摘要:

Metabolism and performance following carbohydrate ingestion late in exercise.Med. Sci.Sports Exerc, Vol. 21, No. 1, pp. 59-65, 1989. To determine whether a single carbohydrate feeding could rapidly restore and maintain plasma glucose availability late in exercise, six trained cyclists were studied on two occasions during exercise to fatigue at 70 ± 1% of VO2mavAfter 135 min of exercise, the men were fed either an artificially sweetened placebo or glucose polymers (3 g·kg-1in a 50% solution). Prolonged exercise led to a decline in plasma glucose from 4.6 ± 0.1 mMat rest to 3.9 ± 0.2 mMafter 135 min (P<0.05). Plasma glucose decreased further (P<0.05) to 3.2 ± 2.0 mM at fatigue following placebo ingestion but increased (P<0.05) and was then maintained at 4.5–4.9 mM following carbohydrate ingestion. Respiratory exchange ratio (R) fell gradually during the placebo trial from 0.88 ± 0.01 after 10 min of exercise to 0.81 ± 0.01 at fatigue (P< 0.01). R also reached a minimum of 0.81-0.82 in each subject after 135-180 min of exercise during the carbohydrate feeding trial but increased again to 0.84-0.86 as plasma glucose rose following the carbohydrate feeding. Exercise time to fatigue was 21 % longer (205 ± 17 vs 169 ± 12 min;P<0.01) during the carbohydrate ingestion trial. Plasma insulin did not increase significantly, whereas plasma free fatty acids and blood glycerol plateaued following carbohydrate ingestion. These data indicate that a single carbohydrate feeding late in exercise can supply sufficient carbohydrate to restore euglycemia and increase carbohydrate oxidation, thereby delaying fatigue.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Lower vertebral bone density in male long distance runners.Med. Sci. Sports Exerc, Vol. 21, No. 1, pp. 66-70, 1989. Bone density in 13 male long distance runners (28.7 + 1.2 yr, 67.6 ± 2.0 kg) and 11 male nonrunners (26.8 ± 1.3 yr, 71.0 ± 2.2 kg) was compared. Bone was measured at the lumbar spine and mid-tibia using dual photon absorptiometry and at the mid-radius using single photon absorptiometry. Runners (mean weekly training 92.2 ± 6.3 km) had significantly lower (P< 0.05) vertebral bone mineral density (1.12 + 0.03 g-cm-2) than nonrunners(1.24 ± 0.04 g-cm-2). Tibial and radial bone mineral density did not differ between the groups. Daily calcium intake for runners (1,373 ± 486 mg) and nonrunners (1,267 ±236 mg) exceeded the RDA. The results of this study suggest that long distance running may lead to decreased vertebral bone mineral density. The hormonal changes that occur with endurance training may contribute to this decrease.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Muscle genetic variants and relationship with performance and trainability.Med. Sci. Sports Exerc, Vol. 21, No. 1, pp. 71-77, 1989. Samples were obtained in a maximum of 295 males and females from the vastus lateralis muscle and proteins fractionated by thin-layer isoelectric focusing. Muscle creatine kinase (CKM) and adenylate kinase (myokinase) (AK1M) were studied for the presence of variants. Six individuals exhibited a CKM variant described here for the first time, for a frequency of the variant gene of 1%. For AK1M, 21 individuals were heterozygotes for an inherited variant protein, an allele frequency of 3.5%. CKM (N=5) and AK1M (N=18) variant individuals were paired with control subjects who had the common CKM or AK1M muscle phenotype and compared for several performance indicators. There was no significant difference between the CKM and AK1M common and variant phenotypes for any of the performance measurements. However, the CKM variant subjects tended to be more effective than controls in a 90-min performance test (by about 22%) and had less percent decline over 60 s in force generation (by about 26%). In a subsequent experiment, a few variant subjects could be compared to controls in terms of response to exercise training. Although trends were observed, the CKM and AK1M variant subjects had a response to training generally comparable to that of the nonvariant individuals. While human variation in performance and trainability cannot be accounted for by the genetic polymorphism of the two kinase enzymes, the trends in the data suggest that allelic variation at these two gene loci may be of some functional significance.