Fig. 1. Frequency distribution of sample sizes used at different ages for body
composition studies (A; N=58) and aerobic physiology and ventilation
measurements (B; N=211).
Fig. 2. Age-related changes in mass and aerobic metabolism in 211 deer mice.
Different symbols are used for males and females for variables with
significant gender differences. BMR, basal metabolic rate;
O2max, maximal
oxygen consumption in exercise;
O2sum, maximal
oxygen consumption in thermogenesis.
Fig. 3. Age-related changes in ventilation and oxygen extraction in 211 deer mice.
Different symbols are used for males and females for variables showing
significant gender differences.
min, minute volume;
VT, tidal volume; f, breathing frequency;
EO2, oxygen extraction.
Fig. 4. Simplified representation of mean age-related changes in body mass (top),
whole-animal maximal oxygen consumption (middle) and mass-specific maximal
oxygen consumption (bottom) in male (broken lines) and female (solid lines)
deer mice. For maximal oxygen consumption, heavy lines indicate
O2max (exercise)
and thin lines indicate
O2sum (cold
exposure). Lines are derived from `breakpoint' (piecewise) regressions based
on data in Fig. 2.
Fig. 5. The relationship between maximal oxygen consumption in thermogenesis
(O2sum) and
maximal oxygen consumption in exercise
(O2max) in 211
deer mice. Data are normalized to
O2max (i.e. a
value of 1.0 indicates that
O2max=O2sum).
The ratio of these two aerobic indices did not vary significantly with either
sex or age.
O2max, maximal
oxygen consumption in exercise;
