ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Dystrophin is a subsarcolemmal protein that interacts with cytoskeletal actin and a glycoprotein complex in the plasma membrane. One potential function of dystrophin is its ability to stabilize the sarcolemmal membrane during muscle contraction. We hypothesized 1) that chronic muscle use and disuse would alter the expression of dystrophin as a compensatory mechanism designed to prevent muscle damage, and 2) that other subsarcolemmal cytoskeletal proteins (vinculin, M-vinculin, aciculin 60/63 kDa) that colocalize with dystrophin in muscle adherens junctions would be changed in parallel. Chronic muscle use induced by voluntary running or 10-Hz chronic stimulation did not alter dystrophin levels in rat muscle. In contrast, muscle disuse induced by 6 d of microgravity, or 7 and 21 d of denervation, increased dystrophin levels by 1.8-, 1.9- and 3.2-fold, respectively. Thus, this increase in dystrophin levels appears to be dependent on the duration of muscle disuse, independent of the presence of the nerve. Denervation also induced 3.3-fold increases in vinculin and aciculin 60 kDa, in parallel with dystrophin. However, in contrast to its effects on dystrophin, chronic stimulation increased the levels of vinculin and aciculin 60 kDa by 3.4- and 6.4-fold, respectively. Thus, both the removal and the augmentation of muscle activity resulted in increases of these two cytoskeletal proteins. The data indicate that the concentrations of these proteins are independently regulated. They further indicate that chronic muscle use is not a stimulus for the induction of dystrophin levels, suggesting that normal levels are sufficient for the protective effect on the sarcolemma that dystrophin may confer. The results reveal an interesting area of muscle plasticity, and the adaptation observed may have profound implications for the structure and function of skeletal muscle responding to changes in contractile activity.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

In addition to factors such as fat free mass, hormonal status, genetics and energy balance, previous physical activity has been shown to influence energy turnover during resting (RMR = resting metabolic rate) or basal conditions(BMR = basal metabolic rate). This article presents data on BMR from elite endurance athletes (4 female and 4 male), at least 39 h after their last training session, in comparison with sedentary nonathletic controls matched for sex and fat free mass (FFM). Comparisons with theoretical calculations of BMR were also made. The athletes were shown to have a significantly higher BMR than was expected from calculations based on body mass (16%,P< 0.05) or body composition (12%,P< 0.05). There were no corresponding differences found in the nonathletic control group. The athletes had a 13% higher (P< 0.001) BMR than controls if related to FFM and 16% (P= 0.001) if related to both FFM and fat mass (FM). The athletes were also found to have 10% lower R-values (P< 0.01) indicating higher fat oxidation. The conformity of these findings with the present literature and the possible mechanisms behind them as well as its influence on theoretical calculations of energy turnover (ET) based on activity factors expressed as multiples of RMR are further discussed.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The purpose of this study was to determine whether physical activity behavior tracks during early childhood. Forty-seven children (22 males, 25 females) aged 3-4 yr at the beginning of the study were followed over a 3-yr period. Heart rates were measured at least 2 and up to 4 d·yr-1with a Quantum XL Telemetry heart rate monitor. Physical activity was quantified as the percentage of observed minutes between 3:00 and 6:00 p.m. during which heart rate was 50% or more above individual resting heart rate(PAHR-50 Index). Tracking of physical activity was analyzed using Pearson and Spearman correlations. Yearly PAHR-50 index tertiles were created and examined for percent agreement and Cohen's kappa. Repeated measures ANOVA was used to calculate the intraclass correlation coefficient across the 3 yr of the study. Spearman rank order correlations ranged from 0.57 to 0.66 (P< 0.0001). Percent agreement ranged from 49% to 62%. The intraclass R for the 3 yr was 0.81. It was concluded that physical activity behavior tends to track during early childhood.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

