摘要:

DUCHATEAU, J. Bed rest induces neural and contractile adaptations in triceps surae: a clinically relevant case study.Med. Sci. Sports Exerc., Vol. 27, No. 12, pp. 1581–1589, 1995. The electromechanical adaptations of the triceps surae muscle were examined in one subject confined to bed for 5 wk due to strong orthostatic headaches. The torque produced by the triceps surae and the electromyographic (EMG) activities of the slow soleus (Sol) and fast lateral gastrocnemius (LG) were studied in response to voluntary and electrically induced contractions. Bed rest caused a 46% decrease in the maximal voluntary contraction (MVC) torque. This loss of strength was associated with a deficit of 33% in central activation and 19% in the estimated muscle force-generating capacity. The EMG activity during MVC was found to be reduced in both muscles, but to a greater extent in the LG (−51%) than in the Sol (−32%). The decrease in amplitude of the maximal M wave (Mmax) recorded in response to supramaximal electrical stimulation was greater in Sol (−28%) than in LG (−12%). After bed rest, the twitch time to peak torque was slightly prolonged (+9%) and the maximal rate of tension development (dT/dt) was reduced by 31 % in electrically induced and 24% in voluntary contractions. Although muscle fatigability during a 60-s sustained MVC was not affected by the bed rest period, the relative contributions of the two muscles differed from control. These results indicate that muscular adaptations were more prominent in Sol while neural adaptations were more significant in LG. Furthermore, the neural changes almost completely recovered within 2 wk, whereas the contractile alterations required at least 5 times longer to return to the control values.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

DE PAZ, J. A., J. G. VILLA, P. LOPEZ, and J. GONZALEZ-GALLEGO. Effects of long-distance running on serum bilirubin.Med. Sci. Sports Exerc., Vol. 27, No. 12, pp. 1590–1594, 1995. This study was undertaken to determine the effects of long-distance running on serum bilirubin fractions. Thirteen male ultramarathon runners participating in a 100-km race volunteered for the study. Venous blood samples were obtained shortly before and immediately after the race. Decreased serum haptoglobin levels (−66%) indicated the presence of hemolysis. After accounting for plasma-volume loss, significant post-race increases were found for creatine kinase (+20-fold), creatine kinase-MB (+252%), alanine aminotransferase (+42%), aspartate aminotransferase (+193%), gammaglutamyl transpeptidase (+56%), and glutamate dehydrogenase (+58%) serum activities, suggesting that running causes alterations of both muscle and liver tissues. Serum concentration of total bilirubin was significantly elevated (+106%) following the race, with changes corresponding to both unconjugated (+96%) and conjugated esters (+283%) of the pigment and significant increases in the ratio of esterified to total bilirubin. Our data show that long-distance running causes increases in the different serum bilirubin fractions which can be accounted for both hemolysis and hepatic disturbances.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

HOLTZHAUSEN, L-M. and T. D. NOAKES. The prevalence and significance of post-exercise (postural) hypotension in ultramarathon runners.Med. Sci. Sports Exerc., Vol. 27, No. 12, pp. 1595–1601, 1995. A consistent finding in exercise-associated collapse is a marked postural fall in the systolic blood pressure associated with a tachycardia. The prevalence and significance of these post-exercise (postural) changes in blood pressure among noncollapsed ultradistance athletes has not been well documented. The aim of this study was to compare pre-and post-race changes in systolic and diastolic blood pressures with changes in body weight and plasma volume and with symptoms of post-exercise hypotension, including the effects of posture, among a group of 31 runners competing in an 80-km footrace. During the race, runners developed a mean (±SD) weight loss of 3.5 (±1.2) kg and plasma volume change of 12.8% (±9.1). Asymptomatic postural hypotension defined as a fall in systolic blood pressure of greater than 20 mm Hg from the supine to the erect position without syncopal symptoms was present in two runners (7%) before the race and in 21 runners (68%) afterward. The degree of postural variation in systolic blood pressure was unrelated to changes in body weight or a fall in plasma volume. We conclude that (i) all runners were dehydrated by the race activity with a range of 1% to 7% and an average of 4.6%; (ii) asymptomatic post-exercise (postural) hypotension developed in the majority (68%) of ultramarathon runners in this study; (iii) the post-exercise hypotension is likely of multifactorial origin and is not entirely related to whole body dehydration or a reduction in plasma volume; and (iv) despite marked levels of dehydration among our sample of runners, their cardiovascular status in the supine position was not greatly compromised.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

FOSTER, C., R. A. GAL, S. C. PORT, and D. H. SCHMIDT. Left ventricular ejection fraction during incremental and steady state exercise.Med. Sci. Sports Exerc., Vol. 27, No. 12, pp. 1602–1606, 1995. Despite extensive study of left ventricular (LV) function during incremental exercise (INC), there is little known about LV function during steady state exercise typical of that used during exercise training. In this study we evaluated LV ejection fraction (LVEF) during upright cycle ergometer exercise using first-pass radionuclide angiography (RNA). Healthy volunteers (N= 10) were studied during both INC and steady state. INC studies were performed at rest, at the ventilatory threshold (VT), and at maximal exercise. During steady state studies were performed after 10, 20, and 30 min of exercise at VT. During INC LVEF increased from rest (61% ± 5%) to exercise at the VT (73% ± 5%). There was no further change in LVEF at maximal exercise (73% ± 5%). During steady state, LVEF increased from rest (61% ± 5%), to exercise at VT (73% ± 5%), with further increases after 20 (78% ± 6%) and 30 (79% ± 3%) min of exercise. The results suggest that LVEF is nearly maximal during submaximal exercise at VT. During steady state LVEF continutes to increase with continuation of steady state exercise.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

