摘要:

Maximization of bone accrual during the growing years is thought to be an important factor in minimizing fracture risk in old age. Mechanical loading through physical activity has been recommended as a modality for the conservation of bone mineral in adults; however, few studies have evaluated the impact of different loading regimes in growing children. The purpose of this study was to compare bone mineral density (BMD) in weight-bearing and non-weight-bearing limbs in 17 children with unilateral Legg Calvé Perthes Disease (LCPD). Children with this condition have an altered weight-bearing pattern whereby there is increased mechanical loading on the noninvolved normal hip and reduced loading on the involved painful hip. Thus, these children provide a unique opportunity to study the impact of differential mechanical loading on BMD during the growing years while controlling for genetic disposition. BMD at four regions of the proximal femur(trochanter, intertrochanter, femoral neck, total of the regions) was measured using dual energy x-ray absorptiometry (DXA), and the values were compared between the involved and noninvolved sides of the children with LCPD. The BMD of both sides also were compared with normative values based on both chronological and skeletal age data. A significantly higher BMD was found on the noninvolved side over the involved side for all regions (P<0.01 and percentage differences of 12-15%) except at the femoral neck(percentage difference of 3.9%). The BMD (at all regions) of the noninvolved side also was significantly greater (P<0.01) than either the chronological or skeletal age based norms for all sites except the trochanter. The results support the concept that mechanical loading of the skeleton during the growing years is an important factor in BMD accrual.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Isokinetic shoulder rotational strength was evaluated in four groups of subjects as follows: 12 nonathelets, 12 runners, 15 tennis players, and 12 baseball players for a total of 51 subjects. The tests were performed in the seated 45° abducted test position in the scapular plane at 60, 180, and 300°·s-1for both shoulders. Peak torque and mean power values were gathered, and from these values the internal/external rotation ratios were calculated. Intergroup comparison showed a progression of the ratio related to the sports discipline. The nonathletes and runners had ratios close to those reported for nonathletes (1.3 to 1.5). The tennis players had ratios close to 1.5, whereas the baseball players had ratios from 1.6 to 2.2. The comparison between dominant and nondominant side showed no significant differences in the tennis players and higher values for the dominant side in the nonathletes and runners under certain conditions(180°·s-1for the nonathletes and 300°·s-1for the runners). Regarding the baseball players, the ratio was systematically higher for the dominant side. These results raise questions about the influence of sports discipline on the internal/external rotator muscle ratio and indicate the need to establish normative values based on the characteristics of the population under study

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Athletes with anterior cruciate ligament (ACL) deficiencies exert decreased knee extension moments during level walking (quadriceps avoidance gait), and yet within a few months of ACL reconstruction they are often expected to return to competitive sport. To investigate this issue further, 10 normal subjects and seven ACL deficient patients were evaluated both pre- and post-operatively (mean follow-up of 6 months), and each performed multiple trials ascending a staircase which consisted of three steps. Bilateral joint angles, moments, powers, and work were measured and the data were ensemble averaged and statistically analyzed (repeated measures ANOVA with significance level set at 0.05). Anterior-posterior knee laxity decreased significantly(from 7.9 mm to 5.8 mm) while subjective knee function also improved following ACL reconstruction (knee score increased from 70.4 to 88.5). Pre-operatively, there were no statistically significant differences in biomechanical parameters between the patients' ACL-deficient and intact sides and the normal subjects. Post-operatively, however, statistically significant reductions were seen for the peak moment (91.9 vs 22.5 Nm), power (181 vs 84 W), and work performed (28.0 vs -5.6 J) at the injured knee, which was also the knee from which the patellar tendon graft had been harvested. These reductions were accommodated by significant increases in excursion, moment, and power at the contralateral ankle joint. The results indicate that while the ACL reconstructions were successful in restoring anterior-posterior knee stability, the decrease in knee power and work performed post-operatively by the injured (i.e., donor) knee suggests that donor site morbidity may need to be critically evaluated over a long-term period.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

