Many physiological markers vary similarly during training and overtraining.
This is the case for the blood lactate concentration ([La-](b)), since a r
ight shift of the lactate curve is to be expected in both conditions. We ex
amined the possibility of separating the changes in training from those of
overtraining by dividing [La-](b) by the rating of perceived exertion ([La-
](b)/RPE) or by converting [La-](b) into a percentage of the peak blood lac
tate concentration ([La-](b,peak)). Ten experienced endurance athletes incr
eased their usual amount of training by 100% within 4 weeks. An incremental
test and a time trial were performed before (baseline) and after this peri
od of overtraining, and after 2 weeks of recovery (REC). The [La-](b) and R
PE were measured during the recovery of each stage of the incremental test.
We diagnosed overtraining in seven athletes, using both physiological and
psychological criteria. We found a decrease in mean [La-](b,peak) from base
line to REC [9.64 (SD 1.17), 8.16 (SD 1.31) and 7.69 (SD 1.84) mmol . l(-1)
for the three tests, respectively; P < 0.05] and a right shift of the lact
ate curve. Above 90% of maximal aerobic speed (MAS) there was a decrease of
mean [La-](b)/RPE from baseline to REC [at 100% of MAS of 105.41 (SD 17.48
), 84.61 (SD 12.56) and 81.03 (SD 22.64) arbitrary units, in the three test
s, respectively; P < 0.05), but no difference in RPE, its variability accou
nting for less than 25% of the variability of [La-](b)/RPE (r = 0.49). Cons
equently, [La-](b)/RPE provides little additional information compared to [
La-](b) alone. Expressing [La-](b) as a %[La-](b,peak) resulted in a suppre
ssion of the right shift of the lactate curve, suggesting it was primarily
the consequence of a decreased production of lactate by the muscle. Since t
he right shift of the curve induced by optimal training is a result of impr
oved lactate utilization, the main difference between the two conditions is
the decrease of [La-](b,peak) during overtraining. We propose retaining it
as a marker of overtraining for long duration events, and repeating its me
asurement after a sufficient period of rest to make the distinction with ov
erreaching.