CHRONOBIOLOGY INTERNATIONAL Vol. 21, No. 3, pp. 485–495, 2004
Time-of-Day Effects on Anaerobic Muscular Power in a Moderately Warm Environment S. Racinais, O. Hue, and S. Blonc* Laboratoire A.C.T.E.S., UPRES-EA 3596, U.F.R.S.T.A.P.S. – U.A.G., Pointe-a`-Pitre, Cedex, France
ABSTRACT This study evaluated the influence of a neutral vs. a moderately warm environment on the diurnal variation in muscular power. Twelve male subjects [27.0 (4) years] performed two different jump tests [a squat jump (SJ) and a counter-movement jump (CMJ)] and a brief maximal sprint on cycle ergometer (CS) in four different conditions (morning/neutral, morning/moderately warm and humid, afternoon/neutral, and afternoon/moderately warm and humid). The morning experiments were conducted between 07:00 and 09:00 h, and the afternoon experiments were conducted between 17:00 and 19:00 h. The mean laboratory temperatures and humidity were 20 (1) C, 70 (5)% and 29 (1) C, 57 (4)% for the neutral and moderately warm and humid conditions, respectively. Rectal temperature and leg skin temperature were significantly dependent on both time-of-day and ambient temperature. An interaction effect (P < 0.05) was noted between time-of-day and ambient temperature for the power developed for the CMJ, the SJ, and half of a pedal revolution during the cycling sprint. In summary, (i) the same subjects were influenced by time-of-day differently, depending on the ambient temperature during testing; (ii) time-of-day
*Correspondence: S. Blonc, Ph.D., Laboratoire A.C.T.E.S., U.F.R.S.T.A.P.S. – U.A.G., Campus de Fouillole, BP 592, 97159 Pointe-a`-Pitre, Cedex, France; Fax: þ33 590 489 279; E-mail:
[email protected]. 485 DOI: 10.1081/CBI-120038632 Copyright & 2004 by Marcel Dekker, Inc.
0742-0528 (Print); 1525-6073 (Online) www.dekker.com
ORDER
REPRINTS
486
Racinais, Hue, and Blonc affected muscular performance only in the neutral condition, (iii) the moderately warm and humid condition blunted the diurnal variation in muscular performance, and (iv) the effect of the ambient temperature was dependent on time-of-day. Key Words: Circadian rhythm; Exercise; Tropical climate.
Temperature;
Short-term
performance;
INTRODUCTION A significant diurnal variation in anaerobic muscular function has been observed both when tests are conducted over an entire 24 h day to study circadian rhythm effects (e.g., Coldwells et al., 1994; Gauthier et al., 1996, 1997; Hill and Smith, 1991; Melhim, 1993; Reilly and Down, 1986, 1992) and when they are conducted only during the diurnal period typical for exercise performance. In this latter case, the tests are said to determine ‘‘time-of-day’’ effects (e.g., Bernard et al., 1998; Deschenes et al., 1998; Javierre et al., 1996). In temperate conditions, maximal short-term performance is generally increased by the end of the afternoon, at the peak of the temperature curve (Bernard et al., 1998; Coldwells et al., 1994; Deschenes et al., 1998; Melhim, 1993; Reilly and Down, 1986, 1992). 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 are causally related (Bernard et al., 1998; Coldwells et al., 1994; Melhim, 1993). In parallel with the diurnal variation in body temperature, a variation in environmental temperature can influence anaerobic power. A moderately hot environment has been shown to enhance jump performance (Hue et al., 2003) and the anaerobic power developed on a cycle ergometer (Falk et al., 1998). In an earlier study conducted in a tropical environment, we failed to show any daytime variation in maximal anaerobic power, suggesting that the hot and humid environment may have blunted the time-of-day effects on muscular power (Racinais et al., 2004). This study raised intriguing questions about the cause of this stability. Two suggestions seem reasonable: (i) a long-term adaptation to the environmental conditions or (ii) an instantaneous effect of the testing conditions. The fact that the circadian rhythm of body core temperature persists in a tropical environment (Racinais et al., 2004) suggests that the absence of a diurnal variation in muscular power in this climate is not due to a long-term adaptation to the environmental conditions. We thus hypothesized that the difference in the time-of-day effects on muscular power observed in temperate vs. tropical conditions is due to the ambient temperature immediately before and during test performance. The aim of this study was to evaluate whether 60-min exposures to neutral and moderately warm and humid environments influence the time-of-day effect on maximal muscular power differently in subjects serving as their own controls.