We are attempting to develop a chemically-induced murine model for the study of atherosclerosis. Injection of poloxamer-407 (P-407) into rats and mice causes significant dose-dependent hypercholesterolemia and hypertriglyglyceridemia. The elevated triglycerides (TG) seem to result primarily from the compound's inhibition of lipoprotein lipase. P-407 also indirectly stimulates the activity of the rate limiting enzyme in cholesterol(CHOL) biosynthesis, HMG CoA reductase. In addition, P-407 promotes changes in the concentration of hepatic CHOL content. These date indicate that the hyper CHOL could be the result of increased CHOL synthesis, as well as a clearing of CHOL from the liver. Chronic injection into mice of P-407 for 145 d produced atherogenic lesions in the aortas of C57BL/6 mice. The response was equivalent to that seen in animals eating a high CHOL diet for 145 d. Cholic acid potentiated the P-407-induced atherogenesis. These data suggest that P-407 could be used as an agent for the study of hyperlipidemia-induced atherogenesis.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Saturated vegetable oils (coconut, palm, and palm kernel oil) containing predominantly saturated fatty acids, lauric (12:0) or myristic (14:0 and palmitic (16:0), raise plasma total cholesterol (TC) and low density lipoprotein cholesterol (LDL-C) levels in animals and humans, presumably by decreasing LDL receptor activity and/or increasing LDL-C production rate. Although stearic acid (18:0) is chemically a saturated fatty acid, both human and animal studies suggest it is biologically neutral (neither raising nor lowering) blood cholesterol levels. Although earlier studies indicated that medium chain fatty acids (8:0-10:0) were also thought to be neutral, more recent studies in animals and humans suggest otherwise.Unsaturated vegetable oils such as corn, soybean, olive, and canola oil, by virtue of their predominant levels of either linoleic acid (18:2) or oleic acid (18:1), are hypocholesterolemic, probably as a result of their ability to upregulate LDL receptor activity and/or decrease LDL-C production rate.Whether trans fatty acids such as trans oleate (t18:1), in hydrogenated products such as margarine, are hypercholesterolemic remains controversial. Studies in humans suggest that their cholesterol-raising potential falls between the native nonhydrogenated vegetable oil and the more saturated dairy products such as butter. Assessment of the magnitude of the cholesterolemic response of trans 18:1 is difficult because in most diet studies its addition is often at the expense of cholesterol-lowering unsaturated fatty acids, making an independent evaluation almost impossible.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Lipoprotein(a) [Lp(a)] represents a class of lipoproteins with some structural similarity to low density lipoprotein (LDL), but containing a unique apoprotein, apoprotein(a). First reported in 1963, Lp(a) is now considered to have an independent role in the development of atherosclerotic lesions. The level of Lp(a) in the blood is under strong genetic influence and does not appear to be alterable by lifestyle factors known to influence other lipoproteins. Regular moderate exercise has been shown to favorably alter other lipoproteins, and recent attention has focused on whether Lp(a) level can be influenced by physical activity. Current data from cross-sectional and intervention studies show little effect of moderate exercise on serum Lp(a) concentration. One possible exception may be an elevation of serum Lp(a) concentration in adult endurance and power athletes who exercise intensely on a daily basis. However, not all studies have taken into account possible racial or ethnic differences in Lp(a) concentrations and the skewed distribution observed within most populations. Standard dietary intervention such as a low fat diet recommended for weight loss and control of other blood lipids has little effect on serum Lp(a) level. At present, serum Lp(a) concentration does not appear to be significantly altered by realistic dietary changes and moderate physical activity as recommended for health. The synergistic effect on cardiovascular disease risk when both LDL-cholesterol and Lp(a) are elevated highlight the importance of attending to those risk factors that can be modified by exercise and other lifestyle changes.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

The swine has many similarities to humans, making it an excellent research model in which to study the role of exercise on lipid metabolism. Swine adapt to exercise-training by increasing muscle oxidative enzymes, maximal stroke volume, cardiac output, ˙VO2max, and high density lipoprotein cholesterol levels, while decreasing total cholesterol levels and resting heart rate. The lipoprotein profile of swine and humans is also similar, and low density lipoprotein is the major cholesterol transporting lipoprotein in both species. Several studies in swine report conflicting results on the effect of exercise-training on lipoprotein profile and atherosclerotic lesion appearance. This may result from differences in total exercise time between the studies. With sufficient total exercise, atherosclerosis was reduced and high density lipoprotein cholesterol levels were increased. Exercise may also play a role in reducing obesity, a risk factor for cardiovascular disease, by enhancing lipid mobilization from adipocytes. Recent research suggests that swine adipocyte sensitivity to adenosine, a locally-produced antilipolytic agent, is reduced after exercise treatment. Cellular mechanisms responsible for this metabolic change include a reduction in adenosine A1receptor number. Current studies are examining the transport of extracellular cyclic AMP from adipocytes and its role as a potential adenosine precursor.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

