Effects of 2-chloropropionate on venous plasma lactate concentration and anaerobic power during periods of incremental intensive exercise in humans

We investigated the effects of a stimulation of pyruvate dehydrogenase (PDH) activity induced by 2-chloropropionate (2-CP) on venous plasma lactate concentration and peak anaerobic power (W _{an, peak}) during periods (6 s) of incremental intense exercise, i.e. a force-velocity (F-) test known to induce a marked accumulation of lactate in the blood. TheF- test was performed twice by six subjects according to a double-blind randomized crossover protocol: once with placebo and once with 2-CP (43 mg · kg^–1 body mass). Blood samples were taken at ingestion of the drug, at 10, 20, and 40 Min into the pretest period, at the end of each period of intense exercise, at the end of each 5-min recovery period, and after completion of theF- test at 5, 10, 15, and 30 min. During theF- test, venous plasma lactate concentrations with both placebo and 2-CP increased significantly when measured at the end of each period of intense exercise (F = 33.5,P < 0.001), and each 5-min recovery period (F = 24.6,P < 0.001). Venous plasma lactate concentrations were significantly lower with 2-CP at the end of each recovery period (P < 0.01), especially for high braking forces, i.e. 8 kg (P < 0.05), 9 kg (P < 0.02), and maximal braking force (P < 0.05). After completion of theF- test, venous plasma lactate concentrations were also significantly lower with 2-CP (P < 0.001). The percentage of lactate decrease between 5- and 30-min recovery was significantly higher with 2-CP than with the placebo [59 (SEM 4)% vs 44.6 (SEM 5.5)%,P < 0.05]. Furthermore,W _{an, peak} was significantly higher with 2-CP than with the placebo [1016 (SEM 60) W vs 957 (SEM 55) W,P < 0.05]. In conclusion, PDH activation by 2-CP attenuated the increase in venous plasma lactate concentration during theF- test. Ingestion of 2-CP led to an increasedW _{an, peak}.     

Relationship between ventilation and arterial potassium concentration during incremental exercise and recovery

The purpose of this study was to compare the relationship of ventilation (VE) with pH, arterial concentrations of potassium [( K+]a), bicarbonate [( HCO3-]a), lactate [( la]a), and acid-base parameters which would affect hyperpnoea during exercise and recovery. To assess this relationship, ten healthy male subjects exercised with intensity increasing as a ramp function of 20 W.min-1 until voluntary exhaustion and they were then allowed a 5-min recovery period. Breath-by-breath gas exchange data, [HCO3-]a, pH, [la]a, [K+]a and blood gases were determined during both exercise and recovery. Using a linear regression method, the VE/[K+]a relationship was analysed during both exercise and recovery. Several interesting results were obtained: a significant relationship between [K+]a and VE was observed during recovery as well as during exercise; the VE at any given values of [K+]a was significantly higher during recovery than during exercise and out of those factors affecting exercise hyperpnoea, only [K+]a had a similar time-course to VE during recovery. Changes in [K+]a during recovery were shown to occur significantly faster than VE with an [K+]a time constant of 70.0 s, SD 16.2 as opposed to 105.5 s, SD 10.0 for VE (P less than 0.01). These results provided further evidence that [K+]a might play an important role as a substance which can stimulate exercise hyperpnoea as has been suggested by other workers. The present study also showed that during recovery [K+]a contributed significantly to the control of VE.     

The effect of acoustic stimulus of different continuity pattern on plasma concentration of catecholamines in humans during submaximal exercise

The purpose of the study was determination of adrenaline and noradrenaline concentrations in peripheral blood in 13 men aged 20--22 years subjected to acoustic stimulation of continuous, intermittent and pulse pattern during graded submaximal exercise. The studied subjects performed physical exercise on a cycle ergometer at workloads of 2 W/kg of body mass. The noise produced during the exercise had peak acoustic pressure of 100--120 dB, at frequencies ranging from 63 Hz to 4000 Hz. The exposure to noise and exercise lasted 15 minutes. Catecholamines in the peripheral blood were determined by spectrofluorometry by the method of Anton and Sayer. The obtained results showed that the concentrations of adrenaline and noradrenaline increased considerably in the peripheral blood during exposure to this acoustic stimulation in relation to the initial concentrations. The highest increases were observed during exposure to impulse noise.     

