Biomedical subjects

B J Whipp

Publications and source records attributed to B J Whipp.

At least 37 records · Page 2Linked to original sources

PubMed2001

Effect of prior metabolic rate on the kinetics of oxygen uptake during moderate-intensity exercise.

Pulmonary oxygen uptake (VO2) dynamics during moderate-intensity exercise are often assumed to be dynamically linear (i.e. neither the gain nor the time constant (tau) of the response varies as a function of work rate). However, faster, slower and unchanged VO2 kinetics have been reported during work-to-work transitions compared to rest-to-work transitions, all within the moderate-intensity domain. In an attempt to resolve these discrepancies and to improve the confidence of the parameter estimation, we determined the VO2 response dynamics using the averaged response to repeated exercise bouts in seven healthy male volunteers. Each subject initially performed a ramp-incremental exercise test for the estimation of the lactate threshold (thetaL). They then performed an average of four repetitions of each of three constant-work-rate (WR) tests: (1) between 20 W and a work rate of 50% (WR50) between 20 W and 90% thetaL (step 1-->2), (2) between WR50 and 90% thetaL (step 2-->3), and (3) between 20 W and 90% thetaL (step 1-->3); 6 min was spent at each work rate increment and decrement. Parameters of the kinetic response of phase II VO2 were established by non-linear least-squares fitting techniques. The kinetics of VO2 were significantly slower at the upper reaches of the moderate-intensity domain (step 2-->3) compared to steps 1-->2 and 1-->3 [group mean (SD) phase II tau: step 1-->2 25.3 (4.9) s, step 2-->3 40.0 (7.4) s and step 1-->3 32.2 (6.9) s]. The off-transient values of tau were not significantly different from each other: 36.8 (16.3) s, 38.9 (11.6) s and 30.8 (5.7) s for steps 1-->2, 2-->3 and 1-->3, respectively. Surprisingly, the on-transient gain (G, deltaVO2/deltaWR) was also found to vary among the three steps [G = 10.56 (0.42) ml x min(-1) W(-1) 11.85 (0.64) ml x min(-1) W(-1) and 11.23 (0.52) ml x min(-1) W(-1) for steps 1-->2, 2-->3 and 1-->3, respectively]; the off-transient G did not vary significantly and was close to that for the on-transient step 1-->3 in all cases. Our results do not support a dynamically linear system model of VO2 during cycle ergometer exercise even in the moderate-intensity domain. The greater oxygen deficit per unit power increment in the higher reaches of the moderate-intensity domain necessitates a greater transient lactate contribution to the energy transfer, or a greater phosphocreatine breakdown, or possibly both.

Adult↗

PubMed2001

Physiological responses to incremental exercise in patients with chronic fatigue syndrome.

PURPOSE: The purpose of this investigation was to characterize the physiological response profiles of patients with chronic fatigue syndrome (CFS), to an incremental exercise test, performed to the limit of tolerance. METHODS: Fifteen patients (12 women and three men) who fulfilled the case definition for chronic fatigue syndrome, and 15 healthy, sedentary, age- and sex-matched controls, performed an incremental progressive all-out treadmill test (cardiopulmonary exercise test). RESULTS: As a group, the CFS patients demonstrated significantly lower cardiovascular as well as ventilatory values at peak exercise, compared with the control group. At similar relative submaximal exercise levels (% peak VO(2)), the CFS patients portrayed response patterns (trending phenomenon) characterized, in most parameters, by similar intercepts, but either lower (VCO(2), HR, O(2pulse), V(E), V(T), PETCO(2)) or higher (B(f), V(E)/VCO(2)) trending kinetics in the CFS compared with the control group. It was found that the primary exercise-related physiological difference between the CFS and the control group was their significantly lower heart rate at any equal relative and at maximal work level. Assuming maximal effort by all (indicated by RER, PETCO(2), and subjective exhaustion), these results could indicate either cardiac or peripheral insufficiency embedded in the pathology of CFS patients. CONCLUSION: We conclude that indexes from cardiopulmonary exercise testing may be used as objective discriminatory indicators for evaluation of patients complaining of chronic fatigue syndrome.

Adult↗

PubMed2000

Intersample fluctuations in phosphocreatine concentration determined by 31P-magnetic resonance spectroscopy and parameter estimation of metabolic responses to exercise in humans.