The purpose of this study was to investigate the association between elite endurance athlete (EEA) status and two restriction fragment length polymorphisms (RFLPs) at the muscle-specific creatine kinase (CKMM) gene locus. Genomic DNA was extracted from white blood cells or lymphoblastoid cell lines of 124 unrelated Caucasian male EEA (˙VO2max>73 mL·kg-1·min-1) and 115 unrelated Caucasian sedentary male controls (SCON). The genetic polymorphism at the CKMM locus was detected by the polymerase chain reaction and DNA digestion with theNcoIandTaqIrestriction endonucleases. The allelic frequencies for theNcoIandTaqIRFLPs were not different(P> 0.05) between EEA and SCON subjects. The three expected genotypes for CKMM-NcoI(1170/1170 bp, 1170/985 + 185 bp, and 985 + 185/985 + 185 bp) and CKMM-TaqI(1170/1170 bp, 1170/1020 + 150 bp, and 1020 + 50/1020 + 150 bp) were observed in the EEA and SCON groups. These genotype frequencies were in Hardy-Weinberg equilibrium, but they were not significantly (P> 0.05) different between the EEA and SCON. A strong (P< 0.001) linkage disequilibrium was detected among theNcoIandTaqIRFLPs in both EEA and SCON. These findings indicate that the skeletal muscle CK-NcoIand CK-TaqIgene polymorphisms are not associated with the elite endurance athlete status.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

An extensive search for linkage between DNA markers and the response of˙VO2maxto training has recently been launched in the HERITAGE Family Study. This is the first report on a genome-wide search strategy to locate chromosomal regions and positional candidate genes for cardiorespiratory endurance phenotypes. Linkage between seven markers spanning chromosome 22 spaced approximately 10 cM apart (D22S264, D22S274, D22S301, D22S304, D22S421, IL2RB, and PDGFB) and ˙VO2maxat baseline, as well as its response to endurance exercise training, was examined using the sib-pair linkage method. Markers were genotyped in at least 210 sib-pairs derived from 128 adult brothers (25 ± 6 yr; mean ± SD) and 138 sisters (24 ± 6 yr) from 86 Caucasian families. ˙VO2max, maximal heart rate, and maximal oxygen pulse were measured during stationary cycle tests before and after a standardized 20-wk endurance training program. On average, the initial ˙VO2maxwas 2654 ± 767 mL·min-1while training increased ˙VO2maxsignificantly by 430 ± 239 mL·min-1or 16% (P< 0.0001). The VO2maxresponse was adjusted for age and initial˙VO2max. No evidence of linkage was found between any of these markers on chromosome 22 and ˙VO2maxor its trainability.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Previous work has demonstrated that 10 wk of exercise training enhances the responsiveness of rat abdominal aortas to acetylcholine (ACh), an endothelium-dependent vasodilator. The purpose of this study was to determine the time course for this training-induced adaptation of vascular endothelium. Additionally, the contribution of the cyclooxygenase and nitric oxide synthase mechanisms to the enhanced endothelium-mediated relaxation were examined. Male rats were divided into sedentary (SED) and exercise groups. Exercised animals were further subdivided into postexercise (POST-EX), 1 DAY, 1 WK, 2 WK, 4 WK and 10 WK groups. Exercise consisted of treadmill running at 30 m·min-1(15° incline) for 1 h·d-1(5 d·wk-1for the 1 WK, 2 WK, 4 WK, and 10 WK groups). Maximal vasodilator responses induced by 10-4M ACh (10-7M norepinephrine preconstriction) were determined on abdominal aortic ringsin vitroimmediately after a single exercise bout in POST-EX rats and 24 h after a single bout of exercise in 1 DAY animals. Maximal 10-4M ACh-induced dilation of aortas from 1 WK, 2 WK, 4 WK, and 10 WK animals was determined 24 h after the last exercise bout. Soleus muscle citrate synthase activity was greater in 2 WK (31 ± 1μmol·min-1·g wet wt-1), 4 WK (34 ± 2), and 10 WK (36 ± 1 μmol·min-1·g wet wt-1) rats than in SED (27 ± 1 μmol·min-1·g wet wt.-1) animals. Maximal ACh-induced relaxation was greater in aorta from 4 WK (72 ± 2%) and 10 WK (79 ± 1%) rats than SED (61± 2%) rats. ACh-mediated dilatory responses remained enhanced in the presence of the cyclooxygenase blocker indomethacin (10-5M), but were abolished by the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (300 μM). In addition, the expression of endothelial nitric oxide synthase (ecNOS) protein in aortas from 4 WK (P= 0.057) and 10 WK (P< 0.05) rats was greater than in aortas from SED animals. These data indicate that the enhanced endothelium-dependent, ACh-mediated dilation of the rat aorta is present by 4 wk of endurance exercise training. This adaptation appears to be mediated primarily through the nitric oxide synthase pathway and is associated with an increased expression of ecNOS.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID