VO2 Response Research Articles

Maximal Oxygen Consumption and Blood Lactate Levels as Measures of Exercise Intensity in Aging Rats

To help quantify and determine appropriate exercise intensities for endurance training of aging animals, we compared measures of oxygen consumption (VO2) and blood lactate accumulation after 6 months of exercise training in aging rats. Blood lactate measures (using a portable lactate analyzer) were compared to VO2 measures in order to validate blood lactate as an appropriate and cost effective method of determining exercise intensity in aging animals. 122 adult (24 month) male Fischer 344 X Brown Norway (FBN) rats were divided into 3 groups based on exercise training intensity; high (H), moderate (M), and sedentary (S). M and H intensity animals trained at 13 m/min for 30 min/day, with the H group at 5% incline and the M group at 0%. VO2 and blood lactate responses to a maximal exercise test were measured at age 24 months and then after 6 months of exercise training. When compared to values at 24 months, VO2 max increased by 29.5%, 23.5%, and decreased by 1.2%, in the H, M, and S group respectively. Similarly lactate threshold increased by 53% in the H group, 34% in the M group, and decreased by 19% in the S group. Thus, with 6 months of endurance training, both VO2max and lactate threshold increased in a training intensity-dependent manner. This suggest that measures of blood lactate may provide an alternative means of assessing exercise intensity and the effects of exercise training in aging animals. Supported by: NIH AG030423

The Effect of Pedaling Cadence on the Kinetics of Oxygen Uptake During Severe Intensity Exercise

During exhaustive severe intensity exercise, the oxygen uptake (VO2) increases exponentially, with a time constant of ∼30 s. After ∼1 to 2 min, a slow component emerges and drives the VO2 to its maximum. Pedaling cadence contributes to the metabolic demand at a given work rate and affects several responses to cycling exercise. PURPOSE: To determine the effect of pedaling cadence on parameters of the two-component VO2 response profile during severe intensity exercise. METHODS: Eight women (mean ± SD: age 22 ± 1 yr, height 161 ± 6 cm, and weight 58.8 ± 2.3 kg) and 10 men (age 23 ± 1 yr, height 180 ± 6 cm, and weight 82.9 ± 4.4 kg) performed exhaustive constant-power cycle ergometer tests using pedaling cadences of 60 rpm, 80 rpm, and 100 rpm. RESULTS: Times to exhaustion were smaller at higher cadences (220 ± 85 < 299 ± 118 < 368 ± 168 s), whereas VO2max values were the same at all cadences (2786 ± 729 = 2768 ± 749 = 2774 ± 732 ml/min). The mean response time of the primary response was faster at higher pedaling cadences (27 ± 5 < 32 ± 5 1890 ± 493 = 1899 ± 515 ml/min); and the time delay before the slow component was smaller at higher cadences (85 ± 11 < 105 ± 17 < 118 ± 19 s). CONCLUSION: These results demonstrate that pedaling cadence affects the VO2 response profile. The higher cadences speed the primary or fundamental response and hasten the emergence of the slow component. This may have implications for the sport of cycling and should be considered when evaluating cardio-respiratory and metabolic responses to cycle ergometer exercise.

Nanoscale probing of electronic band gap and topography of VO2 thin film surfaces by scanning tunneling microscopy

The metal-insulator transition (MIT) in vanadium dioxide in the vicinity of room temperature makes it one of the most interesting materials for novel switching device applications. It is therefore essential to have a fundamental understanding of the VO2 surface when it is incorporated into multilayer structures or nanodevices. This study focuses on the surface modification of VO2 in response to the thermal treatment during phase transition. Vacuum annealing at temperatures in the vicinity of the MIT triggers a partial reduction in the surface, and thus initiates a chemical phase transition. Scanning tunneling microscopy and spectroscopy are used to investigate the electronic properties and surface structure of the VO2 thin film on (0001) sapphire substrates. Band gap maps with a high spatial resolution and single point spectroscopy I-V curves are measured as the sample is cycled through the MIT, and thus provide a direct observation of the surface phase transition at the nanoscale. The VO2 surface exhibits a homogeneous insulating behavior with a typical band gap of ∼0.5 eV at room temperature, and the surface becomes more metallic and spatially inhomogeneous in conductivity during MIT, and wide range of surface oxides can be identified. The surface still remains partially metallic after cooling down from a long period anneal, and such irreversible surface electrical change is attributed to the loss of oxygen. The location of metallic islands after thermal cycling is strongly coupled to the topography of the film, and relaxation processes and continued modification of the spatial distribution of the metallic regions are recognized on a longer timescale. The impact of film morphology, strain, surface chemistry, and structural phase transition on the electronic characteristics of VO2 surfaces are discussed.

