Intensity-dependent tolerance to exercise after attaining V̇o2 max in humans

2003 ◽  
Vol 95 (2) ◽  
pp. 483-490 ◽  
Author(s):  
Edward M. Coats ◽  
Harry B. Rossiter ◽  
James R. Day ◽  
Akira Miura ◽  
Yoshiyuki Fukuba ◽  
...  
Keyword(s):  
High Intensity ◽  
Critical Power ◽  
Load Cycle ◽  
Constant Load ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Hyperbolic Function ◽  
Exercise Tests ◽  
Ergometer Exercise

The tolerable duration of high-intensity, constant-load cycle ergometry is a hyperbolic function of power, with an asymptote termed critical power (CP) and a curvature constant (W′) with units of work. It has been suggested that continued exercise after exhaustion may only be performed below CP, where predominantly aerobic energy transfer can occur and W′ can be partially replenished. To test this hypothesis, six volunteers each performed cycle-ergometer exercise with breath-by-breath determination of ventilatory and pulmonary gas exchange variables. Initially, four exercise tests to exhaustion were made: 1) a ramp-incremental and 2) three high-intensity constant-load bouts at different work rates, to estimate lactate (θ̂L) and CP thresholds, W′, and maximum oxygen uptake (V̇o2 max). Subsequently, subjects cycled to the limit of tolerance (for ∼360 s) on three occasions, each followed by a work rate reduction to 1) 110% CP, 2) 90% CP, and 3) 80% θ̂L for a 20-min target. W′ averaged 20.9 ± 2.35 kJ or 246 ± 30 J/kg. After initial fatigue, 110% CP was tolerated for only 30 ± 12 s. Each subject completed 20 min at 80% θ̂L, but only two sustained 20 min at 90% CP; the remaining four subjects fatigued at 577 ± 306 s, with oxygen consumption at 89 ± 8% V̇o2 max. The results support the suggestion that replenishing W′ after fatigue necessitates a sub-CP work rate. The variation in subjects' responses during 90% CP was unexpected but consistent with mechanisms such as reduced CP consequent to prior high-intensity exercise, variation in lactate handling, and/or regional depletion of energy substrates, e.g., muscle glycogen.

Lactic acidosis as a facilitator of oxyhemoglobin dissociation during exercise

1994 ◽  
Vol 76 (4) ◽  
pp. 1462-1467 ◽  
Author(s):  
W. Stringer ◽  
K. Wasserman ◽  
R. Casaburi ◽  
J. Porszasz ◽  
K. Maehara ◽  
...  
Keyword(s):  
Lactic Acidosis ◽  
Femoral Vein ◽  
Lactate Concentration ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Exercise Tests ◽  
Ergometer Exercise ◽  
Constant Work Rate ◽  
Slow Rise ◽  
Lactic Acidosis Threshold

The slow rise in O2 uptake (VO2), which has been shown to be linearly correlated with the increase in lactate concentration during heavy constant work rate exercise, led us to investigate the role of H+ from lactic acid in facilitating oxyhemoglobin (O2Hb) dissociation. We measured femoral venous PO2, O2Hb saturation, pH, PCO2, lactate, and standard HCO3- during increasing work rate and two constant work rate cycle ergometer exercise tests [below and above the lactic acidosis threshold (LAT)] in two groups of five healthy subjects. Mean end-exercise femoral vein blood and VO2 values for the below- and above-LAT square waves and the increasing work rate protocol were, respectively, PO2 of 19.8 +/- 2.1 (SD), 18.8 +/- 4.7, and 19.8 +/- 3.3 Torr; O2 saturation of 22.5 +/- 4.1, 13.8 +/- 4.2, and 18.5 +/- 6.3%; pH of 7.26 +/- 0.01, 7.02 +/- 0.11, and 7.09 +/- 0.07; lactate of 1.9 +/- 0.9, 11.0 +/- 3.8, and 8.3 +/- 2.9 mmol/l; and VO2 of 1.77 +/- 0.24, 3.36 +/- 0.4, and 3.91 +/- 0.68 l/min. End-exercise femoral vein PO2 did not differ statistically for the three protocols, whereas O2Hb saturation continued to decrease for work rates above LAT. We conclude that decreasing capillary PO2 accounted for most of the O2Hb dissociation during below-LAT exercise and that acidification of muscle capillary blood due to lactic acidosis accounted for virtually all of the O2Hb dissociation above LAT.