SHI, X., R. W. SUMMERS, H. P. SCHEDL, S. W. FLANAGAN, R-T. CHANG, and C. V. GISOLFI. Effects of carbohydrate type and concentration and solution osmolality on water absorption.Med. Sci. Sports Exerc., Vol. 27, No. 12, pp. 1607–1615, 1995. We studied intestinal absorption of solutions containing either one (glucose, Glu, or maltodextrin, Mal) or two (fructose, Fru, and Glu or sucrose, Suc) transportable carbohydrate (CHO) substrates using segmental perfusion technique in eight healthy male subjects. These CHO were either free and directly transportable monosaccharides (Glu, Fru), bound as the disaccharide (sucrose, Suc), or as oligomers (maltodextrins, Mal). [CHO] was varied from 6% to 8% (120–444 mmol·l-1). All solutions contained low [Na+] (15–19 mEq) and [K+]_(3–4 mEq). Solutions osmolalities varied from 165 to 477 mOsm·kg-1. Osmolalities in the test segment ranged from 268 to 314 mOsm·kg-1. The regression line of osmolality with water absorption differed for single as compared with multiple substrate solutions. The significantly different intercepts of these two regression lines suggest that solutions with multiple substrates produce greater water absorption at a given osmolality than those with one. Comparing all solutions, test segment solute flux (partial r = 0.69) was more important than mean osmolality (partial r = 0.32). In conclusion, solutions with multiple substrates stimulate several different solute absorption mechanisms yielding greater water absorption than solutions with only one substrate.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

SCHNEIDER, D. A., G. H. KAMIMORI, S. Y. WU, M. T. MCENIERY, and C. SOLOMON. Plasma catecholamine and ventilatory responses to cycling after propranolol treatment.Med. Sci. Sports Exerc., Vol. 27, No. 12, pp. 1616–1620, 1995. The purpose of the present study was to examine the relationship between minute ventilation (&OV0312;E) and plasma concentrations of epinephrine (EPI) and norepinephrine (NE) during incremental cycling (20 W·2 min-1) performed under conditions of β-adrenergic blockade (80 mg of propranolol) and placebo in six untrained male subjects. No significant differences existed between treatments in O2uptake, CO2output, blood lactate, pH, or &OV0312;Eduring the submaximal work stages of incremental exercise common to both treatments (20–220 W). During exercise with β-blockade, EPI, and NE concentrations were both significantly elevated compared with control levels at every submaximal work stage. Significant positive correlations between &OV0312;Eand plasma levels of EPI and NE were found during both β-blockade (r = 0.98 and 1.00) and control conditions (r = 0.98 and 0.96). Although the high correlations were unchanged during exercise with β-blockade, the slopes of the regression lines for the &OV0312;E-EPI and the &OV0312;E-NE relationships were both significantly reduced compared with control conditions, β-blockade resulted in elevated plasma levels of both EPI and NE compared with control conditions without causing a change in exercise &OV0312;E. These findings suggest that catecholamines may not be important substances in regulating breathing during exercise.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

KOLKHORST, F. W., T. D. TOEPFER, and F. A. DOLGENER. Expired air temperature during steady-state running.Med. Sci. Sports Exerc., Vol. 27, No. 12, pp. 1621–1625, 1995. While some metabolic measurement systems measure expiratory temperature to standardize gas volumes, other systems use only an estimate. This study investigated the effect of prolonged exercise on expiratory temperature near the pneumotachometer to provide a basis for its estimation when actual measurement is unavailable. Seven active females each performed two 45-min treadmill runs at identical speeds (64.5% ± 11.8% of &OV0312;O2max) in which the pneumotachometer heater control was either set to 37°C or turned off. Expired air temperatures were monitored with thermocouples at the nonrebreathing valve (VAL) and 1 cm upstream (UPS) and downstream (DNS) from the pneumotachometer screens. There were no temperature differences over time for any of the conditions, and there were no differences in the VAL or UPS temperatures between the heated and unheated conditions. DNS temperature was higher during the heated condition at all time periods (P< 0.01). Mean DNS temperatures for the heated and unheated condition were 30.2 ± 1.0°C and 27.9 ± 1.1 °C, respectively. We concluded that expired air temperatures near the pneumotachometer remain stable during extended steady-state exercise regardless of whether the pneumotachometer is heated or not.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