The ATP turnover rate during constant-load exercise is often estimated from the initial rate of change of phosphocreatine concentration ([PCr]) using 31P-magnetic resonance spectroscopy (MRS). However, the phase and amplitude characteristics of the sample-to-sample fluctuations can markedly influence this estimation (as well as that for the time constant (tau) of the [PCr] change) and confound its physiological interpretation especially for small amplitude responses. This influence was investigated in six healthy males who performed repeated constant-load quadriceps exercise of a moderate intensity in a whole-body MRS system. A transmit- receive surface coil was placed under the right quadriceps, allowing determination of intramuscular [PCr]; pulmonary oxygen uptake (VO2) was simultaneously determined, breath-by-breath, using a mass spectrometer and a turbine volume measuring module. The probability density functions (PDF) of [PCr] and VO2 fluctuations were determined for each test during the steady states of rest and exercise and the PDF was then fitted to a Gaussian function. The standard deviation of the [PCr] and VO2 fluctuations at rest and during exercise (sr and sw, respectively) and the peak centres of the distributions (xc(r) and xc(w)) were determined, as were the skewness (gamma1) and kurtosis (gamma2) coefficients. There was no difference between sr and sw for [PCr] relative to the resting control baseline (s(r) = 1.554 %delta (s.d. = 0.44), s(w) = 1.514 %delta (s.d. = 0.35)) or the PDF peak centres (xc(r) = -0.013 %delta (s.d. = 0.09), xc(w) -0.197 %delta (s.d. = 0.18)). The standard deviation and peak centre of the 'noise' in VO2 also did not vary between rest and exercise (sr = 0.0427 l min(-1) (s.d. = 0.0104), s(w) = 0.0640 l min(-1) (s.d. = 0.0292); xc(r) = -0.0051 l min(-1) (s.d. = 0.0069), xc(w) 0.0022 l min(-1) (s.d. = 0.0034)). Our results demonstrate that the intersample 'noise' associated with [PCr] determination by 31P-MRS may be characterised as a stochastic Gaussian process that is uncorrelated with work rate, as previously described for VO2. This 'noise' can significantly affect the estimation of tau[PCr] and especially the initial rate of change of [PCr], i.e. the fluctuations can lead to variations in estimation of the initial rate of change of [PCr] of more than twofold, if the inherent 'noise' is not accounted for. This 'error' may be significantly reduced in such cases if the initial rate of change is estimated from the time constant and amplitude of the response.

Adenosine Triphosphate↗

PubMed2000

Estimating the parameters of aerobic function during exercise using an exponentially increasing work rate protocol.

A new exercise protocol has been proposed, with respect to cardiopulmonary exercise testing, which starts at a low work rate (WR) and increases exponentially by a standard percentage of the previous work rate every minute: the test is termed STEEP (standardised exponential exercise protocol). The potential advantage of this protocol is that it can accommodate a wide range of subjects, since it allows a maximum to be attained with a relatively narrow variation of tolerance time, regardless of subjects exercise capacity. To date, only the VO2max has been compared with that from the current standard ramp protocol. The ramp, however, also allows other important parameters of aerobic function to be estimated: the anaerobic threshold (AT); the response time constant; and delta VO2/delta WR. The aim of this study was, therefore, to clarify whether these aerobic parameters can be readily discerned from the responses to the STEEP protocol both from a theoretical and practical viewpoint. As a result of theoretical considerations, we demonstrated that the VO2 time constant and delta VO2/delta WR may not both be estimated uniquely. As a practical expedient, a procedure was proposed for estimating the parameter analogues. The preliminary results for six subjects between the STEEP and ramp protocols showed consistent positive correlation for VO2max (r = 0.997) and AT-VO2 (r = 0.980), whereas the correlation for the VO2 time constant and delta VO2/delta WR were not significant. Further study is needed to clarify the reason(s) for the discrepancies both from a theoretical and practical viewpoint.

Clinical Protocols↗

PubMed2000

The effect of age on the power/duration relationship and the intensity-domain limits in sedentary men.

The time to fatigue (t) in response to high-intensity constant-load exercise decreases hyperbolically with increasing power (W), at least in active and younger individuals [i.e. (W - thetaF)t = W', where thetaF is the critical power asymptote and W' is the curvature constant]. Little is known, however, about the combined effects of age and sedentarity on these parameters. We therefore evaluated 17 non-trained males (9 aged 60-75 years and 8 aged below 30 years) who underwent ramp-incremental cycle ergometry and, on different days, 4 high-intensity constant-load tests to t. Compared to their younger counterparts, the older subjects presented significantly lower maximum oxygen uptake (i.e. the maximum value of oxygen uptake attained at the end of a progressive exercise with the subject exerting a presumably maximal effort, muVO2), estimated lactate threshold (VO2thetaL), VO2thetaF, and W' (P < 0.05). Interestingly, however, both VO2thetaL and VO2thetaF, when expressed as a percentage of muVO2, were higher in older than in younger men [61.8 (6.2)% versus 45.4 (4.6)% and 87.8 (7.3)% versus 79.0 (8.2)%, P < 0.05, respectively]. Therefore, age was associated with an increase in the relative magnitude of the "moderate", sub-thetaL exercise-intensity domain (+30.4%), mainly at the expense of the "very-heavy", supra-thetaF domain (-56%). Our results demonstrate that age and sedentarity are associated with: (1) marked reductions in both the aerobic (thetaF) and anaerobic (W') determinants of the W/t relationship, and (2) changes in either the absolute or relative magnitudes of the exercise-intensity domains. These findings are consistent with the notion that endurance-related parameters are less diminished with ageing than the maximal capacity, thereby mitigating the deleterious effects of senescence in the functional capacity.

Adult↗

PubMed2000

Effects of two types of training on pulmonary and cardiac responses to moderate exercise in patients with COPD.

The effects of two 8-week programmes of exercise reconditioning on the time constants (tau) of the pulmonary gas exchange, ventilatory and heart rate responses to moderate intensity exercise in patients with chronic obstructive pulmonary disease (COPD) were studied. Thirty-five subjects (mean+/-SD 64+/-5 yrs; forced expiratory volume in one second (FEV1) 1.09+/-0.17 L; 41+/-6.2% predicted) were randomly assigned either to supervised (s) training on a treadmill, 4 days x week(-1) (group S; n=21) or self-monitored (SM) walking 3 or 4 km in 1 h 4 days x week(-l) (group SM; n=20). The different levels of supervision resulted in a different estimated intensity of training (35+/-10 W in the SM group and 70+/-22 W in the S group). The kinetics were evaluated with a constant-load exercise test on a cycle-ergometer at a work rate corresponding to 80% the highest oxygen consumption (V'O2) that can be achieved without blood lactic acidosis (V'O2,LAT) or 50% of V'O2,max, if maximum oxygen consumption V'O2,LAT was not found. Mean endurance time at a work rate equivalent to 70% of the pretraining V'O2,max increased by 493+/-281 s in the S group and 254+/-283 s in the SM group (p<0.001). Mean tauV'O2 decreased from 83+/-17 s to 67+/-11 s (p<0.0001) in the S group and from 84+/-12 to 79+/-16 (p=0.04) in the SM group. Mean tau for carbon dioxide output minute ventilation and heart rate were also speeded after training, again more markedly in the S group. In the S group there was a significant correlation between the decrease in tauV'O2 and the increase in endurance time (r=-0.56, SEM=0.21). It is concluded that training speeds the kinetic response of oxygen consumption, carbon dioxide production, minute ventilation and heart rate to moderate exercise and that the effect is greater after supervised, more intense training.

Aged↗

PubMed2000

Peak and kinetic cardiorespiratory responses during arm and leg exercise in patients with spinal cord injury.

STUDY DESIGN: A paired comparison of the peak and submaximal responses of oxygen uptake and heart rate in patients with spinal cord injury (SCI) performing voluntary arm cycle exercise and functional electrical stimulation (FES) leg cycling exercise. OBJECTIVES: To test if the blunted heart rate response and slower rate of adjustment of oxygen uptake seen in patients with SCI performing FES leg cycle exercise are also characteristic of arm exercise in these patients. METHODS: Eight paraplegics performed incremental and constant work rate (CWR) exercise with the legs and arms. Mean response times (MRT) for Vo2 during exercise (on) and in recovery (off) were calculated from the breath-by-breath Vo2 profile. RESULTS: Peak heart rate was higher during incremental arm exercise, and uncorrelated with that observed during incremental FES leg cycling. For the same increase in Vo2, constant work rate arm exercise was associated with faster (and normal) Vo2 kinetics, greater increase in heart rate, and lower end-exercise blood lactate, compared to FES leg cycling. CONCLUSIONS: The consistently higher peak heart rate and Vo2, and faster Vo2 kinetics, for voluntary arm compared to FES leg cycle exercise suggest no intrinsic dysfunction of heart rate control in these paraplegics. Rather, these data suggest that during FES leg cycling the changes seen are due to some characteristic specific to the injury, such as reduced muscle mass and/or deconditioning of the remaining muscle. SPONSORSHIP: This research was supported by The Department of Veterans Affairs, Rehabilitation Research and Development Project #B603-RA. Spinal Cord (2000) 38, 340 - 345.

Adult↗

PubMed2000

Oxygen cost for cycling as related to leg mass in males and females, aged 20 to 80.

In order to evaluate the determinants of the metabolic cost for cycle ergometry, we analyzed the relationship between VO2 and leg mass (LM) and total body mass (TBM) in 71 randomly-selected sedentary subjects (34 men), aged 20 to 80. Participants performed constant work rate (WR) tests at 0, 25, and 50 W (at 60 rpm) for 6 minutes in a randomized sequence: gross VO2, gross efficiency, and work efficiency were related to TBM and LM as assessed by dual energy x-ray absorptiometry. We found that gross VO2 and gross efficiency were more strongly related to LM than TBM but work efficiency values were independent of both (P>0.05). Significantly higher values of VO2TBM were found in subjects with large LM/TBM ratios and vice-versa; VO2/LM, however, did not change with anthropometric characteristics. Gross VO2 (mL/min) was predicted by a LM-based equation (10.6 [WR, W] + 16.8 [LM, kg] +75) with a mean error below 5%: this equation predicted the cost more accurately than previous TBM-based formulations (P<0.01). We conclude that leg mass actually provides the preferred frame of reference for predicting the oxygen cost for cycle ergometry at 60 rpm in sedentary subjects, independent of age or gender.

Absorptiometry, Photon↗

PubMed2000

The effect of glycogen depletion on the curvature constant parameter of the power-duration curve for cycle ergometry.

For high-intensity cycle ergometer exercise, the relation between power (P) and its tolerable duration (t) has been well characterized by the hyperbolic relationship: (P-thetaF) t = W', or P = W' (1/t)+thetaF, where thetaF may be termed the 'fatigue threshold'. The curvature constant (W') reflects a constant amount of work which is postulated to be equivalent to a finite energy store that relates to the oxygen-deficit: phosphagen pool, anaerobic glycolysis and oxygen stores. Compared to thetaF, the physiological nature of W' has received little consideration. The purpose of this study was therefore to establish the parameters of the power-duration curve (thetaF and W') for subjects in normal glycogen (NG) and glycogen depleted (GD) states. Seven healthy male subjects (aged 22 to 41 years) each performed four high-intensity square-wave exercise bouts on an electrically braked cycle ergometer under two different muscular glycogen content conditions, i.e. NG and GD states. Subjects performed the following exercise on the evening before the trial day to induce the GD state. Initially, they performed a 75-min cycling exercise at 60% of VO2max. After a 5-min rest period, they subsequently repeated a 1-min cycling bout at 115% of VO2max (separated by 1-min rest periods) until the subject could no longer maintain the prescribed pedal rate for the full minute. Subjects then reported to the laboratory after an overnight fast and performed a single high-intensity exercise bout. The GD procedure was repeated four times at 1-week intervals. In the GD state, the respiratory exchange ratio (RER) (VO2/VCO2) value during a recumbent control period prior to the trial was significantly lower than that in the NG state [GD: 0.84+/-0.02, NG: 0.94+/-0.04, mean +/- SD]. There was no significant difference for thetaF between GD and NG state [NG: 197.1+/-31.9 W, GD: 190.6+/-28.2 W]. W' in contrast was significantly reduced by the GD procedure [NG: 12.83+/-2.21 kJ, GD: 10.33+/-2.41 kJ]. The present results indicate that the muscular glycogen store seems to be an important determinant of the curvature constant (W') of the power-duration curve for cycle ergometry.

