Abstract
Cyclists often use heart rate limits or power output zones, obtained from lactate
parameters during incremental exercise testing, to control training intensity. However,
the relationship between heart rate or power output, and blood lactate can be changed
by several factors including dehydration. Therefore, in the current study we investigated
the impact of exercise-induced dehydration on lactate parameters during graded exercise.
Nine triathletes completed two test sessions in random order, with a 1-week interval.
Each session consisted of 2 graded cycling tests to exhaustion (pretest, posttest),
interspersed by a 2-h endurance exercise bout. In one session the cyclists received
adequate fluid replacement (EH, 1350 ml · h-1 ) whilst in the other session dehydration was not prevented (DH, 225 ml · h-1 ). Subjects received equal amounts of carbohydrates (150 g) during either condition.
The 4-mmol lactate threshold (OBLA) and the dmax lactate threshold (TH-Dm) were calculated from the power : lactate curves. Weight
loss was 0.5 ± 0.3 kg in EH versus 2.5 ± 0.2 kg in DH (p < 0.05). Heart rate (HR)
at TH-Dm remained unchanged in all test occasions. Conversely, HR at OBLA increased
by ∼ 10 beats · min-1 from the pretest to the posttest (p < 0.05), in both EH and DH. Compared to the pretest,
in the posttest power output at TH-Dm was reduced (minus ∼ 12 %, p < 0.05) in DH,
but not in EH. Gross mechanical efficiency at TH-Dm was 20.7 ± 1 % in the pretest
in EH and was not different from the pretest value in DH (21.4 ± 0.7 %, n.s.). Gross
efficiency decreased in the posttest in DH (18.4 ± 0.6 %, p < 0.05), but not in EH
(20.2 ± 0.8 %, n.s.). It is concluded that heart rate rather than power output should
be used to monitor training load in cyclists exercising in environmental conditions
predisposing to dehydration. Furthermore, in the latter condition, adequate rehydration
is essential to preserve optimal mechanical efficiency.
Key words
Exercise testing - cycling - triathlon - fluid replacement
References
1
Achten J, Venables M C, Jeukendrup A.
Fat oxidation rates are higher during running compared with cycling over a wide range
of intensities.
Metabolism.
2003;
52
747-752
2
American College of Sports Medicine .
Nutrition and athletic performance.
Med Sci Sports Exerc.
2000;
32
2130-2145
3 Astrand P O, Rodahl K. Textbook of Work Physiology: Physiological Bases of Exercise.
3rd ed. Singapore; McGraw-Hill 1986: 622
4
Barr S I.
Effects of dehydration on exercise performance.
Can J Appl Physiol.
1999;
24
164-172
5
Beaver W L, Wasserman K, Whipp B J.
A new method for detecting anaerobic threshold by gas exchange.
J Appl Physiol.
1986;
60
2020-2027
6
Bishop D, Jenkins D G, MacKinnon L T.
The relationship between plasma lactate parameters, Wpeak and 1-h cycling performance
in women.
Med Sci Sports Exerc.
1998;
30
1270-1275
7
Chavarren J, Calbet J A.
Cycling efficiency and pedalling frequency in road cyclists.
Eur J Appl Physiol.
1999;
80
555-563
8
Cheng B, Kuipers H, Snyder A C, Keizer H A, Jeukendrup A, Hesselink M.
A new approach for the determination of ventilatory and lactate thresholds.
Int J Sports Med.
1992;
13
518-522
9
Coyle E F, Sidossis L S, Horowitz J F, Beltz J D.
Cycling efficiency is related to the percentage of type I muscle fibers.
Med Sci Sports Exerc.
1992;
24
782-788
10
el-Sayed M S, Rattu A J, Roberts I.
Effects of carbohydrate feeding before and during prolonged exercise on subsequent
maximal exercise performance capacity.
Int J Sport Nutr.
1995;
5
215-224
11
Febbraio M A, Snow R J, Stathis C G, Hargreaves M, Carey M F.
Blunting the rise in body temperature reduces muscle glycogenolysis during exercise
in humans.
Exp Physiol.
1996;
81
685-693
12
Hargreaves M, Dillo P, Angus D, Febbraio M.
Effect of fluid ingestion on muscle metabolism during prolonged exercise.
J Appl Physiol.
1996;
80
363-366
13
Heaps C L, González-Alonso J, Coyle E F.
Hypohydration causes cardiovascular drift without reducing blood volume.
Int J Sports Med.
1994;
15
74-79
14
Heck H, Mader A, Hess G, Mücke S, Müller R, Hollman W.
Justification of the 4-mmol/l lactate threshold.
Int J Sports Med.
1985;
6
117-130
15
Ivy J L, Costill D L, Van Handel P J, Essig D A, Lower R W.
Alterations in the lactate threshold with changes in substrate availability.
Int J Sports Med.
1981;
2
139-142
16
Kenefick R W, Mahood N V, Mattern C O, Kertzer R, Quinn T J.
Hypohydration adversely affects lactate threshold in endurance athletes.
J Strength Cond Res.
2002;
16
38-43
17 McArdle W D, Katch F I, Katch V L. Exercise Physiology, Energy, Nutrition, and
Human Performance. 5th ed. Philadelphia; Lippincott Williams & Wilkins 2001 193 348
18
Moseley L, Jeukendrup A E.
The reliability of cycling efficiency.
Med Sci Sports Exerc.
2001;
33
621-627
19
Nielsen B.
Olympics in Atlanta: a fight against physics.
Med Sci Sports Exerc.
1996;
28
665-668
20
Nose H, Mack G W, Shi X R, Morimoto K, Nadel E R.
Effect of saline infusion during exercise on thermal and circulatory regulations.
J Appl Physiol.
1990;
69
609-616
21
Passfield L, Doust J H.
Changes in cycling efficiency and performance after endurance exercise.
Med Sci Sports Exerc.
2000;
32
1935-1941
22
Reiser M, Meyer T, Kindermann W, Daugs R.
Transferability of workload measurements between three different types of ergometer.
Eur J Appl Physiol.
2000;
82
245-249
23
Sherman W M, Costill D L, Fink W, Miller J M.
Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization
during performance.
Int J Sports Med.
1981;
2
114-118
24
Van Schuylenbergh R, Vanden Eynde B, Hespel P.
Prediction of sprint triathlon performance from laboratory tests.
Eur J Appl Physiol.
2003;
91
94-99
P. Hespel
Faculty of Physical Education and Physiotherapy, Katholieke Universiteit Leuven
Tervuursevest 101
3001 Leuven
Belgium
Telefon: + 3216329091
Fax: + 32 16 32 91 96
eMail: peter.hespel@flok.kuleuven.ac.be