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Ten kilometer performance and predicted velocity at VO2max among well-trained male runners.Med. Sci. Sports Exerc, oL 21, No. 1, pp. 78-83, 1989. Previous research (study 1) has shown that a significant relationship exists between 10 km run time (RT) and predicted running velocity at VO2max(vVO2max) among welltrained males heterogeneous in VO2max. Since competitive runners often display a homogeneous fitness profile, the purpose of this study was to determine the association between 10 km RT and vYO2maxamong a group of trained runners exhibiting nearly identical VO2maxvalues (study 2). Running economy (RE), vVO2max, and velocity at a 4 mM blood lactate concentration (v at 4 mM BL) were calculated in both studies. Correlations were obtained as shown in Table 2. The relationship between VO2max and 10 km RT achieved statistical significance only in study 1, while RE explained a greater amount of performance variation in study 2. In both studies, variation in 10 km RT attributable to vVO2maxwas similar and exceeded that due to either VO2max or RE. vVO2maxalso accounted for essentially the same amount of variation in 10 km RT as did v at 4 mM BL. It was concluded that, among well-trained subjects homogeneous in VO2max, a strong relationship exists between 10 km RT and vVO2maxthat appears to be mediated to a large extent by RE.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Specificity of limited range of motion variable resistance training.Med. Sci. Sports Exerc, Vol. 21, No. 1, pp. 84- 89, 1989. The present study evaluated the effect of limited range of motion (ROM) variable resistance training on full ROM strength development. Twenty-eight men and 31 women were randomly assigned to one of the three training groups (A, B, AB) or a control group (C). A, B, and AB performed variable resistance bilateral knee extension exercise 2 (N=25) or 3 (N- 19) d-wk-1for 10 wk with an amount of weight that allowed one set of 7-10 repetitions. Group A trained in a ROM limited to 120° to 60° of knee flexion. Group B trained in a ROM limited to 60° to 0° of knee flexion. Group AB trained full ROM. Prior to and immediately following training, isometric knee extension strength was evaluated at 9°, 20°, 35°, 50°, 65°, 80°, 95°, and 110° of knee flexion with a Nautilus knee extension tensiometer. Reliability coefficients for repeated measurements of isometric strength at multiple joint angles were high (r=0.86-0.95,P< 0.01; SEE=23.1-37.2 N·m). Compared to the control group, all training groups improved in isometric strength (P<0.01 at each angle tested except for group A at 9° and 20° of knee flexion and group B at 95° of flexion. Isometric strength gains for group AB were similar throughout the full ROM. Isometric strength gains for the limited ROM trained groups were greater in the trained ROM than in the untrained ROM (P<0.01). These data indicate that angularspecific training effects occur for limited ROM dynamic resistance training.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Physiological responses to nine different exercise:rest protocols.Med. Sci. Sports Exerc, Vol. 21, No. 1, pp. 90-95, 1989. This study determined the metabolic responses to different exercise: rest protocols during circuit exercise using hydraulic resistance. In experiment 1, nine subjects underwent nine different 27 min exercise circuits. There were three variations of three exercise:rest protocols (2:1, 1:1, 1:2). The VO2for the nine circuits averaged (mean ± SEM) 1.94 ± 0.03 1·min-1(43% of treadmill VO2max), with the largest difference between the protocols being 13%. Heart rate averaged 152.2 ± 3.1 beats·min-1, with the largest difference between the protocols being 8%. Increasing the exercise duration per minute or the number of exercise bouts per minute had minimal effects on the mean VO2and heart rate response to hydraulic resistive exercise. In experiment 2, nine subjects underwent three different 9 min exercise circuits using exercise:rest protocols of 2:1, 1:1, and 1:2 while work and VO2were simultaneously measured. Surprisingly, increases in work were not necessarily accompanied by corresponding increases in VO2.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Impact of total body water fluctuations on estimation of body fat from body density.Med. Sci. Sports Exerc, Vol. 21, No. 1, pp. 96-100, 1989. The purpose was to investigate the possibility that variability in body weight in females due to water retention causes differences in body density (Db) values determined by hydrostatic weighing (HW). Determination of total body water (TBW) and Db were concurrently measured in seven females who experienced considerable fluctuations in body weight (1.5-4.5 kg) and seven males, ages 19-24. Females were measured when they felt they were at their lowest (LO) and highest (HI) body weights (BW) during a menstrual cycle. Males were randomly tested approximately 3 wk apart. Mean values of selected variables were compared in the LO vs HI testing sessions by pairedl-tests. Significant mean differences were found in the females (P<0.01) for the following variables: BW (kg) (LO=58.9, HI=61.1), Db (g·cc-1) (LO=1.0430, HI=1.037), and percent body fat (%BF) as determined by HW alone (LO=24.8%, HI=27.6%). Variables significant at theP<0.05 level were TBW(/) (LO=33.6, HI=35.1) and %TBW of the fat-free body (LO=74.5, HI=75.9). However, changes in TBW could not entirely account for observed changes in Db. Only mean BW (kg) was significant {P<0.01) in the males (LO=74.3, HI=74.6). It is concluded that changes in TBW can in part result in significantly different Db values obtained from HW in females who did experience perceptible changes in BW during a menstrual cycle. The remaining differences may be due to changes in fat and protein content or methodological errors.