Adult↗

PubMed2000

Determinants of the exercise endurance capacity in patients with chronic obstructive pulmonary disease. The power-duration relationship.

To characterize the determinants of the power-duration (W-t) relationship in patients with chronic obstructive pulmonary disease (COPD), we evaluated 8 nonhypoxemic patients (FEV(1) = 1.27 +/- 0.26 L) and 10 healthy controls. After an initial maximum-incremental exercise test on cycle ergometer (peak), the subjects underwent four high-intensity constant-load tests to the limit of tolerance (t), each on different days. The W-t relationship was found to be hyperbolic in both groups. Absolute values of both the critical power asymptote (theta(F)) and the curvature constant (W') were lower in patients than in control subjects. However, when expressed as percentage of peak work rate theta(F) was significantly higher in patients compared with control subjects (81.8 +/- 3.3% versus 67.5 +/- 3.7%, respectively, p < 0.01). There were severe reductions in t in the patients that were consistently associated with higher breathlessness scores and V E/MVV ratios. Interestingly, all patients were able to sustain exercise at theta(F) for 20 min despite near-maximum physiological and subjective stresses. We conclude that the reductions of both parameters of the hyperbolic W-t relationship (theta(F) and W') in patients with COPD were due to the ventilatory constraints and their sensory consequences. Importantly, theta(F) separated a "sustainable" from a "nonsustainable" exercise-intensity domain: this parameter consistently occurred closer to peak work rate in patients than the healthy control subjects.

Aged↗

PubMed2000

The off-transient pulmonary oxygen uptake (VO(2)) kinetics following attainment of a particular VO(2) during heavy-intensity exercise in humans.

The oxygen uptake response to moderate-intensity exercise (i.e. < anaerobic threshold (an)) has been characterised with a gain (i.e. response amplitude per increment of work rate) and time constant that do not vary appreciably at different work rates or between the on- and off-transients. Above an, the response becomes more complex with an early component that typically projects to a value that has a gain similar to that of the < an response, but which is supplemented by the addition of a delayed slow kinetic component. We therefore established a constant target VO2 (VO21) for each subject such that with different imposed work rates the contribution to VO21 from the slow phase varied over a wide range. Work rates were chosen so that VO21 was attained at 2-24 min. Five subjects (aged 21-58 years) cycled at four to five different work rates. VO2 was measured breath-by-breath, at VO21 the work rate was abruptly reduced and the subject recovered by cycling unloaded for 15 min. Unlike the on-transient, for which the slow component shows a long delay, the off-transient was best fitted as two simultaneous exponential components. The slower off-transient component had a small amplitude and long time constant, but did not differ significantly among the various tests. The off-transient kinetics for VO2 therefore was independent of the magnitude of the contribution to the slow phase from the on-transient kinetics.

Adult↗

PubMed1999

Inferences from pulmonary O2 uptake with respect to intramuscular [phosphocreatine] kinetics during moderate exercise in humans.

1. In the non-steady state of moderate intensity exercise, pulmonary O2 uptake (Vp,O2) is temporally dissociated from muscle O2 consumption (Vm,O2) due to the influence of the intervening venous blood volume and the contribution of body O2 stores to ATP synthesis. A monoexponential model of Vp,O2 without a delay term, therefore, implies an obligatory slowing of Vp,O2 kinetics in comparison to Vm, O2. 2. During moderate exercise, an association of Vm,O2 and [phosphocreatine] ([PCr]) kinetics is a necessary consequence of the control of muscular oxidative phosphorylation mediated by some function of [PCr]. It has also been suggested that the kinetics of Vp,O2 will be expressed with a time constant within 10 % of that of Vm,O2. 3. Vp,O2 and intramuscular [PCr] kinetics were investigated simultaneously during moderate exercise of a large muscle mass in a whole-body NMR spectrometer. Six healthy males performed prone constant-load quadriceps exercise. A transmit-receive coil under the right quadriceps allowed determination of intramuscular [PCr]; Vp,O2 was measured breath-by-breath, in concert with [PCr], using a turbine and a mass spectrometer system. 4. Intramuscular [PCr] decreased monoexponentially with no delay in response to exercise. The mean of the time constants (tauPCr) was 35 s (range, 20-64 s) for the six subjects. 5. Two temporal phases were evident in the Vp, O2 response. When the entire Vp,O2 response was modelled to be exponential with no delay, its time constant (tau'Vp,O2) was longer in all subjects (group mean = 62 s; range, 52-92 s) than that of [PCr], reflecting the energy contribution of the O2 stores. 6. Restricting the Vp,O2 model fit to phase II resulted in matching kinetics for Vp,O2 (group mean tauVp,O2 = 36 s; range, 20-68 s) and [PCr], for all subjects. 7. We conclude that during moderate intensity exercise the phase II tauVp,O2 provides a good estimate of tauPCr and by implication that of Vm,O2 (tauVm,O2).