ORDER
REPRINTS
Time-of-Day Effects on Anaerobic Muscular Power
487
METHODS Subjects Twelve male physical education students volunteered to participate in the study. After thorough explanation of the protocol, all provided written consent, and the study was approved by the local Ethics Committee. The mean age, height, body mass, and body fat of the subjects were 27.0 (4) years, 1.76 (0.1) m, 70.3 (11) kg, and 12.8 (3.8) %, respectively. The body fat was calculated from skinfold thickness measurements using Durnin and Womersley’s equations (1974). All subjects were natives or had lived for many years in Guadeloupe (French West Indies).
Protocol The tests were performed in four different conditions: morning/neutral, morning/warm, afternoon/neutral, and afternoon/warm. All subjects were tested in the four conditions on separate days in random order. The morning experiments were conducted between 07:00 and 09:00 h, and the afternoon experiments were conducted between 17:00 and 19:00 h. The mean laboratory temperatures and humidity were 20 (1) C, 70 (5) % and 29 (1) C, 57 (4) % for the neutral and moderately warm and humid conditions, respectively. The study was conducted from early March to the end of May in the French West Indies (FWI), with a mean external temperature of 26 (1) C, and a mean external relative humidity of 74 (11) % (data from ‘‘Me´te´o France’’). The laboratory conditions were controlled by an air converter and an electric heater and were recorded using an electronic thermometer-hygrometer (Novo 16755, Novo, France, precision 0.1 C). The subjects were asked to avoid all vigorous activity for 24 h before each test, to sleep normally, to wear the same sportswear and shoes for all tests, and to signal all departures from these instructions to the experimenters.
Test Sessions Sessions began with 1 h of rest in a seated position in a neutral or warm room. At the end of this period, body mass, rectal temperature (Trect), and leg skin temperature (Tskin, mean of the muscular cutaneous temperature of the quadriceps femoris, biceps femoris, and triceps surae) were measured by means of an electronic scale (Teraillon, France, precision 0.1 kg), a clinical electronic thermometer (MT 1691 BMWC, Microlife Ltd., Taiwan, precision 0.1 C, insertion depth 2 cm), and a surface thermometer (Ecoscan, Eutech Instruments, Netherlands), respectively. After this, the subjects began a standardized warm-up consisting of 3 min of pedaling at 70 rev min1 on a cycle ergometer (Monark type 824E, Stockholm, Sweden) against a braking resistive force of 1 kg, corresponding to 70 W, 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 has been used in previous studies based on jump and cycle ergometer testing (Bernard et al., 1998; Racinais et al., 2004). Two different jump
ORDER
REPRINTS
488
Racinais, Hue, and Blonc
tests were then performed: a squat jump (SJ) and a counter-movement jump (CMJ), which were then followed by a brief maximal sprint on cycle ergometer (CS). All the subjects had been familiarized with the tests before participating in the study.
SJ and CMJ Tests The SJ test consisted of a maximal jump from a flexed position with the hands on the hips, and the CMJ test consisted of leg flexion from the standing position immediately followed by a maximal jump with the hands off the hips. These jump tests were monitored with the Takei Kiki Kogyo vertical jump meter (T.K.K.5106), which recorded the jump height. The subjects performed two trials of each jump, and the best was used to calculate the power from the formulae of both Lewis (Cazorla et al., 1984) and Sayers et al. (1999).
CS Test The best of two brief (5 to 6 s) maximal sprints in a seated position on the cycle ergometer was retained for analysis. This test was conducted on a standard frictionloaded cycle ergometer (Monark 824E, Stockholm, Sweden) with a moment of inertia of 0.42 kg m2 for the flywheel (calculated by Lakomy’s method [1986]). A disk and a photoelectric cell were fixed on the flywheel and the frame, respectively, in order to obtain 12 speed readings per flywheel revolution. The force was calculated by summing the braking resistive force (setting between 60 and 70 g kg1 body mass as a function of the subject’s ability) and the inertial force (calculated from the acceleration following the method of Martin et al. [1997]). The power output was calculated by multiplication of the velocity by the force both per pedal revolution and per half pedal revolution. The data were collected by a PCMCIA acquisition card (DAQCard 6062E, National Instruments, Texas, USA) and analyzed by software developed in our laboratory with a LabVIEW interface (LabVIEW, National Instruments, Texas). The subjects were instructed to accelerate as fast as possible and were strongly and similarly encouraged during all testing.
Statistical Analysis The effect of ambient temperature on the time-of-day effect was verified by a two-way analysis of variance with repeated measures (ANOVA 2R2R, time-ofday environmental condition). This analysis provided a global effect of time-of-day, a global effect of environmental condition, and the effect of the interaction between time-of-day and environmental condition. When significant interaction effects were noted with the two-way ANOVA, analyses were broken down into a one-way ANOVA of time-of-day and environmental effect, respectively. The data are expressed in mean SE, and the statistical significance was established at P < 0.05.
ORDER
REPRINTS
Time-of-Day Effects on Anaerobic Muscular Power
489
RESULTS Rest Measures Rectal and mean leg skin temperatures (Table 1): Trect and Tskin showed significant variations according to both time-of-day (P < 0.05) and environmental condition (P < 0.005); however, there was no significant interaction effect of these two factors. Muscular Power Jump Power The interaction of time-of-day and environmental condition had a significant effect (P < 0.05) on the power developed during both the CMJ and SJ jumps, as calculated by the formulae of both Lewis and Sayers et al. The power developed in the neutral environment during the CMJ was significantly higher (P < 0.05) in the afternoon than in the morning, whereas this was not the case in the moderately warm environment. Moreover, a warm environment significantly enhanced both CMJ and SJ power in the morning (P < 0.05), whereas this was not the case in the afternoon. The data calculated from Lewis’s formula were 1012 140, 1053 170, 1046 161, and 1035 147 W, in morning/neutral, morning/warm, afternoon/ neutral, and afternoon/warm conditions, respectively. The data calculated from the formula of Sayers et al. (1999) are presented in Fig. 1. The Cycle Ergometer Sprint (Table 2) The maximal power measured on a half pedal revolution showed an interaction effect of time-of-day and environmental condition (P < 0.05). This interaction effect
Table 1. Rectal (Trect) and leg skin (Tskin) temperature ( C). Afternoon values were significantly higher than morning values, and moderately warm and humid values were significantly higher than neutral values (*P < 0.005). NS: non significant. Morning
Afternoon
Neutral
Warm
Neutral
Warm
Trect ( C)
36.6 0.4
37.0 0.2
37.1 0.4
37.3 0.3
Tskin ( C)
28.4 0.8
31.9 0.7
29.3 0.8
32.8 0.5
*p < 0.005. NS: non significant.
Time-of-day: * Environment: * Interaction: NS Time-of-day: * Environment: * Interaction: NS
ORDER
REPRINTS
490
Racinais, Hue, and Blonc
Power (Watts)
4000
4000
A
NS NS
3900
*
B NS
3900
**
NS
3800
3800
3700
3700
Morning
Afternoon
Morning
NS
§
Afternoon
Figure 1. Time-of-day [morning vs. afternoon] and environmental condition [Moderately warm and humid (–i–) vs. Neutral (—^—)] had a significant interaction effect (P < 0.05) on the power developed during SJ (Fig. A) and CMJ (Fig. B), according to the equations of Sayers et al. (1999). Post-hoc analysis showed a significant increase in the morning for moderately warm and humid conditions vs. neutral condition (*P < 0.05, **P < 0.01) for all tests, and a significant increase in neutral condition for afternoon values vs. morning values (x P < 0.05) for CMJ test. NS: non significant.
Table 2. The difference between morning and afternoon values was significantly dependent on environmental conditions for the power (in watts) calculated on a half pedal revolution (CS half, , P < 0.05) but not on a complete pedal revolution (CS cycle, NS, P ¼ 0.06). Post-hoc analysis showed that in neutral condition, CS half was significantly enhanced in the afternoon (x P < 0.05). Morning Neutral
Afternoon
Warm
Neutral
Warm
CS half (watts) 1943 349x 1999 359 2015 380x 1977 352 Time-of-day: NS Environment: NS Interaction: * CS cycle (watts) 960 184 991 182 990 195 977 184 Time-of-day: NS Environment: NS Interaction: NS (P ¼ 0.06) NS: non significant.
was revealed by the significant difference between the morning and afternoon values in the neutral environment but a lack of difference in the warm environment. The power output calculated over a complete pedal revolution failed to show a significant interaction effect (P ¼ 0.06).
DISCUSSION The major finding of our study was an interaction effect of time-of-day and environmental condition on the power output during a CMJ and a SJ, as calculated
ORDER
REPRINTS
Time-of-Day Effects on Anaerobic Muscular Power
491
by the formulae of both Lewis (Cazorla et al., 1984) and Sayers et al. (1999), and on the power calculated for a half pedal revolution during a cycling sprint. The interaction effect indicated that muscular anaerobic function (i) was influenced differently by time-of-day, depending on whether the subject was in a temperate or moderately warm environment and (ii) was influenced differently by a modification in the environmental condition, depending on whether the tests were performed in the morning or the afternoon. The test times were chosen with regard to the literature. Bernard et al. (1998) showed that both jump performance and cycle ergometer sprint power were significantly higher at 18:00 h than at 09:00 h in a neutral climate, whereas in a study conducted in a moderately warm climate, the researchers failed to observe a diurnal variation in either jump or cycle performance when tests were performed at 08:00 h and 17:00 h (Racinais et al., 2004). The jump and cycle sprint tests were also chosen with regard to the literature, as many studies of both temperature effects (Bergh and Ekblom 1979; Hue et al., 2003; Oksa et al., 1996, 1997, 2000) and time-of-day effects (Bernard et al., 1998; Hill and Smith, 1991; Melhim, 1993; Racinais et al., 2004; Reilly and Down, 1986, 1992) have used these tests. In this study, we determined maximal cycling power in a single exercise sprint with inertia calculation. We took advantage of (i) the calculation of instantaneous power produced on a half pedal revolution and (ii) the calculation of real power integrating flywheel inertia (Lakomy, 1986), which is underestimated with the force-velocity test (Martin et al., 1997). The braking resistive force applied on the flywheel was set between 60 and 70 g kg1 of body mass on the basis of previous results, indicating that a charge between 50 and 75 g kg1 of body mass is adapted for the determination of maximal power in young adults (Dore´ et al., 2000). Our results showed a mean maximal power of 980 W calculated on a pedal revolution, which is close to the 979 W observed by Linossier et al. (1996). We observed a significant interaction (P < 0.05) between time-of-day and environmental condition for power developed both on the cycle ergometer and during the jump tests. The analysis showed that the power developed on a half pedal revolution during the cycle sprint and during the counter-movement jump was significantly dependent on time-of-day in the neutral environment. This result agreed with the previous studies in neutral climate that observed a diurnal variation in brief maximal performance during cycling tests (Bernard et al., 1998; Hill and Smith, 1991; Melhim, 1993; Reilly and Down, 1992) and jump tests (Bernard et al., 1998; Reilly and Down, 1986, 1992). However, we failed to show a significant effect of time-of-day on muscular power in moderately warm and humid climate. This result agreed with a previous study in a moderately warm and humid climate that failed to observe any diurnal variation in either cycle tests or jump tests performed at 08:00 h and 17:00 h, and in jump tests over the entire circadian cycle (Racinais et al., 2004). Anaerobic performance varies throughout the day, following the changes in rectal temperature (Bernard et al., 1998; Coldwells et al., 1994; Melhim, 1993; Reilly and Down, 1986, 1992), and some studies have suggested that the simultaneous increases in body core temperature and anaerobic performance may be causally related (Bernard et al., 1998; Coldwells et al., 1994; Melhim, 1993). Based on an earlier work that observed a modification in muscular power with a change in local temperature but no change in rectal temperature (i.e., Falk et al., 1998), we suggested
ORDER
492
REPRINTS
Racinais, Hue, and Blonc
in a recent study that the variation in local temperature explained the diurnal variation in muscular power better than a variation in core temperature (Racinais et al., 2004). In this study, we show that both rectal temperature and mean leg skin temperature were dependent on environmental condition and time-of-day, but without interaction between these two factors. The delta between the morning and afternoon values (: afternoon value – morning value) of the rectal and skin temperatures remained constant, independently of environmental condition (Trect: 0.4 C in neutral vs. 0.3 C in warm, Tskin: 0.8 C in neutral vs. 0.9 C in warm). Despite this constant difference of temperature, muscular power displayed an effect of the interaction between time-of-day and ambient temperature. This may suggest that the circadian rhythm of body temperature may have influenced muscular power only in the neutral condition. Two findings support this hypothesis. First, body temperatures were higher in the warm and humid environment than in the neutral environment (P < 0.005, Table 1). These higher values of local and central body temperatures may have had the effect of rendering muscular function independent of any slight diurnal variations in them. This in turn suggests a minimal level below which muscular function is perturbed. Many studies have in fact shown that a decrease in local temperature by exposure to a cold environment or a cold bath decreases jump performance (i.e., Bergh and Ekblom, 1979, Oksa et al., 1996, 1997, 2000) and cycling performance (i.e., Crowley et al., 1991; Sargeant, 1987). Oksa et al. (1996, 1997, 2000) showed that a decrease in leg temperature can modify muscular electric activity, causing a change in muscular coordination and, consequently, lower jump performance. This might explain the low values of muscular power observed in the neutral climate in the morning, a time when body temperature was significantly lower (P < 0.02). Second, Gauthier et al. (1996) and Martin et al. (1999) concluded that a diurnal rhythm of muscle contractile processes was responsible for the diurnal variation in muscular short-term performance. In parallel, it was suggested that a modification in muscular temperature could modify muscular contractile processes, such as myosin ATPase activity and calcium uptake (Segal et al., 1986), or the speed of the chemical processes in the muscle (Oksa et al., 1996). It seems that the artificial modification of local temperature and natural diurnal variations in body temperature influence muscular function by similar processes, suggesting that muscle contractile processes were enhanced in the neutral climate with the diurnal increase in body temperature. Moreover, a moderately warm and humid environment could have kept the muscle warmed up throughout the day. In agreement with our hypothesis, the results showed that muscular power was differently influenced by time-of-day as a function of the ambient temperature immediately before and during test performance. We may therefore suggest that the presence of a passive warm-up source, either the diurnal increase in body temperature or the 60-min warm-climate exposure, was sufficient to enhance muscular power. However, the influence of local temperature on the diurnal variation in anaerobic muscular power remains a hypothesis in the absence of muscular temperature measurements. Indeed, skin temperature provides more information about the heat loss–heat gain equilibrium than about the temperature of the active musculature. This data is needed to better determine the respective importance of local and central temperatures on muscular function.
