VO2 Response Research Articles

The effect of prior high-intensity cycling exercise on the VO2 kinetics during high-intensity cycling exercise is situated at the additional slow component.

In previous studies conclusions about the effect of prior exercise on VO2 kinetics of subsequent high-intensity exercise are generally based on observed changes in the overall VO2 response without considering the effects on the VO2 fast and slow component. The aim of the present study was to examine the effect on the VO2 fast and slow component separately. Therefore 10 subjects performed an exercise protocol consisting of an initial 3 min period of unloaded cycling followed by two constant-load work bouts at a work rate corresponding to 90% VO2peak, separated by 3 min of rest and 3 min of unloaded cycling. VO2 was measured on a breath-by-breath basis, and the response curves were analysed by a biexponential model. To increase signal-to-noise ratio, subjects performed four repetitions of the exercise protocol, each separated by at least one day. There was no significant alteration in VO2 kinetic parameters of the primary, fast component after high-intensity exercise. However, there was a significant effect of prior high-intensity exercise on the VO2 kinetic parameters of the slow component. The time constant and the amplitude of the slow component were reduced by respectively 44% (from 231.0 +/- 111.7 s to 130.1 +/- 50.4 s) and 49% (from 824 +/- 270 ml x min(-1) to 417 +/- 134 ml x min(-1)). The results of this study indicate that the effect of high-intensity exercise on the VO2 kinetics of a subsequent high-intensity exercise is probably limited to an effect on the slow component.

Oxygen uptake in one-legged and two-legged exercise.

The purpose of this study was to determine the primary factors causing the differential oxygen uptake (VO2) response at submaximal intensities between one-legged and two-legged exercise, and whether peak oxygen uptake (VO2peak) increases in proportion to the increase in active muscle mass. Two different types of exercise were used for this experiment, each requiring a different movement, a different method of stabilizing posture, and, finally, a different limiting VO2peak. In experiment 1, nine male subjects performed one-legged cycling (OLC) and two-legged cycling exercise (TLC) at a pedaling rate of 80 rpm. The exercise intensity was first set at 80 W and was increased by 40 W every 3 min until exhaustion. In experiment 2, six healthy male subjects performed one-legged knee-extension (OKE) and two-legged knee-extension (TKE) exercise at a rate of 50 contractions per minute. The knee-extension exercise was done at constant work rates for a 3-min session in OKE or a 4-min session in TKE. The exercise bouts were performed intermittently at four to seven different submaximal intensities and VO2 was determined at each intensity in all exercises. At submaximal intensities, VO2 in relation to work rate of one-legged exercise was more steep than those of two-legged exercise, and the mean values of VO2 were significantly higher in one-legged exercise than those in two-legged exercise in both knee extension and cycling exercise. Mean values of VO2peak for two-legged exercise were significantly higher than that for one-legged exercise (P < 0.01); however, it was much lower than two times of that for one-legged exercise even in knee extension exercise where the VO2peak would be limited peripherally. The findings of this study suggest that the differential VO2 response between one-legged and two-legged exercise would be attributed not only to the difference in force application throughout the exercise movement and to the effect of a postural component but also to the inhibited circulatory response caused by the multiple limb exercise. In addition, it was supposed that VO2peak does not increase in proportion to the exercising muscle mass even during smaller muscle activity where the cardiac pumping capacity has not reached its upper limit.

Effect of bright light on cycling performance.

The purpose of this study was to examine the effect of exposure to three levels of light intensity during cycling on average power output during an all-out 20-min bout of cycle ergometry. Twelve male competitive cyclists, with a mean age of 24.3 +/- 3.2 yr, were tested on four separate occasions. During each test session, participants were instructed to produce the highest possible average power output during a 20-min bout of cycle ergometry. Session 1 served as a adaptation trial and was conducted in normal room lighting (approximately 250 lux). In subsequent sessions each participant exercised while sitting in front of a light box. Light intensity was experimentally manipulated through the use of sunglasses that provided high, medium, and low light filtration. Light condition order was counterbalanced. Measurements of heart rate, muscle pain, local perceived exertion, metabolism, and alertness were made during exercise. Mood was assessed before and following exercise with the POMS-BI. There were no statistically significant differences in the average total power output in the 1,411 lux (274.9 +/- 21.8 W), 2,788 lux (274.4 +/- 20.5 W), and 6,434 lux (270.3 +/- 19.8 W) light conditions. The difference between the average power output in the brightest and least bright condition (4.6 W) was approximately one-fourth of a pooled SD (d = 0.22). There were no significant differences among the conditions in alertness, leg muscle pain, perceived exertion, heart rate, VO2, or mood responses to the exercise. It is concluded that exposure to bright light resulting in estimated retinal exposures ranging from 1,411 to 6,434 lux did not have a large or systematic influence on the performance of 20 min of maximal cycle ergometry.

The slow component of O2 uptake kinetics during high-intensity exercise in trained and untrained prepubertal children.

The aim of the present study was to investigate the O2 uptake slow component in prepubertal children of different aerobic capacity during high intensity exercise. Twenty-three (12 well-trained, T and 11 untrained, U subjects) 10-13 year old prepubertal children took part in 3 tests: one incremental test to determine the maximal aerobic power (PMA) and anaerobic threshold (LAT); two constant-power tests performed at intensities corresponding to 80%LAT and 90%PMA. Oxygen uptake (VO2), heart rate, ventilation (VE) and lactate ([L]s) were evaluated during each test. A monoexponential + linear term model (starting after phase 1) was used to assess VO2 kinetics during both constant-power tests. Our results showed that a slow component, represented by the linear coefficient (S) of the mathematical model, was present during the 90%PMA test only (S = 0.86 +/- 0.48 ml x min(-2) x kg(-1) for the whole population). No relationships were found between either S and VE or [L]s, showing that, at least in prepubertal children, these factors play a minor role in the explanation for the VO2 slow component. The slow component contributed approximately to the same amount of the total VO2 response in both groups (T: 21.4 +/- 8.0, U: 19.3 +/- 3.9%, ns). In conclusion, as previously described in adults, our data demonstrated the existence of a slow component in prepubertal children during high-intensity exercise. Moreover, this slow component was similar in trained and untrained children, exercising at the same relative intensity.

Interaction of sulfonylureas and exercise on glucose homeostasis in type 2 diabetic patients.

To determine whether the plasma glucose-lowering effects of sulfonylureas and acute submaximal exercise are additive and, accordingly, to determine whether they may increase the risk of hypoglycemia when combined in fasting patients. Eight postabsorptive type 2 diabetic patients were examined at three occasions: after oral sulfonylurea (7 mg glibenclamide), during 60 min of ergometer cycle exercise at 57 +/- 3% of VO2max, and during exercise after glibenclamide. Heart rate, VO2, and lactate responses to exercise were comparable (P > 0.05) on days with and without glibenclamide. Plasma insulin concentrations were always increased by glibenclamide, and they were lowered identically by exercise with and without glibenclamide. However, throughout exercise, absolute concentrations of insulin were lower on days without glibenclamide compared with days with glibenclamide (34.5 +/- 4.7 vs. 47.4 +/- 5.5 pmol/l; P < 0.05). At the start of exercise, glucose concentrations were similar between experiments (P > 0.05). The rate of decrease in glucose during exercise was higher (P < 0.05) on days with both glibenclamide and exercise, compared with days with glibenclamide alone and days with exercise alone (-0.035 +/- 0.009 vs. -0.016 +/- 0.002 and -0.022 +/- 0.005 mmol.l-1.min-1, respectively). Consequently, the glucose nadir was lower on days with glibenclamide and exercise than on days with glibenclamide or exercise alone (6.7 +/- 1.1 vs. 8.1 +/- 0.9 and 7.6 +/- 1.0 mmol/l, respectively; P < 0.05). During exercise, the rate of appearance of plasma glucose determined by 3-[3H]glucose infusion was lower on days with glibenclamide than on days without glibenclamide (2.3 +/- 0.1 vs. 2.9 +/- 0.1 mg.min-1.kg-1; P < 0.05). In contrast, glucose clearance was identical (P > 0.05). In postabsorptive type 2 diabetic patients, the hypoglycemic action of glibenclamide and exercise is enhanced when the treatments are combined. The interaction reflects an increased inhibition by glibenclamide-enhanced insulin levels of hepatic glucose production when hepatic glucose production is accelerated by exercise.

