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Exertional rhabdomyolysis in an adolescent athlete.

Exertional rhabdomyolysis has been previously reported in adult patients following such strenuous activities as military basic training, weight lifting, and marathon running. Exertional rhabdomyolysis in previously healthy pediatric athletes, however, is rarely encountered. The presentation of rhabdomyolysis is characterized by the classical triad of myalgias, muscle weakness, and darkened urine. This classic presentation, however, is not noted the majority of patients, especially early in the disease course when the patient may complain only of myalgias or weakness. Thus, the emergency physician must have a high index of suspicion for this entity based on the appropriate clinical setting. We report a classic case of exercise-induced rhabdomyolysis complicated by acute renal failure in a previously healthy adolescent athlete, whose initial presentation was nonspecific, prompting the diagnosis of overexertion.

Acute Kidney Injury↗

Trunk muscle co-contraction increases during fatiguing, isometric, lateral bend exertions. Possible implications for spine stability.

STUDY DESIGN: Surface electromyographic activities were recorded from bilateral trunk muscles as test participants maintained a 50% maximum, voluntary, isometric, lateral bend contraction to volitional exhaustion. OBJECTIVES: To challenge the trunk with a prolonged lateral bend task and observe the responses of the agonist and antagonist muscles to the resulting fatigue. SUMMARY OF BACKGROUND DATA: Lateral bend exertions of the trunk have been identified as a risk factor for injury to spine tissues. However, little is known about the response of spine muscles to fatigue and the subsequent implications for spine stability, joint loading, and tissue injury. Surface electromyography provides a window on muscle loading and progressive fatigue. METHODS: Eleven male participants performed a set of maximum lateral bend exertions at the start of the trial, then maintained an upright standing posture while resisting 50% of the maximum moment until volitional exhaustion, then performed another set of maximum contractions. All contractions were isometric. Measurements were made, throughout each contraction, of the lateral bend moment and abdominal and trunk extensor electromyographic activities at six bilateral surface electromyography sites. Electromyographic amplitude and mean power frequency were calculated with 500-millisecond segments recorded serially every 800 milliseconds. Mean values were calculated with data from the first and last 5% of the trial durations. Statistics determined if fatigue had a significant effect on maximum moment and the electromyographic statistics for each muscle site. RESULTS: Fatigue resulted in a significant decrease in maximum lateral bend moment and increase in moment variability. Decreases in mean power frequency, indicating fatigue, were observed in three agonists (the trunk extensors) and one antagonist muscle. Unfatigued agonist electromyographic amplitudes correlated well with the mechanical advantage of muscles to generate lateral bend moments. Unfatigued antagonist activities were low except for the thoracic erector spinae. The agonists and antagonists demonstrated average increases of 17% and 8%, respectively, when pooled across muscles. Much of this change was predicted to have been associated with increases in co-contracting muscle forces. CONCLUSIONS: The trunk responded to a prolonged, lateral bend contraction by increasing co-contraction as agonist trunk muscles fatigued. It was proposed that the fatigue compromised neural coordination and that the co-contraction served to maintain spine stability.

Adult↗

Validity of rating of perceived exertion during graded exercise testing in apparently healthy adults and cardiac patients.

PURPOSE: Recent exercise guidelines recommend a generalized rating of perceived exertion (RPE) range of 12 to 16 (15-point Borg scale) as the perceptual range associated with a physiological training effect. However, whether an individual who selects an RPE within the generalized range during an graded exercise test or exercise training, is actually within the correlated physiological range (50 to 85% maximum oxygen consumption [VO2max]) has not been studied in large samples of apparently healthy individuals or cardiac patients. The purpose of the present study was to assess the validity of the generalized RPE recommendations in a large heterogeneous group of apparently healthy subjects and cardiac patients. METHODS: Subjects included apparently healthy adults (N = 463) and cardiac patients (N = 217) who presented for a sign-symptom limited maximal graded exercise test (SSLMGXT). Ratings of perceived exertion associated with relative exercise intensities of 60 and 80% of maximal heart rate reserve (MHRR) and peak exercise were selected for analyses. RESULTS: Significant interindividual variability in RPE was observed at both relative exercise intensities (6 to 20 RPE range at 60% MHRR; 8 to 20 RPE range at 80% MHRR) for both populations. Thirty-nine percent of healthy subjects and 32% of cardiac patients reported an RPE outside an 11 to 14 range at 60% of MHRR, whereas 32% of healthy subjects and 52% of cardiac patients reported an RPE outside of a 14 to 17 range at 80% of MHRR. Peak RPE was higher for the apparently healthy subjects compared with the cardiac patients (18.8 +/- 1.2 versus 16.5 +/- 1.8; P < 0.01). CONCLUSIONS: These results challenge the applicability of the generalized RPE recommendations described in recent exercise guidelines under typical clinical exercise testing conditions. The basis for the generalized RPE recommendations warrant further investigation. Those who desire to use RPE as a marker of relative exercise intensity during SSLMGXT should take into consideration the large interindividual variability in these measures.

Adult↗

Physical exertion at work and the risk of preterm delivery and small-for-gestational-age birth.

OBJECTIVE: To assess whether exposure to standing, lifting, night work, or long work hours during 3 periods of pregnancy are associated with an increased risk of preterm or small-for-gestational-age birth. METHODS: The Pregnancy, Infection and Nutrition study is a prospective cohort with a nested case-control component that was conducted through clinic and hospital settings in Central North Carolina. A total of 1,908 women pregnant with a singleton gestation were recruited during prenatal visits from January 1995 through April 2000 and provided information during telephone and face-to-face interviews about physical exertion for the 2 longest-held jobs during pregnancy. RESULTS: No significant elevations in preterm delivery were observed among women who lifted repeatedly or stood at least 30 hours per week, with no changes in risk estimates over the course of pregnancy. A 50% elevation in the risk of preterm delivery (relative risk 1.5, 95% confidence interval 1.0-2.0; first trimester) was observed among women who reported working at night (10:00 PM to 7:00 AM), whereas a 40% reduction in risk was observed among women working at least 46 hours per week (relative risk 0.6, 95% confidence interval 0.4-0.9; first trimester), regardless of period of exposure. No elevations in small-for-gestational-age birth were observed among women exposed to any of the 4 types of occupational exertion. CONCLUSION: Physically demanding work does not seem to be associated with adverse pregnancy outcomes, whereas working at night during pregnancy may increase the risk of preterm delivery. Studies to examine the effect of shift work on uterine activity would help to clarify the possibility of a causal effect on preterm birth.

Adult↗

Oxygen cost, walking speed, and perceived exertion in children with cerebral palsy when walking with anterior and posterior walkers.

Walkers with the frame positioned behind the child have been advocated recently, mainly because they may allow a more upright and therefore more normal ambulation and perhaps encourage favourable neuromuscular development. The purpose of this study was to estimate and compare speed, energy cost, and perceived exertion during walking with an anterior walker and a posterior walker. Ten children with spastic diplegia, average age 11 years, who were familiar with both types of walker participated in the study. Spasticity was measured according to the modified Ashworth scale. Oxygen cost was determined by the argon-diluted method using a mixing box mounted on a backpack, and the perceived exertion was graded. The results of the study showed that there are no differences in the measured variables in walking between the anterior and the posterior walker in children familiar with both walkers and also that most of the children preferred the posterior walker.

Adolescent↗

The rate of heat storage mediates an anticipatory reduction in exercise intensity during cycling at a fixed rating of perceived exertion.

The aim of the present study was to examine the regulation of exercise intensity in hot environments when exercise is performed at a predetermined, fixed subjective rating of perceived exertion (RPE). Eight cyclists performed cycling trials at 15 degrees C (COOL), 25 degrees C (NORM) and 35 degrees C (HOT) (65% humidity throughout), during which they were instructed to cycle at a Borg rating of perceived exertion (RPE) of 16, increasing or decreasing their power output in order to maintain this RPE. Power output declined linearly in all three trials and the rate of decline was significantly higher in HOT than in NORM and COOL (2.35 +/- 0.73 W min(-1), 1.63 +/- 0.70 and 1.61 +/- 0.80 W min(-1), respectively, P < 0.05). The rate of heat storage was significantly higher in HOT for the first 4 min of the trials only, as a result of increasing skin temperatures. Thereafter, no differences in heat storage were found between conditions. We conclude that the regulation of exercise intensity is controlled by an initial afferent feedback regarding the rate of heat storage, which is used to regulate exercise intensity and hence the rate of heat storage for the remainder of the anticipated exercise bout. This regulation maintains thermal homeostasis by reducing the exercise work rate and utilizing the subjective RPE specifically to ensure that excessive heat accumulation does not occur and cellular catastrophe is avoided.

Adaptation, Physiological↗

Effect of carbohydrate substrate availability on ratings of perceived exertion during prolonged running.

The purpose of this study was to investigate the effects of carbohydrate substrate availability on ratings of perceived exertion (RPE) during prolonged submaximal running. Thirty marathon runners were recruited as subjects. A double-blind study design was used in which subjects performed an experimental trial that consisted of a 2.5-hr treadmill run at 75-80% VO2max. During the experimental trial, the subjects in the carbohydrate feeding group ingested a 6% glucose and fructose solution at a rate of approximately 60 g.hr, whereas subjects in the placebo group consumed an equal volume of artificially flavored placebo. Statistical analysis of RPE, respiratory exchange ratio, fat and carbohydrate oxidation rate, and blood glucose concentrations indicated that increased carbohydrate substrate availability attenuated the intensity of exertional perceptions during the later stages of prolonged running at 75-80% VO2max in marathon runners.

Adult↗

Exercise intensity and perceived exertion in adolescent boys.

The rating of perceived exertion (RPE) was assessed at power outputs (PO) corresponding to 30%, 60% and 90% of predicted maximal oxygen uptake (VO2 max) on a cycle ergometer in 30 adolescent schoolboys (age range 15-17 years). Analysis of correlations (r) for heart rate (HR):PO (r = 0.74 p less than 0.01) and rating of perceived exertion (RPE): HR (r = 0.74 p less than 0.01) were similar to values drawn from adult samples. It was concluded that there is a close relationship between RPE, HR and relative exercise intensity in adolescent schoolboys.

Adolescent↗

Cooling methods used in the treatment of exertional heat illness.

OBJECTIVE: To review the different methods of reducing body core temperature in patients with exertional heatstroke. METHODS: The search strategy included articles from 1966 to July 2003 using the databases Medline and Premedline, Embase, Evidence Based Medicine (EBM) reviews, SPORTDiscus, and cross referencing the bibliographies of relevant papers. Studies were included if they contained original data on cooling times or cooling rates in patients with heat illness or normal subjects who were subjected to heat stress. RESULTS: In total, 17 papers were included in the analysis. From the evidence currently available, the most effective method of reducing body core temperature appears to be immersion in iced water, although the practicalities of this treatment may limit its use. Other methods include both evaporative and invasive techniques, and the use of chemical agents such as dantrolene. CONCLUSIONS: The main predictor of outcome in exertional heatstroke is the duration and degree of hyperthermia. Where possible, patients should be cooled using iced water immersion, but, if this is not possible, a combination of other techniques may be used to facilitate rapid cooling. There is no evidence to support the use of dantrolene in these patients. Further work should include a randomised trial comparing immersion and evaporative therapy in heatstroke patients.

Body Temperature↗

Effect of anticipation during unknown or unexpected exercise duration on rating of perceived exertion, affect, and physiological function.

OBJECTIVES: To determine the effect of unknown exercise duration and an unexpected increase in exercise duration on rating of perceived exertion (RPE), affect, and running economy during treadmill running. METHODS: Sixteen well trained male and female runners completed three bouts of treadmill running at 75% of their peak treadmill running speed. In the first trial, they were told to run for 20 minutes and were stopped at 20 minutes (20 MIN). In another trial, they were told to run for 10 minutes, but at 10 minutes were told to run for a further 10 minutes (10 MIN). In the final trial, they were not told for how long they would be running but were stopped after 20 minutes (unknown, UN). During each of the running bouts, RPE, oxygen consumption (ml/kg/min), heart rate (beats/min), stride frequency (min(-1)), affect scores (arbitrary units), and attentional focus (percentage associative thought scores) were recorded. RESULTS: RPE increased significantly between 10 and 11 minutes in the 10 MIN compared with the 20 MIN and UN trials (p<0.05). The affect score decreased significantly between 10 and 11 minutes in the 10 MIN compared with the 20 MIN trial (p<0.05). Running economy, as measured by oxygen consumption, was significantly lower in the UN compared with the 20 MIN trial from 10 to 19 minutes (p<0.05). CONCLUSIONS: The change in RPE between 10 and 11 minutes in the 10 MIN trial suggests that RPE is not purely a measure of physical exertion, as treadmill speed was maintained at a constant pace both before and after the unexpected increase in exercise duration. The associated changes in affect score at similar times in the 10 MIN trial supports the hypothesis that RPE has an affective component.

Affect↗

The place of perceived exertion ratings in exercise prescription for cardiac transplant patients before and after training.

OBJECTIVE: Heart rate provides a poor guide to exercise prescription after cardiac transplantation. This study explores whether the rating of perceived exertion (RPE) provides useful alternative information. METHODS: Borg's original categoric scale was applied to 36 male patients [T, age 47(SD 9 years] as they performed a progressive cycle ergometer test an average of seven months (range two to 23 months) after cardiac transplantation. The test was repeated after 16(7) months of progressive exercise centred rehabilitation. Sedentary but healthy controls [C, n = 45, age 45(7) years] performed a similar progressive cycle test. RESULTS: Initially, 13 RPE units corresponded to 66(12)% of peak VO2 in T and 50(11)% in C. Rehabilitation augmented peak VO2 (by 19%) and estimated lean body mass (by 3.5%) in the cardiac transplant patients. The increase of heart rate (HR) at 13 RPE units [delta HR = 10(17) beats.min-1] showed moderate correlations with gains of lean mass (r = 0.72) and gains of peak VO2 (r = 0.58). The relative oxygen intake at 13 RPE units remained unchanged at 68(12)% of peak VO2. CONCLUSIONS: Large inter-individual variations of RPE at a given VO2 limit the value of perceived exertion in exercise prescription. Ratings seem best restricted to fine tuning fixed distance/fixed speed exercise prescriptions in patients undergoing rehabilitation after cardiac transplantation.

Adult↗

Effects of propranolol and metoprolol on haemodynamic and respiratory indices and on perceived exertion during exercise in hypertensive patients.

A double-blind cross-over trial of the non-selective beta-blocker propranolol and the beta1-selective blocker metoprolol was carried out in 8 hypertensive patients. At the end of each 4-week period of treatment haemodynamic and respiratory indices and perceived exertion were studied during moderate exercise. Both beta-blockers resulted in reduced heart rate, cardiac output, and blood pressure, whereas the stroke volume increased. Total peripheral resistance did not change. During exercise the expiratory peak flow rate equally increased in every period. However, the peak flow rate at rest, as well as during exercise, was reduced by propranolol, while metoprolol had no such influence. Neither of the beta-blockers changed O2 consumption, CO2 production, tidal volume, or respiratory rate. Moreover, they did not influence perceived exertion. These results suggest that the arteriolar and bronchiolar beta2-receptors do not play a major role in the alteration of circulation and ventilation during exercise. As far as their practical use as antihypertensive agents is concerned, this study shows no advantage in the use of either of these beta-blockers.

Adult↗

Coronary haemodynamic effects of short-term intravenous administration of gallopamil in patients with stable exertional angina.

The effects of short term intravenous administration of gallopamil on coronary haemodynamic variables were studied in 10 patients with stable exertional angina and angiographically confirmed coronary artery disease that affected the proximal portion of the left anterior descending artery. Blood flow in the great cardiac vein was measured by a thermodilution technique, both at rest and during ischaemia induced by atrial pacing, before and after intravenous administration of gallopamil (0.02 mg/kg as a bolus dose given over three minutes, followed by an infusion of 0.0005 mg/kg/min). Gallopamil significantly prolonged the mean (SD) duration of pacing that was tolerated (11 (2.6) vs 14.8 (2.4] min, significantly increased the mean (SD) peak heart rate attained during pacing (142 (15) vs 158 (11) beats/min), and reduced mean (SD) arterial pressure (133 (17) vs 116 (17) mm Hg). There were no changes in mean (SD) blood flow in the great cardiac vein (134.1 (57) vs 112.9 (38) ml/min, mean (SD) anterior regional coronary resistance (1.18 (0.6) vs 1.15 (0.5) mm Hg/ml/min), and mean (SD) anterior regional myocardial oxygen consumption (16.6 (6) vs 13.7 (4) ml/min). These data confirm that gallopamil is an effective antianginal agent and suggest that a reduction of myocardial oxygen demand is the predominant mechanism by which the drug exerts its beneficial effects.

Angina Pectoris↗

Exertion of stairclimbing in normal subjects and in patients with chronic obstructive bronchitis.

The exertion of stairclimbing has been studied in 10 normal young men, 10 healthy middle-aged men, and 10 middle-aged men with chronic bronchitis. Subjects climbed a staircase with a total vertical ascent of 40.8 m. They were allowed to adopt the most comfortable pattern of ascent, the patients having to stop at intervales for rest pauses. Work rate was determined by timing the raising body weight over measured sections of the staircase. Perception of exertion estimated with a numerical scale, heart rate, and increase of blood lactate concentration were closely similar in all three groups at the top of the staircase. In the patients, average power output was directly dependent on lung function, as indicated by the forced expired volume in 1 second. Stairclimbing offers a simple way of studying a patient's spontaneous activity pattern in a 'real life' environment. Studies of the kind described here could usefully complement formal exercise testing in the laboratory.

Adult↗

Changes in muscle activity and perceived exertion during exercises performed on a swiss ball.

The objective of this study was to determine differences in electromyographic (EMG) activity of prime mover and abdominal muscles while performing squats, push ups, and double leg lowering with a swiss ball. Twelve healthy subjects performed the movements. There was no difference between the surface conditions for muscle activity during the squat exercise; however, individuals had lower perceived exertion for the swiss ball squat. Activity of the triceps and abdominals was highest performing push ups on the swiss ball, whereas the activity of rectus abdominus (RA) only increased during double leg lowering on the swiss ball. Perceived exertion was highest for the push up and leg-lowering exercise performed on the swiss ball. Increased RA activity during double leg lowering can be attributed to its role as a hip flexor, whereas the lack of a rotation aspect to the task prevented increased oblique muscle activity. The swiss ball appears to only increase muscle activity during exercises where the unstable surface is the primary base of support.

Adult↗

Diaphragmatic O2 and lactate extraction during submaximal and maximal exertion in ponies.

Diaphragmatic O2 and lactate extraction were studied in 10 healthy ponies at rest and during treadmill exercise. The phrenic vein was aseptically catheterized via a lateral thoracotomy 8-35 days before the study. Arterial and phrenic venous blood samples were obtained simultaneously at rest and at 30-s intervals during 4 min of exertion. Three levels of exertion were studied (moderate, 10 mi/h; heavy, 15 mi/h; maximal, 20 mi/h), and a rest period of at least 90 min was allowed between them. Each pony was studied twice at least 2-3 days apart. At rest the diaphragmatic venous PO2, O2 saturation, arteriovenous O2 content difference, and O2 extraction were 43.2 +/- 2.0 Torr, 76.1 +/- 3.2%, 3.14 +/- 0.43 ml/dl, and 23.60 +/- 3.61%, respectively. Significant decrease in phrenic venous PO2 and O2 saturation occurred within 30 s of exercise. Phrenic venous PO2 decreased to 20.3 +/- 1.0, 18.9 +/- 1.1, and 15.4 +/- 0.9 Torr at 120 s of moderate, heavy, and maximal exercise, respectively. Corresponding values of phrenic venous O2 saturation were 33.6 +/- 2.2, 25.8 +/- 2.1, and 17.9 +/- 0.5%, respectively. Diaphragmatic arteriovenous O2 content difference expanded to 13.11 +/- 0.49, 15.00 +/- 0.60, and 16.90 +/- 0.60 ml/dl at 120 s of moderate, heavy, and maximal exercise, respectively, as O2 extraction rose to 65.93 +/- 1.98, 73.90 +/- 1.99, and 80.95 +/- 0.47%, respectively. During heavy and maximal exercise, the diaphragmatic venous lactate concentration remained similar to the arterial concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗

Effect of induced alkalosis on perception of exertion during intermittent exercise.

The purpose of this study was to evaluate the effects of metabolic alkalosis on differentiated ratings of perceived exertion during intermittent high-intensity exercise. Six endurance-trained females participated as subjects in this investigation. Each subject underwent three separate experimental trials in which NaHCO3 was ingested in either a single (0.3 g NaHCO3/kg body wt) or periodic schedule (0.12 g NaHCO3/kg body wt initially, with 0.18 g/kg body wt distributed in equal doses before each 5-min exercise bout). Calcium carbonate served as a placebo control. An intermittent exercise protocol was used in which each subject rode a cycle ergometer at 90% maximum O2 consumption for 5 min. Within each acid-base condition, the exercise protocol was repeated three times with 10-min rest periods interspersed. Differentiated ratings of perceived exertion for the legs (RPE-L), chest (RPE-C), and overall body (RPE-O) were attenuated under alkalotic treatment relative to placebo control regardless of pattern of NaHCO3 administration. RPE-L, RPE-C, and RPE-O were negatively correlated to the bicarbonate concentration of venous blood. This investigation suggests that perception of effort during high-intensity intermittent exercise can be related to buffering capacity of the blood.

Acid-Base Equilibrium↗

Furosemide reduces accumulated oxygen deficit in horses during brief intense exertion.

We theorized that furosemide-induced weight reduction would reduce the contribution of anaerobic metabolism to energy expenditure of horses during intense exertion. The effects of furosemide on accumulated O2 deficit and plasma lactate concentration of horses during high-intensity exercise were examined in a three-way balance randomized crossover study. Nine horses completed each of three trials: 1) a control (C) trial, 2) a furosemide-unloaded (FU) trial in which the horse received furosemide 4 h before running, and 3) a furosemide weight-loaded (FL) trial during which the horse received furosemide and carried weight equal to the weight lost after furosemide administration. Horses ran for 2 min at approximately 120% maximal O2 consumption. Furosemide (FU) increased O2 consumption (ml.2 min-1.kg-1) compared with C (268 +/- 9 and 257 +/- 9, P < 0.05), whereas FL was not different from C (252 +/- 8). Accumulated O2 deficit (ml O2 equivalents/kg) was significantly (P < 0.05) lower during FU (81.2 +/- 12.5), but not during FL (96.9 +/- 12.4), than during C (91.4 +/- 11.5). Rate of increase in blood lactate concentration (mmol.2 min-1.kg-1) after FU (0.058 +/- 0.001), but not after FL (0.061 +/- 0.001), was significantly (P < 0.05) lower than after C (0.061 +/- 0.001). Furosemide decreased the accumulated O2 deficit and rate of increase in blood lactate concentration of horses during brief high-intensity exertion. The reduction in accumulated O2 deficit in FU-treated horses was attributable to an increase in the mass-specific rate of O2 consumption during the high-intensity exercise test.

Anaerobiosis↗