Adenosine Triphosphate↗

PubMed1999

Maximal aerobic power and leg muscle mass and strength related to age in non-athlethic males and females.

To investigate the relationships between the age-associated decline in peak oxygen uptake (peak VO2), leg muscle mass (LMM) and leg strength (LS) under the modulating effect of gender and level of physical activity (LPA, as assessed by questionnaire), we evaluated 71 sedentary subjects [males(M):females(F), 34:37], aged 20-80 years. Peak VO2 at maximum cycle ergometry was related to LMM (dual energy X-ray absorptiometry) and LS (isokinetic dynamometry) using both standard (y x x(-1)) and power function ratios (allometry). Absolute values of all variables were higher in males and declined with age (P < 0.01). Differences between the genders disappeared after peak VO2 x LS(-1.46(M)or -1.62(F)) adjustment but remained significant between peak VO2 LMM-(-0.51 (M)or -0.45(F)) and LS LMM- (-091(M) or -1.10(F)) corrected values. Allometric correction of peak VO2 and LS by LMM slowed their age-related declines; the flattening effect however, was more evident in the females. Interestingly, while no age-related decrement in peak VO2 LS(-1) was found, power function ratio values also declined with age, and at a slower rate in females. These findings are consistent with those obtained following a multiple regression analysis using LPA as an independent covariate (P < 0.01). We conclude that using adequate scaling methods and controlling by LPA: (1) no gender differences are observed in peak VO2 adjusted for LS, (2) loss of LS and LMM are important determinants of the age-associated reduction in physical fitness in both genders but (3) age per se has an LS- and LMM-independent influence on the functional decline, although this intrinsic effect of senescence is less pronounced in females.

Adult↗

PubMed1999

Effect of altered body CO2 stores on pulmonary gas exchange dynamics during incremental exercise in humans.

The lactate threshold is a widely used and, at times, controversial construct in exercise physiology and pathophysiology. Its non-invasive estimation during incremental exercise depends upon CO2 output increasing as a function of O2 uptake, i.e. 'V-slope', as a result of bicarbonate buffering during the lactic acidosis. However, we hypothesised that the V-slope deflection could also occur as a consequence of metabolic CO2 being diverted proportionally more into the CO2 stores in the early phase of exercise. Eight healthy males performed two incremental exercise tests on a cycle ergometer, with and without controlled prior hyperventilation; the hyperventilation caused end-tidal PCO2 to decline by 10 mmHg, with the clearance of a CO2 volume averaging 2547 ml. This corresponded to an 'effective' CO2 capacitance of some 3.12 ml mmHg-1 kg-1. Gas exchange was determined breath-by-breath, and blood was sampled from the dorsum of the heated hand. Our results demonstrate that the early dynamics of CO2 wash-in to the previously depleted body stores can result in a 'pseudo-threshold', i.e. significantly before the onset of the actual lactic acidosis. Precautions should therefore be taken to avoid hyperventilation prior to non-invasive estimation of the lactate threshold.

Adolescent↗

PubMed1999

Simultaneous determination of muscle 31P and O2 uptake kinetics during whole body NMR spectroscopy.

