Eur J Appl Physiol (2001) 84: 107±114
Ó Springer-Verlag 2001
ORIGINAL ARTICLE
Laurent Bosquet á Luc LeÂger á Patrick Legros
Blood lactate response to overtraining in male endurance athletes
Accepted: 26 September 2000
Abstract Many physiological markers vary similarly
during training and overtraining. This is the case for the
blood lactate concentration ([La)]b), since a right shift of
the lactate curve is to be expected in both conditions. We
examined 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
lactate concentration ([La)]b,peak). Ten experienced endurance athletes increased their usual amount of training by 100% within 4 weeks. An incremental test and a
time trial were performed before (baseline) and after this
period of overtraining, and after 2 weeks of recovery
(REC). The [La)]b and RPE 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 baseline to REC
[9.64 (SD 1.17), 8.16 (SD 1.31) and 7.69 (SD 1.84)
mmol á l)1, for the three tests, respectively; P < 0.05]
and a right shift of the lactate 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 tests, respectively; P < 0.05), but no di€erence in RPE, its
variability accounting for less than 25% of the variability of [La)]b/RPE (r ˆ 0.49). Consequently, [La)]b/
RPE provides little additional information compared to
[La)]b alone. Expressing [La)]b as a %[La)]b,peak
L. Bosquet (&) á L. LeÂger
DeÂpartement de KineÂsiologie,
Universite de MontreÂal, CP 6128, succ. centre ville,
MontreÂal (QueÂbec),
Canada H3C 3J7
L. Bosquet á P. Legros
Faculte des Sciences du Sport,
Universite de Poitiers, 4 alleÂe Jean Monnet, 86000 Poitiers, France
e-mail: laurent.bosquet@mshs.univ-poitiers.fr
Fax: +33-5-49453396
resulted in a suppression of the right shift of the lactate
curve, suggesting it was primarily the consequence of a
decreased production of lactate by the muscle. Since the
right shift of the curve induced by optimal training is a
result of improved lactate utilization, the main di€erence
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 measurement after a sucient period of rest to make
the distinction with overreaching.
Key words Overtraining á Overreaching á
Blood lactate concentration á Ratings
of perceived exertion á Running
Introduction
The overtraining (OT) syndrome has been reported to
describe a long-term decrement in performance capacity
induced by an accumulation of training and non-training stress (Kreider et al. 1998). Anecdotal evidence and
well-controlled studies over the two last decades have
allowed the compilation of a comprehensive list of
symptoms than can be observed during OT (Kuiper and
Keizer 1988; Fry et al. 1991a; Lehmann et al. 1997;
O'Toole 1998). However, despite determined e€orts by
researchers, there is currently no single marker that allows diagnosis of the disorder (Flynn 1998). Because of
this fact, most of the scienti®c studies have used the
concomitant appearance of both physiological and
psychological symptoms to diagnose OT (Lehmann
et al. 1991; Fry et al. 1992; Hooper et al. 1993; Snyder
et al. 1995; Uusitalo et al. 1998). Since the determination of the blood lactate response to incremental exercise
is routine in the physiological monitoring of the performance of endurance athletes, it is of major importance to determine if it can be used as a diagnostic
criterion. Paradoxically, it appears that both optimal
training and OT induce a right shift of the lactate curve,
108
leading to possible misinterpretation of test results
(Hurley et al. 1984; Jacobs 1986; Kinderman 1986;
Jeukendrup et al. 1992; Jeukendrup and Hesselink 1994;
Snyder et al. 1995; Billat 1996).
In an attempt to disassociate training from OT,
Snyder et al. (1993) proposed complementing the blood
lactate measurement with ratings of perceived exertion
(RPE). According to their hypothesis, a decrease in the
blood lactate concentration ([La)]b) for a given exercise
intensity is accompanied by an increase of RPE during
OT, while RPE remains unchanged or decreases when
the athlete is tested during intensive training (Snyder
et al. 1993). Therefore, the [La)]b/RPE quotient would
be expected to decrease with OT, but stay relatively the
same with intensive training. This hypothesis has been
shown to be true during overreaching (OR), which
corresponds to a short term decrease in performance
capacity induced by an accumulation of training or nontraining stress, but has has never been tested with OT
subjects.
Donovan and Brooks (1983), as well as Donovan and
Pagliassoti (1992) and MacRae et al. (1992), have shown
that the decrease of submaximal [La)]b induced by endurance training is the consequence of an improvement
in lactate utilization. The autonomic and hormone
dysfunctions observed during OT (Barron et al. 1985;
Urhausen et al. 1995; Lehmann et al. 1998) suggest
rather a decreased capacity of the muscle to produce
lactate, as has been suggested by the reported decrease in
the peak blood lactate concentration ([La)]b,peak; StrayGundersen et al. 1986; Lehmann et al. 1991; Jeukendrup
et al. 1992; Jeukendrup and Hesselink 1994; Urhausen
et al. 1998; Hedelin et al. 2000). In such a case, it has
been found that it is possible to distinguish between
training and OT changes by converting [La)]b for a
given exercise intensity from an absolute concentration
(millimoles per litre) into a percentage of [La)]b,peak
(Foster et al. 1988). If the right shift in the lactate curve
is maintained after this procedure of normalization, the
decrease of [La)]b would re¯ect an increase in lactate
utilization, and certainly an increase in performance
capacity resulting from optimal training. Conversely, if
the right shift is suppressed, the primary cause of decreased [La)]b would probably be a decreased capacity
of the muscle to produce lactate, and would indicate a
decrease in performance capacity induced by OT.
Therefore the purpose of the present investigation
was to investigate the physiological response of male
endurance athletes to a 4 week increase in the amount of
training (OVER), followed by a 2 week period of active
recovery (REC), to determine if it is possible to disassociate the changes in the lactate curve brought about by
training and OT. We hypothesized that OT would result
in a decrease in the [La)]b/RPE quotient after OVER
and REC, and that the right shift of the lactate curve
induced by OT would be a consequence of a decreased
capacity of the muscle to produce lactate, which would
be evidenced by a decrease in the [La)]b,peak after both
periods, and the suppression of the right shift of the
lactate curve when the lactate concentrations are expressed as a percentage of [La)]b,peak.
Methods
Subjects
Ten moderately to well-trained male endurance athletes (six
runners, four triathletes) gave their written informed consent to
participate in the study. All of them had been training regularly for
at least 1 year prior to the experiment. Their characteristics are
described in Table 1. This study was approved by the University
of Montreal Ethics Committee for Health Science.
Procedures
The study included two sequences: OT (28 days, OVER), and
recovery training (14 days, REC). The OVER period consisted of
a 4 week distance running cycle modi®ed according to the procedure described by Lehmann et al. (1991). During the 1st week,
the subjects ran as usual (baseline). In the following 3 weeks
(OVER), their amounts of training were successively increased
from baseline by 33%, 66% and 100%. The intensity of training
was determined for each individual based on the velocity reached
during the last stage of the incremental test (maximal aerobic
speed, MAS). Training consisted of interval training (IT; 200±
1,000 m distances, at 90%±110% of MAS), continuous fast
running (CFR; 20±30 min, at 80%±85% of MAS), and continuous slow running (CSR; 40±100 min, at 75% of MAS). The
amount of IT and CFR was held constant each week, whereas
the amount of CSR increased each week during the OVER period (Fig. 1). The REC period consisted of a 2 week distance
running cycle. The CSR was reduced to 50% of baseline,
whereas CFR and IT were suppressed. Dietary intake was not
Table 1 Physical pro®le of the subjects (n = 10). MAS Maximal
aerobic speed
Mean
SD
Age
(years)
Height
(cm)
Body
mass (kg)
Body
fat (%)
MAS
(km á h)1)
26.70
4.80
174.00
7.63
67.50
11.59
11.58
3.09
18.85
1.23
Fig. 1 Amount of training (mean and SD) during each week of the
study. CSR Continuous slow running (75% of maximal aerobic
speed, MAS), CFR continuous fast running (80%±85% of MAS),
IT interval training (90%±110% of MAS)
109
standardized throughout the study, and the subjects continued
to eat the foods they were accustomed to. They were not allowed
to take vitamin tablets or any type of medication.
Measurements
The athletes were familiarized with the experiment procedure
2 weeks prior to the experiment. Before and after the OVER period, and after the REC period, an incremental exercise test and a
time trial were performed. To avoid any residual fatigue induced by
a recent work-out, the subjects performed standardized light
training the day before their visit in the laboratory, consisting in a
30 min run at 75% of MAS.
The incremental exercise test was made on a motorized treadmill (Gymrol S2500, Tecmachine, Andrezieux, France). It consisted
of stages of 3 min, each separated by a recovery of 1 min. Initial
speed was set at 12 km á h)1, and increased by 2 km á h)1 until
16 km á h)1, and by 1 km á h)1 until exhaustion. Blood samples
were taken from the ®ngertip immediately after each stage to analyse for [La)]b using an enzymatic method (YSI 27, Yellow
Springs, Ohio, USA). The RPE was also obtained using the Borg
scale rated from 6 to 20 (Borg et al. 1985). To obtain ratios with the
same magnitude as those reported by Snyder et al. (1993), RPE was
divided by 2, ranging from 3 to 10.
The time trial was performed on the motorized treadmill. It
consisted in a time to exhaustion at 85% of MAS. The subjects
were not informed about the time that had elapsed since the
beginning of the test, but were verbally encouraged to continue for
as long as possible.
Throughout all training periods, the subjects were asked to keep
daily logs including usual training details (duration, intensity, dif®culty) and self ratings of fatigue using a seven-point scale ranging
from (1) very, very low to (7) very, very high, as proposed by
Hooper et al. (1995). Moreover, before and after the OVER period,
and after the REC period, the subjects were asked to complete a
standardized questionnaire designed by the SocieÂte FrancËaise de
MeÂdecine du Sport (SFMS) to detect OT (Legros 1993). They had
to answer the 52 items of this questionnaire using a 5 point scale.
The number of items per point was then totalled and multiplied by
1 if ``never'', 2 if ``rarely'', 3 if ``sometimes'', 4 if ``often'' and 5 if
``always''. These sums allowed the calculation of a score that has
been considered an index of OT (Legros et al. 2000).
Criteria for OT
A subject was considered to be OT if there was no reported illness,
injury, or other factor to explain his performance decrement in his
log book (Hooper et al. 1995), and if he met two of the three
following criteria:
1. A decline in performance in the time to exhaustion at 85% of
MAS (Urhausen et al. 1998)
2. Subjective fatigue ratings greater than 5 on a scale of 1±7 for a
minimum of 7 consecutive days (Hooper et al. 1995)
3. An increase in the score from the questionnaire (Legros et al.
2000).
If there was a stagnation of performance after the OVER period, or
a return to baseline after the REC period, subjects were considered
to be OR. If performance was improved after the OVER period,
subjects were considered to be in a normal state of training, and
were excluded from the subsequent analysis.
Statistical analysis
The MAS, time to exhaustion, [La)]b/RPE, [La)]b,peak, RPE and
the score on the questionnaire were analysed using a one-way
ANOVA with repeated measures on amount of training (Baseline, OVER and REC). Fatigue ratings were analysed by a oneway ANOVA with repeated measures on time (weeks 1±6). To
protect against possible violation of the sphericity assumption,
the signi®cance of F-ratios was adjusted according to the procedure of Greenhouse and Geisser (1959; see also Vincent 1999).
A Tukey's post-hoc analysis was performed when a P < 0.05
was obtained. Linear regression analysis was used to examine the
relationship between the di€erent parameters. Statistica Software
(version 5.1, Statsoft, Tulsa, USA, 1997) was used for all statistical analyses.
Results
All the subjects completed the OVER period. None of
them su€ered from illness or injury of any kind. Three
subjects reported upper respiratory tract infections (sore
throat and swelling of the nose) during the last week of
OVER and the 1st week of REC.
Performance
This study took place in two parts, ®rstly with six subjects (exp. 1), and then with four subjects (exp. 2). All
the procedures and measurements were identical, except
for the criteria of performance. Initially, we used MAS
to follow the performance capacity of each subject. But
for reasons which are discussed in the following section,
we opted for a time to exhaustion at 85% of MAS in the
second part of this experiment. Respiratory parameters
were not available because of technical complications.
Consequently, a subject's report of exhaustion was the
single criterion determining that each test was performed
to the maximum.
Concerning the subjects of exp. 1, we observed
a decrease of mean MAS between the three
tests [18.33 (SD 1.32), 18.15 (SD 1.26) and (SD 17.98
1.43) km á h)1, respectively], which was signi®cant only
between baseline and REC (P < 0.05). Considering individual results, we noted a stagnation over the three
tests in one subject, a decrease in two subjects, and a
stagnation after OVER and a decrease after REC in
three subjects. Interestingly, we found a signi®cant decrease of mean maximal heart rate from baseline to
OVER [182 (SD 11) and 172 (SD 10) beats á min)1, in
the two tests respectively; P < 0.01], with a return to
baseline after REC [179 (SD 10) beats á min)1, P <
0.01 between OVER and REC, and P > 0.05 between
baseline and REC], even in subjects whose performance
remained impaired.
Concerning the subjects of exp. 2, we observed a
decrease in the time to exhaustion at 85% MAS between
the three tests [31.93 (SD 2.59), 25.52 (SD 4.57) and
23.89 (SD 4.59) min, respectively], which was signi®cant
only between baseline and REC (P < 0.05). Considering individual results, we noted a decrease after OVER
and REC in two subjects, a stagnation after OVER and
a decrease after REC in one subject, and a decrease after
OVER with a return to baseline after REC in one subject. Mean heart rate from the 10th min of exercise until
the end of the test at each test was 176 (SD 7),
110
171 (SD 10) and 175 (SD 8) beats á min)1, respectively
(P > 0.05). During OVER, all subjects complained
about heavy legs, and associated their diminished performance with a muscle rather than cardiovascular
limitation.
Questionnaire
We observed an increase in the mean score from the
questionnaire after OVER, with a slight decrease
after REC [100.3 (SD 18.9), 122.7 (SD 24.5) and
113.8 (SD 31.8) arbitrary units, in each test respectively]. The di€erence was signi®cant only between baseline
and OVER (P < 0.05). Considering individual results,
we noted a stagnation over the three tests in two subjects, an increase after OVER and REC in six subjects,
and an increase after OVER with a return to baseline
after REC in two subjects.
Fatigue ratings
Fig. 2 Blood lactate concentrations during the three incremental
tests. Baseline after 1 week of normal training, OVER after 3 weeks
of overtraining, REC after 2 weeks of recovery training. aOVER
di€erent from baseline (P < 0.05), bREC di€erent from baseline
(P < 0.05), cOVER and REC di€erent from baseline (P < 0.05).
MAS Maximal aerobic speed
Blood lactate concentration
We observed an increase of fatigue after OVER, and a
decrease after REC [2.91 (SD 0.97), 5.03 (SD 1.69) and
3.15 (SD 0.86) arbitrary units, in the three tests,
respectively], which was signi®cant only between baseline and OVER (P < 0.001). Considering individual
results, only six subjects rated their level of fatigue over
5 for at least 7 consecutive days. There was a decrease
after REC in all subjects.
Diagnosis of OT
Individual results are summarized in Table 2. It appears
that seven of the ten subjects had two or three of the
criteria of OT. These subjects were gathered in the same
group and classi®ed as overtrained (OT) for subsequent
analysis. As there was no performance improvement in
the three other subjects, a diagnosis of OR has been
retained.
Table 2 Criteria of overtraining for each subject. OT overtraining,
OR overreaching
Subjects
Illness±
Injury
Performance
Questionnaire
Fatigue
ratings
Diagnosis
1
2
3
4
5
6
7
8
9
10
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
OT
OT
OT
OT
OT
OT
OT
OR
OR
OR
X
X
The relationship between [La)]b and relative exercise
intensity in OT is depicted in Fig. 2. We observed both a
signi®cant decrease of [La)]b,peak after OVER and REC
when compared to baseline [9.64 (SD 1.17), 8.16 (SD
1.31) and 7.69 (SD 1.84) mmol á l)1, respectively; P <
0.05), and a right shift of the lactate curve, evidenced by
a signi®cant increase of interpolated velocities for several ®xed [La)]b (Table 3). The normalization procedure
resulted in a suppression of this right shift, since there
was no di€erence between interpolated velocities for
®xed percentages of [La)]b, peak after each test (Table 3).
