INTRODUCTION
The methodology used to determine the lactate threshold, in regards to blood sampling and handling procedures, has made comparisons of many studies difficult (Foxdal, et al., 1994). The choice of blood sampling site (ie. venous, arterial, arterialised-venous and capillary) and the choice of blood medium (ie. plasma, lysed or whole blood) have all been shown to alter the exercise intensity corresponding to a fixed lactate concentration (Yoshida et al., 1982; Harris and Dudley, 1989; Foxdal, et al., 1991).
It has been noted that there is a greater accumulation of lactate in plasma than in whole blood during incremental cycle exercise to exhaustion, (Harris and Dudley, 1989) however, there is little difference at rest (Forrest et al., 1990). Forrest et al. (1990) comments that there seems to be no wide spread agreement as to which method will provide the best results. However, what is well supported is that plotting plasma lactate instead of whole blood lactate from incremental exercise will cause a shift to the left on the lactate accumulation curve and a significant difference will be recorded in the intensity at a set blood lactate concentration such as OBLA (Yoshida et al., 1982; Harris and Dudley, 1989; Foxdal et al., 1991). However, no study has looked at measuring plasma and whole blood lactate and it’s effect on an individual type lactate threshold measurement.
METHODS
Fourteen male cyclists or triathletes volunteered for the experiment (age: 24.9 +/- 4.5yrs, mass: 75.2 +/- 6.0kg, VO2 peak: 63.5 +/- 10.2 ml.kg-1.min-1). All the subjects were from the Northern Rivers region of New South Wales, and all had been at least twelve months cycle trained prior to testing.
All subjects were administered one incremental maximal exercise test on the same cycle ergometer (Monark 868, Sweden). Subjects pedaling at 100 watts for three minutes with the work load increased by 30 watts every three minutes. Venous blood was sampled, at rest and in the last 30 s of each workload. Cadence was maintained at 80 rpm throughout the test and warm up. The lactate threshold was calculated using a modification of the Dmax method reported by Cheng et al. (1992).
A paired samples t-test was calculated between the exercise test intensity at a 4mM response of whole blood lactate (OBLA) and at a 4mM response of Plasma Lactate (OPLA). Additionally, a paired samples t-test was used to compare the intensity at Dmax calculated on whole blood lactate concentration and plasma lactate concentration during the incremental exercise test.
RESULTS AND DISCUSSION
The (mean+/- sd) for OBLA was 259.1 +/- 52.4 watts, compared with OPLA that occured at 233.4 +/- 51.8 watts. A paired sampled t-test calculated between OBLA and OPLA indicated that there was a significant difference between the workload indicated by a 4mM whole blood lactate concentration and a 4mM plasma lactate concentration (t = 5.93, sig .000). These findings are supported by at least two studies (Foxdal et al., 1994: Harris and Dudley, 1989). However, no previous research has documented the effect of analysis medium for an individual lactate threshold concept.
In this study, the Dmax was calculated firstly on whole blood lactate in order to assess it’s validity using that medium, then secondly the Dmax was calculated using plasma lactate concentration, so that the difference between the two calculated points could be determined. The (mean +/- sd) for plasma lactate Dmax was 242.5 +/- 41.64 watts. This compares to whole blood lactate Dmax that occured at 244.5 +/- 43.27 watts. There was no significant difference between the workloads prescribed by the Dmax for the two different assay mediums (t = -0.61, sig .555), despite the fact that there was as clear shift to the left and upwards of the lactate profile in most subjects and a significant difference between OBLA and OPLA.
REFERENCES
Cheng, B., Kuipers, H., Synder, A.C., Keizer, H.A., Jeukendrup, A., Hesselink, M. (1992) A new approach to the determination of ventilatory and lactate thresholds. Int. J. Sports Med. 13(7):518-522.
Forrest, A.R.W., Morton, S., Lambradarios, C. (1990) Blood or plasma lactate? Letter to the Editor - Br. J. Sports Med. 24: 132.
Foxdal, P., Sjodin, A., Ostman, B., Sjodin, E. (1991) The effect of different sampling sites and analyses on the relationship between exercise intensity and 4.0 mM blood lactate concentration. Eur. J. Appl. Physiol.. 63: 52-54.
Foxdal, P., Sjodin, A., Sjodin, E., Ostman, B. (1994) The validity and accuracy of blood lactate measurements for the prediction of maximal endurance running capacity. Int. J. Sports Med.. 15(2): 89-95. Harris, R., Dudley, G. (1989) Exercise alters the distribution of ammonia and lactate in blood. J. Appl. Physiol.. 66: 313-317.
Yoshida, T., Suda, Y., Tankeuchi, N. (1982) Endurance training regimen based on arterial blood lactate: effects on anaerobic threshold. Eur. J. Appl. Physiol.. 49: 223-230.