Effects of aging and training status on ventilatory response during incremental cycling exercise

The aim of this study was to examine the effect of aging and training status on ventilatory response during incremental cycling exercise. Eight young (24 ± 5 years) and 8 older (64 ± 3 years) competitive cyclists together with 8 young (27 ± 4 years) and 8 older (63 ± 2 years) untrained individuals underwent a continuous incremental cycling test to exhaustion to determine ventilatory threshold (VT), respiratory compensation point (RCP), and maximal oxygen uptake (VO?max). In addition, the isocapnic buffering (IB) phase was calculated together with the hypocapnic hyperventilation. Ventilatory threshold occurred at similar relative exercise intensities in all groups, whereas RCP was recorded at higher intensities in young and older cyclists compared to the untrained subjects. The IB phase, reported as the difference between VT and RCP and expressed either in absolute (ml·min?1·kg?1 VO?) or in relative terms, was greater (p < 0.01) in both young and older trained cyclists than in untrained subjects, who were also characterized by a lower exercise capacity. Isocapnic buffering was particularly small in the older untrained volunteers. Although young untrained and older trained subjects had a similar level of VO?max, older athletes exhibited a larger IB. In addition, a higher absolute but similar relative IB was observed in young vs. older cyclists, despite a higher VO?max in the former. In conclusion, the present study shows that aging is associated with a reduction of the IB phase recorded during an incremental exercise test. Moreover, endurance training induces adaptations that result in an enlargement of the IB phase independent of age. This information can be used for the characterization and monitoring of the physiological adaptations induced by endurance training.     

Plasma potassium and ventilation during incremental exercise in humans: modulation by sodium bicarbonate and substrate availability.

It has recently been demonstrated that, compared to normal conditions, ventilation (VE) was increased during exercise after glycogen depletion, in spite of a marked increase in plasma pH (pHP). It was further demonstrated that VE in patients with McArdle's syndrome was reduced when substrate availability was improved. In the present experiments, six endurance trained men performed two successive cyclo-ergometric incremental exercise tests (tests A, B) after normal nutrition (N) and after a fatty meal in conjunction with a sodium bicarbonate (NaHCO3) solution (FSB) or without NaHCO3 (F), and the relationship between VE, plasma potassium concentration ([K+]P), and pHP was checked. Plasma free fatty acid concentration ([FFA]P) was markedly increased in the F and FSB trials (P < 0.001). In FSB pHP was significantly increased, compared to N and F (P < 0.001). In all the B tests, pHP increased during moderate and intense exercise and in FSB, remained alkalotic even during maximal exercise intensity. In contrast, VE and [K+]P changes were almost equal in all the trials and in tests A and B. It was found that exercise-induced changes of VE and [K+]P in the present experiments were not markedly affected by [FFA]P or pHP values and that these changes also occurred independently of changes in pHP or plasma bicarbonate concentration. The often used glycogen depletion strategy may have slightly increased VE but apparently did not overcompensate for a possible decrease in VE due to increased pHP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of different muscle shortening velocities during prolonged incremental cycling exercise on the plasma growth hormone, insulin, glucose, glucagon, cortisol, leptin and lactate concentrations.

BACKGROUND: Strenuous exercise was reported to involve the alteration in the release of some "stress" hormones such as growth hormone (GH), cortisol, catecholamines and appropriate adjustment of energy metabolism but the relative contribution of these hormones to metabolic response, to cycling exercise performed at different muscle shortening velocities, has not been clarified. AIMS: The purpose of this experiment was to assess the effect of applying different pedalling rates during a prolonged incremental cycling exercise test on the changes in the plasma levels of growth hormone, cortisol, insulin, glucagon and leptin in humans. Material and METHODS: Fifteen healthy non-smoking men (means +/- SD: age 22.9 +/- 2.4 years; body mass 71.9 +/- 8.2 kg; height 178 +/- 6 cm; with VO2max of 3.896 +/- 0.544 1 x min(-1), assessed in laboratory tests, were subjects in this study. The subjects performed in two different days a prolonged incremental exercise tests at two different pedalling rates, one of them at 60 and another at 120 rev x min(-1). During this tests the power output has increased by 30 W every 6 minutes. The tests were stopped when the subject reached about 70 % of the VO2max. RESULTS AND CONCLUSIONS: We have found that choosing slow or fast pedalling rates (60 or 120 rev min(-1)), while generating the same external mechanical power output, had no effect on the pattern of changes in plasma cortisol, insulin, glucagon, glucose and leptin concentrations. But, generation of the same external mechanical power output at 120 rev min(-1) causes more stepper increase (p < 0.01) in the plasma growth hormone concentration [GH]pl and plasma lactate concentrations [La]pl when compared to that observed during cycling at 60 rev x min(-1). We have also found that the onset of a significant increase in [GH]pl during cycling at 60 rev x min(-1) was not accompanied by significant increase in [La]pl. While during cycling at 120 rev x min(-1) the onset of a significant increase in [La]pl occurred without increase in [GH]pl, but with continuation of exercise when plasma [La]pl increased, there was also a parallel rise in plasma [GH]pl, as reported before. This results indicates that the increase in [GH]pl during exercise is not closely related to the increase in [La]pl.     

Alterations in plasma volume, electrolytes and protein during incremental exercise at different pedal speeds

We investigated the effects of pedal speed on changes in plasma volume, electrolytes and protein during incremental exercise. Ten adult males participated in two, 30 minute incremental cycle ergometer exercise tests at room temperature (22° C, rh=56%). Exercise load was increased from 20 to 70% of peak . Five minutes were spent at each of six stages which were equally spaced in exercise intensity. Subjects pedaled at 50 (50 RPM) and 90 (90 RPM) rev · min^–1. Venous blood samples were drawn prior to exercise and during the last minute of each stage. Relative plasma volume changes showed a progressive hemoconcentration during the exercise. There were no significant differences due to pedal speed as plasma volume loss averaged –7.3% during exercise. [Na+], [Cl–], and [K+] increased significantly during exercise but were not influenced by pedal speed. Changes in plasma protein and albumin concentrations indicated that there was a loss of globulin from the vascular volume in both conditions and an addition of albumin to the plasma in 50 RPM. The difference in plasma albumin dynamics was possibly related to an effect of pedal speed on movement of fluid in the lymphatic vessels of the legs.This work was supported in part by Grants from the Theresa Monaco Endowment of the University of Houston College of Education and Nautilus Sports/Medical Industries     

Use of arterialized venous blood sampling during incremental exercise tests.

Close agreement between arterialized venous and arterial pH, PCO2, and lactate has previously been demonstrated during steady-state exercise. The purpose of the present study was to compare arterialized venous and arterial pH, PCO2, K+, lactate, pyruvate, and epinephrine during the constantly changing circumstances of an incremental exercise test. Eight normal subjects undertook an incremental exercise test (increasing by 20 W/min) to exhaustion on a cycle ergometer during which simultaneous arterial and arterialized venous samples were drawn over the last 20 s of each work load. Linear regression of arterialized venous on arterial values showed that r varied from 0.97 to 0.99 for the variables examined and, therefore, showed that accurate estimates of arterial values could be made from the arterialized venous results during incremental testing. For many purposes it could be assumed that arterialized venous values equaled arterial values without serious error.     

Effect of exercise-induced muscle damage on the blood lactate response to incremental exercise in humans

