摘要:

The role of the right ventricle during hypobaric hypoxic exercise: insights from patients after the Fontan operation.Med. Sci. Sports Exerc.,Vol. 31, No. 2, pp. 269-276, 1999.Objectives:The principal objective of this study was to examine the importance of the right ventricle for maximal systemic oxygen transport during exercise at high altitude by studying patients after the Fontan operation.Background:High-altitude-induced hypoxia causes a reduction in maximal oxygen uptake. Normal right ventricular pump function may be critical to sustain cardiac output in the face of hypoxic pulmonary vasoconstriction. We hypothesized that patients after the Fontan operation, who lack a functional subpulmonary ventricle, would have a limited exercise capacity at altitude, with an inability to increase cardiac output.Methods:We measured oxygen uptake (&OV0312;O2, Douglas bag), cardiac output (&OV0422;c, C2H2rebreathing), heart rate (HR) (ECG), blood pressure (BP) (cuff), and O2Sat (pulse oximetry) in 11 patients aged 14.5 ± 5.2 yr (mean ± SD) at 4.7 ± 1.6 yr after surgery. Data were obtained at rest, at three submaximal steady state workrates, and at peak exercise on a cycle ergometer. All tests were performed at sea level (SL) and at simulated altitude (ALT) of 3048 m (10,000 ft, 522 torr) in a hypobaric chamber.Results:At SL, resting O2sat was 92.6 ± 4%. At ALT, O2sat decreased to 88.2 ± 4.6% (P< 0.05) at rest and decreased further to 80 ± 6.3% (P< 0.05) with peak exercise. At SL, &OV0312;O2increased from 5.1 ± 0.9 mL·kg−1·min−1at rest to 23.5 ± 5.3 mL·kg−1·min−1at peak exercise and CI (&OV0422;c·m−2) increased from 3.3 ± 0.7 L·m−2to 6.2 ± 1.2 L·m−2. &OV0312;O2peak, 17.8 ± 4 mL·kg−1·min−1(P< 0.05), and CI peak, 5.0 ± 1.5 L·m−2(P< 0.05), were both decreased at ALT. Remarkably, the relationship between &OV0422;c and &OV0312;O2was normal during submaximal exercise at both SL and ALT. However at ALT, stroke volume index (SVI, SV·m−2) decreased from 37.7 ± 8.6 mL·min−1·m2at rest, to 31.3 ± 8.6 mL·min−1·m2at peak exercise (P< 0.05), whereas it did not fall during sea level exercise.Conclusions:During submaximal exercise at altitude, right ventricular contractile function is not necessary to increase cardiac output appropriately for oxygen uptake. However, normal right ventricular pump function may be necessary to achieve maximal cardiac output during exercise with acute high altitude exposure.

ISSN:0195-9131    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Ventilatory responses to dynamic exercise elicited by intramuscular sensors.Med. Sci. Sports Exerc.,Vol. 31, No. 2, pp. 277-286, 1999.Purpose:Eight subjects, aged 27.0 ± 1.6 yr, performed incremental workload cycling to investigate the contribution of skeletal muscle mechano- and metaboreceptors to ventilatory control during dynamic exercise.Methods:Each subject performed four bouts of exercise: exercise with no intervention (CON); exercise with bilateral thigh cuffs inflated to 90 mm Hg (CUFF); exercise with application of lower-body positive pressure (LBPP) to 45 torr (PP); and exercise with 90 mm Hg thigh cuff inflation and 45 torr LBPP (CUFF+PP). Ventilatory responses and pulmonary gas exchange variables were collected breath-by-breath with concomitant measurement of leg intramuscular pressure.Results:Ventilation (&OV0312;E) was significantly elevated from CON during PP and CUFF+PP at workloads corresponding to ≥ 60% CON peak oxygen uptake (&OV0312;O2peak) and during CUFF at workloads ≥ 80% CON &OV0312;O2peak,P< 0.05. The &OV0312;O2at which ventilatory threshold occurred was significantly reduced from CON (2.17 ± 0.28 L·min−1) to 1.60 ± 0.19 L·min−1, 1.45 ± 0.15 L·min−1, and 1.15 ± 0.11 L·min−1during CUFF, PP, and CUFF+PP, respectively. The slope of the linear regression describing the &OV0312;E/CO2output relationship was increased from CON by approximately 22% during CUFF, 40% during PP, and 41% during CUFF+PP.Conclusions:As intramuscular pressure was significantly elevated immediately upon application of LBPP during PP and CUFF+PP without a concomitant increase in &OV0312;E, it seems unlikely that LBPP-induced increases in &OV0312;Ecan be attributed to activation of the mechanoreflex. These findings suggest that LBPP-induced reductions in perfusion pressure and decreases in venous outflow resulting from inflation of bilateral thigh cuffs may generate a metabolite sensitive intramuscular ventilatory stimulus.

