ARTICLE IN PRESS
JSAMS 272 1—4
Journal of Science and Medicine in Sport (2007) xxx, xxx—xxx
3
SHORT REPORT
Does the diurnal increase in central temperature interact with pre-cooling or passive warm-up of the leg?
4
OF
5
6
a
8
Laboratoire ACTES, Pointe-` a-Pitre Cedex, France ASPETAR, Qatar Orthopedic and Sports Medicine Hospital, Exercise and Sports Science Department, Doha, Qatar c Finnish Institute of Occupational Health, Oulu, Physical Work Capacity Team, Oulu, Finland
10
Q1
DP
b
9
11
RO
S´ ebastien Racinais a,b,∗, Stephen Blonc a, Juha Oksa c, Olivier Hue a
7
Received 9 November 2006 ; received in revised form 6 September 2007; accepted 25 September 2007
12
KEYWORDS
Summary Seven male subjects volunteered to participate in an investigation of whether the diurnal increase in core temperature influences the effects of pre-cooling or passive warm-up on muscular power. Morning (07:00—09:00 h) and afternoon (17:00—19:00 h) evaluation of maximal power output during a cycling sprint was performed on different days in a control condition (room at 21.8 ◦ C, 69% rh), after 30 min of pre-cooling in a cold bath (16 ◦ C), or after 30 min of passive warm-up in a hot bath (38 ◦ C). Despite an equivalent increase from morning to afternoon in core temperature in all conditions (+0.4 ◦ C, P < 0.05), power output displayed a diurnal increase in control condition only. A local cooling or heating of the leg in a neutral environment blunted the diurnal variation in muscular power. Because pre-cooling decreases muscle power, force and velocity irrespective of time-of-day, athletes should strictly avoid any cooling before a sprint exercise. In summary, diurnal variation in muscle power output seems to be more influenced by muscle rather than core temperature. © 2007 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
15
Q2
16 17
Previous studies have shown that a warm environment increases power output only in the morning when core temperature is at its lowest,1 but none has investigated the effects of pre-cooling on the ∗
UN
14
CO
Introduction
13
RR
EC
TE
Circadian rhythms; Time-of-day; Cycling sprint; Exercise; Muscle power
Corresponding author. E-mail address:
[email protected] (S. Racinais).
diurnal variation in power output. Furthermore, an increase in cycling power output was observed with an increase in skin temperature before modification in core temperature.2 Thus, the purpose of the present study was to determine the effect of localised heating or cooling of the exercising limbs (a more pronounced thermal stimulus for the leg than environmental temperature) upon morning and evening power output, relative to control conditions.
1
1440-2440/$ — see front matter © 2007 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
2
doi:10.1016/j.jsams.2007.09.008
Please cite this article in press as: Racinais S, et al., Does the diurnal increase in central temperature interact with JSAMS 272 1—4 pre-cooling or passive warm-up of the leg?, J Sci Med Sport (2007), doi:10.1016/j.jsams.2007.09.008
18 19 20 21 22 23 24 25 26 27
ARTICLE IN PRESS
JSAMS 272 1—4
2
S. Racinais et al.
39
Experimental procedure
Statistical analysis
All subjects completed six sprint tests on 6 separate days. Three were conducted in the morning (07:00—09:00 h) and three in the afternoon (17:00—19:00 h). The tests were held in a neutral environment (21.8 ± 0.9 ◦ C, 69 ± 2% rh) after either a 30-min rest in the laboratory (control), a 30-min cold bath at 16 ◦ C (pre-cooling, PC), or a 30-min hot bath at 38 ◦ C (warm-up, WU). Pre-cooling and warm-up were performed in a thermal bath with only the legs from feet to pelvis immersed. Three and a half minutes after the exit of the bath, rectal temperature (Trect ) and leg skin temperature were measured with a clinical electronic thermometer (MT 1691 BMWC, Microlife Ltd., Taiwan, precision 0.1 ◦ C, insertion depth 2 cm, see footnote 1) and a cutaneous probe (YSI 409B, Yellow Springs Instruments, OH, USA), respectively. One and a half minute later, subjects performed a maximal sprint lasting ∼7 s against a friction resistive load set at 60 g kg−1 body mass applied on the periphery of the flywheel. The subjects were instructed to accelerate as fast as possible while remaining in the seated position. The best of three trials was used for calculation.