Eccentric muscle actions are known to induce temporary muscle damage, delayed onset muscle soreness (DOMS) and muscle weakness that may persist for several days. The purpose of the present study was to determine whether DOMS-inducing exercise affects blood lactate responses to subsequent incremental dynamic exercise. Physiological and metabolic responses to a standardised incremental exercise task were measured two days after the performance of an eccentric exercise bout or in a control (no prior exercise) condition. Ten healthy recreationally active subjects (9 male, 1 female), aged 20 (SD 1) years performed repeated eccentric muscle actions during 40 min of bench stepping (knee high step; 15 steps · min⁻¹). Two days after the eccentric exercise, while the subjects experienced DOMS, they cycled on a basket loaded cycle ergometer at a starting work rate of 150 W, with increments of 50 W every 2 min until fatigue. The order of the preceding treatments (eccentric exercise or control) was randomised and the treatments were carried out 2 weeks apart. Two days after the eccentric exercise, all subjects reported leg muscle soreness and exhibited elevated levels of plasma creatine kinase activity (P < 0.05). Endurance time and peak V˙O₂ during cycling were unaffected by the prior eccentric exercise. Minute volume, respiratory exchange ratio and heart rate responses were similar but venous blood lactate concentration was higher (P < 0.05) during cycling after eccentric exercise compared with the control condition. Peak blood lactate concentration, observed at 2 min post-exercise was also higher [12.6 (SD 1.4) vs 10.9 SD (1.3) mM; P < 0.01]. The higher blood lactate concentration during cycling exercise after prior eccentric exercise may be attributable to an increased rate of glycogenolysis possibly arising from an increased recruitment of Type II muscle fibres. It follows that determination of lactate thresholds for the purpose of fitness assessment in subjects experiencing DOMS is not appropriate. Accepted: 27 September 1997     

Interrelationship between pH, plasma potassium concentration and ventilation during intense continuous exercise in man

During resting conditions plasma hydrogen ion concentration ([H+]P) is known to influence ventilation (VE), whereas the control of plasma potassium concentration ([K+]P) at rest and of both [K+]P and VE during exercise are controversial issues. To obtain more information about these variables during muscular work, eight trained men performed two successive intense continuous cycle-ergometer tests, the first (test I) during metabolic acidosis, the second (test II) with an alkalotic pH. No correlation was found between [H+]P and [K+]P or VE in the direction of change of these variables in test I. Furthermore, no correlation between [H+]P and [K+]P in test I and II was seen. Instead [K+]P and VE changed in relation to the exercise intensity. We suggest that the results confirm [K+]P as an indicator of muscular stress. In addition, the similar behaviour of relative values of [K+]P and VE changes in test I (r = 0.9, m = 1.0, where m is the slope of the regression curve) supports the hypothesis that extracellular potassium controls VE and thereby [H+]P also.     

The relationship between plasma potassium concentration and muscle torque during recovery following intense exercise

The present study investigated the relationship between plasma potassium ion concentration ([K⁺]) and skeletal muscle torque during three different 15-min recovery periods after fatigue induced by four 30-s sprints. Four males and one female completed the multiple sprint exercise on three separate days; recovery was passive, i.e. no cycling exercise (PRec), active cycling at 30% peak oxygen consumption O_2peak (30% Rec) and active cycling at 60% O_2peak (60% Rec). Plasma [K⁺] was measured from blood sampled from an antecubital vein of subjects at rest and at 0, 3, 5, 10 and 15 min into each recovery. Isokinetic leg strength was measured at rest and at 1, 6, 11 and 16 min during each recovery. Following the exhaustive sprints, [K⁺] increased significantly from an average mean (SEM) resting value of 3.81 (0.07) mmol · l⁻¹ to 4.48 (0.19) mmol · l⁻¹ (P < 0.01). In all recovery conditions, plasma [K⁺] returned to resting levels within 3 min following the fourth sprint. However, in the two active recovery conditions plasma [K⁺] increased over the remainder of the recovery periods to 4.36 (0.12) mmol · l⁻¹ in the 30% Rec condition and 4.62 (0.12) mmol · l⁻¹ in the 60% Rec condition, the latter being significantly higher than the former (P < 0.01). The maximum torque measured following the sprints decreased significantly, on average, to 61.1 (8.36)% of peak levels (P < 0.01). After 15 min of recovery, maximum torque was highest in the 30% Rec condition at 92.13 (3.06)% of peak levels (P < 0.01), compared to 85.23 (3.64)% and 85.71 (0.82)% for the PRec and 60% Rec conditions, respectively. In contrast to the significant differences in plasma [K⁺] across all three recovery conditions, muscle torque recovery was significantly different in only the 30% Rec condition. In summary, recovery of peak levels of muscle torque following fatiguing exercise does not appear to follow changes in plasma [K⁺]. Accepted: 18 October 1996     

Effect of beta-adrenergic blockade on plasma lactate concentration during exercise at high altitude

When unacclimatized lowlanders exercise at high altitude, blood lactate concentration rises higher than at sea level, but lactate accumulation is attenuated after acclimatization. These responses could result from the effects of acute and chronic hypoxia on beta-adrenergic stimulation. In this investigation, the effects of beta-adrenergic blockade on blood lactate and other metabolites were studied in lowland residents during 30 min of steady-state exercise at sea level and on days 3, 8, and 20 of residence at 4300 m. Starting 3 days before ascent and through day 15 at high altitude, six men received propranolol (80 mg three times daily) and six received placebo. Plasma lactate accumulation was reduced in propranolol- but not placebo-treated subjects during exercise on day 3 at high altitude compared to sea-level exercise of the same percentage maximal oxygen uptake (VO2max). Plasma lactate accumulation exercise on day 20 at high altitude was reduced in both placebo- and propranolol-treated subjects compared to exercise of the same percentage VO2max performed at sea level. The blunted lactate accumulation during exercise on day 20 at high altitude was associated with reduced muscle glycogen utilization. Thus, increased plasma lactate accumulation in unacclimatized lowlanders exercising at high altitude appears to be due to increased beta-adrenergic stimulation. However, acclimatization-induced changes in muscle glycogen utilization and plasma lactate accumulation are not adaptations to chronically increased beta-adrenergic activity.     

Intraerythrocyte and plasma lactate concentrations during exercise in humans

The purpose of this study was to examine plasma and intraerythrocyte lactate concentrations during graded exercise in humans. Seven adult volunteers performed a maximum O2 uptake (VO2max) test on a cycle ergometer. Plasma and intraerythrocyte lactate concentrations (mmol . L-1 of plasma or cell water) were determined at rest, during exercise, and at 15-min post-exercise. The results show that plasma and intraerythrocyte lactate concentrations were not significantly different from each other at rest or moderate (less than or equal to 50% VO2max) exercise. However, the plasma concentrations were significantly increased over the intraerythrocyte levels at 75% and 100% VO2max. The plasma to red cell lactate gradient reached a mean (+/- SE) 1.7 +/- 0.4 mmol . L-1 of H2O at exhaustion, and was linearly (r = 0.84) related to the plasma lactate concentration during exercise. Interestingly, at 15-min post-exercise the direction of the lactate gradient was reversed, with the mean intraerythrocyte concentration now being significantly increased over that found in the plasma. These results suggest that the erythrocyte membrane provides a barrier to the flux of lactate between plasma and red cells during rapidly changing blood lactate levels. Furthermore, these data add to the growing body of research that indicates that lactate is not evenly distributed in the various water compartments of the body during non-steady state exercise.     

Left ventricular mechanical limitations to stroke volume in healthy humans during incremental exercise

During incremental exercise, stroke volume (SV) plateaus at 40-50% of maximal exercise capacity. In healthy individuals, left ventricular (LV) twist and untwisting ("LV twist mechanics") contribute to the generation of SV at rest, but whether the plateau in SV during incremental exercise is related to a blunting in LV twist mechanics remains unknown. To test this hypothesis, nine healthy young males performed continuous and discontinuous incremental supine cycling exercise up to 90% peak power in a randomized order. During both exercise protocols, end-diastolic volume (EDV), end-systolic volume (ESV), and SV reached a plateau at submaximal exercise intensities while heart rate increased continuously. Similar to LV volumes, two-dimensional speckle tracking-derived LV twist and untwisting velocity increased gradually from rest (all P < 0.001) and then leveled off at submaximal intensities. During continuous exercise, LV twist mechanics were linearly related to ESV, SV, heart rate, and cardiac output (all P < 0.01) while the relationship with EDV was exponential. In diastole, the increase in apical untwisting was significantly larger than that of basal untwisting (P < 0.01), emphasizing the importance of dynamic apical function. In conclusion, during incremental exercise, the plateau in LV twist mechanics and their close relationship with SV and cardiac output indicate a mechanical limitation in maximizing LV output during high exercise intensities. However, LV twist mechanics do not appear to be the sole factor limiting LV output, since EDV reaches its maximum before the plateau in LV twist mechanics, suggesting additional limitations in diastolic filling to the heart.