In comparison, we found no signi®cant di€erence of
[La)]b,peak in OR [8.60 (SD 1.08), 8.19 (SD 1.26) and
9.14 (SD 0.60) mmol á l)1, in the three tests, respectively, P > 0.05]. There was a left shift of the lactate curve
after OVER in one subject, and a right shift in the two
other subjects (an individual example is given in Fig. 3).
We noted a return to baseline after REC in the three
subjects.
The [La)]b/RPE quotient
Data obtained from OT subjects are presented in
Table 4. Except for the second stage, probably because
of the early appearance of lactate during the ®rst stage,
we observed an increase of [La)]b/RPE at each stage of
the incremental test. When OVER and REC values were
compared with baseline we found a signi®cant decrease
at 90%, 95% and 100% of MAS. In contrast, we found
no di€erences in OR, whatever the intensity of exercise
(data not shown).
The relationship between RPE and relative exercise
intensity in OT is depicted in Fig. 4. We observed the
expected increase of RPE with the intensity of exercise,
111
)
Table 3 Interpolated running velocities for given blood lactate concentrations ([La ]b) and given percentages of peak blood lactate
concentration (% [La)]b,peak) in overtrained subjects. For other de®nitions see Fig. 2
[La)]b
(mmol á l)1)
Running velocity (km á h)1)
Test
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Baseline
OVER
REC
13.64
14.84b
14.11
1.38
1.44
0.76
15.36
16.05a
15.94a
1.22
1.28
0.93
16.36
16.83
16.97a
1.25
1.13
0.87
16.95
17.51a
17.60b
1.15
1.05
0.97
17.53
18.02a
18.02a
1.06
1.00
1.08
17.98
18.49a
18.40a
1.05
1.00
0.99
[La)]b,peak
(%)
Running velocity (km á h)1)
Test
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Baseline
OVER
REC
15.24
15.54
15.17
1.44
1.59
1.52
16.25
16.31
16.19
1.39
1.42
1.25
16.73
16.91
16.93
1.32
1.33
1.09
17.39
17.43
17.44
1.27
1.19
0.98
17.90
17.90
17.86
1.18
1.11
1.01
18.22
18.31
18.16
1.16
1.08
1.04
a
b
2
3
30
4
40
5
50
6
60
7
70
80
Di€erent from baseline (P < 0.05)
Di€erent from baseline (P < 0.01)
Table 4 Blood lactate concentration/rate of perceived exertion for overtrained subjects. MAS Maximal aerobic speed
Intensity Blood lactate concentration/rate of perceived exertion (arbitrary units)
(%MAS)
60
70
80
85
90
95
100
Test
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
Baseline
OVER
REC
45.21
48.01
47.24
15.76
14.11
15.74
37.34
32.65
41.11
8.75
8.11
12.11
47.99
38.74
45.74
9.20
9.53
10.86
56.75
48.77
46.14b
6.89
12.33
9.23
71.36
59.15a
60.36a
10.55
12.78
9.45
87.32
71.95b
79.26b
8.65
14.63
19.62
105.41 17.48
84.61b 12.56
81.03a 22.64
a
b
SD
Di€erent from baseline (P < 0.05)
Di€erent from baseline (P < 0.01)
but we found no di€erence between baseline, OVER and
REC. Linear regression analysis revealed that the variability in RPE accounted for approximately 25% of the
variability of [La)]b/RPE (r ˆ 0.49), whereas the variability in [La)]b accounted for 73% (r ˆ 0.85).
