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Exertional heat illness remains a major cause of morbidity and occasional mortality within the Armed Forces. This review explores the normal responses to heat, known causes of exertional heatstroke, and suggests possible answers to the question of why one member of a military unit collapses with heat stroke, while matched controls at his side remain unaffected.
AIM: The purpose of this study was to examine if the relationship between physiological changes classically observed with exercise duration and some subjective workload measures would be affected by the complexity of the locomotion mode (running vs racewalking). METHODS: The study was conducted on 24 well trained subjects (12 long distance runners and 12 racewalkers) divided in 3 groups (runners, racewalkers and control). Energy cost of locomotion (C), heart rate (HR), minute ventilation (V(E)), lactate concentration [La], ratings of perceived exertion (RPE 6-20 scale) and ratings of perceived difficulty (RPD 1(-1)5 scale) were recorded during 2 10-min submaximal tests on a treadmill before and immediately after a 3 hour exercise (racewalking or running) conducted at the velocity ventilatory threshold (vVT). RESULTS: No significant variations in physiological parameters and perceived measures were observed in G(c). A significant increase (p<0.05) in energy cost of walking (mean: +9.4%) and running (mean: +7.5%) at the end of exercise was observed. A significant interaction of locomotion mode and exercise duration was found on perceived exertion and perceived difficulty. In racewalkers RPD significantly increased with duration whereas no significant effect was found for RPE. Conversely a significant increase in RPE was found after 3 hours in runners without any significant change in RPD. CONCLUSIONS: This experiment suggests that, for a complex task, the classical relationship between RPE and metabolic load increase during prolonged exercise could be affected by changes in RPD. In this study, stability in RPE and increase in RPD observed in racewalkers may reflect an attentional focus dissociated from internal sensations and directed toward maintaining the required race walking gait.
A case is presented of exertional heat stroke in a military setting with numerous complications that have been previously described. In addition, the complication of late rhabdomyolysis with profound elevation of creatine phosphokinase (CPK) is here described for the first time. This rare condition responded to systemic steroids on this occasion. Late elevation of CPK is a rare complication of exertional heat stroke that appears to respond to systemic steroids.
Exercise-induced exertional compartment syndrome was first described by Vogt in 1945 as "march gangrene." The authors report a case of a 20-year-old United States Marine presenting with the florid findings of acute crural compartment syndrome. The patient's history of prior episodes of crural pain following long hikes led the authors to conclude that this patient had a chronic exertional compartment syndrome.
This study investigated exertion-dependent motor overflow among healthy adults when they performed isometric tasks with contralateral joints in different task directions. Twenty healthy adults (10 males and 10 females, mean age = 26.2 yrs) were instructed to complete a set of isometric contractions of various force vectors with the shoulder, elbow, and wrist joints, in a total of ten motor tasks at submaximal and maximal intensities (50%, 100% maximal voluntary contractions). The electromyographical activities from eight muscles of the unexercised upper limb were recorded to characterize intensity of motor overflow during sustained isometric contraction. Both occurrence frequency and magnitude of motor overflow in terms of standardized net excitation (SNE) increased with exertion level for all joint movements (P < 0.001). Additionally, the motor overflow magnitude depended strongly on the task direction of maximal isometric contraction (P < 0.05). Motor overflow was particularly augmented by the contralateral isometric contractions where task directions were opposed to gravity. However, such a directional effect upon SNE was not evident during submaximal contraction (P > 0.05). The difference of the net excitation between maximal and submaximal contraction (DNE(100%-50%MVC) data) indicated that the pectoralis major and triceps brachii consistently exhibited a marked recruitment in reaction to change in task direction of isometric contraction. Patterned motor overflow may be physiologically relevant to topological mapping of the ipsilateral pathways and altered effectiveness of use-dependent interhemispherical connectivity. The current observations provide better insight into gain in muscle strength due to contralateral exercise.
