Comparison of blood lactate concentrations obtained during incremental and constant intensity exercise.

Differences in blood lactate concentrations obtained during step-wise incremental and constant running exercise at the same intensities were investigated. In addition, the effect of endurance running at a constant intensity obtained by three different incremental modes (OBLA-4, 6 or 8 min) on the blood lactate concentration were studied. Eight firemen and six marathon runners performed: 1) three step-wise incremental running (IR) treadmill tests, each consisting of either 5 x 4, 5 x 6 or 5 x 8 min, and, 2) six 50 min constant intensity running (CR) treadmill tests. Capillary hemolyzed blood was used for lactate determination. The blood lactate during the 5 x 4 min IR-test was 32% (p < 0.001) lower for the firemen and 22% (p < 0.001) lower for the marathon runners compared with the steady state concentration. These differences were diminished in both groups when the 5 x 8 min IR test was used. In the marathon group, constant intensity running at the OBLA intensities obtained by the 5 x 4, 5 x 6 and 5 x 8 min resulted in a lactate accumulation to a mean level of 8.1 mmol.I-1. Also, the marathon runners interrupted the exercise due to maximal perceived exertion after only 19 +/- 3, 26 +/- 4 and 30 +/- 6 min, respectively. In the firemen group, a majority of the subjects were able to complete the 50 min runs, despite a blood lactate accumulation to a mean level of 7.3 mmol.l-1 at the OBLA 5 x 4 and 5 x 6 min intensities. When OBLA 5 x 8 min intensity was performed in this groups, a steady state blood lactate concentration to a mean level of 5.3 mmol.l-1 occurred. It is concluded that step-wise incremental exercise with durations of 4 or 6 min will lead to a high risk of overestimating the maximal lactate steady state exercise intensity and the endurance running capacity.

Intact serum parathyroid hormone levels increase during running exercise in well-trained men.

The purpose of this study was to examine the influence of exercise on the serum concentrations of intact parathyroid hormone (PTH). Serum PTH and plasma lactate were measured in 15 well-trained men, 9 long-distance runners and 6 fire-fighters, during two running exercises. Test one consisted of 40-minute treadmill running with a step-wise increased load and test two consisted of 50-minute treadmill running with a constant velocity. When the load was step-wise increased, the PTH concentrations increased moderately at the slower running paces but reached a final value that was about 50% higher than the starting value. This rise occurred despite a concomitant increase of total serum calcium from 2.38 +/- 0.06 to 2.49 +/- 0.05 mmol/liter (P < 0.01). During the constant running exercise, the long-distance runners, but not the fire-fighters, displayed a significant increase in PTH concentrations although the rise in total serum calcium was similar in both groups. There was a weak correlation between the changes in PTH and lactate in both exercises. The findings demonstrate that both high and low intensity exercise enhance release of PTH in long-distance runners through a mechanism that does not involve serum calcium. This relationship might be of importance for bone mass in men performing long-distance training.

The validity and accuracy of blood lactate measurements for prediction of maximal endurance running capacity. Dependency of analyzed blood media in combination with different designs of the exercise test.

The effect of using different blood lactate sampling sites in combination with different exercise test designs on the validity and accuracy for prediction of maximal endurance running velocity was investigated. Ten aerobically all-round trained firemen and nine aerobically endurance trained long-distance runners performed six differently designed treadmill running blood lactate accumulation tests. Each test consisted of five consecutive running periods on a treadmill of either 4, 6 or 8 min duration, with a mean increase in running velocity between each period of either 0.25 or 0.5 m.s-1. The corresponding treadmill running velocity to a lactate concentration of 4.0 mmol.l-1 in capillary and venous hemolysed blood and plasma for each running velocity. The mean running velocity from a maximal 12 km run for the firemen and a maximal 21 km run for the runners served as the reference of maximal endurance running velocity. There were both significant (p < 0.001) and similar relationships (r = 0.86-0.94) and no difference in mean prediction error between the predicted and measured maximal endurance running velocities with all tested protocols. However, there was a high risk of making both over- and underestimations (5% to -4%). The lowest risk of making an inaccurate prediction was found when a running duration of 8 min for each running period was used in combination with an increase in running velocity of 0.25 m.s-1, and the lactate measurements were performed in hemolysed capillary blood.

Improving lactate analysis with the YSI 2300 GL: hemolyzing blood samples makes results comparable with those for deproteinized whole blood.

To obviate the well-documented problem of hematocrit dependency of the Yellow Springs Instruments (YSI) whole-blood lactate analyzer, we modified the dilution buffer by including a lysing reagent. This makes the results comparable with those of methods performed with deproteinized whole-blood samples. No centrifugation step is needed, thus preserving the convenience of the YSI instrument for stat and field use. The modification works equally well on plasma samples. Lactate concentrations measured in nonhemolyzed whole blood are not comparable with results for hemolyzed whole blood or protein-precipitated whole blood. We therefore recommend to all users of YSI equipment to lyse the erythrocytes before lactate determinations.

The effect of different blood sampling sites and analyses on the relationship between exercise intensity and 4.0 mmol.l-1 blood lactate concentration.

The aim of the study was to examine whether the difference in lactate concentration in different blood fractions is of practical importance when using blood lactate as a test variable of aerobic endurance capacity. Ten male firefighters performed submaximally graded exercise on a cycle ergometer for 20-25 min. Venous and capillary blood samples were taken every 5 min for determination of haematocrit and lactate concentrations in plasma, venous and capillary blood. At the same time, expired air was collected in Douglas bags for determination of the oxygen consumption. A lactate concentration of 4.0 mmol.l-1 was used as the reference value to compare the oxygen consumption and exercise intensity when different types of blood specimen and sampling sites were used for lactate analysis. At this concentration the exercise intensity was 17% lower (P less than 0.01) when plasma lactate was compared to venous blood lactate, and 12% lower (P less than 0.05) when capillary blood lactate was used. Similar discrepancies were seen in oxygen consumption. The results illustrated the importance of standardizing sampling and handling of blood specimens for lactate determination to enable direct comparisons to be made among results obtained in different studies.

Lactate concentration differences in plasma, whole blood, capillary finger blood and erythrocytes during submaximal graded exercise in humans.

The aim of the study was to investigate the distribution of lactate in plasma, whole blood, erythrocytes, and capillary finger blood, before and during submaximal exercise. Ten healthy male subjects performed submaximal graded cycle ergometer exercise for 20-25 min. Venous blood samples and capillary finger blood samples were taken before exercise and every 5th min during exercise for lactate determination. The plasma lactate concentration was significantly higher (P less than 0.001, approximately 50%) than in the erythrocytes. This difference was not altered by the venous blood lactate concentration or exercise intensity. A significant difference (P less than 0.01) in lactate concentration was also found between capillary whole blood and venous whole blood. It was concluded that direct comparisons between lactate in capillary finger blood, venous whole blood and plasma could not be made.