Quantitative Model of Sustained Physical Task Duration at Varying Altitudes.
OBJECTIVE
The objective of this study is to develop a quantitative model that can be used before ascent to altitude (ALT) to predict how much longer a sustained physical task would take for unacclimatized individuals in the early hours of exposure.


METHODS
Using multiple linear regression, we analyzed time-trial (TT) performance on 95 unacclimatized men (n = 83) and women (n = 12) at sea level (SL) and at an ALT ranging from 2500 to 4300 m. The TT was initiated within 4 h of ascent to ALT. The independent variables known before ascent were as follows: ALT, age, height, weight, sex, SL peak oxygen uptake, SL task duration time, and body mass index (BMI) classification (normal weight vs overweight). The dependent variable was the percent increase in TT duration from SL to ALT.


RESULTS
The most significant factor in the model was ALT (P = 0.0001), followed by BMI classification (P = 0.0009) and the interaction between BMI classification and ALT (P = 0.003). The model is as follows: percent increase in TT duration = [100 + e(-1.517+1.323 (ALT)+3.124 (BMI class)-0.769 (ALT) (BMI class)]. The percent increase in TT duration in overweight individuals was 129% greater than for normal-weight individuals at 3000 m. However, as ALT increased beyond 3000 m, the disparity between groups decreased until 4050 m where the percent increase in TT duration became greater for normal-weight individuals.


CONCLUSIONS
This model provides the first quantitative estimates of the percent increase in sustained physical task duration during initial exposure to a wide range of elevations. Because only two easily obtainable factors are required as inputs for the model (ALT and BMI classification), this model can be used by many unacclimatized individuals to better plan their activities at ALT.
1Thermal and Mountain Medicine Division, United States Army Research Institute of Environmental Medicine, Natick, MA; and 2Biophysics and Biomedical Modelling Division, United States Army Research Institute of Environmental Medicine, Natick, MA.
Beth A
BA
Beidleman
Charles S
CS
Fulco
Mark J
MJ
Buller
Sean P
SP
Andrew
Janet E
JE
Staab
Stephen R
SR
Muza
D000064:Acclimatization; D000531:Altitude; D015992:Body Mass Index; D005080:Exercise Test / Q000379:methods*; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D013647:Task Performance and Analysis; D013997:Time Factors; D055815:Young Adult