Our understanding of O2 uptake (VO2) control mechanisms during exercise may be improved by the simultaneous determination of the kinetics of intramuscular high-energy phosphate turnover and pulmonary VO2. We therefore developed a technique for remote gas-exchange analysis while subjects exercised in a whole body 1.5-T NMR system. Knee-extension exercise was performed against restraining rubber bands in the prone position. Free induction decays were acquired every 1,875 ms by using a transmit-receive coil, which was placed under the quadriceps. This allowed 31P spectra of intramuscular ATP, Pi, and creatine phosphate dynamics to be determined every 15 s. Airflow was measured with a custom-designed turbine and a 45-ft.-long cable to reach the volume-measuring module. This was located in an adjacent radio-frequency-shielded room, as was the respiratory mass spectrometer, which also used a 45-ft.-long sampling line. The respired gas profiles were not discernibly different from those that used the standard inlet; the increase in the delay was readily incorporated into the breathby-breath algorithm, allowing the VO2 kinetics to be determined in concert with those of intramuscular phosphate metabolism.

Adenosine Triphosphate↗

PubMed1999

A metabolic limit on the ability to make up for lost time in endurance events.

It has been repeatedly demonstrated that the tolerable duration (t) of high-intensity cycling is well characterized as a hyperbolic function of power (P) with an asymptote that has been termed the "fatigue threshold" and with a curvature constant. This hyperbolic P-t relationship has also been confirmed in running and swimming, when speed (V) is used instead of P; that is, (V - V(F)). t = D', where V(F) is the V at the fatigue threshold, and D' is the curvature constant. Therefore, we theoretically analyzed herein the consequences of an athlete performing the initial part of an endurance event at a V different from the constant rate that would allow the performance time to be determined by the hyperbolic V-t relationship. We considered not only the V-t constraints that limit the athlete's ability to make up the time lost by too slow an early pace but also the consequences of a more rapid early pace. Our analysis demonstrates that both the V(F) and D' parameters of the athlete's V-t curve play an important role in the pace allocation strategy of the athlete. That is, 1) when the running V during any part of the whole running distance is below V(F), the athlete can never attain the goal of achieving the time equivalent to that of running the entire race at constant maximal V (i.e., that determined by one's own best V-t curve); and 2) the "endurance parameter ratio" D'/V(F) is especially important in determining the flexibility of the race pace that the athlete was able to choose intentionally.

Bicycling↗

PubMed1999

Prediction of metabolic and cardiopulmonary responses to maximum cycle ergometry: a randomised study.

All of the most widely-cited studies for the prediction of maximum exercise responses have utilized either volunteers or referred subjects. Therefore, selection bias, with overestimation of the reference values, is a likely consequence. In order to establish a set of predictive equations for the gas exchange, ventilatory and cardiovascular responses to maximum ramp-incremental cycle ergometry, this study prospectively evaluated 120 sedentary individuals (60 males, 60 females, aged 20-80), randomly-selected from >8,000 subjects. Regular physical activity pattern by questionnaire, body composition by anthropometry and dual energy X-ray absorptiometry (n = 75) and knee strength by isokinetic dynamometry were also assessed. Previously reported equations typically overestimated the subjects' peak oxygen uptake (p<0.05). Prediction linear equations for the main variables of clinical interest were established by backward stepwise regression analysis including: sex, age, knee extensor peak torque, bone-free lean leg mass, total and lean body mass, height, and physical activity scores. Reference intervals (95% confidence limits) were calculated: some of these values differed markedly from those formerly recommended. The results therefore might provide a more appropriate frame of reference for interpretation of the responses to symptom-limited ramp incremental cycle ergometry in sedentary subjects; i.e. those usually referred for clinical cardiopulmonary exercise tests.

Adult↗

PubMed1998

Improvement in exercise tolerance in isovaleric acidaemia with L-carnitine therapy.

The effect of 4 weeks' treatment with oral-L-carnitine (100 mg/kg per day) on carnitine status and metabolic parameters during an incremental ramp exercise test in a 12-year-old girl with isovaleric acidaemia was examined to determine its possible therapeutic role. The maximum work rate achieved increased from 110 to 120 watts; oxygen consumption at anaerobic threshold from 600 to 800 L/min; peak oxygen consumption from 1270 to 1450 L/min; and oxygen pulse, a measure of cardiac output, from 7.0 to 8.1 L/beat. These changes were associated with increases in plasma and urinary free and acyl carnitine concentrations but no change in physical activity. This observed effect of L-carnitine on exercise performance may be on cardiac or skeletal muscle function or both. We conclude that, in this single patient with isovaleric acid-aemia, L-carnitine supplementation had objective benefits and further studies on more patients are warranted.

Amino Acid Metabolism, Inborn Errors↗