Heart muscle perfusion was studied by exertion scintigraphy Tal-201 in 24 patients, 16M and 8F, aged 16-45 years, means--28 +/- 7.4 years with hypertrophic cardiomyopathy. The relationship between perfusion disturbances and sudden death risk factors occurring in this group of patients was evaluated. Disturbances of heart muscle perfusion were found in 20 pts (83%); 2 pts had permanent perfusion defects, in 18 pts these defects were completely or partially reversible at rest. Only 4 pts (17%) had normal heart muscle perfusion. In patients with perfusion disturbances there was found a significantly more frequent occurrence of the following sudden death risk factors: 1. syncope (p less than .01) 2. ventricular arrhythmia of IV b class according to Lown (p less than .01) 3. advanced hypertrophy of intraventricular septum (p less than .01) 4. sudden death in patients families (p less than .05) The evaluation of the heart muscle perfusion confirmed the occurrence of myocardial ischemia in most of the examined patients. Normal coronaro-angiography in all the patients over 35 years as well as the young age of the other patients exclude atherosclerosis as the cause of myocardiac ischemia in the group under study. This is a confirmation of nonatherosclerotic etiology of myocardiac ischemia in hypertrophic cardiomyopathy patients. The correlation between perfusion disturbances and sudden death risk factors points to the role of ischemia in the natural course of disease and the value of exertion scintigraphy TI-201 in prognosing patients with hypertrophic cardiomyopathy.
The effect of exercise modality on the relationship between ratings of perceived exertion (RPE), blood lactate concentration, oxygen uptake (VO2), and heart rate (HR) was examined in 29 untrained male subjects who completed counterbalanced VO2max/lactate threshold (LT) protocols on a cycle ergometer (CE) and treadmill (TM). Heart rate, VO2, and RPE were determined at power outputs corresponding to LT and fixed blood lactate concentrations (FBLC) of 2.0, 2.5, and 4.0 mM and during maximal exercise. A repeated measures ANOVA indicated that, despite significant differences across exercise modality in HR and VO2 at LT, FBLC, and maximal exercise, no significant differences in RPE were found between exercise modalities during leg exercise. Mean (+/- SD) respective values for overall RPE at LT and FBLC of 2.0 mM, 2.5 mM, 4.0 mM, and max were 10.2 (2.2), 13.1 (2.1), 14.1 (2.3), 15.9 (2.3), and 18.8 (1.3) for the CE and 10.8 (1.9), 13.8 (1.8), 14.6 (1.6), 16.2 (2.6), and 18.5 (1.5) for the TM. It was concluded that exercise modality does not affect the perception of exertion at LT, FBLC, or maximal exercise and that a strong relationship exists between RPE and blood lactate concentrations.
In this communication, the results of an enzyme histochemical study on m. gluteus medius of horses, sensitive to exertional myopathy, during attacks of rhabdomyolysis are presented. The activity and location of about 25 enzymes were examined. In the present report, the early metabolic changes are discussed. Within 6 min after an attack, some large rounded fibres (approximately 2%) were seen, which showed an intense red staining in the haematoxylin and eosin sections. These hypercontracted fibres showed an increase in activity of mitochondrial adenosine triphosphatase, indicating the presence of uncoupling and/or loose coupling of the mitochondria. This finding may point to a deficient production of ATP in the m. gluteus medius of horses sensitive for exertional myopathy and this deficiency may lead to pathological alterations in the skeletal muscles. The pathological fibres revealed a changed activity of other mitochondrial enzymes as well.
Perceived exertion (RPE) has been used as a subjective indicator of exercise intensity for extremely light to supramaximal-level dynamic exercise. Little data exist on the relationship of RPE to physiological variables during sustained isometric exercise. Ten male subjects volunteered and participated in this investigation. Subjects were instructed to maintain a hand grip contraction of 50% of maximal effort until exhaustion. During this bout of exercise, electromyographic activity (EMG) and RPE values were recorded at 10 s intervals. The raw EMG signals were processed for frequency content (mean power frequency [MPF] and for signal amplitude (root mean squared [RMS]). RPE was recorded as a subjective value selected from a ten-point scale with ratio properties. Analysis of the data indicated that RPE was strongly correlated to both MPF: r2 = (-).922, and RMS: r2 = .729. These data imply that during sustained isometric exercise changes in perceived exertion are related closely to electromyographic activity of the contracting muscle.
