摘要:

Bicycling is a complex sport in which an athlete's energy cost is related to two principal forces: air resistance when traveling on flat terrain, and gravity when traveling uphill. Both wind tunnel data and physiological measurements suggest that air resistance scales as body mass to about the 1/3 power. Thus, large cyclists have only slightly greater frontal drags than small cyclists. If expressed relative to body mass, the frontal drag of small cyclists is considerably greater than that of large cyclists. The difference in frontal drag (energy cost) is not made up for by the advantage to small cyclists in relative &OV0312;O2max(energy supply), since the mass exponent for drag (1/3) is closer to zero than that for &OV0312;O2max(2/3). Thus, small cyclists should be at a disadvantage in flat time trials, which field data support. The energy cost of riding uphill slightly favors the large cyclist, because the weight of the bicycle represents a relatively smaller load than it does to a small cyclist. The mass exponent is 0.79. Since this exponent is greater than that for &OV0312;O2max, the small cyclists have an advantage in climbing, which is supported by field data.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Conservation of energy suggests that during cycling the constrained lower extremity is capable of delivering energy to the bicycle without expending energy to move the limbs. The purpose of this study was to characterize the management of mechanical energy during cycling and, specifically, to evaluate the potential for system energetic conservatism. Mechanical energy contributions derived from lower extremity energy sources were computed for 12 experienced male cyclists riding at five combinations of cadence and power output. The knee joint dominated (>50%) in contributing to system energy and a moderate amount of energy was derived from hip joint reaction forces (>6%). Energy generations and dissipations at the sources were sensitive to power output and, within the range of conditions studied, insensitive to cadence. Two energy models estimated mechanical energy expenditure under hypothetical single-joint and multijoint muscle operating conditions. When multi-joint muscles were incorporated into the energy management analysis, a significant reduction in mechanical work relative to the single-joint muscle operation occurred. Energy savings associated with multijoint muscle energy transfers were enhanced at higher bicycle power levels, suggesting that conservation of mechanical energy is plausible given appropriate actions of two-joint muscles.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

To determine if drinking fluid altered exercise and thermal variables during 2-h immersions in 25°C water, 11 male subjects were tested breathing air at 1 ATA and HeO2at 5.5 ATA (PO2= 0.42 ATA). Each immersion consisted of four periods of 5-min rest, 5-min leg exercise at 50 W, and 20 min of exercise at 68 ± 3% &OV0312;O2max. One test at each depth was done with no fluid (NF); one test was done with subjects consuming 125 ml of a 7% glucose polymer (GP) solution every 30 min (total intake = 500 ml). Compared with NF, GP increased urine volume by 469 ± 118 and 443 ± 82 ml at 1 and 5.5 ATA. Mean minute ventilation (&OV0312;E) was reduced at depth by 10.1 ± 0.6 and 5.1 ± 0.61·min−1for NF and GP, respectively (P < 0.05). GP trials reduced ventilatory equivalent (VEQ, &OV0312;E/&OV0312;O2) at 1 ATA, but increased it at 5.5 ATA, secondary to a small change in &OV0312;E. Exercise heart rate was slightly lower at 5.5 ATA, but O2pulse was the same among all conditions (17.2 ± 0.1 ml O2·bear−1). Rectal temperature increased 0.71 ± 0.04°C for all conditions. Total body heat flux and insulation were unaffected by fluid or hyperbaric treatments. These results indicate that drinking fluid during immersed exercise does not change fluid balance or thermal status at depths to 5.5 ATA. The modest changes in VEQ noted with fluid intake or hyperbaric exposure reflect inconsequential alterations in cardiopulmonary efficiency.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The present study examined the effects of dietary manipulations on six trained runners. The percent energy contributions from carbohydrate, fat, and protein were 61/24/14,50/38/12, and 73/15/12 for the normal (N), fat (F), and carbohydrate (C) diets, respectively. Expiratory gases and blood responses to a maximum (&OV0312;O2max) and a prolonged treadmill run were determined following 7 d on each diet. Free fatty acids (FFA), triglycerides, glycerol, glucose, and lactate were measured. Dietary assessment of subjects' N diet indicated that they were consuming approximately 700 kcal·d−1less than estimated daily expenditures. Running time to exhaustion was greatest after the F diet (91.2 ± 9.5 min, P < 0.05) as compared with the C (75.8 ± 7.6 min, P < 0.05) and N (69.3 ± 7.2 min, P < 0.05) diets. &OV0312;O2maxwas also higher on the F diet (66.4 ± 2.7ml·kg−1·min−1, P < 0.05) as compared with the C (59.6 ± 2.8 ml·kg−1·min−1, P < 0.05) and N (63.7 ± 2.6 ml·kg−1·min−1, P < 0.05) diets. Plasma FFA levels were higher P < 0.05) and glycerol levels were lower (P < 0.05) during the F diet than during the C and N diets. Other biochemical measures did not differ significantly among diets. These data suggest that increased availability of FFA, consequent to the F diet, may provide for enhanced oxidative potential as evidenced by an increase in &OV0312;O2maxand running time. This implies that restriction of dietary fat may be detrimental to endurance performance.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Backward running has long been used in sports conditioning programs and has recently been incorporated into rehabilitative settings as a method of increasing quadriceps strength while decreasing the joint compressive forces about the knee. Although backward locomotion has been studied kinetically, the metabolic cost of backward walking and/or running has not to our knowledge been previously characterized. Oxygen consumption and other cardiopulmonary variables were measured under constant speed exercise during backward and forward walking at 107.2 m·min−1and during backward and forward running at 160.8 m·min−1. Peak oxygen consumption (&OV0312;O2peak) was also measured during maximal incremental backward and forward running. &OV0312;O2, HR, and blood lactate were significantly higher (P < 0.001) during backward walking and running than during forward walking and running. During backward walking and backward running, subjects exercised at 60% and 84% of their forward &OV0312;O2peak, respectively. In conclusion, for a given speed, backward locomotion elicits a greater metabolic demand and cardiopulmonary response than forward locomotion. In general, these data suggest that while undergoing rehabilitation, an injured athlete may continue to exercise using backward walking/running at an intensity sufficient enough to maintain cardiovascular fitness levels.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