ISSN:0195-9131    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Physical fitness and clustering of risk factors associated with the metabolic syndrome.Med. Sci. Sports Exerc.,Vol. 31, No. 2, pp. 287-293, 1999.Purpose:The purposes of this study were to 1) assess the prevalence of clustering of metabolic markers of the MS in a defined population and 2) determine the association between CRF and such clustering in a large group of adult men (N= 15,537) and women (N= 3,899).Methods:Metabolic markers of the MS included systolic blood pressure (BP) ≥ 140 mm Hg, serum triglycerides ≥ 150 mg·dL−1, fasting blood glucose ≥ 110 mg·dL−1, and elevated central adiposity (waist circumference > 100 cm). Cardiorespiratory fitness was defined as total time on a maximal treadmill exercise test. The cohort was grouped by the number of metabolic abnormalities and level of CRF. Associations between CRF and the number of metabolic abnormalities were assessed using proportional odds logit models.Results:Among men, the age-adjusted cumulative odds ratio for abnormal markers of the MS was 3.0 (95% C.I. 2.7-3.4;P< 0.001) for the least-fit men when compared with moderately-fit ones, and 10.1 (95% C.I. 9.1-11.2;P< 0.001) when compared with the most-fit men. Among women, the age-adjusted cumulative odds ratio was 2.7 (95% C.I. 2.1-3.5;P< 0.001) for the least-fit women when compared with moderately-fit ones, and 4.9 (95% C.I. 3.8-6.3;P< 0.001) when compared with the most-fit women.Conclusions:These cross-sectional results suggest that low CRF is associated with an increased clustering of the metabolic abnormalities associated with the MS in both adult men and women and support the need for future prospective analyses.

ISSN:0195-9131    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Muscle coordination and function during cutting movements.Med. Sci. Sports Exerc.,Vol. 31, No. 2, pp. 294-302, 1999.Purpose:The objectives of this study were to: 1) establish a database of kinematic and EMG data during cutting movements, 2) describe normal muscle function and coordination of 12 lower extremity muscles during cutting movements susceptible to ankle sprains, and 3) identify potential muscle coordination deficiencies that may lead to ankle sprain injuries.Methods:Kinematic, EMG, and GRF data were collected from 10 recreationally active male subjects during both a side-shuffle and v-cut movement.Results:The data showed that muscles functioned similarly during both movements. The primary function of the hip and knee extensors was to decelerate the center-of-mass during landing and to provide propulsion during toe-off. The hip add/abductors functioned primarily to stabilize the hip rather than provide mechanical power. The ankle plantar flexors functioned to provide propulsion during toe-off, and the gastrocnemius had an additional burst of activity to plantarflex the foot before touchdown during the side-shuffle to help absorb the impact. The tibialis anterior functioned differently during each movement: to dorsiflex and supinate the foot after toe-off in preparation for the next step cycle during the side-shuffle and to dorsiflex the foot before impact to provide the heel-down landing and ankle stability in the stance phase during the v-cut.Conclusions:The muscles crossing the ankle joint, especially the tibialis anterior and peroneus longus, may play an important role to prevent ankle sprain injuries. Both muscles provided stability about the subtalar joint by preventing excessive joint rotations. Future theoretical studies with forward dynamic simulations incorporating individual muscle actuators are needed to quantify the segment accelerations induced by active muscles which may prevent or lead to ankle sprain injuries.

ISSN:0195-9131    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Dynamics of force and muscle stimulation in human vertical jumping.Med. Sci. Sports Exerc.,Vol. 31, No. 2, pp. 303-310, 1999.Purpose:The purpose of this study was to gain insight into the importance of stimulation dynamics for force development in human vertical jumping.Methods:Maximum height squat jumps were performed by 21 male subjects. As a measure of signal dynamics, rise time (RT) was used, i.e., the time taken by the signal to increase from 10% to 90% of its peak value. RT were calculated for time histories of smoothed rectified electromyograms (SREMG) of seven lower extremity muscles, net moments about hip, knee, and ankle joints, and components of the ground reaction force vector.Results:Average RT values were 105-143 ms for SREMG signals, 90-112 ms for joint moments, and 120 ms for the vertical component of the ground reaction force (Fz). A coefficient of linear correlation of 0.88 was found between RT of SREMG of m. gluteus maximus (GLU) and RT of Fz. To explain this correlation, it was speculated that for an effective transfer from joint extensions to vertical motion of the center of mass (CM), the motion of CM needs a forward component during the push-off. Given the starting position, only the hip extensor muscles are able to generate such a forward acceleration of CM. To preserve the forward motion of CM, RT of knee and ankle joint moments need to be adjusted to RT of the hip joint moment. Thus, the greater RT of the hip joint moment and RT of GLU-SREMG, the greater RT of Fz.Conclusions:Overall, it was concluded that the time it takes to develop muscle stimulation has a substantial effect on the dynamics of force development in vertical jumping, and that this effect should not be neglected in studies of the control of explosive movements.