PEREIRA, M. A., A. M. KRISKA, M. L. JOSWIAK, G. K. DOWSE, V. R. COLLINS, P. Z. ZIMMET, H. GAREEBOO, P. CHITSON, F. HEMRAJ, A. PURRAN, and D. FAREED. Physical inactivity and glucose intolerance in the multiethnic island of Mauritius.Med. Sci. Sports Exerc., Vol.27, No. 12, pp. 1626–1634, 1995. The island nation of Mauritius, located in the southwest Indian Ocean, has a high prevalence of non-insulin-dependent diabetes mellitus (NIDDM) among all of its ethnic groups (Hindu and Muslim Indians, African-origin Creoles, and Chinese). These high rates of NIDDM among groups of varying genetic background provide strong support for the importance of environmental components in the etiology of the disease. Research in Mauritius using a simple activity scale has suggested that physical inactivity may be one of these components. The current investigation further examined the association between glucose tolerance and physical activity in middle-aged nondiabetic residents of Mauritius using a more extensive physical activity questionnaire (the Modifiable Activity Questionnaire). Excluding individuals with NIDDM, a statistically significant (P< 0.05) inverse relationship between physical activity and 2-h post-load glucose concentration was found for both males (rho = −0.14) and females (rho = −0.11). Stratifying by ethnic group, similar inverse correlations were observed in Hindu, Creole, and Chinese males, and in Hindu females (P< 0.05), as well as weaker relationships in Muslim males and Creole females (P< 0.10). Total physical activity remained an independent predictor of 2-h post-load glucose concentration after controlling for body mass index, waist-hip ratio, age, and family history of NIDDM. These data arc supportive of a potentially important role of physical activity in the prevention of NIDDM in middle-aged inhabitants of Mauritius.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

PIVARNIK, J. M., M. S. BRAY, A. C. HERGENROEDER, R. B. HILL, and W. W. WONG. Ethnicity affects aerobic fitness in U.S. adolescent girls.Med. Sci. Sports Exerc., Vol. 27, No. 12, pp. 1635–1638, 1995. The purpose of this investigation was to determine whether aerobic fitness (&OV0312;O2max) differed between black (N= 40) and white (N= 53) adolescent girls who were similar in age (13.5 yr) and percent body fat (24.6%). Expired gases were collected continuously while each girl performed a standard Bruce protocol to volitional exhaustion on a motorized treadmill (TM). Heart rates (HR) were measured during the exercise testing via telemetry. Fat-free mass (FFM) was estimated with total body electrical conductivity (TOBEC). Average (±SD) maximum HR (black = 194 ± 7; white = 198 ± 8) and respiratory exchange ratios (black = 1.17 ± 0.08; white = 1.22 ± 0.09) did not differ between subject groups. Aerobic fitness was significantly (P< 0.01) lower in black versus white girls when &OV0312;O2maxwas expressed relative to body weight (31.8 ± 5.8 vs 38.5 ± 6.8 ml·kg-1·min-1) and body weight raised to the 0.67 power (120.9 ± 19.5 vs 138.5 ± 20.7 ml·kg-0.67min-1). Treadmill time to exhaustion was significantly less (P< 0.01) in the black (8.49 ± 1.30 min) versus white (9.41 ± 1.60) subjects. Also, black subjects demonstrated less ability to utilize O2during maximal exercise at a given FFM. This suggests the black girls' FFM contained a smaller percentage of skeletal muscle mass that could be utilized during treadmill exercise. It is possible that lower aerobic fitness values seen in the black girls are related to a combination of anatomical, physiological and/or behavioral factors.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

AARON, D. J., S. R. DEARWATER, R. ANDERSON, T. OLSEN, A. M. KRISKA, and R. E. LAPORTE. Physical activity and the initiation of high-risk health behaviors in adolescents.Med. Sci. Sports Exerc., Vol. 27, No. 12, pp. 000–000, 1995. The association of physical activity to the initiation of health risk behaviors was examined in a 3-yr prospective study of a population-based cohort of 1245 adolescents aged 12–16 yr. Four hundred thirty-seven students (36% of the cohort) were identified at baseline via self-report survey as never having smoked cigarettes, consumed alcohol, used marijuana, or carried a weapon. Three measures of physical activity were obtained at baseline: leisure-time physical activity (LTPA), level of aerobic fitness (AF), and participation in competitive athletics. Significant associations, with notable gender differences, were observed between physical activity and the initiation of cigarette smoking and alcohol use. The cumulative proportion of male students initiating alcohol use was 48%, 42%, and 24% for high, moderate, and low LTPA, respectively (P< 0.01). Males who participated in competitive athletics were significantly more likely than nonathletes to initiate alcohol use (44% vs 17%,P< 0.01). The cumulative proportion of female students initiating cigarette use was 10%, 23%, and 22% for high, moderate, and low LTPA, respectively (P< 0.05) and 7%, 28%, and 16% for high, moderate, and low AF, respectively (P< 0.05). No association was found between physical activity and weapon carrying. These results indicate that in this cohort of adolescents, the most active or most fit females were less likely to initiate cigarette smoking. In contrast, the most active males or males who participated in competitive athletics appeared more at-risk for initiating alcohol consumption than their less active counterparts.

ISSN:0195-9131    

出版商:OVID    

年代:1995

数据来源: OVID