Medicine and science in sports最新文献

The purpose of this study was to determine the thermal and circulatory responses of seven runners (X VO2max = 66 ml kg min) to two bouts of high intensity prolonged treadmill running (PTR) [each 80-min at 70% VO2max] spaced by a 90-min rest. After the transition to exercise, oxygen uptake (VO2) and percent change in plasma volume remained constant throughout each PTR. Rectal temperature (Tr) and heart rate (HR) increased while stroke volume (SV) and cardiac output (Q) decreased during the course of each PTR. The pattern of response for each variable was similar for both PTRs. However, Tr and HR were higher and SV and Q were lower during the second PTR when compared to the first of each respective time period.

The purpose of the present study was to determine whether the fast-twitch (FT) fiber composition in muscle was a) correlated with performance capacities, b) related to the trainability of the subjects, and c) whether the FT fiber composition could be predicted with standard laboratory tests. From twenty-four young women (ages 24.3 +/- 3.0 yrs) muscle biopsies were obtained from the vastus lateralis of both the left and right legs. In addition, each subject completed four laboratory tests: i) a maximal oxygen intake test on the cycle ergometer, ii) a high-kp power test, iii) a low-kp power test, and iv) a Sargent jump. Prior to training the correlations between %FT fibers and each of the tests (r equal to or less than 0.19) were not significant (P less than 0.05). After training anaerobically (N = 20) significant improvements (P less than 0.05) occurred in a) the high-kp test (delta = + 0.12 +/- 0.02 kpm/sec.kg) b) the low-kp test (delta = + 0.10 +/- 0.01 kpm/sec.kg) and c) the Sargent jump (delta = + 2.5 +/- 1.1 cm). However, these training-induced changes (delta) were not correlated with %FT fiber composition (r equal to or less than 0.35), nor were the post-training performances on the tests correlated with the %FT fibers (r equal to or less than 0.12). Performance capacities before and after training were not significantly different in groups with a low %FT fiber composition (35.8 +/- 1.6%) or a high %FT fiber composition (63.6 +/- 2.2%). None of the performance tests either singly, or in combination in a multiple regression equation, provided a suitable prediction of the FT muscle fiber composition. The results of this study indicate that athletic performances and/or susceptibility for training cannot be determined a priori from simple measurements of muscle fiber composition.

When exercise testing 159 patients with prior myocardial infarction, we identified 39 who were limited by fatigue. This group was all in sinus rhythm; none were taking drugs likely to impair the chronotropic response of the heart; none experienced chest pain or developed ischemic ECG changes. In 18 of this group, maximal heart rate achieved with exercise was 2SD or more below the age predicted value, and their heart rate response to exercise was reduced compared to that of the other 21 whose maximal exercise heart rates were within 2SD of age predicted values. A subgroup of 8 subjects with reduced exercise heart rates was studied before and after vagal blockade. In the 4 subjects whose infarction was inferior, the reduction in heart rate response was more profound and persisted after vagal blockade, suggesting either reduced pacemaker responsivness, due to ischemia or infarction, or autonomic imbalance as possible mechanisms. All 8 showed alinear increases in ventilation at higher power outputs and mean blood lactate postexercise was 7.5 mM/I without vagal blockade. Our findings suggest that a reduced heart rate response to exercise, already shown to imply added coronary risk, may be subdivided aetiologically and possibly prognostically. The use of a "Target Heart Rate" in such patients offers no safety margin, and maximal exercise capacity will be grossly over-estimated if extrapolated from the submaximal heart rate response. A cardiovascular limitation to exercise may be detected by an alinear increase in ventilation.

Cardiac output and stroke volume were measured in two environments and at metabolic rates ranging from rest to the maximum rate that could be sustained for 25 minutes. One environment was indoors at about 23 degrees C, the other outdoors in desert sunshine and low water vapor pressure. The age range of the one female and four of the male subjects was from 19 to 40; the fifth male subject was 85 years old. Cardiac output was the same in the two environments; stroke volume was less at higher metabolic rates in the heat. The cardiac output for the old man was about one-tenth less and stroke volume about 20 ml less than that observed for the same work 50 years earlier.

The most important variables in helmet test methods (headform, impact surface, velocity) were studied by systematically changing the test variables and measuring the effect of these changes on the output responses (peak acceleration and severity index) of helmeted headforms. The degree of correlation between variables was also measured. The metal headform yielded consistently higher results than the humanoid headform but the differences between the two were much greater during impacts at the back site. Also, correlation between humanoid and metal headforms was significantly higher for top impacts than for rear impacts. These discrepancies between top and rear impacts were attributed to difficulties in the neck mounting system with the humanoid headform which causes inordinate bending during impacts. The soft impact surface yielded lower responses than the hard surface for both headforms, correlations between soft and hard surfaces were high in all cases. A small change in impact velocity (4.5 to 5 m/sec) resulted in a substantially higher output response. Correlation between velocities were much lower for the back impact site than the top.

Nine national and world-class female pentathletes were assessed for body composition, maximal aerobic power (Vo2max), strength, and speed. The subjects averaged 175.4 cm in height, 65.4 kg in weight, 11.0% relative body fat, 45.9 ml kg min-1 in Vo2max, and 8.35 m/sec for maximal running speed. When compared with other athletic females, this group was tall and lean with good, but not exceptional, maximal aerobic power. Group means for one-repetition maximum lifts were 59.7 kg (power clean), 61.5 kg (horizontal bench press), 60.0 kg (pull down), 87.9 kg (squat), 44.9 kg (include bench press), and 36.3 kg (leg curl). Within this elite group the most successful performers were stronger and possessed a greater lean body weight which together suggest the importance of muscle mass for success in the pentathlon.