Discussion
All experimental studies on OT are confronted with the
same problem: are the subjects really OT? If we refer to
the strict de®nition of OT, the main diagnostic criterion
should be a decrease in performance capacity, without a
return to baseline after a sucient period of rest (Fry
et al. 1991b). We used the MAS as a performance indicator during exp. 1. Although we found a signi®cant
decrease from baseline to REC [18.33 (SD 1.32) and
17.98 (SD 1.43)] km á h)1, in the two tests respectively,
P < 0.05], it was dicult to be sure whether the difference of only 2% was a consequence of OT, or came
under the normal day-to-day variations of MAS. There
is little consensus on this issue, since performance decrements reported in the literature as a result of OT have
ranged from 0.7% to 25% (Barron et al. 1985; Lehmann
et al. 1991; Fry et al. 1992; Jeukendrup et al. 1992;
Verde et al. 1992; Hooper et al. 1993; Snyder et al. 1995;
Urhausen et al. 1998; Uusitalo et al. 1998).
During exp. 2, we used a measure of aerobic endurance, a time to exhaustion in this case, to follow the
performance capacity of each subject. We opted for 85%
of MAS, because it corresponded approximately to the
average intensity maintained by our subjects in competition (cross-country, road races of 10±15 km). We
found a decrease of 20% after OVER (P ˆ 0.07) and
25% after REC (P < 0.05). Independently of the diagnosis, the di€erences were large enough to avoid any
doubt about their interpretation (18%±36%, except for
the subject for whom there was a stagnation after
OVER). In parallel, we noted only small variations of
MAS for these four subjects [20.20 (SD 0.95),
19.77 (SD 0.88) and 20.10 (SD 0.77) km á h)1, respectively; P > 0.05]. As has already been suggested by the
reports of Fry et al. (1992) and Urhausen et al. (1998), it
appears that aerobic endurance is more a€ected by OT
than is maximal aerobic power. Consequently, a time to
exhaustion at a ®xed percentage of MAS is certainly a
better indicator than MAS in monitoring performance
capacity in OT studies with endurance athletes. Moreover, our results highlight the absolute necessity to
repeat the battery of tests after a sucient period of rest
112
Fig. 3 Blood lactate concentration during the incremental tests in
an overreached subject. De®nitions as in Fig. 2
(14 days). Without this precaution, we would have diagnosed a state of OT in one of the three OR subjects,
and a state of OR in one of the seven OT subjects.
The aim of this study was to assess the validity of
[La)]b and RPE, measured during an incremental test,
for detecting OT. The lowered submaximal and maximal
[La)]b observed in OT are in accordance with previous
reports (Kindermann 1986; Stray-Gundersen et al. 1986;
Costill 1986; Lehmann et al. 1991; Jeukendrup et al.
1992; Snyder et al. 1993, 1995; Jeukendrup and Hesselink 1994). It implies that a right shift of the lactate curve
does not systematically re¯ect an improvement of
aerobic endurance and performance capacity for long
duration events. For that reason, it has been suggested
that the lactate curve must be interpreted with caution
(Jeukendrup et al. 1992).
Snyder et al. (1993) proposed to make the distinction
between changes induced by optimal training and
changes induced by OT by dividing [La)]b by RPE. We
found e€ectively a signi®cant decrease of [La)]b/RPE
after OVER and REC from 90% to 100% of MAS in
Fig. 4 Ratings of perceived exertion (RPE) during the incremental
tests in overtrained subjects (mean and SD). Other de®nitions as in
Fig. 2
OT. But, in contrast to their hypothesis, we noted only
few variations of RPE (Fig. 3), which accounted for less
than 25% of the variability of [La)]b/RPE (r ˆ 0.49).
Jeukendrup et al. (1992) have already noticed that RPE
was not a sensitive enough indicator to detect OT. Since
RPE provides little additional information compared to
that from [La)]b alone, and has been found not always
to be reliable during incremental exercise (Lamb et al.
1999), we question the usefulness of the quotient of these
two measures. The RPE was designed to be used once
after any exercise. If used repeatedly after each stage of
an incremental test, RPE scores tend to be in¯ated at
higher intensities because subjects feel obliged to adjust
their estimations with the increasing intensities.
