Eur J Appl Physiol (1992) 64:26-31


.ou .,of A p p l i e d Physiology and Occupational Physiology © Springer Verlag 1992

Metabolic, body temperature and hormonal responses to repeated periods of prolonged cycle-ergometer exercise in men H. Kaciuba-Uscilko 1, B. Kruk 1, M. S z c z y p a c z e w s k a 1, B. O p a s z o w s k i 2, E. Stupnicka ~, B. Bicz 1, and K. N a z a r 1 Department of Applied Physiology, Medical Research Centre, Polish Academy of Sciences, Jazgarzewska 17, 00-730 Warsaw, Poland

2 Department of Physiology,Academy of Physical Education, Warsaw, Poland Accepted July 5, 1991

Summary. This study was designed to find out whether

rest intervals and prevention of dehydration during prolonged exercise inhibit a drift in metabolic rate, body temperature and hormonal response typically occurring during continuous work. For this purpose in ten healthy men the heart rate (fo), rectal temperature (Tre), oxygen uptake (I;'O2), as well as blood metabolite and some hormone concentrations were measured during 2h exercise at approximately 50% maximal oxygen uptake split into four equal parts by 30-min rest intervals during which body water losses were replaced. During each 30-min exercise period there was a rapid change in Tr~ and fc superimposed on which, these values increased progressively in consecutive exercise periods (slow drift). The VO2 showed similar changes but there were no significant differences in the respiratory exchange ratio, pulmonary ventilation, mechanical efficiency and plasma osmolality between successive periods of exercise. Blood glucose, insulin and C-peptide concentrations decreased in consecutive exercise periods, whereas plasma free fatty acid, glycerol, catecholamine, growth hormone and glucagon concentrations increased. Blood lactate concentrations did not show any regular drift and the plasma cortisol concentration decreased during the first two exercise periods and then increased. In conclusion, in spite of the relatively long rest intervals between the periods of prolonged exercise and the prevention of dehydration several physiological and hormonal variables showed a distinct drift with time. It is suggested that the slow drift in metabolic rate could have been attributable in the main to the increased concentrations of heat liberating hormones. Key words: Intermittent prolonged exercise - Body temperature - Metabolism - Water replacement - Hormones

Offprint requests to: H. Kaciuba-Uscilko


In man, a true steady-state of physiological variables is not maintained when performing prolonged exercise, as has been indicated by the increasing values of oxygen uptake (~?O2), heart rate (fc), and body core temperature (Ekelund 1967; Kalis et al. 1988; Michael et al. 1961; Nielsen 1969; Nielsen et al. 1984). These have been accompanied by an enhancement of the magnitude of some hormonal changes (Galbo 1983; Viru 1985). The pattern of such responses can be related to the development of fatigue enhancing activity of motor centres, a progressive depletion of body carbohydrates, dehydration and accumulation of heat. Both in sports training and in some other forms of human activity, including tasks requiring prolonged effort, rest periods have been introduced to alleviate the development of fatigue. There have been several reports on intermittent exercise at high intensity and short duration but no detailed studies on physiological and hormonal responses to intermittent, prolonged exercise of relatively low intensity. In our previous work (Kaciuba-Uscilko et al. 1985) it was found that, in dogs performing four 30-rain treadmill exercise periods of moderate intensity, increments in rectal (/'re), hypothalamic and muscle temperatures as well as some metabolic responses during successive exercise periods were greater in spite of the rest periods (30 rain) separating them. It should be mentioned that during the rest intervals all measured temperatures returned to the initial levels and dehydration was prevented by giving water to the dogs. Since in the dogs beta-adrenergic blockade significantly lowered the thermal responses to exercise, it was suggested that the drift in both metabolic and body temperature during the intermittent exercise may have depended on progressive activation of the sympatho-adrenal system. In the present study an attempt was made to find out whether in human subjects a reduction in the development of fatigue by the introduction of rest periods during prolonged effort and prevention of dehydration

27 Table 1. Physiological characteristics of subjects (n = 10)

Mean SD

Age (years)

