2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
breath-by-breath oxygen uptake (Model K4, COSMED, Italy) as a measure of
shivering thermogenesis.
RESULTS
There were no statistically significant differences in the responses of rectal
temperature, mean skin temperature, heat flux, ΔTdiff, and oxygen uptake observed
prior to and immediately after the 35-days of horizontal bed rest. Cooling rate of Tre
was also identical during the pre- and post bed rest immersions.
DISCUSSION
The present results demonstrate that the thermogenic drive evoked by immersion in
15°C water was sufficiently strong to override any bed-rest induced attenuation of
shivering thermogenesis and cutaneous vasoconstriction (c.f. Mekjavic et al. 2005).
Previously (Mekjavic et al. 2005), we hypothesised that the substantial lower limb
muscle atrophy associated with 35 days of horizontal bed rest (Berg et al. 2007) may
be responsible for the observed attenuation of shivering heat production in 28°C
water. The results of the present study demonstrate that despite the loss of muscle
mass in the lower limbs as indicated by the 15% decrease in the cross sectional area
(Narici et al. 2007, this volume), shivering thermogenesis remains unaffected in 15°C
water. This finding suggests that this magnitude of loss of muscle mass in the lower
limbs does not affect the shivering heat production during a moderate-to-strong cold
stimulus.
The similar response of cold-induced vasoconstriction indicates that in the presence of
a greater cold afferent drive from peripheral, core, and central cold sensors, the coldinduced
vasoconstriction is unaffected. We previously suggested (Mekjavic et al.
2005) that the attenuation of this response might, in part, be associated with the
observed decrease in responsiveness of precapillary resistance vessels following bed
rest (Eiken and Mekjavic, 2002), but this does not appear to be manifest in cutaneous
vascular beds during progression into mild hypothermia.
ACKNOWLEDGEMENTS
This work was funded, in part, by the Ministries of Defence, and of Science (Republic
of Slovenia).
REFERENCES
Berg H.E., Eiken O., Miklavcic L, Mekjavic I.B. (2007). Hip, thigh and calf muscle
atrophy and bone loss after 5-week bedrest inactivity. Eur. J. Appl. Physiol. 99:
283-289.
Eiken O. and Mekjavic I.B. (2002). The Valdoltra Bedrest Study: Effects of
horizontal bedrest on the function of peripheral blood vessels, the
thermoregulatory system and on the function and structure of the musculoskeletal
system. FOI Report No. FOI-0748-SE. NBC Defence, Defence Medicine: Umea,
Sweden.
Mekjavic I.B., Golja P., Tipton M.J., Eiken O. (2005). Human thermoregulatory
function during exercise and immersion after 35 days of horizontal bed-rest and
recovery. Eur. J. Appl. Physiol. 95: 163-171.
Rubinstein E.H., Sessler D.I. (1990). Skin-surface temperature gradients correlate
with fingertip blood flow in humans. Anesthesiology 75: 541-545.
48