摘要:

Few studies have examined the effect of prolonged exercise training on left ventricular diastolic function in previously sedentary subjects. We performed M-mode, 2-D, and Doppler echocardiography on 16 previously sedentary men before and after 1 yr of exercise training. Six men served as controls. Exercise subjects participated in four 1-h supervised sessions weekly at 60-80% of their measured maximal heart rate. Maximal oxygen uptake, maximal exercise cardiac output, and resting left ventricular systolic and diastolic function were determined before and after training. Maximal oxygen uptake and peak cardiac output increased 27.3% and 8.5% in the trainers (P< 0.001 for both) and 1.3% and 1.0% in the controls. Left ventricular diastolic and systolic dimensions changed slightly in both groups. Maximal early inflow velocity decreased in both trainers (-9.9 ± 14.0 cm·s-1, mean ± SD,P≤ 0.01) and controls (-7.2 ± 10.2 cm·s-1). Maximal atrial inflow velocity decreased (-7.8 ± 10.9 cm·s-1,P≤ 0.01) only in the trainers possibly because of a reduction in resting heart rate (-6 ± 11 beats·m-1,P≤ 0.05). Acceleration and deceleration times were unchanged in both groups. These results demonstrate that substantial increases in exercise performance and exercise cardiac output can occur without detectable changes in resting cardiac dimensions or left ventricular systolic and diastolic function.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

This study was conducted to investigate injury patterns at three major off-road bicycle races in the western United States in 1995. All cyclists forced out of the cross-country (CC) and downhill (DH) competitions due to injury were examined and interviewed. The overall injury rates were 0.49%(20/4074) for the CC and 0.51% (11/2158) for the DH event. In the CC there were 0.37 injured cyclists for every 100 h of racing time versus 4.34 injured cyclists/100 h in the DH (P= 0.01). Injury rates in the CC were higher for women than for men (1.05% vs 0.40%,P= 0.04; 0.75/100 h vs 0.31/100 h,P= 0.01). Injured CC cyclists who fell forward over their handlebars had higher mean injury severity scores (3.0 vs 1.3,P= 0.01) and required more emergency room visits (6/10 vs 1/10,P= 0.02) than cyclists who fell off their bicycles to the side. Women injured in the CC fell forward off their bicycles (5/6 vs 5/14,P= 0.05) and were taken to the hospital (4/6 vs 3/14,P= 0.05) more often than men. These data suggest that 1) the risk of being injured during a race is similar in the CC and DH events, 2) the long-term risk may be greater to DH racers than to CC competitors, 3) the severity of injury is greater when a CC cyclist falls forward off the bicycle, and 4) women CC competitors are more likely to fall forward off their bicycles and be injured than men.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The effects of 12 wk of progressive resistance strength training onin vivoandin vitroimmune parameters were evaluated in a controlled study of eight subjects with rheumatoid arthritis (RA), eight healthy young (22-30 yr), and eight healthy elderly (65-80 yr) individuals. Six healthy elderly (65-80 yr) nontraining control subjects were also evaluated to account for seasonal and psychosocial effects. Training subjects exercised at 80% of their one-repetition maximum and performed eight repetitions per set, three sets per session on a twice weekly basis. Peripheral blood mononuclear cell (PBMC) subpopulations, cytokine and prostaglandin (PG) E2production, proliferative response, and delayed type hypersensitivity (DTH) skin response were measured before and after 12 wk of training. Training did not induce changes in PBMC subsets, interleukin(IL)-1 β, tumor necrosis factor-α (TNF), IL-6, IL-2, or PGE2production, lymphocyte proliferation, or DTH response in any of the training groups compared with control subjects. These data suggest that 12 wk of high-intensity progressive resistance strength training does not affect immune function in young or elderly healthy individuals or subjects with RA.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Despite the voluminous amount of research that has been published in the field of exercise science over the past three decades, there remains a paucity of information on the activity patterns and physiological responses to exercise in persons with disabilities. In an era when physical activity has grown to new heights in terms of its importance in promoting health and preventing disease, many questions pertaining to how it affects the lives of individuals with physical and mental disabilities remain unanswered. The purpose of this paper is to review the prevalence of disability in the United States and to present recommendations for future research on physical activity and disability. A related objective of this paper is to encourage exercise scientists to undertake research on this increasingly significant group of American citizens.