Comparison of incremental and steady state tests of endurance training

To compare the results obtained by incremental or constant work load exercises in the evaluation of endurance conditioning, a 20-week training programme was performed by 9 healthy human subjects on the bicycle ergometer for 1 h a day, 4 days a week, at 70-80% VO2max. Before and at the end of the training programme, (1) the blood lactate response to a progressive incremental exercise (18 W increments every 2nd min until exhaustion) was used to determine the aerobic and anaerobic thresholds (AeT and AnT respectively). On a different day, (2) blood lactate concentrations were measured during two sessions of constant work load exercises of 20 min duration corresponding to the relative intensities of AeT (1st session) and AnT (2nd session) levels obtained before training. A muscle biopsy was obtained from vastus lateralis at the end of these sessions to determine muscle lactate. AeT and AnT, when expressed as % VO2max, increased with training by 17% (p less than 0.01) and 9% (p less than 0.05) respectively. Constant workload exercise performed at AeT intensity was linked before training (60% VO2max) to a blood lactate steady state (4.8 +/- 1.4 mmol.l-1) whereas, after training, AeT intensity (73% VO2max) led to a blood lactate accumulation of up to 6.6 +/- 1.7 mmol.l-1 without significant modification of muscle lactate (7.6 +/- 3.1 and 8.2 +/- 2.8 mmol.kg-1 wet weight respectively). It is concluded that increase in AeT with training may reflect transient changes linked to lower early blood lactate accumulation during incremental exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of exercise modality on oxygen uptake kinetics during heavy exercise

The mechanisms responsible for the oxygen uptake (VO2) slow component during high-intensity exercise have yet to be established. In order to explore the possibility that the VO2 slow component is related to the muscle contraction regimen used, we examined the pulmonary VO2 kinetics during constant-load treadmill and cycle exercise at an exercise intensity that produced the same level of lactacidaemia for both exercise modes. Eight healthy subjects, aged 22-37 years, completed incremental exercise tests to exhaustion on both a cycle ergometer and a treadmill for the determination of the ventilatory threshold (defined as the lactate threshold, Th1a) and maximum VO2 (VO2max). Subsequently, the subjects completed two "square-wave" transitions from rest to a running speed or power output that required a VO2 that was halfway between the mode-specific Th1a and VO2max. Arterialised blood lactate concentration was determined immediately before and after each transition. The VO2 responses to the two transitions for each exercise mode were time-aligned and averaged. The increase in blood lactate concentration produced by the transitions was not significantly different between cycling [mean (SD) 5.9 (1.5) mM] and running [5.5 (1.6) mM]. The increase in VO2 between 3 and 6 min of exercise; (i.e. the slow component) was significantly greater in cycling than in running, both in absolute terms [290 (102) vs 200 (45) ml x min(-1); P<0.05] and as a proportion of the total VO2 response above baseline [10 (3)% vs 6 (1)%; P < 0.05]. These data indicate that: (a) a VO2 slow component does exist for high-intensity treadmill running, and (b) the magnitude of the slow component is less for running than for cycling at equivalent levels of lactacidaemia. The greater slow component observed in cycling compared to running may be related to differences in the muscle contraction regimen that is required for the two exercise modes.     

Oxidation/reduction state of cytochrome oxidase during repetitive contractions

There is disagreement regarding whether inadequate O2 determines maximal O2 uptake (VO2max) and lactic acid output (L) during muscular activity. Direct assessment of mitochondrial cytochrome oxidase (cytochrome a-a3) oxidation/reduction (O/R) state should provide an unequivocal answer for this issue. A new near-infrared spectrophotometric method was used to measure the O/R state of cytochrome a-a3 of dog gastrocnemius-plantaris muscle in situ during repetitive isotonic twitch and tetanic contractions. Three contraction frequencies were used for each contraction type in alternating sequence to provide a wide range of VO2 up to VO2max. VO2 and L were measured after 3 and 9 min of a 10-min contraction period, and 15 min were allowed for recovery between contraction periods. VO2 increased with contraction frequency. L was variably increased with contraction frequency at 3 min and uptake usually occurred at 9 min, except at the highest tetanic frequency. The O/R span of cytochrome a-a3 was determined by respiring the animals with 100% N2 to determine the most reduced state. This was followed by respiration with 100% O2, which gave the most oxidized state transiently during recovery. Within this span in muscles at rest, cytochrome a-a3 was 50-80% oxidized. During contractions of both types at all frequencies, cytochrome a-a3 always became more oxidized by an additional 10-20%. These findings should put to rest any arguments that inadequate O2 is a determinant of VO2max or L under the conditions of these experiments: repetitive contractions with free flow in self-perfused muscles and normoxia.     