ISSN:0195-9131    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

The energy cost of horizontal walking and running in adolescents.Med. Sci. Sports Exerc.,Vol. 31, No. 2, pp. 311-322, 1999.Purpose:This study developed and cross-validated generalized equations for predicting &OV0312;O2(mL·kg−1·min−1) and caloric expenditure (kcal·kg−1·min−1) during horizontal walking and running in adolescents.Methods:Subjects were 47 male and 35 female adolescent volunteers, ages 12-18. Each subject underwent a submaximal treadmill exercise test to determine &OV0312;O2at randomly selected walking and jogging speeds (67-215 m·min−1). Caloric expenditure was estimated from &OV0312;O2and RER. Multiple regression was used to develop prediction equations for estimating &OV0312;O2and caloric expenditure from a derivation sample of 77 random observations, both walking and running.Results:The group relationship between running speed and energy cost in the derivation sample was linear, whereas the relationship between walking speed and energy cost was quadratic. Gender, age, and height each failed to account for significant additional variation in energy cost after speed and mode were considered. Skinfolds accounted for a small yet significant amount of additional variation in energy cost. The derived equations were cross-validated on a sample of 76 separate random observations. The cross-validation statistics are: for &OV0312;O2, R = 0.95, error = 3.58 mL·kg−1·min−1, and for caloric expenditure, R = 0.94, error = 0.019 kcal·kg−1·min−1. Most selected adult equations consistently underestimated both &OV0312;O2and caloric expenditure in the cross-validation sample.Conclusions:These results suggest that in adolescents, within the range of speeds tested, the relationship between speed of movement and energy cost for running is linear, but for walking is curvilinear. Also, adult models for estimating &OV0312;O2or caloric expenditure do not account for the higher relative energy cost of walking and running in adolescents.

ISSN:0195-9131    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Effects of ballistic training on preseason preparation of elite volleyball players.Med. Sci. Sports Exerc.,Vol. 31, No. 2, pp. 323-330, 1999.Purpose:The purpose of this study was to determine whether ballistic resistance training would increase the vertical jump (VJ) performance of already highly trained jump athletes.Methods:Sixteen male volleyball players from a NCAA Division I team participated in the study. A Vertec was used to measure standing vertical jump and reach (SJR) and jump and reach from a three-step approach (AJR). Several types of vertical jump tests were also performed on a Plyometric Power System and a forceplate to measure force, velocity, and power production during vertical jumping. The subjects completed the tests and were then randomly divided into two groups, control and treatment. All subjects completed the usual preseason volleyball on-court training combined with a resistance training program. In addition, the treatment group completed 8 wk of squat jump training while the control group completed squat and leg press exercises at a 6RM load. Both groups were retested at the completion of the training period.Results:The treatment group produced a significant increase in both SJR and AJR of 5.9 ± 3.1% and 6.3 ± 5.1%, respectively. These increases were significantly greater than the pre- to postchanges produced by the control group, which were not significant for either jump. Analysis of the data from the various other jump tests suggested increased overall force output during jumping, and in particular increased rate of force development were the main contributors to the increased jump height.Conclusions:These results lend support to the effectiveness of ballistic resistance training for improving vertical jump performance in elite jump athletes.

