Time-of-day Effects in Maximal Anaerobic Leg Exercise in Tropical Environment: A First Approach Physiology & Biochemistry 186
Abstract The aim of this study was to establish the effect of time of day on maximal anaerobic leg power in a tropical environment (French West Indies). Twenty-three physical education students (15 males and 8 females) who trained 10.5 hours a week (SD 6) volunteered to participate in the study. Their mean age, height and body mass were 22.8 (SD 3) years, 172.6 (SD 8) cm, and 64.6 (SD 7) kg, respectively. The chronotype of all subjects was moderate or intermediate. Tests were scheduled at 08 : 00, 13 : 00 and 17: 00 hours on separate days in random order and constant conditions (room temperature: 28.1 8C [SD 0.6], relative room humidity: 62.6 % [SD 3.4]). On test days, the subjects were first
S. Racinais O. Hue C. Hertogh M. Damiani S. Blonc
measured at rest for body mass, heart rate and rectal temperature and they then performed vertical jump tests and a forcevelocity test. The results showed a time-of-day effect on rectal temperature, which was significantly (p < 0.005) higher by the afternoon (13 : 00 and 17: 00) than the morning (08 : 00). However, our results failed to show any daytime variation in maximal anaerobic power under the influence of tropical climate, which suggests that a hot and humid environment may have blunted the time-of-day effect by a passive warm-up effect. Keys words Circadian rhythm ´ anaerobic power ´ hot environment ´ forcevelocity ´ vertical jump
ported by the many studies showing that passive warm-up increases the maximal anaerobic power (e. g. [4 ± 5, 8 ± 9, 23]).
Introduction It was previously shown that anaerobic performance varies throughout the day on the field (e. g. [15]) or in laboratory and follows the changes in body temperature [6 ± 7,17, 21 ± 22]. In consequence, maximal anaerobic power is generally increased by the end of the afternoon, at the peak of the temperature curve. Even if the circadian rhythm in core temperature is not necessarily the cause of the rhythm in muscle performance, some studies have suggested that the simultaneous increases in both body temperature and anaerobic performance could be causally related [6 ± 7,17]. This hypothesis is based on earlier works [5, 25] showing that an increase in muscular temperature induces a warm-up effect that could enhance anaerobic performance.
It therefore appears that both the time of day with its effect on body temperature and the environmental condition ± notably warm temperature ± influence maximal anaerobic power, although these two factors have never been studied together. To date, chronobiological research on anaerobic metabolism has been carried out in laboratory settings at 18.2 8C [22] or 19.2 8C [6]. The purpose of this study was thus to investigate the effect of time of day on maximal anaerobic leg power in a tropical environment.
In addition to the time of day, the environment may also modify anaerobic performance. A recent study [10] showed that a hot climate (35 8C) enhanced anaerobic power. This result was supAffiliation Laboratoire A.C.T.E.S., U.F.R. S.T.A.P.S. ± U.A.G., Campus de Fouillole, Pointe-à-Pitre, France Correspondence S. Blonc ´ Laboratoire A.C.T.E.S. U.F.R.S.T.A.P.S. ± U.A.G. ´ Campus de Fouillole, BP 592 ´ 97159 Pointe-à-Pitre Cedex ´ France Phone: +33 5 90 48 92 07 ´ Fax: +33 5 90 93 86 16 ´ E-mail:
[email protected] Accepted after revision: July 20, 2003 Bibliography Int J Sports Med 2004; 25: 186±190 Georg Thieme Verlag Stuttgart ´ New York ISSN 0172-4622 ´ DOI 10.1055/s-2003-45258
Material and Methods
Protocol All subjects participated in 3 test sessions in random order at 08 : 00 (morning), 13 : 00 and 17: 00 (afternoon) hours. The tests were performed on separate days with a minimum of 19 hours of recovery between each. The experiment was conducted during the month of April in Guadeloupe, where daylight lasts from 06 : 00 to 18 : 00 hours all year round. During this period, the mean external temperature and relative humidity between 08 : 00 and 17: 00 was, respectively, 27.9 (range 26 to 29) 8C and 65.4 (range 59 to 75) % (data from ªMØtØo Franceº). The laboratory was maintained at a constant temperature of 28.1 8C (27.8, 28.3 and 28.2 8C at 08 : 00, 13 : 00 and 17: 00, respectively) and a relative humidity of 62.6 % (71.0, 59.3 and 56.9 at 08 : 00, 13 : 00 and 17: 00, respectively). An electronic thermometer-hygrometer (Novo 16 755) collected the data of temperature and relative humidity (precision 0.1 8C and 1 % for temperature and relative humidity, respectively). The subjects were asked to avoid all vigorous activity for 24 hours before each test, to sleep normally, and to consume a light meal with a caffeine-free beverage at least 2 hours before the beginning of the test sessions. They