O2 uptake kinetics after acetazolamide administration during moderate- and heavy-intensity exercise

1998 ◽  
Vol 85 (4) ◽  
pp. 1384-1393 ◽  
Author(s):  
Barry W. Scheuermann ◽  
John M. Kowalchuk ◽  
Donald H. Paterson ◽  
David A. Cunningham
Keyword(s):  
Energy Demand ◽  
Ventilatory Threshold ◽  
Venous Blood ◽  
Lactate Concentration ◽  
Exponential Model ◽  
Constant Load ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Ergometer Exercise ◽  
Single Response

Inhibition of carbonic anhydrase (CA) is associated with a lower plasma lactate concentration ([La−]pl) during fatiguing exercise. We hypothesized that a lower [La−]plmay be associated with faster O2uptake (V˙o 2) kinetics during constant-load exercise. Seven men performed cycle ergometer exercise during control (Con) and acute CA inhibition with acetazolamide (Acz, 10 mg/kg body wt iv). On 6 separate days, each subject performed 6-min step transitions in work rate from 0 to 100 W (below ventilatory threshold, <V˙eT) or to a V˙o 2 corresponding to ∼50% of the difference between the work rate atV˙eT and peakV˙o 2(>V˙eT). Gas exchange was measured breath by breath. Trials were interpolated at 1-s intervals and ensemble averaged to yield a single response. The mean response time (MRT, i.e., time to 63% of total exponential increase) for on- and off-transients was determined using a two- (<V˙eT) or a three-component exponential model (>V˙eT). Arterialized venous blood was sampled from a dorsal hand vein and analyzed for [La−]pl. MRT was similar during Con (31.2 ± 2.6 and 32.7 ± 1.2 s for on and off, respectively) and Acz (30.9 ± 3.0 and 31.4 ± 1.5 s for on and off, respectively) for work rates <V˙eT. At work rates >V˙eT, MRT was similar between Con (69.1 ± 6.1 and 50.4 ± 3.5 s for on and off, respectively) and Acz (69.7 ± 5.9 and 53.8 ± 3.8 s for on and off, respectively). On- and off-MRTs were slower for >V˙eT than for <V˙eT exercise. [La−]plincreased above 0-W cycling values during <V˙eT and >V˙eT exercise but was lower at the end of the transition during Acz (1.4 ± 0.2 and 7.1 ± 0.5 mmol/l for <V˙eT and >V˙eT, respectively) than during Con (2.0 ± 0.2 and 9.8 ± 0.9 mmol/l for <V˙eT and >V˙eT, respectively). CA inhibition does not affect O2 utilization at the onset of <V˙eT or >V˙eT exercise, suggesting that the contribution of oxidative phosphorylation to the energy demand is not affected by acute CA inhibition with Acz.

Self-pacing increases critical power and improves performance during severe-intensity exercise

2015 ◽  
Vol 40 (7) ◽  
pp. 662-670 ◽  
Author(s):  
Matthew I. Black ◽  
Andrew M. Jones ◽  
Stephen J. Bailey ◽  
Anni Vanhatalo
Keyword(s):  
Critical Power ◽  
Cycle Ergometer ◽  
Exercise Tests ◽  
Mean Response Time ◽  
Pacing Strategy ◽  
Severe Intensity ◽  
Trial Protocols ◽  
Constant Work Rate ◽  
Duration Relationship

The parameters of the power-duration relationship for severe-intensity exercise (i.e., the critical power (CP) and the curvature constant (W′)) are related to the kinetics of pulmonary O2 uptake, which may be altered by pacing strategy. We tested the hypothesis that the CP would be higher when derived from a series of self-paced time-trials (TT) than when derived from the conventional series of constant work-rate (CWR) exercise tests. Ten male subjects (age, 21.5 ± 1.9 years; mass, 75.2 ± 11.5 kg) completed 3–4 CWR and 3–4 TT prediction trial protocols on a cycle ergometer for the determination of the CP and W′. The CP derived from the TT protocol (265 ± 44 W) was greater (P < 0.05) than the CP derived from the CWR protocol (250 ± 47 W), while the W′ was not different between protocols (TT: 18.1 ± 5.7 kJ, CWR: 20.6 ± 7.4 kJ, P > 0.05). The mean response time of pulmonary O2 uptake was shorter during the TTs than the CWR trials (TT: 34 ± 16, CWR: 39 ± 19 s, P < 0.05). The CP was correlated with the total O2 consumed in the first 60 s across both protocols (r = 0.88, P < 0.05, n = 20). These results suggest that in comparison with the conventional CWR exercise protocol, a self-selected pacing strategy enhances CP and improves severe-intensity exercise performance. The greater CP during TT compared with CWR exercise has important implications for performance prediction, suggesting that TT completion times may be overestimated by CP and W′ parameters derived from CWR protocols.