Height (cm)

Body mass (kg)

Body fat (%)

Maximal 02 uptake (1. rain-1)

22.0 1.4

177.9 4.8

76.4 6.1

14.7 2.3

4.2 0.4

w o u l d inhibit a progressive increase in b o d y t e m p e r a ture, m e t a b o l i c rate a n d h o r m o n a l changes w h i c h normally o c c u r during c o n t i n u o u s work. F o r this p u r p o s e , thermal, metabolic a n d h o r m o n a l changes were f o l l o w e d in healthy subjects p e r f o r m i n g 2-h exercise at a p p r o x i m a t e l y 50% m a x i m a l o x y g e n uptake (1202ma~) split into four 30-min sessions by 30-min rest periods. D u r i n g the rest periods the b o d y fluid losses o f the subjects were replaced but no c a r b o h y drates were given to c o m p e n s a t e for b o d y c a r b o h y d r a t e depletion.


Subjects. Ten male physical education students volunteered to participate in this study after giving their informed consent. The students' characteristics are presented in Table 1. In a preliminary test all the subjects incremental cycle-ergometer exercise test to determine their VO2.... Experimentalprocedure. Each subject had abstained from physical exercise for the previous 48 h. On the day of the experiment each subject ate a standarized, light breakfast between 6.0 a.m. and 7.0 a.m. The experimental session, which started 3 h afterwards, consisted of four 30-min periods of cycle-ergometer (Monark-Crescent AB, Varburg, Sweden) exercise each at an intensity corresponding to approximately 50% of the subjects VO2max (125150 W). The exercise-periods were separated by a 30-min rest in the sitting position. Ambient temperature was 22 (SD 1)° C, and relative air humidity 60%. To prevent exercise-induced dehydration during each rest interval the subjects drank a glass (250 ml) of light, cooling tea without sugar. This volume of fluid was equal or in most cases exceeded the body mass loss during each exercise period. Measurements. An Ergo-Oxyscreen (Jaeger GmbH, Wuerzburg, FRG) was used to measure V02 and COz output which were calculated from continuous recordings of the fractions of 02 and CO2 in expired air and then corrected to standard temperature and pressure, dry. From resting and exercise 1702 the metabolic rate and mechanical efficiency (ME) were calculated. Mechanical work efficiency was calculated as follows: ME (%) =

Work rate × 100


where ME is mean metabolic rate during 30 min exercise (W), MR is metabolic rate during the last 10 min of rest preceding each exercise (W). Theft was recorded every 10 min from the electrocardiogram (ECG). The Tre was measured with a thermistor (Ellab Instruments, Copenhagen, Denmark) at a depth of 100 ram. The probe was covered by a new sterile plastic sheath each time it was used. Before and at the end of each exercise period venous blood samples for estimation of metabolic and hormonal variables were taken from an indwelling catheter inserted into an antecubital vein 30 min prior to the start of the experiment.

Plasma osmolality was measured by Fiske osmometer (Uxbridge, Mass., USA). Blood glucose ([Glc]b), lactate ([la]b), plasma triacylglycerol ([TG]p0 and glycerol ([Gll]pl) concentrations were determined enzymatically using commercial kits (Boehringer Diagnostica Mannheim, Mannheim, FRG). Plasma free fatty acids ([FFA]p0 were measured enzymatically according to Shimazu et al. (1979). Plasma insulin ([IRI]p0 and human growth hormone ([hGH]o0 concentrations were determined radio immunologically using RIA-MJ-63 and RIA-MJ-99 sets (Institute of Atomic Energy, Swierk, Poland), respectively. Radio immunoassay kits were also used for measurements of plasma glucagon ([IRG]pl) and Cpeptide ([Cp]p0 concentrations (Biodata Glucagon kit, 10904, Milan, Italy; RIA-mat C-peptide test, Byk-Mallinckrodt, Dietzenbach, FRG, respectively). Plasma adrenaline ([A]pl)and noradrenaline ([NA]pl) concentrations were measured by the radio-enzymatic method of Da Prada and Zurcher (1979) using the catechola tests produced by the Institute for Research, Production and Application of Radio-isotopes (Prague, Czechoslovakia). Plasma cortisol concentration was determined by radio immuno-assay using antibodies kindly provided by Prof. R. Stupnicki (Warsaw, Poland).