were asked to wear the same sportswear and shoes for all tests and to signal all departures from this instruction to the experimenters. Tests and measures The subjects were asked to arrive 15 min before testing. All test sessions were identical and lasted less than an hour. Sessions began with 15 min of rest followed by rest measures. After this, the subjects began a standardized warm-up consisting of 3 min of pedalling at 70 rpm on a cycle ergometer (Monark type 824E, Stockholm, Sweden) with a brief acceleration of 6 s at the end of each minute. The warm-up was strictly the same for all test sessions and was the same as that of a previous study which also used jump and force-velocity tests [6]. After the warm-up, the subjects had 3 min of recovery before performing the vertical jump tests. The subjects again had a 3-min recovery before beginning the force-velocity test. Rest measures After a passive 15 min in a seated position in the laboratory, subjects underwent measurement of heart rate (HR), rectal temperature (Trect) and body mass with a Polar Sports Tester heart rate
Table 1 Characteristics of male and female subjects Male (n = 15)
Female (n = 8)
Age (years)
23.1 0.8
21.9 1.1
Height (cm)
177.4 5.5
163.5 4.4
Weight (kg)
68.3 4.5
57.7 5.2
Body fat (%)
12.7 2.9
26.1 3.8
Training (h weeks±1)
10.1 1.6
11.2 2.2
monitor (Polar Electro OY, Kempele, Finland), a clinical electronic thermometer (MT 1691 BMWC, precision 0.1 8C, insertion depth 2 cm) and an electronic balance (Teraillon, precision 0.1 kg), respectively. Vertical jump test This test was conducted with the Takei Kiki Kogyo vertical jump meter (T.K.K.5106). Subjects performed 2 maximal vertical jumps separated by 2 min of rest. The best of the 2 was retained for the determination of maximal jump height (Hj) and maximal jump power (Pj). The maximal jump power was calculated by the formulae of Sayers et al. [24] for counter-movement jumps and all the subjects were habituated to the test before participating in the experimental study. Force-velocity Maximal cycling power (Pmax) was determined by a force-velocity test [26] conducted on a standard friction-loaded cycle ergometer (Monark 824E, Stockholm, Sweden). This test was composed of 5 short (6 s) maximal sprints against increasing braking forces, with 5 min of recovery between sprints. The sprints began with the subject's legs motionless. When the experimenter gave the start signal, the subject pedalled to maximal frequency as fast as possible. Individual workloads were adapted to sex, morphology and anterior results of the subjects, but were the same for the 3 sessions. Subjects remained in a seated position during the sprints. The seat height, handlebar angle and toe clip tightening were adjusted for each subject. The recovery between each sprint was in a seated position and the subject could drink water. It is known that the relationship between the braking resistive force (F) and the maximal velocity of the subject (V) is linear and can be expressed as: V = b ± aF (e. g. [26]). The coefficient of this relation was calculated from the linear regression linking F and V for each test and the intercepts with velocity axis (V0) and with force axis (F0). Power corresponded to the product of F and V and followed a parabolic evolution with a maximal value for (0.5 V0) (0.5 F0). The maximal anaerobic power (Pmax), the relative power (Prel, corresponding to Pmax divided by body mass at the time of the test), and the optimal force (Fopt, corresponding to the force at Pmax) and velocity (Vopt, corresponding to the velocity at Pmax) were calculated with software developed by the laboratory. Statistics The normality of the distribution was verified by an index of symmetry. The daily variations in all measured or calculated parameters were verified by a 2-way analysis of variance (ANOVA) with repeated measures (time-of-day sex). When the
Racinais S et al. Diurnal Variation of Muscular Power ¼ Int J Sports Med 2004; 25: 186 ± 190
Physiology & Biochemistry
Subjects Twenty-three physical education students (15 males and 8 females) volunteered to participate in the study and all provided informed written consent. The study was approved by the local Ethics Committee. Their mean age, height, body mass and body fat were 22.8 (SD 3) years, 172.6 (SD 8) cm, 64.6 (SD 7) kg and 17.4 (SD 7) %, respectively, and all practiced sports regularly (10.5 [SD 6] hours a week). The characteristics of males and females are presented in Table 1. All were natives or had lived for many years in Guadeloupe (French West Indies) and their chronotypes, as determined by the questionnaire of Horne and Östberg [14], were moderate or intermediate. For this questionnaire, the scale of time was brought forward one hour to adapt it to the local and social environmental conditions.