ISSN:0195-9131    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Physical work capacity after 7 wk of wheelchair training: effect of intensity in able-bodied subjects.Med. Sci. Sports Exerc.,Vol. 31, No. 2, pp. 331-341, 1999.Purpose:The purpose of this study was to study the effects of a 7-wk wheelchair training program on physical work capacity in able-bodied subjects. Effects of training intensities of 50 and 70% heart rate (HR) reserve (HRR) were studied for different subject groups.Methods:Twenty-seven able-bodied male subjects participated in this study. They were randomly divided into a control group (N= 8), a 50%-intensity group (N= 9), and a 70%-intensity group (N= 10). The 50%- and the 70%-intensity groups received a 7-wk wheelchair training program: three times a week, one-half hour wheelchair exercise on a motor driven treadmill at an average intensity of 50 and 70% of the HRR, respectively. Before and after the training period, parameters for physical work capacity (maximal isometric strength (Fiso), sprint power (P30), maximal power output (POmax) and peak oxygen uptake (&OV0312;O2peak)), and submaximal performance (mechanical efficiency, HR) at 20 and 40% of the estimated POmax(ME20, ME40; HR20, HR40) were obtained during tests on a stationary wheelchair ergometer.Results:A two-factor ANOVA for repeated measures on the within-subjects factor "pre-post tests," the between-subject factor training (50% and 70% training vs control) and the interaction term showed that the 50%-intensity group significantly increased on P30 and POmaxcompared with the control group. The 70% intensity group significantly increased on P30, POmax, and &OV0312;O2peakcompared with the control group (P< 0.05). The 70% group did not show significantly higher increases in P30 and POmaxover training than the 50% intensity. No significant effects were found for the Fisoand the parameters at submaximal PO.Conclusions:The wheelchair training at both intensities can have favorable effects on maximal physical work capacity in able-bodied subjects, and possibly also on mechanical efficiency at submaximal power output. Effects are seen in parameters for both aerobic and anaerobic work capacities. Although training at 70% intensity was more effective than the 50% intensity, training at 50% HRR may initially be more appropriate in untrained individuals, such as novice wheelchair users at the start of their rehabilitation, to prevent fatigue and enhance motivation.

ISSN:0195-9131    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Oxygen uptake, heart rate, and blood lactate responses during and following karate training.Med. Sci. Sports Exerc.,Vol. 31, No. 2, pp. 342-347, 1999.Purpose:The purpose of this study was to examine whether each exercise and an entire karate training session can achieve: 1) accepted training intensity thresholds for effective aerobic capacity training, 2) energy expenditure (EE) thresholds for total body mass and fat weight loss, and 3) elevation in excess postexercise oxygen consumption (EPOC).Methods:We investigated physiological responses during five types of karate training: basic techniques without (S-Basics) and with (M-Basics) movements, sparring techniques without (TECH I) and with (TECH II) an opponent, and kata.Results:The mean percent of maximal oxygen uptake (%&OV0312;O2max) and HR (%HRmax) for S-Basics were below the accepted threshold (60% of HRmaxor 50% of &OV0312;O2max) and for M-Basics, TECH I and TECH II were above the threshold for increasing &OV0312;O2max. For kata and the entire 70 min of karate training, the mean %HRmaxwere slightly above the threshold, and %&OV0312;O2maxwere slightly below the threshold. The mean EPOC measured for 5 min immediately following 70 min of karate training did not differ from the resting &OV0312;O2. The mean EE resulting from 70 min of karate exercise and EPOC were 2355.4 ± 316.3 kJ and 38.8 ± 32.7 kJ, respectively.Conclusions:Although the training intensity of karate exercises studied was moderate and the effects of karate training on EPOC were minimal, the mean value of EE was well above the accepted threshold for total body mass and fat weight loss.

ISSN:0195-9131    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Utility of pwc75% as an estimate of aerobic power in epidemiological and population-based studies.Med. Sci. Sports Exerc.,Vol. 31, No. 2, pp. 348-351, 1999.Purpose:Studies of physical activity often assess physical work capacity (pwc) and this is usually achieved with extrapolated estimates of maximal aerobic power (&OV0312;O2max). However, extrapolation beyond the measured values may be problematic, particularly for older subjects. On a population basis, interpolated measures of pwc may provide the same information and avoid the errors associated with extrapolated measures.Methods:This study assessed extrapolated (pwc at 150 and 170 beats·min−1heart rate (HR) and estimated &OV0312;O2max) and interpolated (pwc at 75% of maximum HR: pwc75%) measures of pwc in a population sample of 1043 men and women aged 18-78 yr. Each measure was assessed to determine whether it showed the key characteristics of measured &OV0312;O2max: a decrease with age and an increase with reported physical activity.Results:Both pwc150 and pwc170 did not decline with age, estimated &OV0312;O2max(est.&OV0312;O2max) exhibited a spurious plateau for older age groups, while pwc75% declined ∼9% per decade of age. All four pwc measures detected a significant difference (∼10-15%) between inactive and active groups classified according to a questionnaire of leisure time physical activity.Conclusions:Although the pwc75% test requires direct validation, these results suggest that it may be a useful submaximal exercise measure for epidemiological studies of aerobic power.

ISSN:0195-9131    

出版商:OVID    

年代:1999

数据来源: OVID