Article Figures & Tables
Figures
- 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; V̇O2max, maximal oxygen consumption in exercise; V̇O2sum, 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. V̇min, minute volume; VT, tidal volume; f, breathing frequency; EO2, oxygen extraction.
- Table 1.
Effects of sex, age and body mass on mass, metabolism and ventilation during cold exposure in 211 deer mice ranging in age from 27 days to 1863 days
Sex Mass Age Mass F1,205=24.5, P<0.000001* M: r=0.432, P=0.000004* F: r=0.521, P<0.000001* BMR F1,201=8.2, P=0.0046* M: r=0.56, P<0.000001* M: r=-0.12, P=0.23 F: r=0.57, P<0.000001* F: r=0.010, P=0.92 V̇ O2max F1,203=1.2, P=0.275 r=0.664, P<0.000001* r=-0.201, P=0.00316* V̇ O2sum F1,202=0.002, P=0.96 r=0.506, P<0.000001* r=-0.217, P=0.00209* f F1,200=7.8, P=0.00572* M: r=0.083, P=0.40 M: r=-0.27, P=0.00495* F: r=0.006, P=0.95 F: r=-0.384, P=0.000094* V T F1,198=1.7, P=0.20 r=0.329, P=0.0000017* r=0.092, P=0.19 V̇ min F1,198=0.002, P=0.97 r=0.336, P<0.000001* r=-0.071, P=0.31 E O2 F1,198=0.13, P=0.72 r=0.10, P=0.14 r=-0.19, P=0.0070* -
BMR, basal metabolic rate; V̇O2max, maximal oxygen consumption in exercise; V̇O2sum, maximal oxygen consumption in thermogenesis; f, breathing frequency; VT, tidal volume; V̇min, minute volume; EO2, oxygen extraction.
Age, mass and metabolism were loge-transformed prior to analysis. ANCOVA with mass and age as covariates was used to test for sex differences, and multiple regression was used to examine the effects of age and mass. Separate partial correlation coefficients (r) and P values are given for males (M) and females (F) for variables where the sexes differed significantly. P values with an asterisk (*) remained significant after sequential Bonferroni correction (adjustedα =0.008; Rice, 1989).
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- Table 2.
Breakpoint regression results (shown as partial correlation coefficients) for the effects of age on V̇O2max and V̇O2sum in deer mice ranging in age from 27 days to 1863 days
Age breakpoint Age < breakpoint Age > breakpoint V̇ O2max 485 days N=83 N=125 Mass: r=0.774, P<0.000001* Mass: r=0.569, P<0.000001* Age: r=-0.103, P=0.36 Age: r=-0.291, P=0.00102* V̇ O2sum 483 days N=82 N=124 Mass: r=0.621, P<0.000001* Mass: r=0.419, P=0.000015* Age: r=-0.046, P=0.68 Age: r=-0.410, P=0.000024 -
Regressions were derived from loge-transformed mass, age, maximal oxygen consumption in exercise (V̇O2max) and maximal oxygen consumption in thermogenesis (V̇O2sum); nearly identical results were obtained when regressions were based on mass-corrected V̇O2 (Fig. 4). The overall r values (including the effects of both mass and age and combined across both age groups) were 0.85 for V̇O2max and 0.805 for V̇O2sum. P values with an asterisk (*) remained significant after sequential Bonferroni correction (adjusted α=0.017).
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- 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 V̇O2max (exercise) and thin lines indicate V̇O2sum (cold exposure). Lines are derived from `breakpoint' (piecewise) regressions based on data in Fig. 2.
- Table 3.
Combined effects of mass, age and V̇O2sum on breathing frequency (f), tidal volume (VT), minute volume (V̇min), and oxygen extraction efficiency (EO2) in deer mice ranging in age from 27 days to 1863 days
Mass Age V̇ O2sum f (M) r=-0.11, P=0.26 r=-0.201, P=0.042 r=0.435, P=0.000044* f (F) r=-0.088, P=0.39 r=-0.337, P=0.00084* r=0.160, P=0.120 V T r=0.175, P=0.0394 r=0.149, P=0.0353 r=0.256, P=0.000259* V̇ min r=0.146, P=0.0131 r=0.009, P=0.90 r=0.363, P<0.000001* E O2 r=-0.130, P=0.065 r=-0.101, P=0.125 r=0.413, P<0.000001* -
N=109 males (M), 102 females (F). P values that remained significant after sequential Bonferroni correction (adjusted α=0.0045) are indicated with an asterisk.