Pacing-Induced Cardiac Failure of Hypertrophic Hearts: Effects of Cyclic GMP Reduction

Background. We tested the hypothesis that pacing-induced cardiac failure of hypertrophic hearts would reduce the functional and metabolic responses of these hearts to guanylate cyclase inhibition and this was associated with alterations in cyclic GMP.Materials and methods. Methylene blue (MB, 2 mg/kg/min, guanylate cyclase inhibitor) was infused into the left anterior descending coronary artery in 5 control, 5 left ventricular hypertrophy (LVH), and 5 LVH pacing-induced failure dogs. Regional myocardial work was calculated as the integrated product of force and segment shortening and regional myocardial O2 consumption (VO2) from coronary blood flow and O2 extraction measurements. Cyclic GMP was determined by radioimmunoassay.Results. MB increased regional work (635 ± 169 vs 1649 ± 500, 781 ± 184 vs 1569 ± 203 g ∗ mm/min) and VO2 (8.3 ± 1.4 vs 10.9 ± 1.4, 7.3 ± 0.7 vs 9.1 ± 0.7 ml O2/min/100 g) in both control and LVH dogs but not in failure dogs (536 ± 234 vs 623 ± 193, 3.6 ± 1.1 vs 4.7 ± 1.9). MB also decreased cyclic GMP in control dogs (1170 ± 142 vs 812 ± 105 pmol/g). LVH dogs had elevated baseline cyclic GMP (5875 ± 949) compared to control dogs but also demonstrated decreased cyclic GMP in response to MB (2820 ± 372). In failure dogs, basal cyclic GMP was also elevated (4650 ± 613) compared to control dogs but there was a lack of response to MB (3670 ± 640).Conclusions. We conclude that the myocardial function, VO2 and cyclic GMP responses to methylene blue are diminished in the transition from hypertrophy to cardiac failure.

A COMPARISON OF HR AND VO2 RESPONSES TO TREADMILL EXERCISE IN BLACK AND WHITE MEN.

661 This study compared heart rate (HR) and oxygen consumption (VO2) responses to submaximal and maximal treadmill exercise between White (n=21) and Black (n=21) men aged 18-35 years. Maximal and submaximal steady-state HR and VO2 values during the last 30 s of each 3 min stage of a maximal graded exercise test (GXT) were used for statistical analysis. The Blacks were on the average 4 years older (p<.05) than their White counterparts but were similar (p>.05) in body mass index, height, weight, and resting blood pressure. There were no ethnic differences in maximal HR (Blacks = 193.6 ± 9.6 bpm, Whites = 194.3 ± 8.4 bpm) or VO2 (Blacks = 46.8 ± 5.6 ml·kg−1·min−1, Whites = 48.9 ± 8.5 ml·kg−1·min−1) values. There were no significant differences in HR or VO2 responses between the Blacks and Whites while walking at 3 mph, jogging at 6 mph, jogging at 6 mph at 3% grade, and jogging at 6 mph at 6% grade. Regressing submaximal absolute HRs against corresponding VO2 values resulted in coincidental (F(2, 151)=1.62, p>.05) regression lines for Blacks and Whites. The HR/VO2 relationships expressed as a percentage of maximal values were also similar (F(2, 151)=0.27, p>.05). The dispersement of data points about the regression line was greater in Blacks (r=.87, SEE=16.8 bpm) than for Whites (r=.92, SEE 13.8 bpm). We conclude that Black and White males of similar fitness levels had similar HR and VO2 responses to submaximal exercise on a treadmill. Supported by ACSM Foundation - Polar Research Grant

SUBMAXIMAL EXERCISE ON LAND AND IN WATER WITH AND WITHOUT HAND-HELD WEIGHTS: COMPARATIVE EXERCISE PHYSIOLOGY

651 The purpose of this study was to compare the metabolic and physiologic responses of submaximal exercise on land and in water with and without .90 kg (2.0 pounds) hand-held weights. Eight women (X age = 19.8 ± 1.6 yrs) completed a maximal graded exercise test (GXT) and four submaximal exercise tests: 1) on land with hand-held weights; 2) on land without hand-held weights; 3) in neck-depth water with hand-held weights and 4) in neck-depth water without hand-held weights. Analyses of heart rate (HR), oxygen consumption (VO2), ventilation (VE), respiratory exchange ratio (RER), blood lactate (BLa−) and rating of perceived exertion (RPE) were conducted in all tests. A 2 X 2 (Environment X Weights) analysis of variance (ANOVA) revealed significantly lower HR and VO2 responses during water exercise, and the addition of the hand-held weights in the water significantly increased the HR at 21 minutes of exercise. The addition of the weights in the water did not increase the resistance or "drag" in the water, as indicated by the non significant changes in the water with weights versus water without weights conditions. Responses for VE and BLa− produced significantly higher responses on land with weights. The lowest values for RPE were generated during water exercise. These data indicate that water exercise is a suitable mode of activity for those who are elderly, overweight or suffer from orthopedic injury while reducing the effort perception of the exercise. Supported by a Research and Disciplinary Grant of Bloomsburg University

