Anderson, G. S., & Rhodes, E. C. (1991). Relationship between blood lactate and excess CO2 in elite cyclists. Journal of Sports Sciences, 9, 173-181.

It has been recognized that the OBLA correlated highly with break points in ventilation (VE), carbon dioxide excretion (VCO2), and the respiratory exchange ratio. OBLA is suggested as being the point where metabolism shifts to anaerobic energy use. These transition points were postulated as being non-invasive indices that could be used to predict the LT/OBLA/ANTh.

The excess CO2 threshold correlated highly (r = .95) with lactate threshold. However, the excess CO2 threshold did not represent the lactate threshold because it preceded the LT by 1.5 min. The VE/VO2 threshold was correlated with LT (r = .91) as has been known in the past.

The authors warn: "Studies which have used blood lactate as their criterion measure must be interpreted with caution. Recent studies have suggested that blood lactate may not reflect intracellular lactate production or concentration. Although VE/VO2 and blood lactate have been found to break away at similar points, these similarities may in no way reflect the accumulation of intracellular lactate." (p. 178)

It is suggested that excess CO2 diffuses across the muscle membrane more readily than the lactate molecule which would be reoxidized inside the cell or more slowly released.

In these elite cyclists (Canadian National Team trialists) the mean absolute OBLA value was 3.35 (+- .83) mM, occurring over a 1.72 to 5.3 mM range. These results suggest that individual differences must be recognized and that individual determination of the lactate threshold at a set value of 2 to 4 mM is not possible, being subject to large error factors. Thus, if a turnpoint is to be estimated between two points in field tests, it could be quite erroneous. The wide range of threshold values suggests that the OBLA is highly dependent upon the individual and the setting of predetermined threshold values would not allow for inter-individual variation.

Implications.

• OBLA levels vary greatly between individuals and should only be interpreted on an intra-individual basis, and
• non-invasive estimates of OBLA are particularly suspect.

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