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The aim of this study was to examine the effect of carbohydrate (CHO) ingestion during the first hour of treadmill running on endurance capacity. Eleven male subjects ran at 70% ˙VO2maxto exhaustion on three occasions one week apart. On two occasions two CHO-electrolyte solutions (a 5.5% (E) and a 6.9% (L)) were ingested for the first hour of exercise; water was then ingested until exhaustion. On the third occasion water (W) was ingested throughout the run. The order of testing was randomly assigned. Exhaustion times for the W, E, and L trials were 109.6 ± 9.6 min, 124.5± 8.4 min, and 121.4 ± 9.4 min, respectively. There was no difference between the two CHO trials, but time to exhaustion was longer only for the E trial (P< 0.05), compared with the W trial. Nevertheless the average performance times for the combined results of the two CHO trials were longer than the water trial. Carbohydrate ingestion resulted in higher blood glucose concentration (P< 0.01) at 20 min in the E trial only and lower (P< 0.05) serum growth hormone and plasma FFA and glycerol concentrations at 60 min but not at exhaustion in both the E and L trials compared with the W trial. Blood lactate, plasma ammonia, electrolytes, catecholamines, and serum insulin and cortisol concentrations were not different in the three trials. In conclusion, CHO ingestion during the first hour of exercise improves endurance capacity to a greater extent compared with water alone.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Two series of experiments were conducted to examine the effect of ingesting beverages with differing carbohydrate (CHO) concentrations and osmolalities on metabolism and performance during prolonged exercise in different environmental conditions. In series 1, 12 subjects performed three cycling exercise trials to fatigue at 70% ˙VO2peakin either 33°C(N= 6) (HT1) or 5°C (N= 6) (CT). Subjects ingested either a 14% CHO solution (osmolality = 390 mosmol·l-1) (HCHO); a 7% CHO solution (330 mosmol·l-1) (NCHO) or a placebo (90 mosmol·l-1) (CON1). In series 2, six subjects performed the same three trials at 33°C (HT2), while ingesting either NCHO, a 4.2% CHO solution (240 mosmol·l-1) (LCHO) or a placebo) (240 mosmol·l-1) (CON2). Plasma glucose was higher (P< 0.05) in HCHO than NCHO, which in turn was higher (P< 0.05) than CON1 in both CT and HT1. Plasma glucose was lower (P< 0.05) in CON2 compared with NCHO and LCHO in HT2. The fall in plasma volume was greater(P< 0.05) in HCHO than other trials in both CT and HT1 but was not different when comparing the three trials in HT2. Exercise time was not different when comparing the trials in either HT1 or HT2 but was longer(P< 0.05) in NCHO compared with HCHO, which, in turn, was longer(P< 0.05) than CON1 in CT. These data demonstrate that, during prolonged exercise in the heat, fatigue is related to factors other than CHO availability. In addition, during exercise in 5°C a 7% CHO solution is more beneficial for exercise performance than a 14% CHO solution.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The aim of this study was to test the hypothesis that cardiopulmonary baroreflex control of forearm vascular resistance (FVR) during central hypervolemic loading was less sensitive in exercise trained high fit individuals (HF) compared to untrained average fit individuals (AF). Eight AF(age: 24 ± 1 yr and weight: 78.9 ± 1.7 kg) and eight HF (22± 1 yr 79.5 ± 2.4 kg) voluntarily participated in the investigation. Maximal aerobic power (determined on a treadmill), plasma volume and blood volume (Evans blue dilution method) were significantly greater in the HF than AF (60.8 ± 0.7 vs. 41.2 ± 1.9 ml·kg-1·min-1, 3.96 ± 0.17 vs 3.36 ± 0.08 l, and 6.33 ± 0.23 vs 5.28 ± 0.13 l). Baseline heart rate(HR), central venous pressure (CVP), mean arterial pressure (MAP, measured by an intraradial catheter or a Finapres finger cuff), forearm blood flow (FBF, plethysmography), and FVR, calculated from the ratio (MAP-CVP)/FBF, were not different between the HF and the AF. Lower body negative pressure (LBNP, -5,-10, -15, and -20 torr) and passive leg elevation (LE, 50 cm) combined with lower body positive pressure (LBPP, +5, +10, and +20 torr) were utilized to elicit central hypovolemia and hypervolemia, respectively. Range of CVP (from LBNP to LE+LBPP) was similar in the AF (from -3.9 to + 1.9 mm Hg) and HF (from-4.0 to +2.2 mm Hg). However, FVR/CVP was significantly less in the HF (-1.8± 0.1 unit·mm Hg-1) than AF (-3.4 ± 0.1 unit·mm Hg-1). The FVR decrease in response to increase in CVP was significantly diminished in the HF (-1.46 ± 0.45 unit·mm Hg-1) compared to the AF (-4.40 ± 0.97 unit·mm Hg-1), and during LBNP induced unloading the FVR/CVP of the HF (-2.01± 0.49 unit·mm Hg-1) was less (P< 0.08) than the AF (-3.28 ± 0.69 unit·mm Hg-1). We concluded that the cardiopulmonary baroreceptor mediated FVR reflex response was significantly less sensitive to changes in CVP in individuals who practice exercise training.