PHYSIOLOGICAL RESPONSES DURING CARDIOVASCULAR KICKBOXING: A PILOT STUDY

403 Cardiovascular kickboxing (CVK) is an exercise routine combining aerobics with the martial arts. A commercial manikin, constructed of plastic covered with molded foam, was used to standardize the striking patterns of healthy trained (n=4) and untrained (n=3) male and female volunteers. The purpose of this pilot study was to compare cardiorespiratory, metabolic, and electromyographic responses of the subjects during a single bout of CVK. The CVK consisted of four, 5 min stages (ST): ST1, 60 punches/min; ST2, 45 punches and kicks/min; ST3, 30 three-series punches/min; and ST4, 60 punches and kicks/min. VO2 was measured using open circuit spirometry and heart rate (HR) via telemetry. ANOVA revealed that trained subjects had significantly (p<0.05) lower VO2 responses than untrained subjects during ST1, 2, and 3. Furthermore, a small but significant correlation (r=.397; p<0.05, r2=15.7%) was found between HR and VO2. One trained female and untrained male of comparable age, height, and weight executed four different punches (upper cut, power punch, hook, and jab) several times. Integrated EMG data were measured at a rate of 500 Hz for eleven muscles from surface electrodes. The trained subject had greater IEMG activity from the rectus abdominis, rectus femoris, and gastrocnemius muscles. The untrained subject had greater activity from the external oblique, latissimus dorsi, and gluteus maximus muscles. Additional research is warranted to determine the basis for the observed differences in physiological responses between trained and untrained subjects.

EFFECTS OF VARYING CRANK LENGTHS ON EXERCISE VO2 RESPONSE AND LOWER LIMB KINEMATICS

1814 The energetic response to exercise is dependent, in part, upon the fiber type composition of the exercising muscle and its recruitment pattern. Altered crank lengths produce a change in the magnitude of force application and, theoretically, movement patterns associated with the cycling movement. We hypothesized that altered crank lengths would produce a change in the pedaling kinematics and recruitment pattern of fiber within the exercised muscles and thereby alter the VO2 response (kinetics and maximum). Seven male cyclists performed incremental and constant load cycle ergometry for measurement of VO2 max and VO2 kinetics, respectively. Each cyclist used his own bicycle which was then attached to a Schwinn Velodyne. The three crank lengths used were 165, 170, and 175 mm. The cadence was individualized. Analysis of videotapes taken during the first and last minute of each exercise bout provided two-dimensional kinematic data on the lower extremities. Results indicated that: (1) there was a higher VO2 max at fatigue for the 170 mm crank arms for 5 of the 7 cyclists (p≤.02); (2) the rapid VO2 kinetics, defined as VO2 at 3 minutes, was significantly higher while cycling with the 170 mm crank arms; (3) crank length did not affect the slow component response (p≥.10); (4) hip joint range of motion was the only kinematic parameter affected by fatigue, increasing with the onset of fatigue; and (5) the range of motion about the knee and hip joints was greater for increasing crank lengths. We conclude that varying the crank length within the range normally used by competitive cyclists affects exercise VO2, lower limb kinematics, and possibly fiber type recruitment patterns.

Thermogenic effects of sibutramine and its metabolites.

