assessments and to measure their readiness to change and improve lifestyle behaviour. METHODS: Employees (n = 1954) from 18 companies were invited to take part in a wellness day, which included a health-risk assessment. Self-reported health behaviour and health status was recorded. Clinical measures included cholesterol finger-prick test, blood pressure and Body Mass Index (BMI). Health-related age was calculated using an algorithm incorporating the relative risk for all case mortality associated with smoking, physical activity, fruit and vegetable intake, BMI and cholesterol. Medical claims data were obtained from the health insurer. RESULTS: The mean percentage of participation was 26% (n = 1954) and ranged from 4% in transport to 81% in the consulting sector. Health-related age (38.5 +/- 12.9 years) was significantly higher than chronological age (34.9 +/- 10.3 yrs) (p < 0.001). Both chronological and risk-related age were significantly different between the sectors (P < 0.001), with the manufacturing sector being the oldest and finance having the youngest employees. Health-related age was significantly associated with number of days adversely affected by mental and physical health, days away from work and total annual medical costs (p < 0.001). Employees had higher rates of overweight, smoking among men, and physical inactivity (total sample) when compared the general SA population. Increased health-related expenditure was associated with increased number of risk factors, absenteeism and reduced physical activity. CONCLUSION: SA employees' health and lifestyle habits are placing them at increased risk for NCD's, suggesting that they may develop NCD's earlier than expected. Inter-sectoral differences for health-related age might provide insight into those companies which have the greatest need for interventions, and may also assist in predicting future medical expenditure. This study underscores the importance of determining the health and risk status of employees which could assist in identifying the appropriate interventions to reduce the risk of NCD's among employees. collapse abstract

Heatstroke during endurance exercise: is there evidence for excessive endothermy?

PURPOSE: Five of 28,753 cyclists participating in an annual 109-km bicycle race died, four within 24 h of the race and the fifth 17 d later. All five deaths were reported to be the consequence of exertional heatstroke. One runner of 6874 participatin... expand abstractg in an annual 56-km ultramarathon developed heatstroke and required active cooling for 10 h to achieve normothermia. The purpose of this article was to postulate (i) why only 6 of 35,627 athletes were hospitalized for heatstroke in these races, (ii) if exercise alone could have elevated their body temperatures sufficiently to cause heatstroke, and (iii) why the runner required such prolonged cooling. METHODS: Clinical and autopsy data are presented for three of the cyclists and the runner for whom access to this information was granted. Calculations were made to predict the work rates necessary to produce their measured rectal temperatures. RESULTS: The rectal temperatures of two of the cyclists were 42.0 and 41.2 degrees C on hospitalization, and that of the runner was 41.8 degrees C on collapse. Standard calculations showed that in the prevailing environmental conditions and with their exercise speeds, none should have developed exertional heatstroke. The third cyclist experienced a cardiac arrest to which his elevated (rectal) temperature may have contributed. CONCLUSION: The hyperthermic states experienced by the cases presented may have resulted from failure of their heat-losing mechanisms. Alternatively, they might have resulted from excessive endothermy, triggered by physical exertion and other unknown initiating factors. Excessive endothermy should be considered in cases of heatstroke that occur in mild to moderate environmental conditions. Furthermore, prompt initiation of cooling is crucial in all cases of suspected heatstroke. collapse abstract

Practical management of exercise-associated hyponatremic encephalopathy: the sodium paradox of non-osmotic vasopressin secretion.

Exercise-associated hyponatremia (EAH) is a potentially fatal fluid imbalance largely resulting from sustained fluid intake beyond the capacity for fluid excretion during endurance exercise. Common symptoms include vomiting, confusion, altered mental... expand abstract status, and seizures; however, these symptoms can also be seen with hypernatremic encephalopathy, making measurement of plasma sodium concentration imperative when athletes present with these symptoms. Recent evidence supports the inappropriate secretion of the antidiuretic hormone, arginine vasopressin (AVP), as the primary pathophysiological mechanism underlying the development of dilutional EAH. It appears that AVP is stimulated normally during prolonged endurance running by non-osmotic factors such as an exercise-induced plasma volume decrease; therefore, any excess fluid intake will likely be retained, and sodium will likely be excreted. The capacity for a small concentrated bolus of a hypertonic saline solution to rapidly reverse cerebral edema and remove any decreased plasma volume stimulus to AVP secretion is the most efficacious treatment for acute EAH encephalopathy to date. The prompt administration of an intravenous (IV) bolus of hypertonic saline in the field or hospital setting can be lifesaving once EAH is documented. Conversely, oral sodium supplementation will not prevent the development of EAH encephalopathy if exuberant fluid intake combined with non-osmotic secretion of AVP occurs during prolonged physical activity. As a result, the seemingly paradoxical use of sodium supplementation as the most effective practical management therapy (IV bolus) and ineffective preventive strategy can be reconciled through a more complete understanding of the pathophysiological mechanisms underlying EAH. collapse abstract

Elite Kenyan endurance runners are hydrated day-to-day with ad libitum fluid intake.