Over a period of three years 829 cases of greater than or equal to 16-year-old athlete exertion injuries and syndromes were collected. There were 75 women and 754 men in the series. About 90% of the athletes had been training regularly for more than two years, and 75% of them trained 6 times a week or more. Approximately 52% of the injuries occurred in track and field athletics, about 17% in ball events, 13.6% in skiing, 7.4% in orienteering, and 4.7% in power events. Other sports were associated with fewer exertion injuries. 28.7% of the conditions occurred in the knee, 17% in the ankle, foot and heel, 14.8% in the leg, 8.2% in the back and trunk, 8.1% in the thigh, 7.4% in the achilles tendon. The rest were in the shoulder, neck and upper extremities. In 92% of the patients conservative treatment and rest were used. Only 8% of the cases were treated surgically.
A 3-year-old mare repeatedly had clinical signs of rhabdomyolysis on mild exertion. Serum creatine kinase and aspartate transaminase activities were high at rest. Responses to dietary sodium bicarbonate were tested through 7 alternating periods of supplementation of a basal ration of timothy hay and oats. Physical signs; venous blood pH and gases; blood glucose and lactate; serum electrolytes, enzymes, and creatinine; and urine pH were monitored before and after exercise. Dietary sodium bicarbonate raised resting venous blood pH and bicarbonate slightly and significantly increased urine pH from pH 7.46 to 8.2 (P less than 0.001). An exercise test included 5 minutes at the walk followed by 20 minutes at the trot. The exercise induced gait stiffness, muscle fasciculations, and muscle induration when the diet was not supplemented, but not when it was supplemented with sodium bicarbonate. Myoglobin was present in 16 of 21 urine samples after exercise during nonsupplemented periods, but only in 3 of 28 urine samples during supplemented periods (P less than 0.0001). Bicarbonate supplementation significantly decreased the responses of blood lactic acid, serum creatine kinase, and aspartate transaminase to exercise. Supplementation of the diet was associated with higher venous blood pH and bicarbonate ion concentrations throughout exercise. Dietary sodium bicarbonate apparently mitigated or prevented physical, chemical, and enzymatic characteristics of exertional rhabdomyolysis in this mare, possibly through its enhancement of buffering capacity in muscle tissue fluids.
The incidence and nature of exertion-related injuries were studied at a South African Defence Force basic training centre. A total of 404 separate injuries were sustained by 359 of 947 recruits during the 10-week basic training cycle. Of these injuries, 18,3% were sustained with (group 1) and 81,7% without (group 2) an obvious sudden precipitating event. Exertion-related injuries were responsible for a loss of 2711 recruit-days of basic training. While the knee sustained the largest number of group 2 injuries, lower leg trauma resulted in the greatest loss of basic training time. Forty-two separate radio-graphically confirmed stress fractures were incurred by 39 recruits, an incidence of 4,12%, which is considerably higher than that in the US Army. These data leave little doubt that the present training programme is costly in terms of training-time lost and may prevent large numbers of recruits from deriving the optimum conditioning benefits.
Three different techniques of middle distance running (fast/slow, slow/fast, and steady pace) have been compared in terms of oxygen intake, blood lactate and ratings of perceived exertion (RPE). The subjects (10 middle distance and long distance male runners) carried out the three patterns of running on the laboratory threadmill according to a randomly ordered sequence, on each occasion covering 1400 m in 4 min. The fast/slow protocol resulted in a rapid and sustained on-transient of oxygen intake, less lactate accumulation, and a lower rating of perceived exertion during the final 2 min of th4 min run. Physiological data thus support coaching impressions of the superiority of the fast/slow protocol.
Changes in the coagulation properties of blood under the effect of physical exertion on a bicycle ergometer were studied in 111 patients with hypertensive disease. The activity of their blood coagulation system was found to be increased and fibrinolysis simultaneously intensified as compared to these values in healthy persons. The degree of these changes depended on the age of the disease and the load of the exertion. Effective hypotensive therapy improved the functional condition of hemostasis, intensifying the activity of the anticoagulation mechanisms among others.
Beta adrenergic blocking agents are effective antianginal agents and reduce the frequency of anginal attacks, nitroglycerin consumption, and improve exercise tolerance in patients with stable exertional angina pectoris. These drugs are effective in the management of exertional angina pectoris primarily due to their ability to block beta 1 receptors and thereby competitively blocking the effects of sympathetic stimulation (i.e. increase in myocardial oxygen demand) during exercise. In this report other pharmacological properties of these agents i.e. membrane stabilizing activity, intrinsic sympathomimetic activity and cardioselectivity are of little importance. Comparative studies with beta adrenergic blocking agents with different ancillary properties, utilizing intravenous preparations, acute single and multiple oral dosing and sustained oral therapy prescribed for several weeks or months, show that if used in equipotent doses all beta adrenergic blocking agents are equally effective antianginal agents. It should be recognized that therapy with these agents may precipitate heart failure or aggravate bronchospasm in susceptible patients. This can occur with cardioselective agents and with beta blockers which also have intrinsic sympathomimetic activity.
The efficacy of two beta-receptor antagonists, propranolol and pindolol, was compared with that of a calcium antagonist, verapamil, in the treatment of exertional angina pectoris in 22 men (mean age 51 years). The clinical response and left ventricular function were evaluated with treadmill exercise and with radionuclide ventriculography performed while the patient was at rest or exercising supine with a bicycle ergometer. All the treatments significantly prolonged exercise duration (p less than 0.001) and reduced the number of patients terminating treadmill exercise because of angina (p less than 0.05). The resting heart rate was decreased markedly (p less than 0.001) by propranolol but only slightly (p less than 0.05) by pindolol and verapamil. The left ventricular ejection fraction during rest was unchanged by any treatment, but that during exercise was improved (p less than 0.05) by all the treatments. Patients who failed to gain relief from angina with one of the drugs often responded to another, and adverse reactions occurring with one drug did not necessarily occur with another. In summary, pindolol and verapamil were safe and effective alternatives to propranolol in the treatment of the exertional angina pectoris of these patients.
A retrospective study was conducted on 488 patients admitted in our rehabilitation center after a recent acute myocardial infarction. Purpose of the study was to assess the incidence and prognostic value of exertional hypotension in these patients. Of 488 patients admitted to the study 33 (6%) were found to have exertional hypotension; 14 patients had an inferior myocardial infarction, 18 patients had an anterior myocardial infarction, 3 patients had a history of previous myocardial infarction. In the follow-up period (28.3 +/- 13.2 months) the worse prognosis (death or pulmonary oedema) was associated with the presence during exercise of hypotension, ST segment elevation in leads were Q waves were present and no ST depression in other leads. In conclusion, recent anterior myocardial infarctions associated with hypotension and ST segment elevation during exercise appear to be at risk for future cardiac events.
Twenty-one calves, 16 weeks of age, comprised 3 treatment groups. All calves in 2 of these groups were anemic. Several variables were measured before and immediately after an imposed exertion period. The anemic calves had significantly faster heart rates than did nonanemic calves, but there was no significant difference either in respiratory rates or acid-base variables. However, anemic calves became more acidic when made to work and also showed greater increase in respiratory rate than did nonanemic calves. The partial pressure of oxygen in venous blood was significantly lower in the anemic calves than in nonanemic calves both before and after exertion, but still represented adequate saturation of hemoglobin with oxygen.