1. The thermogenic activity of the serotonin and noradrenaline reuptake inhibitor sibutramine (BTS 54524; Reductil) was investigated by measuring oxygen consumption (VO2) in rats treated with sibutramine or its two pharmacologically-active metabolites. 2. Sibutramine caused a dose-dependent rise in VO2, with a dose of 10 mg kg(-1) of sibutramine or its metabolites producing increases of up to 30% that were sustained for at least 6 h, and accompanied by significant increases (0.5-1.0 degrees C) in body temperature. 3. Based on the accumulation in vivo of radiolabelled 2-deoxy-[3H]-glucose, sibutramine had little or no effect on glucose utilization in most tissues, but caused an 18 fold increase in brown adipose tissue (BAT). 4. Combined high, non-selective doses (20 mg kg(-1)) of the beta-adrenoceptor antagonists, atenolol and ICI 118551, inhibited completely the VO2 response to sibutramine, but the response was unaffected by low, beta1-adrenoceptor-selective (atenolol) or beta2-adrenoceptor-selective (ICI 118551) doses (1 mg kg(-1)). 5. The ganglionic blocking agent, chlorisondamine (15 mg kg(-1)), inhibited completely the VO2 response to the metabolites of sibutramine, but had no effect on the thermogenic response to the beta3-adrenoceptor-selective agonist BRL 35135. 6. Similar thermogenic responses were produced by simultaneous injection of nisoxetine and fluoxetine at doses (30 mg kg(-1)) that had no effect on VO2 when injected individually. 7. It is concluded that stimulation of thermogenesis by sibutramine requires central reuptake inhibition of both serotonin and noradrenaline, resulting in increased efferent sympathetic activation of BAT thermogenesis via beta3-adrenoceptor, and that this contributes to the compound's activity as an anti-obesity agent.

Oxygen uptake kinetics during exercise.

The characteristics of oxygen uptake (VO2) kinetics differ with exercise intensity. When exercise is performed at a given work rate which is below lactate threshold (LT), VO2 increases exponentially to a steady-state level. Neither the slope of the increase in VO2 with respect to work rate nor the time constant of VO2 responses has been found to be a function of work rate within this domain, indicating a linear dynamic relationship between the VO2 and the work rate. However, some factors, such as physical training, age and pathological conditions can alter the VO2 kinetic responses at the onset of exercise. Regarding the control mechanism for exercise VO2 kinetics, 2 opposing hypotheses have been proposed. One of them suggests that the rate of the increase in VO2 at the onset of exercise is limited by the capacity of oxygen delivery to active muscle. The other suggests that the ability of the oxygen utilisation in exercising muscle acts as the rate-limiting step. This issue is still being debated. When exercise is performed at a work rate above LT, the VO2 kinetics become more complex. An additional component is developed after a few minutes of exercise. The slow component either delays the attainment of the steady-state VO2 or drives the VO2 to the maximum level, depending on exercise intensity. The magnitude of this slow component also depends on the duration of the exercise. The possible causes for the slow component of VO2 during heavy exercise include: (i) increases in blood lactate levels; (ii) increases in plasma epinephrine (adrenaline) levels; (iii) increased ventilatory work; (iv) elevation of body temperature; and (v) recruitment of type IIb fibres. Since 86% of the VO2 slow component is attributed to the exercising limbs, the major contributor is likely within the exercising muscle itself. During high intensity exercise an increase in the recruitment of low-efficiency type IIb fibres (the fibres involved in the slow component) can cause an increase in the oxygen cost of exercise. A change in the pattern of motor unit recruitment, and thus less activation of type IIb fibres, may also account for a large part of the reduction in the slow component of VO2 observed after physical training.

Hemodynamic characteristics during treadmill and bicycle exercise in chronic heart failure: mechanism for different responses of peak oxygen uptake.

The exercise capacity of patients with chronic heart failure (CHF) is greater when assessed by the treadmill rather than the bicycle ergometer, but the mechanism of this difference has not been clarified. The present study aimed to determine the difference between the hemodynamics of these exercise modes and the mechanism underlying the different peak oxygen uptake (VO2). Patients (n = 18) underwent a bicycle test and treadmill test using individual ramp protocols. Respiratory gas analysis and hemodynamic measurements with an opti-catheter were performed during both exercise tests. The peak VO2 was significantly larger in the treadmill test than the bicycle test (1410+/-292 vs. 1630+/-331 ml/min, p<0.001). Both the peak cardiac output (Q; 10.2+/-2.2 vs. 10.9+/-2.1 L/min, p<0.001) and the peak arteriovenous oxygen difference (a-v 02 diff; 13.9+/-1.5 vs. 15.0+/-1.2 vol%, p<0.001) were also significantly higher in the treadmill test. The relative contribution of Q and a-v O2 diff to the increased peak VO2 was equivalent, which suggests that both Q and a-v O2 diff. Contribute equally to the different peak VO2 responses in CHF.

