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Exercise thermoregulation in men after 1 and 24-hours of 6 degrees head-down tilt.
Aviat Space Environ Med. 2000 Feb; 71(2):150-5.AS

Abstract

BACKGROUND

Exercise thermoregulation is dependent on heat loss by increased skin blood flow (convective and conductive heat loss) and through enhanced sweating (evaporative heat loss). Reduction of plasma volume (PV), increased plasma osmolality, physical deconditioning, and duration of exposure to simulated and actual microgravity reduces the ability to thermoregulate during exercise.

HYPOTHESIS

We hypothesized that 24 h of head down tilt (HDT24) would alter thermoregulatory responses to a submaximal exercise test and result in a higher exercise rectal temperature (Tre) when compared with exercise Tre after 1 h of head down tilt (HDT1).

METHODS

Seven men (31+/-SD 6 yr, peak oxygen uptake (VpO2peak) of 44+/-6 ml x kg(-1) x min(-1)) were studied during 70 min of supine cycling at 58+/-SE 1.5% VO2peak at 22.0 degrees C Tdb and 47% rh.

RESULTS

Relative to pre-tilt sitting chair rest data, HDT1 resulted in a 6.1+/-0.9% increase and HDT24 in a 4.3+/-2.3% decrease in PV (delta = 10.4% between experiments, p<0.05) while plasma osmolality remained unchanged (NS). Pre-exercise Tre was elevated after HDT24 (36.71 degrees C +/-0.06 HDT1 vs. 36.93 degrees C+/-0.11 HDT24, p<0.05). The 70 min of exercise did not alter this relationship (p<0.05) with respective end exercise increases in Tre to 38.01 degrees C and 38.26 degrees C (degrees = 1.30 degrees C (HDT1) and 1.33 degrees C (HDT24)). While there were no pre-exercise differences in mean skin temperature (Tsk), a significant (p<0.05) time x treatment interaction occurred during exercise: after min 30 in HDT24 the Tsk leveled off at 31.1 degrees C, while it continued to increase reaching 31.5 degrees C at min 70 in HDT1. A similar response (NS) occurred in skin blood velocity. Neither local sweating rates nor changes in body weight during exercise of -1.63+/-0.24 kg (HDT1) or - 1.33+/-0.09 kg (HDT24) were different (NS) between experiments.

CONCLUSION

While HDT24 resulted in elevated pre-exercise Tre, reduced PV, attenuation of Tsk and skin blood velocity during exercise, the absolute increase in exercise Tre was not altered. But if sweat rate and cutaneous vascular responses were similar at different core temperatures (unchanged thermoregulation), the Tre offset could have been caused by the HDT-induced hypovolemia.

Authors+Show Affiliations

NASA-Ames Research Center, Moffett Field, CA, USA.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Comparative Study
Journal Article
Research Support, U.S. Gov't, Non-P.H.S.

Language

eng

PubMed ID

10685589

Citation

Ertl, A C., et al. "Exercise Thermoregulation in Men After 1 and 24-hours of 6 Degrees Head-down Tilt." Aviation, Space, and Environmental Medicine, vol. 71, no. 2, 2000, pp. 150-5.
Ertl AC, Dearborn AS, Weidhofer AR, et al. Exercise thermoregulation in men after 1 and 24-hours of 6 degrees head-down tilt. Aviat Space Environ Med. 2000;71(2):150-5.
Ertl, A. C., Dearborn, A. S., Weidhofer, A. R., Bernauer, E. M., & Greenleaf, J. E. (2000). Exercise thermoregulation in men after 1 and 24-hours of 6 degrees head-down tilt. Aviation, Space, and Environmental Medicine, 71(2), 150-5.
Ertl AC, et al. Exercise Thermoregulation in Men After 1 and 24-hours of 6 Degrees Head-down Tilt. Aviat Space Environ Med. 2000;71(2):150-5. PubMed PMID: 10685589.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Exercise thermoregulation in men after 1 and 24-hours of 6 degrees head-down tilt. AU - Ertl,A C, AU - Dearborn,A S, AU - Weidhofer,A R, AU - Bernauer,E M, AU - Greenleaf,J E, PY - 2000/2/24/pubmed PY - 2000/3/4/medline PY - 2000/2/24/entrez KW - NASA Center ARC KW - NASA Discipline Regulatory Physiology KW - NASA Program Biomedical Research and Countermeasures SP - 150 EP - 5 JF - Aviation, space, and environmental medicine JO - Aviat Space Environ Med VL - 71 IS - 2 N2 - BACKGROUND: Exercise thermoregulation is dependent on heat loss by increased skin blood flow (convective and conductive heat loss) and through enhanced sweating (evaporative heat loss). Reduction of plasma volume (PV), increased plasma osmolality, physical deconditioning, and duration of exposure to simulated and actual microgravity reduces the ability to thermoregulate during exercise. HYPOTHESIS: We hypothesized that 24 h of head down tilt (HDT24) would alter thermoregulatory responses to a submaximal exercise test and result in a higher exercise rectal temperature (Tre) when compared with exercise Tre after 1 h of head down tilt (HDT1). METHODS: Seven men (31+/-SD 6 yr, peak oxygen uptake (VpO2peak) of 44+/-6 ml x kg(-1) x min(-1)) were studied during 70 min of supine cycling at 58+/-SE 1.5% VO2peak at 22.0 degrees C Tdb and 47% rh. RESULTS: Relative to pre-tilt sitting chair rest data, HDT1 resulted in a 6.1+/-0.9% increase and HDT24 in a 4.3+/-2.3% decrease in PV (delta = 10.4% between experiments, p<0.05) while plasma osmolality remained unchanged (NS). Pre-exercise Tre was elevated after HDT24 (36.71 degrees C +/-0.06 HDT1 vs. 36.93 degrees C+/-0.11 HDT24, p<0.05). The 70 min of exercise did not alter this relationship (p<0.05) with respective end exercise increases in Tre to 38.01 degrees C and 38.26 degrees C (degrees = 1.30 degrees C (HDT1) and 1.33 degrees C (HDT24)). While there were no pre-exercise differences in mean skin temperature (Tsk), a significant (p<0.05) time x treatment interaction occurred during exercise: after min 30 in HDT24 the Tsk leveled off at 31.1 degrees C, while it continued to increase reaching 31.5 degrees C at min 70 in HDT1. A similar response (NS) occurred in skin blood velocity. Neither local sweating rates nor changes in body weight during exercise of -1.63+/-0.24 kg (HDT1) or - 1.33+/-0.09 kg (HDT24) were different (NS) between experiments. CONCLUSION: While HDT24 resulted in elevated pre-exercise Tre, reduced PV, attenuation of Tsk and skin blood velocity during exercise, the absolute increase in exercise Tre was not altered. But if sweat rate and cutaneous vascular responses were similar at different core temperatures (unchanged thermoregulation), the Tre offset could have been caused by the HDT-induced hypovolemia. SN - 0095-6562 UR - https://www.unboundmedicine.com/medline/citation/10685589/Exercise_thermoregulation_in_men_after_1_and_24_hours_of_6_degrees_head_down_tilt_ DB - PRIME DP - Unbound Medicine ER -