Statistical analysis. A repeated measurement analysis of variance (ANOVA) followed by the Student's t-test for paired samples was used. In addition, Pearson's correlation coefficient was calculated.


Body temperature and cardio-respiratory data C h a n g e s in Tre a n d f o during the f o u r successive 30-min exercise periods as well a g i n the rest intervals are given in Fig. 1. Values o f Tre during the second, third a n d fourth exercise periods as well as during the following rest periods were significantly higher in c o m p a r i s o n with those seen in the first exercise and the pre-exercise rest periods, respectively. The rate o f the t e m p e r a t u r e increase at the beginning o f exercise (first 10 min) accelerated during the s e c o n d exercise period. H o w e v e r , the net increases in Tre within each 30-min exercise were similar. Within the first a n d s e c o n d exercise periods f~ increased similarly [by 69.0 ( S E M 4.0) and 74.0 ( S E M 3.0) b e a t s . r a i n -1, respectively]. The increases in fc measured during the third [83.0 ( S E M 5.1) b e a t s . m i n -1] a n d f o u r t h [90.7 ( S E M 5.7) b e a t s . m i n -1] exercise periods were significantly higher t h a n those in the first a n d s e c o n d ones (P 0.05). Plasma osmolality Plasma osmolality did not change during consecutive exercise periods. The average values before the first pe-


respiratory exchangeratio (R) during four consecutive 30-min exerciseperiods and postexercise rest intervals. Definitionsas in Fig. 1

riod of exercise and the end of the last one were 293 (SEM 2) and 290 (SEM 3) mosmol-1-1, respectively. Blood metabolites Although there was no significant trend towards higher values of [la]b in consecutive exercise periods during the whole experiment the [la]b after the second period, differed significantly from that after the first (P< 0.05). In none of the 30-min post-exercise intervals did [la]b return to resting values. During each 30-min exercise period [Glc]b decreased significantly. Within the rest periods increases in [Glc]b were observed (P< 0.01) but the values did not return to the initial level (Fig. 3). The [FFA]pt and [Gll]pt increased significantly during the whole period of the experiment. The [TG]pl did not change significantly in either stage of the experiment (Table 2).



Each exercise period caused a decrease in both [Cp]pl and [IRI]pl (Fig. 3). During the postexercise rest intervals their values increased but never returned to the initial levels. A highly significant correlation (r=0.916, n = 80, P < 0.001) was found between them. The [IRG]pl ÷

showed significant but only slight increases in response to exercise (Fig. 3). A significant increase in [hGH]p~ was found after each exercise period (Fig. 4). During the first two exercise periods there was a tendency towards a decrease in the plasma cortisol concentration but it increased significantly during the third and fourth exercise periods (Fig. 4). The [NA]pl increased significantly from the second exercise period with the highest values after the fourth. A significant increase in [A]p~was already evident after the first exercise (Fig. 5).

2O *



2°°r c°'T's°L



. . . . . L__.S---I00 L

°"t 02


-10 0








120 TIP1E { rain )











Fig. 3. Glucagon, insulin, C-peptide and glucose (Glc) responses to four consecutive 30 min exercise periods separated by 30-min rest intervals. Means and SEM are given. Significance of differences between the values after and before each exercise period: + P < 0.05, + + P < 0.01, + + + P < 0.001 ; significance of differences between values at the end of the second, third and fourth exercise period and the end of the first period as well as between resting values before the second, third and fourth periods in comparison with the initial levels: * P

Metabolic, body temperature and hormonal responses to repeated periods of prolonged cycle-ergometer exercise in men.

This study was designed to find out whether rest intervals and prevention of dehydration during prolonged exercise inhibit a drift in metabolic rate, ...
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