We conducted a prospective study to assess the association between cardiorespiratory fitness and prostate cancer. The subjects were men, aged 20-80 yr, who received a preventive medical exam at the Cooper Clinic in Dallas, TX, during 1970-1989 and provided information on cardiorespiratory fitness and prostate cancer (N= 12,975). Cardiorespiratory fitness was assessed at a baseline examination between 1971 and 1989 using a maximal exercise treadmill test. Questionnaires were mailed to the men in 1982 and 1990 to ascertain incident cases of prostate cancer. Ninety-four cases of incident prostate cancer were identified. Higher cardiorespiratory fitness levels were inversely associated with the probability of development of incident prostate cancer controlling for age, body mass index, and smoking habits; adjusted estimates of the incidence rate ratio declined from 1.1 (95% CI 0.63-1.77) to 0.73 (95% CI 0.41-1.29) to 0.26 (95% CI 0.10-0.63) across increasing quartiles of fitness (Pfor trend <0.004). This protective effect was limited to participants <60 yr old. Also, an inverse association was observed between physical activity and prostate cancer. Compared with expending <1000 kcal·wk-1, participants who expended 1000-<2000, 2000-<3000, or ≥3000 kcal·wk-1had adjusted incidence rate ratios of 0.37 (95% CI 0.17-0.79), 0.62 (95% CI 0.27-1.41), and 0.37 (95% CI 0.14-0.98), respectively. The results suggest that cardiorespiratory fitness and physical activity levels may protect against the development of incident prostate cancer.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Exercise may increase accretion of bone, potentially reducing the risk of osteoporosis. Previous physical activity was assessed in 204 minimally active young women (18-31 yr). Bone mineral content (BMC) and bone mineral density(BMD) for the total body, femoral neck, and spine were assessed by a dual x-ray absorptiometer, and the radius by a single photon absorptiometer. Self-reported occupation and leisure activity for the 5 yr before enrollment in the study, as well as high school and college sports participation, were assigned energy expenditure (EE) values. From this information, EE variables were created as follows: 1) occupation EE + leisure EE + high school sport and/or college sport EE if within prior 5 yr (5-yr EE); 2) occupation EE + leisure EE (occupation + leisure EE); and 3) high school sport EE (high school EE). These variables were correlated with bone mineral measures and significant results follow (P< 0.05). Five-year EE and occupation + leisure EE correlated with all measures of bone health (r from 0.13 to 0.39). High school EE correlated with total body BMD (r = 0.25) and BMC (r = 0.28), femoral neck BMD (r = 0.28), radius BMC (r = 0.20), as well as spine BMD (r = 0.20) and BMC (r = 0.27). When weight was controlled, 5-yr EE and occupation + leisure EE remained correlated with all BMC measures (r from 0.14 to 0.22). When controlled for weight, high school EE remained associated with femoral neck BMD (r = 0.24), total body BMD (r = 0.20) and BMC (r = 0.26), and spine BMC (r = 0.17). To partially control for selection bias, data were also controlled for total body BMD. Five-year EE and occupation + leisure EE remained positively correlated with all measures of BMC. High school EE remained correlated both with femoral neck BMD and total body BMC. In multiple regression analyses, 5-yr EE or occupation + leisure EE were significant predictors of all measures of bone health, except femoral neck BMD. High school EE was a significant predictor for total body BMD and BMC, femoral neck BMD, and spine BMC.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Several authors have defined velocities which may, as a group, be described as the velocity associated with ˙VO2max. Although several names, definitions, and abbreviations have been introduced, in this paper we shall use ν˙VO2maxfor them all. These ν˙VO2maxhave been reported to be an indicator of performance in distance running events. However, protocols for data collection and definitions used in the calculation of ν˙VO2maxhave differed between studies. The purpose of this investigation was to compare values of ν˙VO2maxobtained using five definitions that have been described in the literature.ν˙VO2maxwas determined in 22 women track athletes as (a) the speed at which ˙VO2maxwas attained in a speed-incremented 0%-slope treadmill test, (b) the highest speed in the test that could be sustained for 1 min, (c) the ratio of ˙VO2maxto the oxygen cost of submaximal running (C), (d) the ratio of (˙VO2max- ˙VO2at rest) to (C - ˙VO2at rest), and (e) the velocity determined by extrapolation of the submaximal velocity: ˙VO2relationship. Results of ANOVA suggested that there were significant differences among the values derived using the different methods (F4,84= 7.80,P< 0.001). Correlations among the various pairs of values ranged from 0.68 to 1.00. It is concluded that there are five distinct parameters described by the five definitions. The value of each of these parameters is influenced by ˙VO2maxand the energy cost of running. In theory, three of the parameters have an anaerobic component; two do not.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The “sitting” posture of speed skating may result in compromised blood flow to the working muscles, thus limiting oxygen uptake. To examine this metabolic problem, male (N= 7) short track speed skaters performed running (TR), in-line skating upright (US), and in-line skating in the “sitting” position (LS) on a motor driven treadmill on randomized days. Each test consisted of four 4-min stages at 2.24, 2.68, 3.13, and 3.58 m·s-1(5, 6, 7, and 8 mph) at 5% incline. After a brief rest, athletes performed at 4.03 m·s-1(9 mph) with elevation increasing 1% each minute to exhaustion. Two on-ice 1000-m time trials (TT) were performed to assess the relationship between performance and laboratory measurements. Peak ˙VO2was lower during LS (57.2± 2.7, 62.3 ± 4.0, and 64.3 ± 1.6; for LS, US, and TR, respectively;P< 0.05). At equivalent speeds, submaximal O2uptake was lower for LS and blood lactate was higher (P< 0.05). LS peak ˙VO2(ml·kg-1·min-1) was strongly related to TT(P< 0.05). The depressed ˙VO2and higher blood lactate during LS may be related to decreased knee or trunk angle. Peak˙VO2values during skating did not approach values during running. Evaluation of speed skaters in a sports-specific test is congruent with performance and demonstrates potential in addressing the unique physiological demands of the sport.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