Submaximal exercise and maturation in 12-year-olds

The aim of this study was to examine the maturation responses of young people to submaximal treadmill exercise. Body mass was controlled using both the conventional ratio standard and allometric modelling. Ninetyseven boys and 97 girls with a mean age of 12.2 years completed a discontinuous, incremental exercise test to voluntary exhaustion. We measured peak oxygen uptake (VO2peak) and VO2 when running at 8, 9 and 10km.h -1. Sexual maturation was assessed visually using Tanner's indices of pubic hair. Peak V O2 was significantly higher in boys (P<0.001); this was still the case when the influence of body mass was covaried out. During submaximal exercise, no significant differences in absolute VO2 were observed between the sexes (P>0.05); however, values of VO2, expressed both in ratio with body mass and adjusted for body mass using allometry, were significantly greater in boys than in girls (P<0.001). For absolute V O2, significant main effects (P<0.05) were seen for maturity at each exercise stage. With the influence of body mass controlled using either the ratio standard or allometry, no significant main effects (P>0.05) for maturity were observed. Our results indicate that boys are less economical than girls while running at 8–10 km.h-1 and that, independently of body mass, maturation does not influence the VO2 response to submaximal exercise.

Energy system contributions in middle-distance running events

The aim of this study was to estimate the energy contributions in middle-distance running events for male and female university athletes. The oxygen uptake (VO2) response during high-speed running was measured directly during exhaustive treadmill tests. Muscle mass was estimated using anthropometry. Each athlete completed an average of three races over 400 m, 800 m or 1500 m. Five minutes after each race, they provided a blood sample for determination of blood lactate concentration. For each race, energy cost, which was expressed as oxygen equivalents, was calculated as the sum of the aerobic and anaerobic components. The aerobic contribution was calculated as the sum of oxygen stores (2.3 ml O2.kg body mass-1) and total VO2 (based on the VO2 response to treadmill running). The anaerobic contribution was calculated as the sum of the energy available from phosphocreatine stores (37 ml O2.kg muscle mass-1) and the energy from glycolysis (3.0 ml O2.kg body mass-1 per mmol.l-1 increase in blood lactate concentration). For the women, the anaerobic energy contributions for the 400 m, 800 m and 1500 m averaged 62% 33% and 17% respectively. For the men, the anaerobic contributions averaged 63%39% and 20%respectively. This information will help coaches and sport scientists to design and implement individualized training programmes.

Velocity of Oxygen Uptake Response at the Onset of Exercise: A Comparison Between Children After Cardiac Surgery and Healthy Boys

A comparison was carried out concerning maximal oxygen uptake, oxygen uptake adjustment at the onset of high-intensity exercise, and maximal blood lactate between 10 healthy prepubertal boys and 35 children after repair of cardiac malformations or after Fontan operation. Mean maximal oxygen uptake (VO2) was moderately reduced in children after repair of tetralogy of Fallot or after Mustard or Senning operations and severely reduced after Fontan operations. Conversely, mean half-time of VO2 response was moderately prolonged in children after repair of tetralogy of Fallot or after Senning and Mustard operations and considerably prolonged after Fontan operations. According to our results unfavorable kinetics of VO2 response to physical exercise are present in addition to reduced aerobic power in many of the operated children. Besides being less qualified for endurance performance, these children are also less prepared for short, high-intensity exercise.

Effect of Step Platform Height on Stepping Efficiency in Children

This study was conducted to determine if VO2, of stepping in children is affected by altering the step platform height based on leg length. The effect of leg length on VO2 and heart rate (HR) during stepping was examined in 19 children, ages 8–17, who stepped onto 5 different bench heights that corresponded to hip angles of 65°, 73°, 82°, 90°, or 98°. VO2 and HR response to a work load of 8 m · min−1 assumed a U-shaped curve with 82° assuming the lowest point of the curve. Efficiency of stepping was significantly higher at 82° when compared to the other hip angles. It was concluded that VO2 and HR in children is influenced by leg length during stepping, and there is an optimum step height for stepping that can be determined from the ratio of leg length to stature.

Influence of the oxygen uptake slow component on the aerobic energy cost of high-intensity submaximal treadmill running in humans.

During high-intensity running, the oxygen uptake (VO2) kinetics is characterised by a slow component which delays the attainment of the steady-state beyond the 3rd min of exercise. To assess if the aerobic energy cost of running measured at the 3rd min (C3) adequately reflects the variability of the true aerobic energy cost measured during the steady-state (Css), 13 highly-trained runners completed sessions of square-wave running at intensities above 80% maximal oxygen uptake (VO2max) on a level treadmill. To evaluate the time at which the steady-state VO2 was attained (tss), the VO2 responses were described using a general double-exponential equation and tss was defined as the time at which VO2 was less than 1% below the asymptotic value given by the model. All the subjects achieved a steady state for intensities equal to or greater than 92% VO2max, and 8 out of 13 achieved it at 99% VO2max. In all cases, tss was less than 13 min. For intensities greater than 85% VO2max, Css was significantly higher than C3 and was positively related to %VO2 max (r=0.44; P < 0.001) while C3 remained constant. The C3 only explained moderately the variability of Css (0.39 < r2 < 0.72, depending on the velocity or the (relative intensity at which the relationship was calculated). Moreover, the excess aerobic energy cost of running the (difference between Css and C3) was well predicted by age (0.90 < r2 < 0.93). Therefore, when the aerobic profile of runners is evaluated, it is recommended that their running efficiencies at velocities which reflect their race intensities should be determined, with VO2 data being measured at the true steady-state.

Transient oxygen uptake response to exercise characterizes functional capacity of the cardiocirculatory system in patients with chronic heart failure: a random stimulus approach.

The transient response of oxygen uptake (VO2) to submaximal exercise, known to be abnormal in patients with cardiovascular disorders, can be useful in assessing the functional status of the cardiocirculatory system, however, a method for evaluating it accurately has not yet been established. As an alternative approach to the conventional test at constant exercise intensity, we applied a random stimulus technique that has been shown to provide relatively noise immune responses of system being investigated. In 27 patients with heart failure and 24 age-matched control subjects, we imposed cycle exercise at 50 W intermittently according to a pseudo-random binary (exercise-rest) sequence, while measuring breath-by-breath VO2. After determining the transfer function relating exercise intensity (W) to VO2 and attenuating the high frequency ranges (> 6 exercise-rest cycles x min(-1)), we computed the high resolution band-limited (0-6 cycles x min(-1)) VO2 response (0-120 s) to a hypothetical step exercise. The VO2 response showed a longer time constant in the patients than in the control subjects [47 (SD 37) and 31 (SD 8) s, respectively, P < 0.05]. Furthermore, the amplitude of the VO2 response after the initial response was shown to be significantly smaller in the patients than in the control subjects [176 (SD 50) and 267 (SD 54) ml x min(-1) at 120 s]. The average amplitude over 120 s correlated well with peak VO2 (r = 0.73) and deltaVO2/deltaW (r = 0.70), both of which are well-established indexes of exercise tolerance. The data indicated that our band-limited VO2 step response using random exercise was more markedly attenuated and delayed in the patients with heart failure than in the normal controls and that it could be useful in quantifying the overall functional status of the cardiocirculatory system.

PHYSIOLOGICAL RESPONSES TO THREE COMMERCIALLY PRODUCED EXERCISE VIDEOS

315 Ratings of commercial exercise videos are generally based on subjective critiques related to presentation. Thus, this study measured physiological responses to three popular videos via objective laboratory methods. The videos were: “Reebok Dance Step (DS)” a step workout, “Crunch Fat Blaster (FB)” a high-low impact video, and “Peak Fat Burning by Kathy Smith (KS)” an interval video. VO2 and HR were determined with 10 adult females (VO2 max = 45.0 ± 3.9 ml·kg-1·min-1) by open-circuit calorimetry and telemetry. The mean (± SD) data and the results of the Repeated Measures ANOVA (p < 0.05) are presented below: TableTableDS yielded higher VO2, HR, and kcal responses compared to FB and KS. In contrast, KS elicited a higher RER than DS and FB. When considering specific means associated with the KS work and recovery segments, all variables (except HR) were higher during KS work intervals compared to any other condition. In terms of total energy cost, the 20 min. DS and FB videos required approximately 160 and 145 kcals, respectively. The longer (24 min.) KS workout elicited an expenditure of 170 kcals. The studied videos provide a range of intensities sufficient to meet the ACSM criteria for promoting cardiovascular fitness in heathy adults. However, their relatively short (20-24 min.) durations do not yield the threshold kcal expenditure recommended by the ACSM for effective weight/fat loss. Thus, titles employing terms “Fat Burn” or“Blast” may be misconstrued by consumers.