This study determined if the generalized equations created for the Rockport Fitness Walking Test were a valid estimation of cardiorespiratory fitness for adults with mental retardation (MR). Subjects included 25 males and females (&OV0398; age = 33.3 ± 7.4 yr) with MR. A maximal treadmill test was administered (&OV0398; &OV0312;O2peak= 29.5 ± 7.2 ml·kg−1·min−1; 2.2 ± 0.62 1·min−1). Subjects' age, weight, sex, walk time, and immediate post-HR were used in the generalized equations for predicting &OV0312;O2peak(&OV0398; &OV0312;O2peak= 36.5 ± 7.6 ml·kg−1·min−1and 2.7 ± 0.66 1·min−1). Significant correlations (P < 0.01) were obtained between the measured and predicted peak &OV0312;O2levels. However, significant and consistent differences were also observed between the measured and predicted &OV0312;O2peakvalues (P < 0.02). Only 28% (1·min−1) and 36% (ml·kg−1min−1) of the subjects' measured &OV0312;O2peakfell within the prespecified value of the predicted &OV0312;O2peak, thus indicating that the prediction equations overestimated the &OV0312;O2peakand cardiovascular fitness levels of adults with MR.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The purpose of this study was to determine whether the parameters commonly used to evaluate a training effect can be compared when serial tests are performed using different protocols. Thirty-two patients with stable coronary artery disease performed both the standard and modified Bruce protocols in a random order, 1 h apart. Physiologic variables at matched exercise stage I including heart rate (99 ± 12 vs 101 ± 14 bpm), rate-pressure product (15 ± 3 vs 15 ± 3 bpm·mm Hg · 103), and &OV0312;O2(13.5 ± 2.1 vs 13.0 ± 3.0 ml·kg−1-min−1) were not significantly different for exercise tests performed using the standard vs modified Bruce protocols, respectively. Similarly, these parameters were also nearly identical at matched exercise stage II. However, peak &OV0312;O2was significantly higher using the standard vs modified Bruce protocol, although the difference was small. Therefore, these data indicate that a difference in the heart rate response at matched sub-maximal workrates on tests using these two protocols before and after a training program is most likely due to a training effect. Conversely, improvements in peak &OV0312;O2using the standard vs modified Bruce are at least in part due to inherent differences in responses between these two protocols.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The purpose of this study was to determine the validity and evaluate the accuracy of a portable telemetric oxygen uptake analyzer (K2). Two experiments were carried out: a) using a mechanical lung, the accuracy of the K2 to measure oxygen fractions and minute ventilation following 10 and 60 min of warm-up was determined; and b) two maximal graded exercise tests (GXT) on 15 subjects, one with the K2 system and the other with a standardized breath-by-breath (BBB) system, while heart rate (HR), minute ventilation (&OV0312;E), and oxygen uptake (&OV0312;O2) were compared. Following 10-min warm-up prior to calibration, the K2 underestimated the true oxygen fraction as early as 5 min into the test, and this value continued to decrease throughout the 30-min test. After 60 min of warm-up prior to calibration, the K2 accurately measured the true oxygen fraction for the first 15 min; at minute 20, and on to minute 30, the K2 underestimated the oxygen fraction. Ventilation volumes were not affected by warm-up time. Minute ventilation during the K2 GXT was significantly higher than &OV0312;Efor the BBB test. No significant differences were found between the HRs obtained with the BBB or K2 systems. No differences in &OV0312;O2for any stage of the GXT were identified between the K2 device, BBB device or when a respiratory exchange ratio (RER) correction factor was applied to the K2 derived values. However, the RER correction factor did minimize the &OV0312;O2differences between the BBB and K2 systems. Therefore, we conclude that the K2 accurately measures &OV0312;O2during a GXT; however, its accuracy can be compromised by limitations inherent to the system.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The American College of Sports Medicine (ACSM) recommends the use of 40%, 60%, 80%, and 85% of maximal oxygen consumption (&OV0312;O2max) as target values in developing exercise prescriptions. Further, the ACSM states that 55%, 70%, 85%, and 90% of maximal heart rate (HRmax) may be used as indices of these respective levels of %&OV0312;O2maxfor the general population. The current study evaluated this relationship between %HRmaxand %&OV0312;O2maxin apparently healthy, young adults. Eighty-one men and 81 women between the ages of 18 and 34 engaged in an incremental exercise test to exhaustion. Linear regressions of %HRmaxand %&OV0312;O2maxwere performed on each subject. From these regressions, target values of %HRmaxwere computed for each individual. Mean percentages of HRmaxwere 63%, 76%, 89%, and 92% at 40%, 60%, 80%, and 85% of &OV0312;O2max, respectively. At all of these values of %&OV0312;O2max, the values obtained for %HRmaxwere significantly greater (P<0.001) than those used by the ACSM. Fitness affected these results, particularly among men. High fit men averaged 2% higher in %HRmaxthan low fit men at any given value of %&OV0312;O2max.

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:0195-9131    

出版商:OVID    

年代:1994

数据来源: OVID