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effect of time of day was significant, the Fisher's PLSD post hoc comparison was used. The data are expressed in mean standard deviation, and the statistical significance was chosen at p < 0.05.
Results Mean body mass (64.6 [SD 7] kg at 08 : 00, 64.7 [SD 7] kg at 13 : 00, 64.7 [SD 7] kg at 17: 00) and heart rate before exercise (67 [SD 9] b min±1 at 08 : 00, 69 [SD 8] b min±1 at 13 : 00, 70 [SD 9] b min±1 at 17: 00) did not vary significantly during the day (p > 0.05).
Physiology & Biochemistry
Rectal temperatures before the tests showed a significant variation related to time of day (p < 0.0001). The value of Trect measured in the morning at 08 : 00 (37 [SD 0.3]8C) was significantly lower than the values measured in the afternoon at 13 : 00 (37.3 [SD 0.3] 8C) and 18 : 00 (37.3 [SD 0.4] 8C) (p < 0.005). The results as measured or calculated from the 2 anaerobic tests are presented in Table 2. None showed any significant variations. The effect of sex was significant for values of Hj, Pj, Pmax, Prel, Vopt and Fopt but not for Trec and HR. However, the interactions between sex and time-of-day effects were not significant for any of the physiological variables.
Discussion
188
The purpose of this study was to evaluate the effect of time of day on the maximal anaerobic leg power in a tropical environment. In agreement with previous research, our results showed a significant increase in rectal temperature and no significant variation in body mass throughout the day. However, contrary to earlier studies we failed to observe any variation in anaerobic power between 08 : 00, 13 : 00 and 17: 00 hours in a hot and humid environment. Methodological aspects As in many other studies, our subjects were young and active. The time of the test was chosen with regard to both the literature and our environment. Previous studies have used tests at 09 : 00, 14 : 00 and 18 : 00 [2, 6], an organization which we maintained, though we scheduled testing one hour earlier for two reasons. The first was to have a test closer to the temperature curve peak in tropical climate (16 : 03, see below) and the second was to be synchronized with the night and day synchronizer. The sessions lasted less than an hour. Subjects were habituated to the testing. The test order was randomized and the tests were performed over 3 or 4 consecutive days. Six of the 23 initial subjects participated in 6 other test sessions performed at 02 : 00, 06 : 00, 10 : 00, 14 : 00, 18 : 00 and 22 : 00 hours, on separate days and in random order. The data of this complementary experiment revealed that rectal temperature (measured with the same materials and methods as in the initial experiment) displayed a significant circadian rhythm with an acrophase at 16 : 03. Jump performance was measured by the same materials and methods as in the initial experiment and, in accordance with the first study, failed to
Table 2 Anaerobic performance from vertical jump and forcevelocity tests at 3 different times of day. Data in mean SD. NS: No significant variations Variables
Jump height (cm) Jump power (Watts) Maximal anaerobic power (Watts) Optimal velocity (rpm)
8 : 00
Time of day (hours) 13 : 00 17 : 00
p-value
60 8
62 10
60 10
NS
4270 714
4350 777
4289 784
NS
773 189
785 187
788 197
NS
112 8
113 7
114 11
NS
6.86 1.4
6.90 1.5
6.89 1.5
NS
Relative power (Watts kg±1) 11.8 2.1
12.0 2.0
12.1 2.3
NS
Optimal force (kg)
show a significant variation in jump height or jump power as a function of time of day over the whole circadian cycle. In circadian studies, test reliability has to be sufficient to detect variations of small magnitude. Thus, as in the study of Bernard et al. [6], the reproducibility of measurements was studied by regression analyses between the 2 vertical jumps and between the different test times. For the power developed on the vertical jump, the reproducibility was r = 0.971 (p < 0.000), r = 0.954 (p < 0.000) and r = 0.955 (p < 0.000) for 08 : 00 vs. 13 : 00, 08 : 00 vs. 17: 00 and 13 : 00 vs. 17: 00, respectively. The reproducibility between the first and the second vertical jump tests was r = 0.883 (p < 0.000). The second test performed was a forcevelocity test. When this test is correctly performed, a linear relation between force and velocity is noted [26], so correct performance can easily be verified. The reproducibility for Pmax was r = 0.953 (p < 0.000), r = 0.972 (p< 0.000) and r = 0.956 (p< 0.000) for 08 : 00 vs. 13 : 00, 08 : 00 vs. 17: 00 and 13 : 00 vs. 17: 00, respectively. Rest measures No variations in body mass were observed between 08 : 00, 13 : 00 and 17: 00, which has been noted by several studies (i. e. [6, 22]), and our results were independent of sex, as observed by Hill et al. [13]. However, in a chronobiological study with female subjects, we had to consider the influence of menstrual cycle phase. An earlier study showed no influence on the daily variation [3] and a recent study [12] showed that menstrual cycle had no effect on maximal anaerobic performance in a forcevelocity test or a jump test. It is well known that the rectal temperature curve peaks in late afternoon in temperate environment and Little and Rummel [16] showed that 60 minutes of exposure to a temperature of 46 8C and a relative humidity of 31 % did not modify the circadian rhythm of core temperature. Our results showed a significant (p < 0.0001) time-of-day effect on rectal temperature in tropical environment, which was significantly (p < 0.005) higher in the afternoon (13 : 00 and 17: 00) than the morning (08 : 00). The time-of-day effect observed in this study was in accordance with the many studies that have shown diurnal variation in body temperature, whereas the method differed (oral temperature with a clinical thermometer (i. e. [17]), rectal temperature with a probe (i. e. [6]), or rectal temperature with a clinical ther-
Racinais S et al. Diurnal Variation of Muscular Power ¼ Int J Sports Med 2004; 25: 186 ± 190
mometer (i. e. [1]). Moreover, rectal temperature with a clinical thermometer is a valid and reliable method, usually used as the reference method in research.
It was previously shown that a change in environmental temperature could modify muscular performance and muscular and skin temperature, without modifying rectal temperature [18 ± 20]. These results suggested that local temperature influenced muscular short term power more than central temperature. Falk et al. [10] showed that skin temperature was significantly higher in hot condition (35 8C, 30 % rh) than in neutral condition (22 8C, 40 % rh), whereas rectal temperature was not modified. These results indicated that local temperature was responsible for the modification in muscular short term performance after the passive warm-up. The same may have occurred in our study and, even though muscular and skin temperatures were not measured, we assume that our rectal temperatures were only slightly influenced by the environmental condition whereas the local limb temperature was increased. Many studies have shown that an increase in muscle temperature could enhance anaerobic power, and notably performance during the vertical jump test [6, 9] or the cycloergometer test [4 ± 5, 8, 23]. Furthermore, Falk et al. [10] observed an increase in anaerobic power in a hot environment compared with a neutral condition and this power increase was accompanied by an increase in skin temperature, whereas rectal temperature was not modified. In view of this point, we can suppose that it was the local passive warm-up engendered by the moderate hot climate that may have blunted the time-of-day effect on muscular power. This hypothesis is in accordance with the data of Reilly and Down [22]: in a study where they observed no daily variation in anaerobic power on a Wingate test, they suggested that a warm-up resulting from a prior test could have masked the daily variations.
Our results failed to show any daytime variation in maximal anaerobic power under the influence of a tropical climate. These data suggest that a hot and humid environment may have blunted the effects of the diurnal variation in body temperature on muscular power and probably enhanced the maximal anaerobic power in the morning by a passive warm-up effect. But the failure to find significant diurnal variation in the performance measures leaves unanswered questions. A comparative study with the same subjects in both tropical and temperate conditions would be necessary to understand the importance of the environmental condition of test and life. Another study with control of the skin and/or muscular temperature would be necessary as well to understand the respective roles and interactions between environmental, body core and muscular temperatures.
Acknowledgements The authors especially thank Pr. Guy Falgairette for his relevant remarks. The experiments comply with current laws and were approved by the local Ethics Committee.
Physiology & Biochemistry
Muscular short-term performance Our values of relative power were not very high; however, our subjects were involved in many different sports and were not specifically trained in explosive activity. Several studies have used jump tests, with either the broad jump [21, 22] or the vertical jump [6]. These studies observed an increase in performance throughout the day in phase with the temperature curve. An increase in the maximal anaerobic power calculated from the force-velocity test has also been shown to follow the temperature variation [6]. These studies were conducted in temperate environments and the authors concluded that the increase in body temperature could act as a warm-up and could enhance the anaerobic performance. We assume that the difference of our results could be attributed to the environmental condition and its influence on local temperature. The first chronobiological studies did not specify the environmental condition of the experiment. However, in view of the importance of temperature on performance, more recent studies have controlled laboratory temperature. If we take, for example, the studies that investigated anaerobic performance by means of a jump test and a cycle ergometer test, Reilly and Down ([22], Wingate test and broad jump test) and Bernard et al. ([6], force-velocity and vertical jump test) maintained their laboratories at 18.2 8C and 19.2 8C, respectively. Our environmental conditions were different: The tests of this study were performed in a laboratory maintained at 28.1 8C.
Conclusion
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