Time required for the restoration of normal heavy exercise VO2 kinetics following prior heavy exercise.

Prior heavy exercise markedly alters the O2 uptake (VO2) response to subsequent heavy exercise. However, the time required for VO2 to return to its normal profile following prior heavy exercise is not known. Therefore, we examined the VO2 responses to repeated bouts of heavy exercise separated by five different recovery durations. On separate occasions, nine male subjects completed two 6-min bouts of heavy cycle exercise separated by 10, 20, 30, 45, or 60 min of passive recovery. The second-by-second VO2 responses were modeled using nonlinear regression. Prior heavy exercise had no effect on the primary VO2 time constant (from 25.9 +/- 4.7 s to 23.9 +/- 8.8 s after 10 min of recovery; P = 0.338), but it increased the primary VO2 amplitude (from 2.42 +/- 0.39 to 2.53 +/- 0.41 l/min after 10 min of recovery; P = 0.001) and reduced the VO2 slow component (from 0.44 +/- 0.13 to 0.21 +/- 0.12 l/min after 10 min of recovery; P < 0.001). The increased primary amplitude was also evident after 20-45 min, but not after 60 min, of recovery. The increase in the primary VO2 amplitude was accompanied by an increased baseline blood lactate concentration (to 5.1 +/- 1.0 mM after 10 min of recovery; P < 0.001). Baseline blood lactate concentration was still elevated after 20-60 min of recovery. The priming effect of prior heavy exercise on the VO2 response persists for at least 45 min, although the mechanism underpinning the effect remains obscure.     

Pulmonary clearance of 99mTc-DTPA: influence of background activity

To study the effects of circulatory occlusion on the time course and magnitude of postexercise O2 consumption (VO2) and blood lactate responses, nine male subjects were studied twice for 50 min on a cycle ergometer. On one occasion, leg blood flow was occluded with surgical thigh cuffs placed below the buttocks and inflated to 200 mmHg. The protocol consisted of a 10-min rest, 12 min of exercise at 40% peak O2 consumption (VO2 peak), and a 28-min resting recovery while respiratory gas exchange was determined breath by breath. Occlusion (OCC) spanned min 6-8 during the 12-min work bout and elicited mean blood lactate of 5.2 +/- 0.8 mM, which was 380% greater than control (CON). During 18 min of recovery, blood lactate after OCC remained significantly above CON values. VO2 was significantly lower during exercise with OCC compared with CON but was significantly higher during the 4 min of exercise after cuff release. VO2 was higher after OCC during the first 4 min of recovery but was not significantly different thereafter. Neither total recovery VO2 (gross recovery VO2 with no base-line subtraction) nor excess postexercise VO2 (net recovery VO2 above an asymptotic base line) was significantly different for OCC and CON conditions (13.71 +/- 0.45 vs. 13.44 +/- 0.61 liters and 4.93 +/- 0.26 vs. 4.17 +/- 0.35 liters, respectively). Manipulation of exercise blood lactate levels had no significant effect on the slow ("lactacid") component of the recovery VO2.     

Disposal of blood [1-13C]lactate in humans during rest and exercise

Lactate irreversible disposal (RiLa) and oxidation (RoxLa) rates were studied in six male subjects during rest (Re), easy exercise [EE, 140 min of cycling at 50% of maximum O2 consumption (VO2max)] and hard exercise (HE, 65 min at 75% VO2max). Twenty minutes into each condition, subjects received a Na+-L(+)-[1-13C]lactate intravenous bolus injection. Blood was sampled intermittently from the contralateral arm for metabolite levels, acid-base status, and enrichment of 13C in lactate. Expired air was monitored continuously for determination of respiratory parameters, and aliquots were collected for determination of 13C enrichment in CO2. Steady-rate values for O2 consumption (VO2) were 0.33 +/- 0.01, 2.11 +/- 0.03, and 3.10 +/- 0.03 l/min for Re, EE, and HE, respectively. Corresponding values of blood lactate levels were 0.84 +/- 0.01, 1.33 +/- 0.05, and 4.75 +/- 0.28 mM in the three conditions. Blood lactate disposal rates were significantly correlated to VO2 (r = 0.78), averaging 123.4 +/- 20.7, 245.5 +/- 40.3, and 316.2 +/- 53.7 mg X kg-1 X h-1 during Re, EE, and HE, respectively. Lactate oxidation rate was also linearly related to VO2 (r = 0.81), and the percentage of RiLa oxidized increased from 49.3% at rest to 87.0% during exercise. A curvilinear relationship was found between RiLa and blood lactate concentration. It was concluded that, in humans, 1) lactate disposal (turnover) rate is directly related to the metabolic rate, 2) oxidation is the major fate of lactate removal during exercise, and 3) blood lactate concentration is not an accurate indicator of lactate disposal and oxidation.     

Effects of prolonged exercise at a similar percentage of maximal oxygen consumption in trained and untrained subjects

Six trained male cyclists and six untrained but physically active men participated in this study to test the hypothesis that the use of percentage maximal oxygen consumption (%VO2max) as a normalising independent variable is valid despite significant differences in the absolute VO2max of trained and untrained subjects. The subjects underwent an exercise test to exhaustion on a cycle ergometer to determine VO2max and lactate threshold. The subjects were grouped as trained (T) if their VO2max exceeded 60 ml.kg-1.min-1, and untrained (UT) if their VO2max was less than 50 ml.kg-1.min-1. The subjects were required to exercise on the ergometer for up to 40 min at power outputs that corresponded to approximately 50% and 70% VO2max. The allocation of each exercise session (50% or 70% VO2max) was random and each session was separated by at least 5 days. During these tests venous blood was taken 10 min before exercise (- 10 min), just prior to the commencement of exercise (0 min), after 20 min of exercise (20 min), at the end of exercise and 10 min postexercise (+ 10 min) and analysed for concentrations of cortisol, [Na+], [K+], [Cl-], glucose, free fatty acid, lactate [la-], [NH3], haemoglobin [Hb] and for packed cell volume. The oxygen consumption (VO2) and related variables were measured at two time intervals (14-15 and 34-35 min) during the prolonged exercise tests. Rectal temperature was measured throughout both exercise sessions. There was a significant interaction effect between the level of training and exercise time at 50% VO2max for heart rate (fc) and venous [la-].(ABSTRACT TRUNCATED AT 250 WORDS)     

Leukocyte, lymphocyte and platelet response to dynamic exercise. Duration or intensity effect?

The influence of work intensity and duration on the white blood cell (WBC), lymphocyte (L) and platelet (P) count response to exercise was studied in 16 trained subjects (22 +/- 5.4 years, means +/- SD). They performed three cyclo-ergospirometric protocols: A) 10 min at 150 W followed by a progressive test (30 W/3 min) till exhaustion; B) constant maximal work (VO2max); C) a 45 min Square-Wave Endurance Exercise Test (SWEET), (n = 5). Arterial blood samples were taken: at rest, submaximal and maximal exercise in A; maximal exercise in B; 15th, 30th and 45th min in the SWEET. Lactate, [H+], PaCO2, PaO2, [Hct], Hb, cortisol, ACTH, total platelet volume (TPV), total blood red cell (RBC), WBC, L and P were measured. At 150 W, WBC, L, P, and TPV increased. VO2max did not differ between A and B, but a difference was found in total exercise time (A = 25 +/- 3 min; B = 7 +/- 2 min, p less than 0.001). In A, at VO2max, the increase was very small for Hct, [Hb], and RBC (10%), in contrast with large changes for WBC (+93%), L (+137%), P (+32%), TPV (+35%), [H+] (+39%), lactate (+715%), and ACTH (+95%). At VO2max there were no differences in these variables between A and B. During the SWEET: WBC, L, P, TPV and ACTH increased at the 15th min as much as in VO2max, but no difference was observed between the 15th, 30th and 45th min, except for ACTH which continued to rise; the lactate increase during the SWEET was about half (+341%) the value observed at VO2max, and [H+] did not vary with respect to values at rest.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute altitude exposure and altered acid-base states. I. Effects on the exercise ventilation and blood lactate responses

This study examined the influence of acute altitude (AL) exposure alone or in combination with metabolic acid-base manipulations on the exercise ventilatory and blood lactate responses. Four subjects performed a 4 min, 30 W incremental test to exhaustion at ground level (GL) and a 4 min, 20 W incremental test during three acute exposures to a simulated altitude of 4200 m; (i) normal (NAL), (ii) following 0.2 g.kg-1 ingestion of sodium bicarbonate (BAL), and (iii) following 0.5 g.day-1 ingestion of acetazolamide for 2 days prior to exposure (AAL). VE.VO2-1 increased progressively throughout the incremental tests at AL and the minimum value was not related to a change in the blood lactate response. In contrast, the VE.VCO2-1 decreased initially to reach a minimum value at the same power output for each altitude trial and was related to a lactate threshold defined by a log-log transformation (r = 0.78). This transformation of the blood lactate data was not influenced by the altered acid-base states. The relative exercise intensity corresponding to both a delta lactate of 1 mM and an absolute lactate of 4 mM was significantly increased during the AAL (79.9 +/- 12.9 and 93.9 +/- 13.7% VO2max, respectively) compared with NAL (59.1 +/- 5.5 and 78.0 +/- 5.8% VO2max, respectively). These data suggest that strong relationships exist between the ventilatory and blood lactate response during AL exposure and altered acid-base states. Further, it is concluded that, unless the acid-base status is known, the use of an absolute or delta lactate value to compare submaximal exercise should be interpreted with caution.     

Effects of severe prior exercise on assessment of maximal oxygen uptake

Five moderately fit males (50.8 ml.kg-1.min-1) performed 14 continuous type VO2 max tests on a motor-driven treadmill. Randomly assigned experimental sessions, consisting of three tests each and separated by 10 (tests 1, 2, 3), 20 (tests 4, 5, 6), 30 (tests 7, 8, 9), or 40 (tests 10, 11, 12) min, were conducted at a consistent hour for each subject every 4th day. Two separately performed tests were also included in the random assignment with the test eliciting the highest VO2 max value designated as the standard reference (SR). VO2 max values for tests 1 through 12 were not significantly different from the SR in spite of elevated pretest blood lactate concentrations ranging from 5 mM to 16 mM. Performance time was reduced for all tests other than tests 1, 4, 7, and 10, reaching the level of statistical significance (P less than 0.05) in tests 2, 3, 5, 6, and 9. It was concluded that valid and reliable assessment of VO2 max is possible even though testing is initiated with subjects in varying stages of exhaustion.     

Effect of lung resection on blood lactate threshold in lung cancer patients

We studied the effect of a decrease in vital capacity (VC) on the blood lactate threshold detected during exercise in 16 preoperative (PRE) and 10 postoperative (POST) lung cancer patients who had undergone lobectomy or pneumonectomy. The PRE patients were selected on the basis of having normal preoperative pulmonary function. The POST patients were selected on the basis of having normal preoperative pulmonary function and a postoperative VC of less than 80%. The oxygen consumption/body surface area at a 2.2 m.mol.l-1 arterial lactate concentration (VO2/BSA at La-2.2) was adopted as the blood lactate threshold. VC/BSA in the POST group significantly correlated with VO2/BSA at La-2.2 (r = 0.85, P less than 0.01), but not in the PRE group. SaO2 at La-2.2 was 95.4 +/- 1.5% in the PRE group and 95.2 +/- 1.3% in the POST group. SaO2 at La-2.2 did not correlated with VC/BSA in either group. The hemoglobin concentration (Hb) in the arterial blood correlated significantly with VC/BSA in the POST group (r = 0.65, P less than 0.05) but not in the PRE group. These results indicate that VO2/BSA at La-2.2 was restricted by VC in patients with restrictive pulmonary function disorder. Of the three elements of oxygen delivery, Hb was a limiting factor for VO2/BSA at La-2.2 but SaO2 was not. Cardiac output, which was not measured in our study, was speculated to be another limiting factor for VO2/BSA at La-2.2.     

Cardiorespiratory and lactate responses to a 1-hour submaximal running at the lactate threshold

Cardiorespiratory and blood lactate (La) responses to prolonged submaximal running at an intensity relative to lactate threshold (LT) were examined in 15 recreational runners, aged 19 to 32. In test 1 where treadmill speed was progressively incremented by 10-20m/min until exhaustion, oxygen uptake at the LT (VO2 @ LT: 2.34 +/- 0.331/min or 41.6 +/- 5.7 ml/kg/min) and VO2max (3.58 +/- 0.341/min or 63.6 +/- 5.5 ml/kg/min) were measured. In test 2, the subject was required to run on the treadmill for 1 hour at a fixed velocity (Vt) which corresponded to his Vt @ LT. As expected, mean VO2 ranged during the 1-h submaximal running from 2.31 +/- 0.411/min or 63.0 +/- 7.8% VO2max at min 10-20 to 2.52 +/- 0.351/min or 69.2 +/- 6.2% VO2max at min 50-60, both of which were close to VO2 @ LT (65.2 +/- 4.4% VO2max). The slight decrease in blood La was found from min 20 to min 60, and this was accompanied by a parallel decline in respiratory exchange ratio. Shifts in the energy substrate toward a reliance on fat oxidation may occur during the course of 1-h running at Vt @t LT. The small oxygen debt observed after the 1-h running may confirm the assumption that prolonged running at Vt at LT would be performed in an almost fully aerobic steady state. We conclude that prolonged running at Vt @ LT may possibly maximize health-related benefits in the healthy adult.     

Effects of prolonged exercise in highly trained traumatic paraplegic men

This study investigated the cardiovascular and metabolic responses to prolonged wheelchair exercise in a group of highly trained, traumatic paraplegic men. Six endurance-trained subjects with spinal cord lesions from T10 to T12/L3 underwent a maximal incremental exercise test in which they propelled their own track wheelchairs on a motor-driven treadmill to exhaustion to determine maximal O2 uptake (VO2max) and related variables. One week later each subject exercised in the same wheelchair on a motorized treadmill at 60-65% of VO2max for 80 min in a thermoneutral environment (dry bulb 22 degrees C, wet bulb 17 degrees C). Approximately 10 ml of venous blood were withdrawn both 20 min and immediately before exercise (0 min), after 40 and 80 min of exercise, and 20 min postexercise. Venous blood was analyzed for hematocrit (Hct), hemoglobin (Hb), and lactate, and the separated plasma was analyzed for glucose, K+, Na+, Cl-, free fatty acid (FFA), and osmolality. VO2, CO2 production (VCO2), minute ventilation (VE), respiratory exchange ratio (R), net efficiency, and wheelchair strike rate were determined at four intervals throughout the exercise period. Data were analyzed with an analysis of variance repeated-measures design and a Scheffé post hoc test. VO2max was 47.5 +/- 1.8 (SE) ml.min-1.kg-1 with maximal VE BTPS and maximal heart rate (HR) being 100.1 +/- 3.8 l/min and 190 +/- 1 beats/min, respectively. During prolonged exercise there were no significant changes in VO2, VCO2, VE, R, net efficiency, wheelchair strike rate, and lactate, glucose, and Na+ concentrations. Significant increases occurred in HR, FFA, K+, Cl-, osmolality, Hb, and Hct throughout exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intensity-controlled treadmill running in rats: VO(2 max) and cardiac hypertrophy

Physiological studies of long-term cardiovascular adaptation to exercise require training regimens that give robust conditioning effects and adequate testing procedures to quantify the outcome. We developed a valid and reproducible protocol for measuring maximal oxygen uptake (VO(2 max)), which was reached at a 25 degrees inclination with a respiratory exchange ratio > 1.05 and blood lactate > 6 mmol/l. The effect of intensity-controlled aerobic endurance training was studied in adult female and male rats that ran 2 h/day, 5 days/wk, in intervals of 8 min at 85-90% of VO(2 max) and 2 min at 50-60% of VO(2 max), with adjustment of exercise level according to VO(2 max) every week. After 7 wk, the increase in VO(2 max) plateaued at 60-70% above sedentary controls. Ventricular weights and myocyte length were up 25-30% and 6-12%, respectively. Work economy, oxygen pulse, and heart rate were sufficiently changed to indicate substantial cardiovascular adaptation. The model mimics important human responses to training and could be used in future studies on cellular, molecular, and integrative mechanisms of improved cardiovascular function.     

Metabolic and ventilatory responses to steady state exercise relative to lactate thresholds

The metabolic and ventilatory responses to steady state submaximal exercise on the cycle ergometer were compared at four intensities in 8 healthy subjects. The trials were performed so that, after a 10 min adaptation period, power output was adjusted to maintain steady state VO2 for 30 min at values equivalent to: (1) the aerobic threshold (AeT); (2) between the aerobic and the anaerobic threshold (AeTAnT); (3) the anaerobic threshold (AnT); and (4) between the anaerobic threshold and VO2max (AnTmax). Blood lactate concentration and ventilatory equivalents for O2 and CO2 demonstrated steady state values during the last 20 min of exercise at the AeT, AeAnT and AnT intensities, but increased progressively until fatigue in the AnTmax trial (mean time = 16 min). Serum glycerol levels were significantly higher at 40 min of exercise on the AeAnT and the AnT when compared to AeT, while the respiratory exchange ratios were not significantly different from each other. Thus, metabolic and ventilatory steady state can be maintained during prolonged exercise at intensities up to and including the AnT, and fat continues to be a major fuel source when exercise intensities are increased from the AeT to the AnT in steady state conditions. The blood lactate response to exercise suggests that, for the organism as a whole, anaerobic glycolysis plays a minor role in the energy release system at exercise intensities upt to and including the AnT during steady state conditions.     

Hydrogen ion concentration and oxygen uptake in an isolated canine hindlimb.

Oxygen utilization (VO2) and lactate production by an isolated perfused canine hindlimb was evaluated at various hydrogen ion concentrations. A membrane lung perfusion system was established such that blood flow and temperature could be fixed at normal levels. Oxygen, nitrogen, and carbon dioxide (CO2) gas flows to the membrane lung were independently regulated to provide a fixed arterial oxygen content (CaO2). By changing CO2 flow, the pH of the arterial blood was varied between 6.9 and 7.6 at 10-min intervals. The mean O2 delivery (CaO2 X blood flow) was between 16.3 ML O2/min and 20.5 ml O2/min. Standard error of the mean in each dog, however, was less than 0.4 ml O2/min. VO2 was linearly related to the pH of the perfusing blood: VO2% = 100.1 pH - 643 (r = 0.866). Oxygen consumption was inversely related to PCO2: VO2% = -0.62 PCO2 + 124, but the correlation was less good (r = 0.729). Lactate production was linearly related to the pH of the perfusing blood (above a pH of 7.4): lactate produced = 22.5 pH - 162.5 (r = 0.75). At a pH below 7.4, lactate was not produced. Oxygen consumption of skeletal muscle appears critically dependent on extracellular fluid pH. A change in pH of 0.1 alters VO2 almost exactly 10%. Alkalosis is a potent stimulus to lactic acid production by skeletal muscle.     

Seasonal aerobic performance variations in elite soccer players

The purpose of this study was to examine the seasonal changes in body composition and aerobic performance in elite soccer players. Twelve elite professional soccer players (aged 25 6 5 years, weight 75.7 6 5.3 kg, height 1.79 6 0.06 m) were measured for body fat (%), maximum oxygen consumption (VO2max), running velocity at VO2max (VO2max), running velocity at a fixed blood lactate concentration of 4 mmol · L21 (v-4 mM) at the start of the preseason period, at the beginning of the competitive period, and at midseason. VO2max, v-4 mM, and vVO2max increased significantly (p , 0.05) by 4.5, 10.5, and 7.8,respectively, after the preseason period. Thereafter, the aerobic performance parameters remained relatively constant, with no significant changes throughout the competitive period. The results of this study suggest that moderate improvements were observed in VO2max, and the %VO2max at 4 v-4 mM, whereas higher improvements were observed in VO2max and v-4 mmol · L21 after the preseason training period. On the other hand, during the competitive period, aerobic performance remained unchanged.In addition, this study suggests that heart rate, lactate, vVO2, and VO2max are useful and practical predictors that help monitor aerobic performance changes during a soccer season.