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Generalized equation for predicting body density of women from girth measurements.Med. Sci. Sports Exerc, Vol. 21, No. 1, pp. 101-104,1989. This study's purpose was to develop a generalized regression equation to predict body density in adult women. Subjects, 482 women, were hydrostatically weighed and circumference (girths) recorded for thigh, hips (buttocks), iliac, and abdomen (mean of abdomen 1 and abdomen 2). Age (range=15-79 yr), weight (38.3-132.9 kg), and height (145.5-186.3 cm) were also recorded. Percent body fat ranged from 12.7 to 63.1%. Stepwise multiple regression was used to select the best set of predictors (from seven) of body density. Capitalization on chance was negligible due to the favorable subject to predictor ratio (57 subjects per predictor). The regression equation (N=400) developed for predicting body density was: body density=1.168297 — (0.002824 x abdomen) + (0.0000122098 x abdomen2) - (0.000733128 x hips) + (0.000510477 X height) - (0.000216161 x age) [SEE=0.009486784 (4.2% body fat), R=0.889, adjusted R2=0.787]. Using this equation on a cross-validation sample (N=82) produced a predicted mean (±SD) of 1.016 ± 0.017 (validation sample mean=1.016 + 0.021) and a total error (SE) of 0.0082 (3.6% body fat). The use of three girth measurements, height, and age enabled us to develop regression equations to predict body density in women that are comparable in accuracy to those using skinfold calipers and, thus, are a viable alternative.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Isokinetic strength and body composition of high school wrestlers across age.Med. Sci. Sports Exerc, Vol. 21, No. 1, pp. 105-109, 1989. The purpose of this study was to determine the changes in body composition as well as absolute and relative isokinetic forearm and leg strength of high school wrestlers across age. One hundred ninety-five wrestlers (X age ± SD=16.36 ± 1.12 yr) volunteered to be measured for strength using a Cybex II dynamometer at 30, 180, and 300° ·s-1. In addition, underwater weighing was used to determine body composition characteristics. The subjects were divided into four age groups: group 1 (Gl)=14.17-15.00 yr(N=20); group 2 (G2)=15.01-16.00 yr (N=60); group 3 (G3)=16.01-17.00 yr (N=52); and group 4 (G4)=17.01-18.50 yr (N=63). One-way ANOVA or ANCOVA with Tukey post hoc comparisons indicated significant (P<0.05) changes across age for height, body weight, and fat-free weight, as well as absolute and relative forearm and leg strength. The results of this study indicated that, while a large portion of the improvements in strength across age were associated with increases in lean tissue, there was an additional “age effect” which could not be accounted for by changes in fat-free weight. Although the mechanism responsible for the “age effect” is unclear, it is possible that neural development contributed to the strength increases across age.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Asymmetries in ground reaction force patterns in normal human gait.Med. Sci. Sports Exerc, Vol. 21, No. 1, pp. 110-114, 1989. The purpose of this study was to propose a measure of symmetry/asymmetry for normal human gait and to quantify symmetries/asymmetries of normal human gait for selected gait variables using a force platform. Sixty-two subjects performed ten gait trials each, stepping on the force platform five times with each leg. From these gait trials a symmetry index was calculated for 34 gait variables. The upper and lower limits of normal gait were calculated such that 95% of all symmetry indices obtained from this subject population fell within these limits. Upper and lower limits were found to vary from ±4% to over ±13,000%. Extremely high percentages were found for variables which had absolute magnitudes close to zero and/or variables which occurred at distinctly different instants during the gait cycle. The results of these variables need to be interpreted with caution.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID