Capillary-venous differences of free plasma catecholamines at rest and during graded exercise

Levels of free plasma catecholamines were simultaneously determined in 10 cyclists using capillary blood from one ear lobe and venous blood from one cubital vein. Catecholamine concentrations were higher in the ear lobe blood than in the venous blood at rest and during graded exercise. Average differences amounted to 1.7 nmol X 1(-1) (dopamine), 2.1 nmol X 1(-1) (noradrenaline) and 1.9 nmol X 1(-1) (adrenaline) at rest and increased only to 8.8 nmol X 1(-1) for noradrenaline during exercise. We assume that higher concentrations of dopamine and adrenaline in the capillary blood point to a significant neuronal release of these catecholamines, similar to noradrenaline. Catecholamine concentrations in capillary blood may better reflect sympathetic drive and delivery of catecholamines to the circulation than the concentrations in venous blood.     

Response of left ventricular diastolic filling to graded exercise relative to the lactate threshold

During incremental exercise, the left ventricular ejection fraction increases up to the intensity of the anaerobic threshold and tends to level off at higher exercise intensities. Since there is a correlation between the response of peak filling rate and ejection fraction to exercise, this study was conducted to determine whether the response of left ventricular diastolic function is similar to the response of systolic function relative to lactate threshold. Twelve healthy men performed two exercise tests on a cycle ergometer. In the first test, lactate threshold and maximal power output were determined. In the second exercise test, gated radionuclide ventriculography was performed at rest, at the lactate threshold intensity, and at peak exercise to measure ejection fraction and peak filling rate. Ejection fraction increased significantly from rest [mean (SD): 62 (5)%] to lactate threshold [76 (7) %] and did not change significantly from lactate threshold to peak exercise [77 (7)%]. Likewise, peak filling rate (normalized for stroke counts) increased from resting [6.1 (0.9)V _s · s^–1] to lactate threshold [9.4 (1.8)V _s · s^–1] and did not change significantly from lactate threshold to peak exercise [9.6 (2.9)V _s · s^–1]. There was no correlation between the change in peak filling rate and the change in ejection fraction from rest to lactate threshold. Thus, during incremental exercise, left ventricular diastolic function responds qualitatively similar to systolic function.     

Influence of mild exercise at the lactate threshold on glucose effectiveness.

The effect of a single bout of mild exercise on glucose effectiveness (S(G)) and insulin sensitivity (S(I)) was studied in six young male subjects by using a minimal model. An intravenous glucose tolerance test was performed under two conditions as follows: 1) 25 min after a bout of exercise on a cycle ergometer at the lactate threshold level for 60 min (Ex) and 2) without any prior exercise (Con). Leg blood flow (LBF) was also measured by strain-gauge plethysmography simultaneously with blood sampling. S(I) did not significantly change after exercise (18.1 +/- 1.5 vs. 17.7 +/- 1.9 x 10-(5) min/pM), whereas S(G) significantly increased (0.016 +/- 0.002 vs. 0.025 +/- 0.002 min(-1), P < 0.01). The increased blood flow after exercise remained high during the time period for measurement of the glucose disappearance constant and may be a determinant of S(G). The incremental lactate area under the curve until insulin loading was also significantly higher in Ex than in Con (2.6 +/- 0.9 vs. -3.5 +/- 1.5 mM/min, P < 0.05). These results suggest that increased S(G) after mild exercise may be due, at least in part, to increased LBF and lactate production under a hyperglycemic state.     

Sex-related differences in free plasma catecholamines in individuals of similar performance ability during graded ergometric exercise

Sex-related differences of catecholamine responses were evaluated in nine healthy women and six age-matched men at rest and during incremental treadmill exercise. Heart rate, oxygen uptake (VO2), glucose and lactate blood levels as well as the free plasma catecholamines, noradrenaline and adrenaline, were determined. No significant differences were observed for these parameters between the two groups at rest. The females had relative VO2max and maximal running velocities similar to the males, which points to a comparable dynamic performance ability. However, at identical work loads, noradrenaline, adrenaline and glucose levels were significantly higher in women than in men. Lactate, heart rate and relative VO2 showed a similar tendency at submaximal exercise levels, indicating higher strain at identical stress levels in women. The reason for the higher sympathetic activity in women at identical work loads may be their relatively smaller skeletal muscle mass in relation to the loads during this test.     

Blood lactate and ammonium ion accumulation during graded exercise in humans

The purpose of this study was to determine the pattern of blood lactate and ammonium ion (NH+4) accumulation during graded exercise in humans. Six adult volunteers performed a maximum O2 uptake (VO2 max) test on a bicycle ergometer. Blood samples were collected each minute of the test. Both blood lactate (r = 0.92) and NH4+ (r = 0.70) increased exponentially in relation to increased work. However, closer examination of individual curves revealed that both metabolites remained near resting levels during mild exercise (less than 40% VO2 max) and then demonstrated abrupt upward break points at increased work loads (greater than 50% VO2 max). There was a significant linear relationship (r = 0.96) between the work load at which the lactate break point (LBP) and NH4+ break point (ABP) occurred in each subject. In addition, there was a significant linear relationship (r = 0.82) between the blood concentrations of NH4+ and lactate during exercise. The results suggest a connection between NH4+ production and glycolytic energy metabolism during exercise. Several possible explanations are offered; however, further work at the cellular level is needed before the exact relationship between NH4+ and lactate can be determined.     

Failure to obtain a unique threshold on the blood lactate concentration curve during exercise

The purpose of this study was to compare various methods and criteria used to identify the anaerobic threshold (AT), and to correlate the AT obtained with each other and with running performance. Furthermore, a number of additional points throughout the entire range of lactate concentrations [La⁻] were obtained and correlated with performance. A group of 19 runners [mean age 33.7 (SD 9.6) years, height 173 (SD 6.3) cm, body mass 68.3 (SD 5.4) kg, maximal O₂ uptake (V˙O_{2 max} ) 55.2 (SD 5.9) ml · kg⁻¹ · min⁻¹] performed a maximal multistage treadmill test (1 km · h⁻¹ every 3.5 min) with blood sampling at the end of each stage while running. All AT points selected (visual [La⁻], 4 mmol · l⁻¹ [La⁻], 1 mmol · l⁻¹ above baseline, log-log breakpoint, and 45° tangent to the exponential regression) were highly correlated one with another and with performance (r > 0.90) even when there were many differences among the AT (P < 0.05). The additional points (ranging from 3 to 8 mmol · l⁻¹ [La⁻], 1 to 6 mmol · l⁻¹ [La⁻] above the baseline, and 30 to 70° tangent to the exponential curve of [La⁻]) were also highly correlated with performance (r > 0.90). These results failed to demonstrate a distinct AT because many points of the curve provided similar information. Intercorrelations and correlations between AT and performance were, however, reduced when AT were expressed as the percentage of maximal treadmill speed obtained at AT or percentage of V˙O_{2 max} . This would indicate that different attributes of aerobic performance (i.e. maximal aerobic power, running economy and endurance) are measured when manipulating units. Thus, coaches should be aware of these results when they prescribe an intensity for training and concentrate more on the physiological consequences of a chosen [La⁻] rather than on a “threshold”. Accepted: 22 October 1997     

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.     

Aerobic training effects on maximum oxygen consumption, lactate threshold and lactate disappearance during exercise recovery of dogs

1. Dogs were submitted to an aerobic training schedule and its maximum oxygen consumption, lactate threshold and lactate concentration during recovery were compared among the following conditions: not trained (UT), after 1 month of training (T1), after 2 months of training (T2) and after detraining (DT). 2. Maximum oxygen consumption increased significantly in relation to UT condition only at T2 condition. The detraining reversed this alteration. 3. Lactate threshold when expressed as Vo2 or absolute work load increased significantly after aerobic training (T2) but did not present any alteration when it was expressed as % of Vo2 max. 4. The lactate decreasing during recovery did not differ between the four experimental conditions (after 10 min). 5. The latency time for the lactate concentration to reach the top values was reduced by aerobic training (T2).     

Influence of cold exposure on blood lactate response during incremental exercise

This study examined the effect of acute exposure of the whole body to cold on blood lactate response during incremental exercise. Eight subjects were tested with a cycle ergometer in a climatic chamber, room temperature being controlled either at 24 degrees C (MT) or at -2 degrees C (CT). The protocol consisted of a step increment in exercise intensity of 30 W every 2 min until exhaustion. Oxygen consumption (VO2) was measured at rest and during the last minute of each exercise intensity. Blood samples were collected at rest and at exhaustion for estimations of plasma norepinephrine (NE), epinephrine (E), free fatty acid (FFA) and glucose concentrations, during the last 15 s of each exercise step and also during the 1st, 4th, 7th, and the 10th min following exercise for the determination of blood lactate (LA) concentration. The VO2 was higher during CT than during MT at rest and during nearly every exercise intensity. At CT, lactate anaerobic threshold (LAT), determined from a marked increase of LA above resting level, increased significantly by 49% expressed as absolute VO2, and 27% expressed as exercise intensity as compared with MT. The LA tended to be higher for light exercise intensities and lower for heavy exercise intensities during CT than during MT. The E and NE concentrations increased during exercise, regardless of ambient temperature. Furthermore, at rest and at exhaustion E concentrations did not differ between both conditions, while NE concentrations were greater during CT than during MT. Moreover, an increase off FFA was found only during CT.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of exercise duration during incremental exercise on the determination of anaerobic threshold and the onset of blood lactate accumulation

To determine the effect of the duration of incremental exercise on the point at which arterial blood lactate concentration (HLa) increases above the resting value (anaerobic threshold: AT) and on the point at which HLa reaches a constant value of 4 mM (onset of blood lactate accumulation: OBLA), eight male students performed two different kinds of incremental exercise. A comparison of arterial HLa and venous HLa was made under both conditions of incremental exercise. The incremental bicycle exercise tests consisted of 25 W increase every minute (1-min test) and every 4 min (4-min test). At maximal exercise, there were no significant differences in either gas exchange parameters or HLa values for the two kinds of incremental exercise. However, the peak workloads attained during the two exercises were significantly different (P less than 0.01). At OBLA and AT, there were no significant differences in gas exchange parameters during the 1-min and 4-min tests except for the workload (at OBLA P less than 0.01; at AT P less than 0.05). When venous blood HLa was used instead of arterial HLa for a 4-min test, AT was not significantly different from that obtained by arterial HLa, but OBLA was significantly different from that obtained by arterial HLa (P less than 0.05). On the other hand, for the 1-min test, venous HLa values yielded significantly higher AT and OBLA compared with those obtained using arterial HLa (P less than 0.01). It was concluded that when arterial blood was used, there was no effect of duration of workload increase in an incremental exercise test on the determination of the AT and OBLA expressed in VO2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma catecholamine and lactate response during graded exercise with varied glycogen conditions.

The relationships between the lactate threshold (TLa), plasma catecholamines, and ventilatory threshold (TVE) were examined under normal and glycogen-depleted conditions. Nine male subjects performed a graded exercise test on a bicycle ergometer in a normal glycogen (NG) state and in a glycogen-depleted (GD) state to determine if manipulation of muscle glycogen content would affect their ventilatory, lactate, and catecholamine responses. High correlations were found between plasma lactate and the two catecholamines, epinephrine (r = 0.964) and norepinephrine (r = 0.965) under both conditions. The GD protocol resulted in a shift in the TLa to a later work rate; inflections in epinephrine and norepinephrine shifted in a coordinated manner. TVE and TLa occurred at similar work loads under NG conditions [67.2 +/- 1.5 and 65.6 +/- 2.3% maximal oxygen consumption (VO2max), respectively], but TLa occurred at a later work load (75.3 +/- 1.9% VO2max) compared with TVE (68.3 +/- 1.6% VO2max) under GD conditions. These results suggest a causal relationship between plasma lactate and epinephrine during a graded exercise test under the glycogen conditions studied. Although an association existed between ventilation and lactate, this relationship was not as strong.     

Age-related augmentation of plasma catecholamines during dynamic exercise in healthy males

Although plasma norepinephrine (NE) increases with age in response to a variety of submaximal adrenergic stimuli, the effect of age on plasma catecholamine levels during maximal aerobic effort and during submaximal work at a fixed percent of peak O2 consumption (VO2) is unknown. We therefore measured NE, epinephrine (E), and VO2 at rest and during graded maximal treadmill exercise in 24 healthy male volunteers (ages 22-77 yr) from the Baltimore Longitudinal Study of Aging who were rigorously screened to exclude the presence of cardiovascular disease. At rest neither heart rate (HR) nor VO2 were age related. Resting NE (pg/ml) was not age related, but resting E (pg/ml) was higher in male subjects 68-77 yr old (group III) than in those aged 22-37 (group I) or 44-55 yr (group II), P less than 0.01. Maximal HR (beats/min) showed a strong inverse relationship to age (203.5 - 0.65 age, r = -0.80, P less than 0.001). Peak VO2 in milliliters per kilogram total body weight per minute decreased with age (47.7 - 0.23 age, r = -0.71, P less than 0.001). At maximal effort both NE (P less than 0.01) and E (P less than 0.05) were higher in group III than in either of the younger groups. At submaximal work levels NE and E also increased with age, and when normalized for relative effort at loads between 45 and 80% of peak VO2 both NE and E were higher in the group III male subjects, although statistical significance was reached for NE (P less than 0.01) but not for E (P = 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of graded dehydration on hyperthermia and cardiovascular drift during exercise.

This investigation determined the effect of different rates of dehydration, induced by ingesting different volumes of fluid during prolonged exercise, on hyperthermia, heart rate (HR), and stroke volume (SV). On four different occasions, eight endurance-trained cyclists [age 23 +/- 3 (SD) yr, body wt 71.9 +/- 11.6 kg, maximal O2 consumption 4.72 +/- 0.33 l/min] cycled at a power output equal to 62-67% maximal O2 consumption for 2 h in a warm environment (33 degrees C dry bulb, 50% relative humidity, wind speed 2.5 m/s). During exercise, they randomly received no fluid (NF) or ingested a small (SF), moderate (MF), or large (LF) volume of fluid that replaced 20 +/- 1, 48 +/- 1, and 81 +/- 2%, respectively, of the fluid lost in sweat during exercise. The protocol resulted in graded magnitudes of dehydration as body weight declined 4.2 +/- 0.1, 3.4 +/- 0.1, 2.3 +/- 0.1, and 1.1 +/- 0.1%, respectively, during NF, SF, MF, and LF. After 2 h of exercise, esophageal temperature (Tes), HR, and SV were significantly different among the four trials (P < 0.05), with the exception of NF and SF. The magnitude of dehydration accrued after 2 h of exercise in the four trials was linearly related with the increase in Tes (r = 0.98, P < 0.02), the increase in HR (r = 0.99, P < 0.01), and the decline in SV (r = 0.99, P < 0.01). LF attenuated hyperthermia, apparently because of higher skin blood flow, inasmuch as forearm blood flow was 20-22% higher than during SF and NF at 105 min (P < 0.05). There were no differences in sweat rate among the four trials. In each subject, the increase in Tes from 20 to 120 min of exercise was highly correlated to the increase in serum osmolality (r = 0.81-0.98, P < 0.02-0.19) and the increase in serum sodium concentration (r = 0.87-0.99, P < 0.01-0.13) from 5 to 120 min of exercise. In summary, the magnitude of increase in core temperature and HR and the decline in SV are graded in proportion to the amount of dehydration accrued during exercise.     

Influence of moderate cold exposure on blood lactate during incremental exercise.

This study examined the effect of exposure of the whole body to moderate cold on blood lactate produced during incremental exercise. Nine subjects were tested in a climatic chamber, the room temperature being controlled either at 30 degrees C or at 10 degrees C. The protocol consisted of exercise increasing in intensity in 35 W increments every 3 min until exhaustion. Oxygen consumption (VO2) was measured during the last minute of each exercise intensity. Blood samples were collected at rest and at exhaustion for the measurement of blood glucose, free fatty acid (FFA), noradrenaline (NA) and adrenaline (A) concentrations and, during the last 15 s of each exercise intensity, for the determination of blood lactate concentration [la-]b. The VO2 was identical under both environments. At 10 degrees C, as compared to 30 degrees C, the lactate anaerobic threshold (Than,la-) occurred at an exercise intensity 15 W higher and [la-]b was lower for submaximal intensities above the Than,la-. Regardless of ambient temperature, glycaemia, A and NA concentrations were higher at exhaustion while FFA was unchanged. At exhaustion the NA concentration was greater at 10 degrees C [15.60 (SEM 3.15) nmol.l-1] than at 30 degrees C [8.64 (SEM 2.37) nmol.l-1]. We concluded that exposure to moderate cold influences the blood lactate produced during incremental exercise. These results suggested that vasoconstriction was partly responsible for the lower [la-]b observed for submaximal high intensities during severe cold exposure.