Oxygen uptake, cardiac output and muscle deoxygenation at the onset of moderate and supramaximal exercise in humans

VO₂, Q and muscular deoxyhaemoglobin (HHb) kinetics were determined in 14 healthy male subjects at the onset of constant-load cycling exercise performed at 80% of the ventilatory threshold (80%(VT)) and at 120% of VO₂max (120%(Wmax)). An innovative approach was applied to calculate the time constant (τ₂) of the primary phase of VO₂ and Q kinetics at 120%(Wmax). Data were linearly interpolated after a semilogarithmic transformation of the difference between required/steady state and measured values. Furthermore, VO₂, Q and HHb data were fitted with traditional exponential models. τ₂ of VO₂ kinetics was longer (62.5 ± 20.9 s) at 120%(Wmax) than at 80%(VT) (27.8 ± 10.4 s). The τ₂ of Q kinetics was unaffected by exercise intensity and, at 120% of VO₂max, it was significantly faster (τ₂ = 35.7 ± 28.4 s) than that of VO₂ response. The time delay of HHb kinetics was shorter (4.3 ± 1.7 s) at 120%(Wmax) than at 80%(VT) (8.5 ± 2.6 s) suggesting a larger mismatch between O₂ uptake and delivery at 120%(Wmax). These results suggest that VO₂ at the onset of exercise is not regulated/limited by muscle's O₂ utilisation and that a slower adaptation of capillary perfusion may cause the deceleration of VO₂ kinetics observed during supramaximal exercise.

The Fractional Utilisation of Maximal Oxygen Consumption during Execution of Ground Strokes and Simulated Match in 14 to 18 years Malaysian Singles Tennis Players

The purpose of the present study was to determine the fractional utilisation of maximum oxygen uptake capacity (% VO2max) during execution of ground strokes and tennis match play. Ten male Malaysian state-level tennis players participated in this study. Age, height, weight and VO2max of the players were 15.3 + 1.2 years, 164.0 + 7.4 cm, 52.3 + 11.5 kg and 51.7 + 7.3 ml·kg - ¹·min - ¹ respectively. This study was conducted in 3 phases: laboratory test (Phase I), on-court test (Phase II) and simulated match (Phase III). Fraction of VO2max during execution of forehand and backhand strokes were 71.6 + 10.9% and 72.3 + 8.8% respectively, whereas tennis match play demanded 69.3 + 9.8% of VO2max. Execution of forehand and backhand strokes led to a blood lactate concentration of approximately 6 mmol·L??1, indicating the involvement of anaerobic glycolysis. On the other hand, due to the intermittent nature of the game and the work-rest ratio of 1 : 2.2, the post-match blood lactate was found to be 3.21 + 0.2 mmol·L??1, reflecting an aerobic dominance in the game. The mean match heart rate (154.3 + 15.4 beats·min - ¹) was lower than mean anaerobic threshold heart rate (164.7 + 5.7 beats·min - ¹), signifying a lower blood lactate level less than 4.0 mmol·L??1 in a tennis match. It This might be due to the fact that long rest pauses caused removal of blood lactate as well as recovery of heart rate. Video analysis of the matches revealed that the players executed more forehand strokes (P<0.001) than the backhand strokes. Since similar heart rate and VO2 responses were observed for forehand and backhand strokes, it is suggested that the players should train themselves equally on both ground strokes. During the longest rally, mean heart rate of the players was 174.9 + 3.1 beats·min - ¹, which corresponded to 84.5 + 2.2% of VO2max. In addition, rallies per game, mean rally duration and strokes per rally were found to be 5.7 + 2.4, 4.5 + 1.5 seconds and 2.8 + 0.8 shots, respectively. Hence, it is concluded that the Malaysian state-level tennis players possessed a moderately good aerobic capacity. This can be improved to the international standard through endurance and intermittent type of training. Improvement in VO2max may enhance the playing intensity of the match as well a better recovery in the rest pauses and also delay the onset of fatigue during a match. From video match analysis and heart rate VO2 relationship, it is suggested that the players should also improve the alactic anaerobic component through short bursts of repeated movements of 5-8 seconds durations.

Implementing a Mathematical Model to Compare Oxygen Uptake Kinetics Between Cyclists and Noncyclists During Steady State

The purpose was to compare a mathematical model of oxygen uptake and bioenergetic systems to an experimental protocol. Twelve (N = 12) noncyclists (NC), age (21.8 ± 1.4 years), and 8 (N = 8) cyclists (C), age (30.5 ± 5.7 years), were subjects. All subjects signed an informed consent. Oxygen consumption (VO2, ml·kg⁻¹·min⁻¹) was measured with steady-state VO2 requirements and responses determined using the mathematical model from the following equation: VO2 (WR) = VO2 (rest) + VO2 (unloading pedaling) + α.WR; ΔVO2(t, WR) = ΔVO2 (WR) = [1-e[-(t-td)/tO2]. Exercise means (SD) included the following: VO2NC(WR) = 48.4 (16.6) ml⁻¹·min⁻¹ for NCs and VO2C(WR) = 56.4 (24.95) ml⁻¹·min⁻¹ for Cs ; ΔVO2C(t, WR) = 6:38 ml⁻¹·min⁻¹ for NCs and ΔVO2C(t, WR) = 7.44 ml⁻¹·min⁻¹ for Cs. The correlation between the mathematical model and actual measure was statistically significant (p < 0.01) with a coefficient of r = 0.947. The experimental protocol was significantly associated with the mathematical model. This allows for a quantitative analysis and safe prediction of steady-state oxygen uptake conditions on populations before exposure to exercising conditions. Through more precise analysis of conditions, greater specificity of training may lead to more predictable adaptation outcomes.

Lactate Threshold Prediction by Blood Glucose and Rating of Perceived Exertion in People with Type 2 Diabetes

The validity of rating of perceived exertion (RPE) in predicting lactate threshold during an incremental test was analyzed in 15 men with type 2 diabetes (M age = 53.4 yr., SD = 12.9). Blood glucose, lactate, and minute ventilation (VE)/VO2 responses identified the lactate, ventilatory, and glucose thresholds. Workloads (W) corresponding to RPEs 12, 13, 14, and 15 were determined. Second-order polynomials fit to VE/W and [lac]/W ratios corresponding to RPEs of 9-10, 12-13, and 16-17 also identified workloads above which there was an overproportional increase in VE and [lac]. These workload breakpoints did not differ, although at RPE 12 underestimated and at RPE 15 overestimated lactate threshold. RPE 13 and 14 and the responses of VE/W and [lac]/W to submaximal exercise accurately predicted lactate threshold.

Cinética do consumo de oxigênio e tempo limite na vvo2max: comparação entre homens e mulheres

Foi investigada a influência do gênero no tempo limite (Tlim) e na cinética do VO2 durante corrida na velocidade associada ao VO2max (vVO2max) em nove homens e nove mulheres, todos adultos, jovens e sedentários, com idades entre 20 e 30 anos. Homens e mulheres realizaram dois testes em esteira rolante, sendo um teste incremental para determinar VO2max (42,66 ± 4,50 vs. 32,92 ± 6,03mL.kg-1.min-1) e vVO2max (13.2 ± 1.5 vs. 10,3 ± 2,0km.h-1), respectivamente. Um segundo teste com carga constante na vVO2max até a exaustão. O Tlim e a cinética do VO2 foram determinados. Não houve diferença significante entre homens e mulheres para constante de tempo (τ) (35,76 ± 21,03 vs. 36,5 ± 6,21s, respectivamente; P = 0,29); Tlim (308 ± 84,3 vs. 282,11 ± 57,19s, respectivamente; P = 0,68), tempo para atingir o VO2max (TAVO2max) (164,48 ± 96,73 vs. 167,88 ± 28,59s, respectivamente; P = 0,29), tempo para atingir o VO2max em percentual do Tlim (%Tlim) (50,24 ± 16,93 vs. 62,63 ± 16,60%, respectivamente; P = 0,19), tempo mantido no VO2max (TMVO2max) (144,08 ± 42,55 vs. 114,23 ± 76,96s, respectivamente; P = 0,13). Estes resultados sugerem que a cinética do VO2 e o Tlim são similares entre homens e mulheres sedentários na vVO2max.

Does Exercise Identity Influence Psychological and Physiological Responses to Wii Fit and Wii Sport

Exercise identity measures the extent to which an individual identifies as an exerciser. If an individual identifies as an exerciser, they are likely to engage in behaviors that support that identity. Exergames such as Wii Fit and Wii Sport could potentially be viewed as novel forms of exercise. PURPOSE: To examine the influence of exercise identity on psychological and physiological responses to Wii Fit and Wii Sport in college students. A secondary aim is to examine if Wii Fit and Wii Sport are of sufficient intensity to meet ACSM moderate intensity exercise recommendations. METHODS: A convenience sample 44 undergraduate students (age 20.89 + 1.77 yrs; male N = 15; female N = 29) completed two sessions. Session (1) involved completing the Physical Activity Readiness Questionnaire (PAR-Q), Exercise Identity Scale (EI), physical measures (e.g., BF%, est VO2max), and Wii Fit and Wii Sport familiarization. Session (2) required participants to complete 20 minutes of Wii Fit (i.e., 5-min Step, 5-min, Soccer, 5-min Ski, 5-min Strength) and 20 minutes of Wii Sport (i.e., 5-min Tennis, 5-min Baseball, 5-min Bowling, 5-min Boxing). Heart rate and VO2 were measured and participants completed the Physical Activity Enjoyment Scale (PACES) after playing Wii Fit and Wii Sport. RESULTS: ANOVA revealed significant differences in EI between males (54.67+6.49) and females (47.36+10.29), F(1,41)=6.21, p< 0.05. A median split of EI scores (HI vs. LO) was conducted and 2 (Sex) X 2 (EI) MANOVAs examined differences in Wii Fit and Wii Sport enjoyment; Wii Fit and Wii Sport VO2; and physical measures. MANOVA results revealed no significant differences in enjoyment between Wii Fit and Wii Sport; no significant differences in Wii Fit or Wii Sport VO2 responses; and a significant Sex and EI effect for physical measures. Univariate results revealed females had significantly greater BF and lower est VO2max (BF% 24.00+1.69; est VO2max 42.97+1.00) than males (BF% 11.58+2.71; est VO2max 53.45+1.61); and est VO2max differed between HI (50.66+1.16) and LO (45.75+1.50) exercise identity participants. CONCLUSION: Participants enjoyed Wii Fit and Wii Sport independent of sex and exercise identity. VO2 responses for Wii Fit and Wii Sport activities were below ACSM moderate intensity exercise recommendations for healthy adults.

VO2 Kinetics and the Power Duration Relationship during Supine Exercise

PURPOSE: To investigate the effects of supine exercise on pulmonary oxygen uptake (VO2) kinetics and the parameters of the power-duration relationship (critical power (CP) and the curvature constant (W')) during severe-intensity exhaustive exercise. METHODS: Nine trained male cyclists (age 31 ± 8 y, height 178.4 ± 6.4 cm; mass 83.2 ± 14.2 kg, performed initial ramp tests to exhaustion in the upright and supine body positions to determine the gas exchange threshold and maximal oxygen uptake (VO2max) on an electrically braked cycle ergometer. Four work rates were calculated, requiring between 60% Δ and 100% VO2max for upright (UP) and supine (SP) positions. These work rates were then performed to exhaustion in each body position, in a randomized order, on separate days. Time to exhaustion (Tlim) was recorded, and VO2, and heart rate (HR) were measured throughout all tests. The VO2 responses were modeled using a mono-exponential function applied to the primary VO2 response to determine the time constant (t). The peak VO2 was determined as the highest 30 s value recorded during the tests. The linear work-time relationship was used to calculate CP and W' from the power and Tlim data in each position. RESULTS: Severe-intensity work rates ranged from 298 ± 40 to 397 ± 44 W in UP, and 244 ± 25 to 334 ± 31 W in SP. The primary t was increased in SP compared to UP at 60% Δ and 100% VO2max (60% Δ, UP 26.6 ± 4.9 s vs. SP 35.3 ± 13.1 s; 100% VO2max, 25.0 ± 11.3 s vs. 35.3 ± 11.0 s; P <0.05). At all work rates, the peak VO2 was significantly reduced in SP (from ∼4.47 ± 0.39 to ∼3.91 ± 0.32 L/min; p<0.01). The CP was significantly greater during UP (277 ± 39 vs. 216 ± 19 W; p<0.01) whereas no difference was seen in W' between conditions (Up = 17.2 ± 5.1, SP = 17.1 ± 5.8 kJ, p=0.97). CONCLUSIONS: The reduction in CP during SP was associated with slowed primary VO2 kinetics and reduced peak VO2 during severe-intensity exercise. These data suggest that reduced muscle perfusion pressure during SP when compared to upright exercise serves to acutely reduce O2 delivery, which in turn slows VO2 kinetics, reduces peak VO2 and the power-duration asymptote (CP) but without altering the curvature constant (W').

Influence of priming exercise on muscle [PCr] and pulmonary O2 uptake dynamics during ‘work-to-work’ knee-extension exercise

Metabolic transitions from rest to high-intensity exercise were divided into two discrete steps (i.e., rest-to-moderate-intensity (R-->M) and moderate-to-high-intensity (M-->H)) to explore the effect of prior high-intensity 'priming' exercise on intramuscular [PCr] and pulmonary VO₂ kinetics for different sections of the motor unit pool. It was hypothesized that [PCr] and VO₂ kinetics would be unaffected by priming during R-->M exercise, but that the time constants (tau) describing the fundamental [PCr] response and the phase II VO₂ response would be significantly reduced by priming for M-->H exercise. On three separate occasions, six male subjects completed two identical R-->M/M-->H 'work-to-work' prone knee-extension exercise bouts separated by 5min rest. Two trials were performed with measurement of pulmonary VO₂ and the integrated electromyogram (iEMG) of the right m. vastus lateralis. The third trial was performed within the bore of a 1.5-T superconducting magnet for (31)P-MRS assessment of muscle metabolic responses. Priming did not significantly affect the [PCr] or VO₂ tau during R-->M ([PCr] tau Unprimed: 24+/-16 vs. Primed: 22+/-14s; VO₂ tau Unprimed: 26+/-8 vs. Primed: 25+/-9s) or M-->H transitions ([PCr] tau Unprimed: 30+/-5 vs. Primed: 32+/-7s; VO₂ tau Unprimed: 37+/-5 vs. Primed: 38+/-9s). However, it did reduce the amplitudes of the [PCr] and VO₂ slow components by 50% and 46%, respectively, during M-->H (P<0.05 for both comparisons). These effects were accompanied by iEMG changes suggesting reduced muscle fiber activation during M-->H exercise after priming. It is concluded that the tau for the initial exponential change of muscle [PCr] and pulmonary VO₂ following the transition from moderate-to-high-intensity prone knee-extension exercise is not altered by priming exercise.

Competition effects on physiological responses to exercise: Performance, cardiorespiratory and hormonal factors

The purpose of this study was to explore the mechanisms for increased exercise performance in conditions of competition. Endurance trained subjects (n=14) performed incremental treadmill running to exhaustion in control laboratory conditions (non-competition) and in conditions of simulated competition to assess performance (running duration). Heart rate and respiration gases were monitored continuously through each exercise condition. Blood lactate, cortisol, growth hormone and testosterone concentrations were also determined at pre- (rest) and postexercise in each condition. Results indicated competition exercise performance was significantly increased 4.2% (+49 sec; p<0.05) as was peak VO2 response 4.4% (+2.5 ml O2 x kg(-1) x min(-1); p<0.05) versus non-competition. No significant differences were found in peak measurements of minute ventilation, respiratory exchange ratio, ventilation threshold, post-exercise lactate, heart rate, or the ventilation equivalent for O 2 between the exercise conditions. In both conditions growth hormone and testosterone concentrations increased significantly in response to exercise (p<0.001), whereas cortisol responses post-exercise were significantly elevated in the competition (p<0.05) but not in the control condition (p>0.05). These findings support that in competitive situations the affective state (motivation) experienced by athletes can enhance performance in exercise events, and lead to an increased peak oxygen uptake. The magnitude of the improvement is of a substantial nature and of a level seen with some training programs. Competitive conditions also augment the cortisol response to exercise, suggesting that enhanced sympatho-adrenal system activation occur in such situations which may be one of the key "driving forces" to performance improvement.

Investigation relationship between %VO2MAX versus %HRMAX in children with cerebral palsy

Certain studies demonstrated that some factors particularly kinds of disease are influenced the relationship between exercise intensity indexes. %HRmax and %VO2max are two indexes of exercise intensity on exercise- rehabilitation in some diseases. Recently, the some research showed that relationship between %HRmax and %VO2max described by ACSM is not applicable to the some patients or no handicapped people. Objective: This study performed with aim to determine relationship between %HRmax and %VO2max in leg exercise in 20 adolescent with dipelegic spastic cerebral palsy(12±2 year of age). METHOD: Twenty children with dipelegic spastic cerebral palsy participated in this study by voluntarily and the consent of their parents as well as specialist physician. HR and VO2 responses to McMaster ergometery protocol monitored continuously at rest, end of each stage and the end of protocol. These parameters were then used for calculation %HRmax and %VO2max in subjects. The correlation between these indexes determined via statically SPSS. Regression analyses were conducted to determine correlation between these indexes. RESULTS: The statically data indicated that percentage of heart rate max is not equivalent with percentage of VO2max. In the other words, at each stage of protocol the values of %HRmax was very upper than %VO2max in comparison with those used by the ACSM. CONCLUSION: Our findings demonstrated that the relationship between %HRmax and %VO2max in these patients is not equal to guideline of ACSM. In addition; in each disease depend on influence in physical and cardio respiratory fitness affect the relationship between exercise intensity indexes. Therefore, the %HRmax versus %VO2max relationship should be determined directly in each patient.

Oxygen Uptake Kinetics: An Underappreciated Determinant of Exercise Performance

The rate at which VO(2) adjusts to the new energy demand following the onset of exercise strongly influences the magnitude of the "O(2) deficit" incurred and thus the extent to which muscle and systemic homeostasis is perturbed. Moreover, during continuous high-intensity exercise, there is a progressive loss of muscle contractile efficiency, which is reflected in a "slow component" increase in VO(2). The factors that dictate the characteristics of these fast and slow phases of the dynamic response of VO(2) following a step change in energy turnover remain obscure. However, it is clear that these features of the VO(2) kinetics have the potential to influence the rate of muscle fatigue development and, therefore, to affect sports performance. This commentary outlines the present state of knowledge on the characteristics of, and mechanistic bases to, the VO(2) response to exercise of different intensities. Several interventions have been reported to speed the early VO(2) kinetics and/or reduce the magnitude of the subsequent VO(2) slow component, and the possibility that these might enhance exercise performance is discussed.

Influence of All-Out and Fast Start on 5-min Cycling Time Trial Performance

To examine the influence of two different fast-start pacing strategies on performance and oxygen consumption (VO2) during cycle ergometer time trials lasting ∼5 min. Eight trained male cyclists performed four cycle ergometer time trials whereby the total work completed (113 ± 11.5 kJ; mean ± SD) was identical to the better of two 5-min self-paced familiarization trials. During the performance trials, initial power output was manipulated to induce either an all-out or a fast start. Power output during the first 60 s of the fast-start trial was maintained at 471.0 ± 48.0 W, whereas the all-out start approximated a maximal starting effort for the first 15 s (mean power: 753.6 ± 76.5 W) followed by 45 s at a constant power output (376.8 ± 38.5 W). Irrespective of starting strategy, power output was controlled so that participants would complete the first quarter of the trial (28.3 ± 2.9 kJ) in 60 s. Participants performed two trials using each condition, with their fastest time trial compared. Performance time was significantly faster when cyclists adopted the all-out start (4 min 48 s ± 8 s) compared with the fast start (4 min 51 s ± 8 s; P < 0.05). The first-quarter VO2 during the all-out start trial (3.4 ± 0.4 L·min(-1)) was significantly higher than during the fast-start trial (3.1 ± 0.4 L·min(-1); P < 0.05). After removal of an outlier, the percentage increase in first-quarter VO2 was significantly correlated (r = -0.86, P < 0.05) with the relative difference in finishing time. An all-out start produces superior middle distance cycling performance when compared with a fast start. The improvement in performance may be due to a faster VO2 response rather than time saved due to a rapid acceleration.

Dietary Arginine Supplementation Speeds Pulmonary V˙O2 Kinetics during Cycle Exercise

To test the hypothesis that L-arginine (the substrate for nitric oxide synthase [NOS]) administration slows the VO2 kinetics at the onset of moderate-intensity exercise in humans. Seven physically active males were randomly assigned to receive either placebo (lactose) or L-arginine hydrochloride capsules (7.2 g x d(-1)) for 14 d in a double-blind crossover design, with a 7-d washout period between the two conditions. On day 11 and day 14 of each condition, the subjects completed two consecutive 6-min bouts of cycle exercise at 80% of the ventilatory threshold with a 12-min rest interval. VO2 was measured on a breath-by-breath basis, and VO2 kinetics were determined with a single exponential model from the averaged data derived from four repetitions. Capillary and venous blood samples were taken to determine plasma [La] and serum [arginine], respectively. There were no differences in circulating lactate either before or during exercise. However, serum [arginine] was higher (P < 0.05) in the arginine condition at rest (119.0 +/- 12.6 vs 103.6 +/- 15.7 micromol x L(-1) in the control condition) and after exercise (113.3 +/- 26.0 vs 103.8 +/- 12.6 micromol x L(-1) in the control condition). With regard to the pulmonary VO2 kinetics, no significant difference was observed in the time at which the phase II response emerged or in the phase II amplitude between the two conditions. However, contrary to our hypothesis, the time constant was significantly reduced after arginine administration (i.e., 13.9 +/- 3.1 vs 15.8 +/- 2.6 s in the control condition, P < or = 0.014). Exogenous L-arginine administration speeds the phase II pulmonary VO2 response by 12% at the onset of moderate-intensity exercise in humans.

Oxygen Uptake, Heart Rate, and Ratings of Perceived Exertion at the PWC JOURNAL/jscr/04.03/00124278-200907000-00035/OV0312_11/v/2021-02-09T093622Z/r/image-png o2

The purpose of the present study was to examine the oxygen uptake (Vo2), heart rate (HR), and ratings of perceived exertion (RPE [OMNI-Leg 0-10]) responses during continuous 1-hour cycle ergometer rides at the PWCVo2 (physical working capacity at the oxygen consumption threshold). Eight subjects (mean age +/- SD = 23 +/- 3.2 years) performed a maximal test to exhaustion for the determination of Vo2peak and ventilatory threshold (VT). The subjects also performed 4 randomly ordered 8-minute workbouts at different power outputs (ranging from 84 to 245 W) to determine the PWCVo2 and a continuous 1-hour cycle ergometer ride at the PWCVo2 during which Vo2, HR, and RPE data were collected every 2 minutes. The PWCVo2 (114 +/- 39 W) and VT (133 +/- 44 W) were not significantly different and occurred at 56 and 63% Vo2peak, respectively. Linear regression showed that the slope coefficients for the Vo2, HR, and RPE vs. time relationships for the continuous 1-hour workbouts were significantly greater than zero. Furthermore, a t-test about a single mean indicated that the mean slope coefficient for the HR vs. time relationship was significantly greater than 0.1 bpm x min(-1) (the rate of increase in HR that can be maintained for an 8-hour day). The results of this study indicated that PWCVo2 could be maintained for an extended period. However, the maximal power output associated with steady state Vo2, HR, and RPE responses was overestimated. The mean increase in Vo2 during the continuous 1-hour ride was 270 mL, which suggested that the PWCVo2 may demarcate the moderate from heavy exercise domains. The mean HR slope coefficient of 0.3 bpm x min(-1) indicated that the power output at the PWCVo2 could likely be maintained for greater than 2 hours.

Oxygen deficits and oxygen delivery kinetics during submaximal intensity exercise in humans after 14 days of head-down tilt-bed rest

Beat-by-beat Q(a)O2 and breath-by-breath VO2 were assessed in ten male subjects (24 +/- 3.5 years; 78 +/- 7.7 kg; 182 +/- 5.6 cm) during cycling exercise at 50 W before and after a 14-day period of head-down tilt-bed rest (HDTBR). O2 deficit (DefO2) was calculated as the difference between the volume of O2 that would have been consumed if a steady state had been immediately attained minus that actually taken up during exercise. Q(a)O2 kinetics was described fitting the data with a non-linear mono-exponential model with time delay. Mean response times (MRT) of VO2 and Q(a)O2 kinetics were then calculated. DefO2 and MRT of VO2 response did not change after HDTBR, whereas MRT of Q(a)O2 kinetics increased. The invariance of VO2 kinetics after HDTBR suggests that, although Q(a)O2 response became slower after HDTBR, it did not affect the kinetics of peripheral gas exchange, which probably remained under the control of local muscular mechanisms.

Maximal exercise oxygen pulse as a predictor of mortality among male veterans referred for exercise testing

Maximal oxygen pulse (O(2) pulse) mirrors the stroke volume response to exercise, and should therefore be a strong predictor of mortality. Limited and conflicting data are, however, available on this issue. Nine hundred forty-eight participants, classified as those with cardiopulmonary disease (CPD) and those without (non-CPD), underwent cardiopulmonary exercise testing (CPX) for clinical reasons between 1993 and 2003. The ability of maximal O(2) pulse and maximal oxygen uptake (peak VO(2)) to predict mortality was investigated using proportional hazards and Akaike information criterion analyses. All-cause mortality was the endpoint. Over a mean follow-up of 6.3+/-3.2 years, there were 126 deaths. Maximal O(2) pulse, expressed in either absolute or relative to age-predicted terms, and peak VO(2) were significant and independent predictors of mortality in those with and without CPD (P<0.04). Akaike information criterion analysis revealed that the model including both maximal O(2) pulse and peak VO(2) had the highest accuracy for predicting mortality. The optimal cut-points for O(2) pulse and peak VO(2) (<12; > or =12 ml/beat and <16; > or =16 ml/(kg.min) respectively) were established by the area under the receiver-operating-characteristic curve. The relative risks of mortality were 3.4 and 2.2 (CPD and non-CPD, respectively) among participants with both maximal O(2) pulse and peak VO(2) responses below these cut-points compared with participants with both responses above these cut-points. These results indicate that maximal O(2) pulse is a significant predictor of mortality in patients with and without CPD. The addition of absolute and relative O(2) pulse data provides complementary information for risk-stratifying heterogeneous participants referred for CPX and should be routinely included in the CPX report.

Oxygen Uptake Kinetics During Arm Cranking Within The Moderate Intensity Domain

Recent studies have demonstrated that on-transient oxygen uptake (VO2) kinetics are slowed when constant-load exercise is initiated from the upper compared to lower region of the moderate intensity domain (below the lactate threshold, LT). These studies, focusing exclusively on lower limb exercise, attributed this intensity-dependent slowing of VO2 kinetics during moderate-intensity exercise to different muscle fiber recruitment patterns or altered oxygen transport dynamics. PURPOSE: To determine if pulmonary VO2 and heart rate (HR) kinetics are slowed during constant-load arm exercise (arm-cranking) performed in the upper (90%LT) compared to lower (45%LT) regions of the moderate intensity domain. METHODS: Seven healthy male subjects (26 ± 3 yr) performed 4-8 repetitions of arm-cranking exercise involving: 1) a single, 6-min step transition from 9 W to 90% of the estimated LT (AC90%); two continuous, equal, 6-min step transitions from 9 W to 45% LT (AC45%), and then to 90% LT (AC45-90%); and 3) the AC90% protocol superimposed upon low-intensity leg-cycling (AC90%+LC), where baseline HR >100 beats·min-1 (range: 100-120 beats·min-1). RESULTS: The time constants (t) of the VO2 and HR responses were longer (P<0.05) during AC45-90% (tVO2: 70 ± 5 s; tHR: 59 ± 4 s) compared to AC45% (tVO2: 54 ± 6 s; tHR: 47 ± 5 s) and AC90% (tVO2: 53 ± 4 s; tHR: 46 ± 3 s). The gain (DVO2/DW) and blood lactate concentration were also significantly greater (P<0.05) for AC45-90% than AC45%. During arm-cranking superimposed upon leg-cycling (AC90%+LC), HR kinetics were significantly slowed when compared to AC90% (mean difference for tHR: 9 ± 4 s, P<0.05) and AC45% (mean difference for tHR: 9 ± 5 s, P<0.05). Similar comparisons between conditions for tVO2 yielded no significant differences. CONCLUSION: During arm exercise performed within the moderate intensity domain, VO2 and HR kinetics do not conform to a dynamically linear model. Since HR, but not VO2 kinetics were slowed during AC90%+LC, factors other than convective oxygen delivery (e.g. those intrinsic to the exercising muscle) may explain the slower VO2 response in the upper reaches of the moderate intensity domain for arm exercise.