DR. JOHNSON: We have collected data where we have looked at these variables. We have found that performance of militarily relevant tasks such as marksmanship, is related to heat exposure. Specifically, up to 6 hours exposure to 95°F with 60 percent relative humidity significantly impairs steadiness of the soldier's outstretched arm and hand. Rifle marksmanship for stationary targets, which requires extreme steadiness of the arm and hand, is also impaired during the same heat exposure.
PARTICIPANT: I remember years ago when I was working in the military ergonomics, that subjective ratings depended on who asked the question. For example, if a woman asked male soldiers how they felt, the soldiers tended to report that they felt better than if the questioner was a man.
DR. JOHNSON: That is a good point and it is often overlooked by casual users of subjective report techniques. It is also one of the reasons that we adopted a standardized questionnaire. We wanted to avoid the subtle influences on subjective response due to inadvertent rewording of the questions and due to variability in the characteristics of the questioner. In this study, the questionnaire was always administered by the same person and at a table far removed from the rest of the staff and from other subjects.
PARTICIPANT: Since the administration of the two salt diets was double blind, I am curious as to whether the subjects could guess which diet they had received.
DR. JOHNSON: We did collect the data and found that the subjects were unable to guess at better than a chance level. The double blind procedure was a success.
PARTICIPANT: I missed how the meals were administered.
DR. JOHNSON: The diets were constructed around MREs. For the high salt diet, we used standard off-the-shelf MRE entrees. For the low salt diet, a food engineer altered MREs by removing the sodium glutamate and all the salt-containing preservatives. Ninety percent of the difference in the sodium in the two diets was due to these re-engineered entrees. All other food was obtained from a supermarket. These other foods were mixed so that they looked the same. Taste tests done before the study indicated that independent judges could not tell the difference. Those MRE entrees with the low salt could not be distinguished from those with more salt.