Previous studies of elite Kenyan endurance runners reported that athletes did not consume liquids before or during training and infrequently consumed modest amounts of liquids after training that contributed to low daily fluid intake. PURPOSE: To ass... expand abstractess hydration status of elite Kenyan endurance runners during an important training period. METHODS: Hydration status was monitored in fourteen elite Kenyan endurance runners over a 5-d training period 1 wk prior to the Kenyan national trials for the 2005 IAAF Athletics World Championships by measuring body mass, urine osmolality, total body water, and daily fluid intake. Dietary sodium (Na) intake was estimated using a 5-d nutritional diary and biochemical analysis, whilst [Na] was determined in urine and sweat. Intestinal temperature was monitored continuously during training sessions. RESULTS: Daily fluid intake was consistent with previous observations. There was a significant body mass loss during the morning, interval, and afternoon training sessions (P < 0.05). Nevertheless, mean total body water and pretraining body mass were well maintained day-to-day throughout the 5-d recording period (P = 0.194 and P = 0.302, respectively). Furthermore, there was no significant difference between the osmolality of the morning urine sample and the evening sample (P = 0.685). Mean Na intake was not significantly different to Na loss in sweat and urine (P = 0.975). No athlete showed signs or symptoms of heat strain at any time. CONCLUSIONS: These results demonstrate that elite Kenyan endurance runners remain well hydrated day-to-day with an ad libitum fluid intake; a pattern and volume of fluid intake that is consistent with previous observations of elite Kenyan endurance runners. collapse abstract

The rate of increase in rating of perceived exertion predicts the duration of exercise to fatigue at a fixed power output in different environmental conditions.

This study tested the hypothesis that the increase in rating of perceived exertion (RPE) predicts the duration of exercise to exhaustion during exercise in hot conditions. Seven subjects performed five cycling trials in an environmental chamber at te... expand abstractmperatures of 15 degrees C (C) and 35 degrees C (H). The cool trials were performed at intensities of 65 and 70% and the hot trials at 55, 60 and 65%. RPE, rectal and skin temperature were measured during trials. Duration to fatigue was significantly shorter in H65 and C70 than H60, C65 and H55 (P < 0.05). RPE rose linearly throughout each trial and the rate of increase in RPE was significantly faster in H65 and C70 than H55 (P < 0.05). There was an inverse linear relationship between trial duration and rate of increase in RPE (r = 0.83). Rectal temperature increased linearly throughout the trial and correlated significantly with RPE (r = 0.92). This study shows that the rate of increase in RPE predicts the duration of exercise to exhaustion at a constant power output in different environmental conditions. collapse abstract

Osmotic and nonosmotic regulation of arginine vasopressin during prolonged endurance exercise.

CONTEXT: Although the primary cause of exercise-associated hyponatremia (EAH) is relative overconsumption of fluids beyond the kidneys' ability to excrete excess fluid, the mechanisms limiting maximum renal excretory ability during exercise remain to... expand abstract be elucidated. OBJECTIVE: The objective of the study was to: 1) perform a comprehensive evaluation of the endocrine secretion of pituitary, natriuretic and adrenal steroid hormones, and cytokines immediately before and after running an ultramarathon; and 2) evaluate the relationship between osmotic and nonosmotic stimuli to arginine vasopressin (AVP) secretion within the overall context of assessing the hormonal regulation of fluid balance during prolonged endurance exercise. DESIGN: This was an observational study. SETTING: The study setting was a 56-km ultramarathon. PARTICIPANTS: Eighty-two runners participated in the study. INTERVENTIONS: There were no interventions. MAIN OUTCOME MEASURES: Plasma sodium concentration [Na(+)] and plasma volume [(AVP)(p)] were measured. RESULTS: Fluid homeostasis during exercise (356 +/- 4 min) was maintained with ad libitum fluid intakes. [Na(+)] was maintained from before the race (139.3 +/- 0.3 mmol/liter) to after the race (138.1 +/- 0.4 mmol/liter) with a significant decrease in plasma volume (-8.5 +/- 0.1%, P < 0.01). Increases in the plasma (AVP)(p) (3.9-fold), oxytocin (1.9-fold), brain natriuretic peptide (4.5-fold), and IL-6 (12.5-fold) were highly significant (P < 0.0001). Changes in brain natriuretic peptide, oxytocin, and corticosterone were associated with 47% of the variance noted in (AVP)(p) and 13% of the variance in plasma [Na(+)] in pathway analyses. CONCLUSIONS: (AVP)(p) was markedly elevated after the ultramarathon despite unchanged plasma [Na(+)](.) Therefore, an inability to maximally suppress (AVP)(P) during exercise as a result of nonosmotic stimulation of AVP secretion may contribute to the pathogenesis of exercise-associated hyponatremia if voluntary fluid intake were to exceed fluid output. collapse abstract

The limits of human endurance: what is the greatest endurance performance of all time? Which factors regulate performance at extreme altitude?