This study investigated the evolution of skiing velocity, cycle length, and cycle rate in elite and subelite skiers during cross-country ski races. Senior male cross-country skiers engaged respectively in a 30-km skating race(N= 34) or a 50-km classical race (N= 27) were videotaped as they skied two different sections of 30 m, a 7° uphill, and a flat section. In the skating race, most skiers used the offset technique on uphill and the 2-skate on flat, while the preferred techniques during the classical race were the diagonal stride for uphill and double-poling on flat. Results demonstrated that faster skiers had longer cycle lengths than slower skiers, except for the flat sections of the classical race. Cycle rate was not different between skiers of different performance levels in any circumstances or races. Decreased velocity observed during the second half of the skating race was almost entirely due to a decrease in cycle length. We conclude that slower athletes should emphasize extending cycle length during their technical training. Therefore, skiers should place an emphasis on strength and power training to increase their kick and pole pushes and enhance cycle length.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Sixteen untrained males (23 ± 4 yr), were studied to determine the effects of chromium (Cr) supplementation (200 μg · d-1) and a 12-wk resistive exercise training program on muscle strength, body composition, and Cr excretion. The subjects trained 3 times per week with two sets of 8-10 repetitions at 90% of 1 repetition maximum using Keiser variable resistance machines. Food records were used to estimate Cr intake (≈36μg · d-1), energy intake, and the percent kJ from protein. The resistive training program resulted in significant increases in total body muscular strength in both the Cr and placebo groups (24% and 33%;P< 0.05). Body weight, percent body fat, lean body mass, and skinfold thicknesses were unchanged in either group after resistive training. Cr excretion increased in the Cr group after 6 wk of Cr supplementation (0.15± 0.08 vs 1.52 ± 1.26 μg · d-1;P< 0.01) and remained higher at 12 wk of training (2.03 ± 1.73). These results indicate that Cr supplementation, in conjunction with a progressive, resistive exercise training program, does not promote a significant increase in strength and lean body mass, or a significant decrease in percent body fat. Cr supplementation results in a significant increase in Cr excretion that is not altered by resistive training.

ISSN:0195-9131    

出版商:OVID    

年代:1996

数据来源: OVID