Each variable was tested for normality using Skewness and Kurtosis tests with acceptable Z values not exceeding plus or minus 1.5. Upon confirmation of normality, the effect of pre-cooling and passive warm-up were analyzed by two-way ANOVA with repeated measures (conditions × timeof-day), while the effect of time-of-day was specifically analysed in each condition by a one-way ANOVA. Data are displayed as means (±S.D.) and the statistical significance was set at P < 0.05.
36 37
40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
66
67 68 69 70 71 72 73 74 75 76
RO
35
DP
34
TE
33
EC
32
RR
31
Cycling sprint
CO
30
Subjects
The total force developed by the subject was calculated from both the force developed against the friction load (constant) and the force developed against inertia to accelerate the flywheel. The data were collected every 8 degrees of pedal revolution by an acquisition card (DAQ-Pad 6020E, National Instruments, TX, USA) and analyzed by software developed in our laboratory with a LabVIEW interface (LabVIEW, National Instruments, TX, USA).
UN
29
Methods
OF
38
Seven male physical education students (27 ± 2 years, 1.74 ± 0.1 m and 70.7 ± 11 kg) gave written informed consent to participate in this study. The protocol was approved by the appropriate human research ethics committee. Subjects were classified as either ‘‘neither type’’ (n = 4) or ‘‘moderately evening type’’ (n = 3) from their responses a self-assessment questionnaire determining morningness—eveningness.3
Maximal power (Pmax ), maximal force (Fmax ) and maximal velocity (Vmax ) were calculated from the pedal revolution with the highest power development, the highest force production and the fastest velocity, respectively. The Fmax was generally obtained at the start of the sprint, when the subject develops a high force in order to initiate the rotation of the flywheel from a stationary position (very low velocity), whereas the Vmax was generally obtained at the end of the sprint. The coefficient of variation within the two best trials of each session was lower than 5%.
28
Results Body mass did not vary between morning (70.7 ± 10 kg) and afternoon (70.6 ± 10 kg) sessions (P = 0.59). Rectal temperature was significantly higher in the afternoon than in the morning (+0.4 ◦ C, P < 0.05) for all test conditions (Fig. 1A). However, the diurnal increases in leg skin temperature (+0.4 ◦ C), Pmax (+12%), Fmax (+5%) and Vmax (+6%) were only observed in the control condition (all P < 0.05, Fig. 1B—E). The warm bath significantly increased rectal temperature (+0.5 ◦ C, P < 0.05), whereas PC significantly decreased skin temperature (−5.6 ◦ C), Pmax (−14%), Fmax (−8%) and Vmax (−11%) (all P < 0.05, Fig. 1B—E). Time-of-day interacted with WU effect on Pmax (P < 0.05) as WU increased Pmax in the morning only (+4%, P < 0.05).
Discussion Our data showed for the first time that a direct local heating of the leg only increased muscular power in the morning blunting its diurnal variation. Despite similar core temperature
Please cite this article in press as: Racinais S, et al., Does the diurnal increase in central temperature interact with JSAMS 272 1—4 pre-cooling or passive warm-up of the leg?, J Sci Med Sport (2007), doi:10.1016/j.jsams.2007.09.008
77 78 79 80 81 82 83 84 85 86 87 88 89
90
91 92 93 94 95 96 97 98 99 100 101
102
103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118
119
120 121 122 123
ARTICLE IN PRESS
JSAMS 272 1—4
RT Time-of-day, warm-up, cooling
3
CO
RR
EC
TE
DP
RO
OF
increases from morning to afternoon across all conditions, Pmax displayed a diurnal increase only in the control trial. This suggests that core temperature is not the causal factor of this increment. Given that Pmax , Fmax and Vmax follow the same pattern of evolution as skin temperature, it appears that muscle rather than core temperature leads to a modification in muscle performance. Power decrements following pre-cooling seem to be larger in the afternoon (−17%) than in the morning (−9%) but without significant statistical difference. Pre-cooling decreased Pmax , Fmax and Vmax in both the morning and afternoon, indicating that diurnal increase in core temperature failed to prevent the negative effects of local cold exposure on muscle function. The deleterious effect of pre-cooling on muscle performance whatever time-of-day can be explained by the fact that circadian rhythm acts upon skeletal muscle contractility,4—6 whereas pre-cooling leads to an alteration in motor drive.7 In summary, modification of the leg skin temperature by cold or warm water bath blunts the diurnal variation in muscular power. Athletes could perform a passive warm-up of the exercising limb (e.g. hot bath) if a maximal power production is expected in the morning. Pre-cooling decreases muscle power as well as force and velocity components. Athletes should strictly avoid any cooling before a sprint exercise irrespective of time-ofday.
UN
Figure 1 Morning () and afternoon () values of both rectal (A) and skin temperature (B) as well as muscular power (C), maximal force (D) and velocity (E). The temperature data were recorded after the rest period just before the sprint exercises. * Significant effect of time-ofday; $ significantly different from the control condition, both P < 0.05.
Acknowledgement This work was supported in part by the General Council of the Department of Guadeloupe, from the French West Indies.
References 1. Racinais S, Hue O, Blonc S. Time-of-day effects on anaerobic muscular power in a moderately warm environment. Chronobiol Int 2004;21:483—93. 2. Falk B, Radom-Isaac S, Hoffmann JR, Wang Y, Yarom Y, Magazanik A, et al. The effect of heat exposure on performance of and recovery from high-intensity, intermittent exercise. Int J Sports Med 1998;19:1—6. ¨ 3. Horne JA, Ostberg O. A self-assessment questionnaire to determine morningness—eveningness in human circadian rhythms. Int J Chronobiol 1976;4:97—110. 4. Racinais S, Blonc S, Jonville S, et al. Time-of-day influences the environmental effects on muscle force and contractility. Q3 Med Sci Sports Exerc 2005;37:256—61.
Please cite this article in press as: Racinais S, et al., Does the diurnal increase in central temperature interact with JSAMS 272 1—4 pre-cooling or passive warm-up of the leg?, J Sci Med Sport (2007), doi:10.1016/j.jsams.2007.09.008
124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156
157
158 159 160
161
162 163 164 165 166 167 168 169 170 171 172 173 174
ARTICLE IN PRESS
JSAMS 272 1—4
4
DP
RO
OF
Available online at www.sciencedirect.com
TE
179
EC
178
7. Oksa J, Rintam¨ aki H, M¨ akinen T, et al. EMG-activity and muscular performance of lower leg during stretchshortening cycle after cooling. Acta Physiol Scand 1996;157: 71—8.
RR
177
5. Gauthier A, Davenne D, Martin A, et al. Time of day effects on isometric and isokinetic torque developed during elbow flexion in humans. Eur J Appl Physiol 2001;84:249—52. 6. Martin A, Carpentier A, Guissard N, et al. Effect of time of day on force variation in a human muscle. Muscle Nerve 1999;22:1380—7.
CO
176
UN
175
S. Racinais et al.
Please cite this article in press as: Racinais S, et al., Does the diurnal increase in central temperature interact with JSAMS 272 1—4 pre-cooling or passive warm-up of the leg?, J Sci Med Sport (2007), doi:10.1016/j.jsams.2007.09.008
180 181 182 183
