Time of day influences the environmental effects on muscle force and contractility

Racinais, Sebastien, Blonc, Stephen, Jonville, Sophie and Hue, Olivier (2005) Time of day influences the environmental effects on muscle force and contractility. Medicine and Science in Sports and Exercise, 37 2: 256-261. doi:10.1249/01.MSS.0000149885.82163.9F

Author Racinais, Sebastien
Blonc, Stephen
Jonville, Sophie
Hue, Olivier
Title Time of day influences the environmental effects on muscle force and contractility
Journal name Medicine and Science in Sports and Exercise   Check publisher's open access policy
ISSN 1530-0315
Publication date 2005-02-01
Sub-type Article (original research)
DOI 10.1249/01.MSS.0000149885.82163.9F
Open Access Status Not Open Access
Volume 37
Issue 2
Start page 256
End page 261
Total pages 6
Place of publication Maryland MD., U.S.A.
Publisher Lippincott Willams & Wilkins
Language eng
Subject 1106 Human Movement and Sports Science
Formatted abstract
Purpose: To investigate the effects of environmental temperature and the diurnal increase in body temperature on muscle contractile processes, 11 male subjects performed maximal and submaximal isometric contractions of the knee extensors with recording of the electromyographic activity in four different conditions (morning/neutral, morning/moderately warm and humid, afternoon/neutral, and afternoon/moderately warm and humid).
Methods: The morning experiments were conducted between 0700 and 1900 h, and the afternoon experiments were conducted between 0500 and 0700 h. The mean laboratory temperatures and humidity were 20.5 (+/-1)[degrees]C + 67 (+/-4)% and 29.5 (+/-0.8)[degrees]C + 74 (+/-10)% for the neutral and moderately warm and humid conditions, respectively.
Results: Results showed a significant diurnal increase in both rectal and skin temperatures whatever the environmental conditions, and an increase in the skin temperature after a 60-min moderately warm exposure. The major finding of this study was an interaction effect of time of day and environmental conditions on the force/electromyographic activity ratio. That suggests that skeletal muscle contractility was differently increased by the passive warm-up effect of a moderately warm exposure, depending on the diurnal variation in body temperature. This conclusion is supported by an increase in force in the morning only after a 60-min warm exposure (+19%) and in a neutral environment only with the diurnal increase in body temperature (+12%).
Conclusion: In summary, our data showed that both the warm exposure and the diurnal increase in body temperature influence muscle contractility and consequently muscle strength. However, the improvement in muscle contractility after these two passive warm-ups cannot be combined in order to improve force to a greater level.
Keyword Circadian rhythm
Isometric strength
Moderately warm and humid climate
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
School of Human Movement and Nutrition Sciences Publications
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Citation counts: TR Web of Science Citation Count  Cited 54 times in Thomson Reuters Web of Science Article | Citations
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Created: Thu, 08 Apr 2010, 22:00:12 EST by Sue Green on behalf of Faculty Of Health Sciences