According to the model of Brooks et al. (1996), any
decrease of submaximal [La)]b can result from a decreased production by the muscle, or an increased utilization by the muscle and other organs (Weltman 1995).
Donovan and Brooks (1983), as well as Donovan and
Pagliassoti (1990) and Mac Rae et al. (1992), have
shown that the decrease of submaximal [La)]b induced
by endurance training is the consequence of an improvement in lactate utilization. Our results suggest that
this is not the case during OT, since the decreased submaximal [La)]b was not observed when the concentrations were normalized to [La)]b,peak. The right shift of
the lactate curve noted in OT seemed to be primarily the
consequence of a decreased muscle production capacity,
evidenced by the decrease of [La)]b,peak after OVER and
REC. Since [La)]b,peak is relatively una€ected by endurance training (MacArdle et al. 1991), this criterion
can be proposed as a marker of OT.
Several mechanisms have been proposed to explain
this decrease. Costill et al. (1988) have shown that days
of repeated intense training could lead to delayed glycogen resynthesis. It has now been recognized that any
decrease of substrate availability can alter the blood
lactate response to exercise (Ivy et al. 1981; Maasen and
Busse 1989). However, Snyder et al. (1995) have clearly
shown that a decrease of [La)]b,peak can also occur in OT
subjects with normal muscle glycogen stores at rest. This
suggests that the capacity to mobilize available substrate
is a more critical factor than substrate availability as
such. In this respect, Barron et al. (1985) have reported a
blunted growth hormone and cortisol response after an
insulin-induced hypoglycaemia in ®ve OT marathon
runners. This means that an exercise hypoglycaemia
independent of muscle glycogen stores can occur during
OT, decreasing the capacity of the muscle to produce
lactic acid.
Mazzeo and Marshall (1989), as well as Ahlborg
et al. (1985) and Gaesser et al. (1992), have shown that
[La)]b is closely related to plasma noradrenaline concentration. From this fact, any perturbation of the
sympathetic nervous system drive can a€ect lactic acid
production in the muscle. The investigations of Lehmann et al. (1997) have brought forward experimental
data suggesting both a desensitization of the body to
catecholamines, evidenced by a decrease of heart rate,
113
)
glucose and [La ]b during submaximal exercise despite
an increase of plasma noradrenaline concentration
(Lehmann et al. 1992a), and a sympathetic nervous
system insuciency, evidenced by a decrease in the
nocturnal excretion rate of catecholamines (Lehmann
et al. 1992b). These autonomic perturbations can also
contribute to the decrease of lactic acid production by
the muscle during OT.
If a biological marker is to be e€ective in diagnosing OT, it must allow the distinction to be made
between OT and OR (Hooper and MacKinnon 1995;
Rowbottom et al. 1998). Because of the limited number of subjects (n ˆ 3), our study does not allow the
proposal of a reliable description of the blood lactate
response to OR. However, according to the OR
studies of Jeukendrup et al. (1992) and Snyder et al.
(1993), a decrease of [La)]b,peak and a right shift of the
lactate curve are to be expected after OVER, with a
return to baseline after REC. This response was
observed in two of our three OR subjects. We noted
a left shift of the lactate curve in the third subject,
but also a return to baseline after REC. Therefore,
as already suggested by Rowbottom et al. (1998), the
only way to make the distinction between OT and OR
is to repeat the tests after a sucient period of rest.
Still further research with larger numbers of subjects is
necessary to con®rm this.
In conclusion, the present study shows that RPE does
not provide useful information for detecting OT during
an incremental test. Therefore, [La)]b/RPE is not a
better marker of OT than [La)]b alone. On the other
hand, we noted that the right shift of the lactate curve
was accompanied by a decrease of [La)]b,peak when there
was a decrease of performance capacity, which was
maintained after 2 weeks of recovery when the subjects
were OT, but not when they were OR. Consequently, we
propose retaining a decrease of [La)]b,peak as a marker of
OT in long duration events, and repeating its measurement after a sucient period of rest to make the distinction with OR.
Acknowledgements The authors wish to thank Christine Baldoni,
Arthur Long and Bruno Bernard for their technical assistance.
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