Exercise training and 3-day head down bed rest deconditioning: exercise thermoregulation.
Bed rest (BR) deconditioning causes excessive increase of exercise core body tempera-ture, while aerobic training improves exercise thermoregulation. The study was designed to determine whether 3 days of 6 degrees head-down bed rest (HDBR) affects body temperature and sweating dynamics during exercise and, if so, whether endurance training before HDBR modifies these responses. Twelve healthy men (20.7+/-0.9 yrs, VO2max: 46+/-4 ml x kg(-1) x min(-1) ) underwent HDBR twice: before and after 6 weeks of endurance training. Before and after HDBR, the subjects performed 45 min sitting cycle exercise at the same workload equal to 60% of VO2max determined before training. During exercise the VO2, HR, tympanic (Ttymp) and skin (Tsk) temperatures were recorded; sweating dynamics was assayed from a ventilated capsule on chest. Training increased VO2max by 12.1% (p<0.001). Resting Ttymp increased only after first HDBR (by 0.22 +/- 0.08 degrees C, p<0.05), while exercise equilibrium levels of Ttymp were increased (p<0.05) by 0.21 +/- 0.07 and 0.26 +/- 0.08 degrees C after first and second HDBR, respectively. Exercise mean Tsk tended to be lower after both HDBR periods. Total sweat loss and time-course of sweating responses were similar in all exercise tests. The sweating threshold related to Ttymp was elevated (p<0.05) only after first HDBR.


CONCLUSIONS
six-week training regimen prevents HDBR-induced elevation of core temperature (Ttymp) at rest but not during ex-ercise. The post-HDBR increases of Ttymp without changes in sweating rate and the tendency for lower Tsk suggest an early (<3d) influence of BR on skin blood flow.
Smorawinski
J
J
Department of Sport Medicine, Academy of Physical Education, Poznan, Poland.
Młynarczyk
C
C
Ziemba
A W
AW
Mikulski
T
T
Cybulski
G
G
Grucza
R
R
Nazar
K
K
Kaciuba-Uscilko
H
H
Greenleaf
J E
JE
D000328:Adult; D001510:Bed Rest / Q000379:methods; D001833:Body Temperature Regulation / Q000502:physiology*; D018493:Cardiovascular Deconditioning / Q000502:physiology*; D015444:Exercise / Q000502:physiology; D018475:Head-Down Tilt / Q000502:physiology*; D006801:Humans; D008297:Male; D010807:Physical Endurance / Q000502:physiology*