Determination of Accumulated O2 Deficit in Exhaustive Short-Duration Exercise

1996 ◽  
Vol 21 (1) ◽  
pp. 63-74 ◽  
Author(s):  
David W. Hill
Keyword(s):  
High Intensity ◽  
Anaerobic Capacity ◽  
Initial Step ◽  
Cycle Ergometer ◽  
Submaximal Exercise ◽  
Time To Exhaustion ◽  
Exercise Tests ◽  
Ergometer Exercise ◽  
Power Outputs ◽  
Two Parameters

Usually, an initial step in determining accumulated O2 deficit is the estimation of the O2 demand of high intensity exercise by extrapolation from [Formula: see text] measured during steady-state submaximal exercise. It was hypothesized that O2 deficit could be determined without the need to estimate O2 demand by extrapolation. Ten women performed all-out cycle ergometer exercise tests at each of four power outputs selected so that exhaustion would occur after 90 to 600 s. Power output (W), accumulated VO2 (ml), and time to exhaustion (s) were measured in each test and then fit to the following equation: O2 deficit (ml) = O2 demand (ml∙min−1∙W−1)∙time (min)∙power (W) - accumulated VO2 (ml). This procedure generated values for two parameters (O2 demand and O2 deficit) for each subject. The O2 deficit was also calculated for each individual using conventional methods. The values for O2 deficit obtained using the two methods were correlated (r =.96, p <.01), and the value obtained using the experimental method tended to be larger, t(9) = 2.15, p =.06. It is concluded that O2 demand and O2 deficit can be determined from the results of several high-intensity tests without the need to extrapolate from submaximal exercise to estimate the O2 demands of supramaximal exercise. Key words: anaerobic, anaerobic capacity

scholarly journals Oxygen uptake dynamics during high-intensity exercise in children and adults

1991 ◽  
Vol 70 (2) ◽  
pp. 841-848 ◽  
Author(s):  
Y. Armon ◽  
D. M. Cooper ◽  
R. Flores ◽  
S. Zanconato ◽  
T. J. Barstow
Keyword(s):  
High Intensity ◽  
Cycle Ergometer ◽  
Work Rate ◽  
High Intensity Exercise ◽  
O2 Uptake ◽  
Low Intensity ◽  
Ergometer Exercise ◽  
Constant Work Rate ◽  
The Difference ◽  
Low Intensity Exercise

We hypothesized that the O2 uptake (Vo2) response to high-intensity exercise would be different in children than in adults. To test this hypothesis, 22 children (6-12 yr old) and 7 adults (27-40 yr old) performed 6 min of constant-work-rate cycle-ergometer exercise. Sixteen children performed a single test above their anaerobic threshold (AT). In a separate protocol, six children and all adults exercised at low and high intensity. Low-intensity exercise corresponded to the work rate at 80% of each subject's AT. High-intensity exercise (above the AT) was determined first by calculating the difference in work rate between the AT and the maximal Vo2 (delta). Twenty-five, 50, and 75% of this difference were added to the work rate at the subject's AT, and these work rates were referred to as 25% delta, 50% delta, and 75% delta. For exercise at 50% delta and 75% delta, Vo2 increased throughout exercise (O2 drift, linear regression slope of Vo2 as a function of time from 3 to 6 min) in all the adults, and the magnitude of the drift was correlated with increasing work rates in the above-AT range (r = 0.91, P less than 0.0001). In contrast, no O2 drift was observed in over half of the children during above-AT exercise. The O2 drifts were much higher in adults (1.76 +/- 0.63 ml O2.kg-1.min-2 at 75% delta) than in children (0.20 +/- 0.42, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Mediation of reduced ventilatory response to exercise after endurance training

1987 ◽  
Vol 63 (4) ◽  
pp. 1533-1538 ◽  
Author(s):  
R. Casaburi ◽  
T. W. Storer ◽  
K. Wasserman
Keyword(s):  
Endurance Training ◽  
Venous Blood ◽  
Normal Subjects ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Exercise Tests ◽  
Average Decrease ◽  
Cycle Ergometer Exercise ◽  
Ergometer Exercise ◽  
The Difference

To investigate the mechanism by which ventilatory (VE) demand is modulated by endurance training, 10 normal subjects performed cycle ergometer exercise of 15 min duration at each of four constant work rates. These work rates represented 90% of the anaerobic threshold (AT) work rate and 25, 50, and 75% of the difference between maximum O2 consumption and AT work rates for that subject (as determined from previous incremental exercise tests). Subjects then underwent 8 wk of strenuous cycle ergometer exercise for 45 min/day. They then repeated the four constant work rate tests at work rates identical to those used before training. During tests before and after training, VE and gas exchange were measured breath by breath and rectal temperature (Tre) was measured continuously. A venous blood sample was drawn at the end of each test and assayed for lactate (La), epinephrine (EPI), and norepinephrine (NE). We found that the VE for below AT work was reduced minimally by training (averaging 3 l/min). For the above AT tests, however, training reduced VE markedly, by an average of 7, 23, and 37 l/min for progressively higher work rates. End-exercise La, NE, EPI, and Tre were all lower for identical work rates after training. Importantly, the magnitude of the reduction in VE was well correlated with the reduction in end-exercise La (r = 0.69) with an average decrease of 5.8 l/min of VE per milliequivalent per liter decrease in La. Correlations of VE with NE, EPI, and Tre were much less strong (r = 0.49, 0.43, and 0.15, respectively).

scholarly journals Technical feasibility of constant-load and high-intensity interval training for cardiopulmonary conditioning using a re-engineered dynamic leg press

2019 ◽  
Vol 1 (1) ◽  
Author(s):  
Farouk Chrif ◽  
Tobias Nef ◽  
Kenneth J Hunt
Keyword(s):  
High Intensity ◽  
Ventilatory Threshold ◽  
Interval Training ◽  
Constant Load ◽  
Work Rate ◽  
High Intensity Interval Training ◽  
Leg Press ◽  
Cardiopulmonary Exercise ◽  
The Difference ◽  
High Intensity Interval

Abstract Background Leg-press devices are one of the most widely used training tools for musculoskeletal strengthening of the lower-limbs, and have demonstrated important cardiopulmonary benefits for healthy and patient populations. Further engineering development was done on a dynamic leg-press for work-rate estimation by integrating force and motion sensors, power calculation and a visual feedback system for volitional work-rate control. This study aimed to assess the feasibility of the enhanced dynamic leg press for cardiopulmonary exercise training in constant-load training and high-intensity interval training. Five healthy participants aged 31.0±3.9 years (mean ± standard deviation) performed two cardiopulmonary training sessions: constant-load training and high-intensity interval training. Participants carried out the training sessions at a work rate that corresponds to their first ventilatory threshold for constant-load training, and their second ventilatory threshold for high-intensity interval training. Results All participants tolerated both training protocols, and could complete the training sessions with no complications. Substantial cardiopulmonary responses were observed. The difference between mean oxygen uptake and target oxygen uptake was 0.07±0.34 L/min (103 ±17%) during constant-load training, and 0.35±0.66 L/min (113 ±27%) during high-intensity interval training. The difference between mean heart rate and target heart rate was −7±19 bpm (94 ±15%) during constant-load training, and 4.2±16 bpm (103 ±12%) during high-intensity interval training. Conclusions The enhanced dynamic leg press was found to be feasible for cardiopulmonary exercise training, and for exercise prescription for different training programmes based on the ventilatory thresholds.

Validity of pulse oximetry during exercise in elite endurance athletes

1992 ◽  
Vol 72 (2) ◽  
pp. 455-458 ◽  
Author(s):  
D. Martin ◽  
S. Powers ◽  
M. Cicale ◽  
N. Collop ◽  
D. Huang ◽  
...  
Keyword(s):  
Pulse Oximeter ◽  
High Intensity ◽  
Aerobic Power ◽  
Constant Load ◽  
Cycle Exercise ◽  
Exercise Tests ◽  
Arterial Blood ◽  
Highly Correlated ◽  
Pulse Oximeters ◽  
Finger Probe

Eleven highly trained male cyclists [maximal aerobic power (VO2max) = 70.6 +/- 4.2 ml.kg-1.min-1] performed both high intensity constant load (90–95% VO2max) and incremental cycle exercise tests with arterial blood sampling to evaluate the accuracy of pulse oximeter estimates (%SpO2) of arterial oxyhemoglobin fraction of total hemoglobin (%HbO2). Three subjects also performed an incremental exercise test in hypoxic conditions (inspired partial pressure of O2 = 89, 93, or 100 Torr). Arterial %HbO2 was determined via CO-oximetry and ranged from 72 to 99%. Three Ohmeda 3740 pulse oximeters were used to estimate %HbO2, one on each ear lobe and a finger probe. The finger probe tended to provide the best estimate of %HbO2 during exercise: the mean %SpO2 - %HbO2 difference for 232 exercise observations was 0.52 +/- 1.36% (SD). Finger probe %SpO2 and %HbO2 were highly correlated [r = 0.98, standard error of the estimate (SEE) = 1.32%, P less than 0.0001]. The accuracy of pulse oximeters has been questioned during high-intensity exercise. When aerobic power was greater than 81% of VO2max (n = 75), the finger probe's mean error was -0.01 +/- 1.40%. Finger probe %SpO2 and %HbO2 were highly correlated (r = 0.97, SEE = 1.32%, P less than 0.0001). These results indicate that this pulse oximeter is a valid predictor of %HbO2 in elite athletes during cycle exercise.

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