Work performance after dehydration: effects of physical conditioning and heat acclimatization. 1958.

Three groups of five men each were dehydrated overnight in the heat (115 degrees F) on two occasions (D1 and D2) to approximately 5.5% of their starting body weight. During the 3-week period between D1 and D2, one group (AC) was acclimatized to heat and physically conditioned, the second group (C) was physically conditioned and the third group (S) remained sedentary. The response to work after dehydration was assessed by the following criteria: pulse rate (P), rectal temperature (Tr) and maximal oxygen intake (Max. VO2). Pulse rates during and after walking and after running were elevated with dehydration. This elevation was reduced in groups AC and C at D2 as compared to D1, but not in group S. An elevation in T1 with walking also occurred with dehydration, but this elevation was not significantly different at D2 as compared with D1 in any group. Physical conditioning elicited an elevation in Max. VO2 (group AC and C), but the elevation was no greater in group AC than in group C. Dehydration was associated with an equal decrement in Max. VO2 at D1 and D2 in all groups, but the conditioned men (AC and C) maintained a relatively higher Max. VO2 than group S. Thus, physical conditioning was associated with enhanced work performance during dehydration (assessed by the above criteria), whereas acclimatization to heat did not appreciably supplement this effect.

Physiologic effects of seatback angles 45degrees (from the vertical) relative to G.

Eight experimental subjects from the USAF Sschool of Aerospace Medicine (SAM) and four YF-16/17 test pilots were exposed to a simulated aerial combat maneuver (SACM) which included a maximum G exposure of 6 s at 8 G. The following physiologic parameters were examined relative to seatback angles of 23degrees, 28degrees, and 40degrees; heart rate and rhythm; arterial oxygen saturation; performance; intrathoracic (esophageal) pressure; arterial pressure; and subject comfort, effort, and fatigue. Relaxed and straining high sustained G (HSG) tolerances (6 G for 60 s) were also determined using only SAM subjects. The advantages of the 40 degree setback angle during the SACM included increased subject comfort, less fatigue and effort, greater pilot acceptance and a statisically significant reduction in the increased mean heart rate associated with G exposure. On the other hand, a statistically significant reduction in arterial oxygen saturation was obtained during the SACM at 40 degrees compared with the 23 degree back angle. An increase in relaxed G tolerance was found with the 40degree seatback angle--statistically significant only compared with the 28 degree seatback angle.