2007, Piran, Slovenia

Cold physiology
INTRA-INDIVIDUAL DIFFERENCES IN BURST SHIVERING
ACTIVITY: PROXIMAL VERSUS DISTAL MUSCLES
Marie-Andrée Imbeault 1 , Anali Maneshi 2 , Stéphane R. Legault 3 and François Haman 2
1 Institute of Neuroscience, Faculty of Medicine and 2 Faculty of Health Sciences, University of
Ottawa, Ottawa, Canada; 3 Defence R&D Canada – Ottawa, Ottawa, Ontario, Canada
Contact person: fhaman@uottawa.ca
INTRODUCTION
Cold-induced shivering is characterised by two distinct muscle contraction patterns:
continuous low-intensity shivering [4-8 Hz; ~1 to 5% of maximal voluntary contraction
(MVC)] and bursts of high-intensity shivering (0.1-0.2 Hz; 10 to 35% MVC) (Meigal, 2002,
Haman et al., 2004). Recently, large overall variations in this dual shivering pattern have been
observed amongst individuals even at the same relative thermogenic rate (Haman et al.,
2004). The purpose of this descriptive study was to quantify potential intra-individual
disparities in burst shivering activity between proximal and distal muscles within individuals.
METHODS
Moderate shivering (~3.5 times resting metabolic rate) was induced in eight non-acclimatized
men (23±0.4 years) using a thermal chamber set at 5°C and a liquid conditioned suit perfused
with 4°C water. Burst shivering rate (BR) was determined from electromyographic (EMG)
recordings from 8 muscles (4 proximal and 4 distal) located on the right side of the body as
described by Haman et al. (2004a). Proximal muscles are trapezius (TR), latissimus dorsi
(LA), pectoralis (PE), rectus abdominis (RA) and distal muscles are vastus lateralis (VL),
rectus femoris (RF), vastus medialis (VM), abductor magnus (AD).
RESULTS
Bursts·min -1
Bursts·min -1
7
6
5
4
3
2
1
Proximal
Distal
0
0 20 40 60 80
DISCUSSION
We conclude that important differences in shivering activity occur between proximal and
distal muscles within the same individual. Proximal muscles display a higher burst shivering
rate than distal muscles. The physiological importance and origins of these differences in
shivering EMG activity remain to be established.
REFERENCES
*
* *
Time (min)
Bell D.G., Tikuisis P. & Jacobs I. (1992). Relative intensity of muscular contraction during shivering. J Appl
Physiol 72 (6), pp 2336-2342.
Haman F., Legault SR. & Weber J.M. (2004a) Effects of carbohydrate availability on sustained shivering II.
Relating muscle recruitment to fuel selection. J Appl Physiol 96(1), pp 41-49.
Haman F., Legault SR., Rakobowchuck M., Ducharme M. & Weber J.M. (2004b). Fuel selection during intense
shivering in humans: EMG pattern reflects carbohydrate oxidation. J Physiol 556.1, pp 305-313.
Meigal A. (2002). Gross and fine neuromuscular performance at cold shivering. Int J Circumpolar Health 61(2),
pp 163-72.
*
100
Figure1: Differences between proximal
and distal muscle shivering rates over a
90 minutes cold exposure. Bars (±
standard error) represent mean of
shivering rate (bursts/min) of 8 subjects
of 2 different muscle groups (proximal
and distal muscles). * represents
significant differences (α < 0.05)
between muscle groups. As shivering
intensified from the beginning to the end
of cold exposure, BR increased
progressively for both muscles group
(P=0.001).
307