Humans evolved as an athletic species able to run in the midday heat, to throw with exquisite accuracy and to strike powerfully despite relatively weak upper arms compared to those of the great apes. The true extent to which humans could run long dis... expand abstracttances was first tested in a unique series of 6-day foot races contested between 1874 and 1888 by professional athletes from England and the United States. These athletes typically would have expended approximately 60,000 kcal (24.12 MJ) of energy during these races. The discovery of the bicycle soon caused the replacement of these races by 6-day cycling races which, in turn, led to the modern day Tour de France, the cycling race across America (RaAM) and two running races across the width of the United States in 1928 and 1929. The total energy expenditures during these different events can be estimated at approximately 168,000, 180,000 and 340,000 kcal respectively. But, in terms of the total energy expenditure, all these performances pale somewhat when compared to that of Robert Falcon Scott's Polar party during the 1911/12 British Antarctic Expedition. For most of 159 consecutive days, Scott's team man-hauled for 10 hours a day to the South Pole and back covering a distance of 2500 km. Their predicted total energy expenditure per individual would have been about 1 million kcal, making theirs, by some margin, the greatest sustained endurance athletic performance of all time. Interestingly, the dogs that provided the pulling power for Norwegian Roald Amundsen's team that was the first to reach the South Pole, 35 days before Scott's party, would have expended about 500,000 kcal in their 97 day trip, making theirs the greatest animal "sporting" performance on record. By contrast, mountain climbers expend only approximately 4000 kcal/day when climbing at extreme altitudes (above 4000 m). This relatively low rate of energy expenditure results from the low exercise intensities that can be sustained at extreme altitude. Here I argue that this slow rate of energy expenditure is caused, not by either myocardial or skeletal muscle hypoxia as is usually argued, but is more likely the result of a process integrated centrally in the brain, the function of which is to protect the body from harm. At extreme altitude the organ at greatest risk is the brain which must be protected from the catastrophic consequences of profound hypoxia. A key feature of this control is that it acts "in anticipation" specifically to insure that a catastrophic biological failure does not occur. The evidence for this interpretation is presented. collapse abstract

Maximal oxygen uptake as a parametric measure of cardiorespiratory capacity: comment.

Addressing conflicts of interest and clouding of objectivity: BJSM's "peer review: fair review" section.

Fatigue during a 5-km running time trial.

This study investigated fatigue-induced changes in neuromuscular and stride characteristics during and immediately after the 5-km running time trial. Eighteen well-trained male distance runners performed a maximal 20-m sprint test and maximal volunta... expand abstractry contraction (MVC) in a leg press machine before and immediately after the 5-km running time trial. In all the tests the EMG of five lower limb muscles was measured. The results of the present study showed that muscle fatigue measured in maximal exercises like 20-m sprint and MVC are not related to the fatigue induced changes during the 5-km time trial. The fatigue in the 20-m sprint test was related to the maximal 20-m pretest velocity (r=0.58, p<0.05), but the velocity loss during the 5-km time trial was inversely related to 5-km performance (r= - 0.60, p<0.05) and training volume (r= - 0.58, p<0.05). It was concluded that the fatigue in 5-km running measured pre- and postexercise at maximal effort is more related to sprint performance rather than endurance performance, but the fatigue measured during the 5-km running is related to endurance performance and factors affecting pacing strategy. collapse abstract

Heat stress in sport--fact and fiction.

Why does exercise terminate at the maximal lactate steady state intensity?

OBJECTIVE: The purpose of this study was to measure physiological responses during exercise performed until exhaustion at the exercise intensity corresponding to the maximal lactate steady state (MLSS) in order to determine why subjects stopped. METH... expand abstractODS: Eleven male trained subjects performed a test at MLSS on a cycle ergometer until exhaustion. RESULTS: Time to exhaustion was 55.0 (SD 8.5) min. No variation was observed between the 10th and the last minute for arterial pyruvate, bicarbonate, and haemoglobin concentrations, redox state, arterial oxygen pressure, arterial oxygen saturation, osmolality, haematocrit, oxygen uptake, carbon dioxide output, and gas exchange ratio (p>0.05). Arterial lactate concentration and arterial carbon dioxide pressure decreased significantly whereas pH, base excess and the Ratings of Perceived Exertion (RPE) increased significantly (p<0.05). Although respiratory rate, minute ventilation and heart rate increased significantly until exhaustion (p<0.05), values at termination of the MLSS test were significantly lower than values measured during a maximal exercise test (p<0.05). Blood ammonia concentrations rose progressively during the MLSS test. However, there is no known mechanism by which this change could cause peripheral fatigue. CONCLUSIONS: Exercise termination was not associated with evidence of failure in any physiological system during prolonged exercise performed at MLSS. Thus the biological mechanisms of exercise termination at MLSS were compatible with an integrative homoeostatic control of peripheral physiological systems during exercise. collapse abstract