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Estimates of muscular efficiency in competitive and recreational cyclists at similar work intensities and cycling frequencies were examined. Twelve healthy college-age male nonsmoker volunteers were grouped as either competitive (CC;N= 6) or recreational (RC;N= 6) cyclists based upon previous cycling experience. Subjects were studied at pedaling frequencies of 50 and 80 rpm during bouts of graded and submaximal endurance (75% ˙VO2peak) exercise. Between rest and 250 W, we observed no intergroup differences in ˙VO2(energy input) at either 50 or 80 rpm. Estimates of whole body (gross) muscular efficiency ranged from 15% to 24% in competitive and 13% to 22% in recreational cyclists at 50 rpm but were not different. Delta (Δ) efficiencies ranged from 20% to 34% in competitive and from 21% to 28% in recreational cyclists. Delta efficiency decreased from 27% to 21% in competitive cyclists, from 25% to 21% in recreational cyclists as a function of pedaling frequency, and was not different between groups. Competitive cyclists rode longer at both 50 rpm (27± 5 min vs 14 ± 2 min;P< 0.05) and 80 rpm (35± 4 min vs 20 ± 4 min;P< 0.05). At 50 rpm (3.08± 0.02 l·min-1vs 2.78 ± 0.05 l·min-1;P< 0.01) and 80 rpm (3.14 ± 0.01 l·min-1vs 2.7 ± 0.04 l·min-1;P< 0.001), the mean ˙VO2was also greater in competitive cyclists. Although both groups showed superior endurance at 80 compared with 50 rpm and total work was approximately double competitive cyclists at each pedaling frequency, we observed no differences in whole body muscular efficiency during sustained exercise at 75% ˙VO2peak. Our results suggested that previous cycling experience was of minor importance when comparing cycle ergometer efficiency between these two groups. The increased endurance at higher pedaling frequencies during submaximal exercise is not explained by altered muscular efficiency.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

In the literature, it is well established that subjects are able to jump higher in a countermovement jump (CMJ) than in a squat jump (SJ). The purpose of this study was to estimate the relative contribution of the time available for force development and the storage and reutilization of elastic energy to the enhancement of performance in CMJ compared with SJ. Six male volleyball players performed CMJ and SJ. Kinematics, kinetics, and muscle electrical activity (EMG) from six muscles of the lower extremity were monitored. It was found that even when the body position at the start of push-off was the same in SJ as in CMJ, jump height was on average 3.4 cm greater in CMJ. The possibility that nonoptimal coordination in SJ explained the difference in jump height was ruled out: there were no signs of movement disintegration in SJ, and toe-off position was the same in SJ as in CMJ. The greater jump height in CMJ was attributed to the fact that the countermovement allowed the subjects to attain greater joint moments at the start of push-off. As a consequence, joint moments were greater over the first part of the range of joint extension in CMJ, so that more work could be produced than in SJ. To explain this finding, measured and manipulated kinematics and electromyographic activity were used as input for a model of the musculoskeletal system. According to simulation results, storage and reutilization of elastic energy could be ruled out as explanation for the enhancement of performance in CMJ over that in SJ. The crucial contribution of the countermovement seemed to be that it allowed the muscles to build up a high level of active state (fraction of attached cross-bridges) and force before the start of shortening, so that they were able to produce more work over the first part of their shortening distance.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The purpose of this study was to investigate the relationship of uphill cycle velocity, cycle length, and cycle rate in top U.S. female skiers during a multiple lap cross-country ski skating race. Eighteen female cross-country skiers served as subjects at the United States Women's 10-km Freestyle 1995 National Championships. The course consisted of two laps of the same 5-km loop. The selected filming section was an 11-12% uphill grade approximately 400 m long located at the 2.5- and 7.5-km mark. The video sector was approximately 12 m long at the conclusion of the climb. During the climb, the skating technique used by all skiers was the V-1. The results demonstrated that cycle length is positively related to cycle velocity during uphill ski skating and ultimately translates to faster race times by female cross-country ski racers. Lap 2 cycle velocity and cycle length demonstrated the strongest relationship to lap time and total race time. Moreover, cycle rate was not related to cycle velocity or lap race times and was not different between successful and less successful skiers. The slower climbing velocity noted during the latter half of the 10-km race was a consequence of a decreased cycle length and not cycle rate. This suggests that the degree of physical conditioning could be a factor in the ability to maintain cycle length and thus uphill cycle velocity.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID