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1 Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool L3 2ET; 2 University Department of Anaesthesia, Withington Hospital, Manchester M20 2LR; 3 Oxford Lipid Metabolism Group, Radcliffe Infirmary, Oxford OX2 6HE, United Kingdom; and 4 Department of Human Biology, Maastricht University, The Netherlands
We aimed to examine the effect of
age on energy balance, metabolism, hydration, and performance during 10 days of strenuous hill walking. Seventeen male subjects were divided
into two groups according to their age. The nine subjects in
group 1 constituted the younger group (age 24 ± 3 yr),
whereas eight older subjects were in group 2 (age 56 ± 3 yr). Both groups completed 10 consecutive days of high-intensity hill
walking. Mean (range) daily walking distances and ascent were 21 km
(10-35 km) and 1,160 m (800-2,540 m), respectively. Energy
intake was calculated from weighed food intake, and energy expenditure
was measured by the doubly labeled water method. Blood and urine were
sampled on alternative days to determine any changes in metabolism and
hydration during the 10 days. Subjects also completed a battery of
tests that included muscular strength (handgrip), jump performance,
cognitive processing time, and flexibility. The younger group remained
hydrated, whereas the older group became progressively dehydrated,
indicated by a near twofold increase in urine osmolality concentration
on day 11. This increased urine osmolality in the older
group was highly correlated with impairment in vertical-jump
performance (r = 
0.86; P < 0.05) and
decreased cognitive processing time (r = 0.79;
P < 0.05). Despite energy expenditure of ~21 MJ/day,
body mass was well maintained in both groups. Both groups displayed a
marked increase in fat mobilization, reflected in significantly lowered prewalk insulin concentrations and elevated postwalk glycerol and
nonesterified fatty acid concentrations. Despite the dehydration and
impaired performance in the older group, blood glucose concentrations were well maintained in both groups, probably mediated via the increased mobilization of fat.
field study; metabolism; age and hill walking
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