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- Fig. 5.
The relationship between maximal oxygen consumption in thermogenesis (V̇O2sum) and maximal oxygen consumption in exercise (V̇O2max) in 211 deer mice. Data are normalized to V̇O2max (i.e. a value of 1.0 indicates that V̇O2max=V̇O2sum). The ratio of these two aerobic indices did not vary significantly with either sex or age.
- Table 4.
Effects of body composition on metabolism in deer mice ranging in age from 27 days to 1827 days
V̇O2max V̇O2sum BMR Age < breakpoint Age > breakpoint Age < breakpoint Age > breakpoint Body composition (N=54) (N=25) (N=30) (N=25) (N=30) Heart mass r=0.337, P=0.0145* r=0.642, P=0.00126* r=0.236, P=0.233 r=0.443, P=0.0387 r=0.333, P=0.0827 Lung mass r=0.266, P=0.0565 r=0.604, P=0.00287* r=0.358, P=0.0612 r=0.420, P=0.0515 r=0.392, P=0.0394 % fat content r=0.298, P=0.0320 r=0.601, P=0.00307* r=0.128, P=0.516 r=0.439, P=0.0408 r=0.424, P=0.0245 Hematocrit r=0.280, P=0.0443 r=0.413, P=0.056 r=0.231, P=0.237 r=0.462, P=0.0305 r=0.347, P=0.0705 -
BMR, basal metabolic rate; V̇O2max, maximal oxygen consumption in exercise; V̇O2sum, maximal oxygen consumption in thermogenesis.
Age breakpoints for V̇O2max and V̇O2sum (485 days and 483 days, respectively) were obtained from the complete data set (Table 2). Regressions were based on loge-transformed metabolic data and included the effects of loge-transformed lean tissue mass and age. Partial r and P values are shown; P values that remained significant after Bonferroni correction are indicated with asterisks (adjustedα =0.0167 for BMR and 0.0036 for V̇O2max and V̇O2sum).
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- Table 5.
Effects of age and body mass on several aspects of body composition in `old' deer mice (age >485 days)
Body mass Age Lean mass r=0.601, P=0.00045* r=0.0941, P=0.621 Lean mass (as % body mass) r=-0.592, P=0.00056* r=0.415, P=0.0227 Fat mass r=0.615, P=0.00030* r=-0.406, P=0.026 Fat content (as % body mass) r=0.574, P=0.00091* r=-0.457, P=0.011 Heart mass r=0.614, P=0.00031* r=0.173, P=0.360 Lung mass r=0.490, P=0.0060* r=0.080, P=0.675 -
The table shows partial correlation coefficients (r) and P values. Asterisks indicate P values remaining significant after sequential Bonferroni correction (adjusted α=0.0071). In younger animals, no body composition variable was significantly correlated with age after correction for body mass.
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- Table 6.
Effects of age and body composition (lean tissue and fat) on BMR, V̇O2max and V̇O2sum in deer mice from 27 to 1827 days old
Variable Fat and lean (absolute values) Fat and lean (fractions of body mass) BMR Fat r=0.312, P=0.0228 r=-0.096, P=0.499 Lean tissue r=0.321, P=0.0191 r=-0.106, P=454 Age r=0.150, P=0.283 r=0.038, P=0.787 V̇ O2max Fat r=0.401, P=0.00295* r=0.237, P=0.091 Lean tissue r=0.505, P=0.000113* r=0.203, P=0.149 Age r=-0.101, P=0.470 r=-0.227, P=0.106 V̇ O2sum Fat r=0.437, P=0.00107* r=-0.014, P=0.920 Lean tissue r=0.423, P=0.00161* r=-0.065, P=0.646 Age r=-0.14, P=0.315 r=-0.214, P=0.127 -
BMR, basal metabolic rate; V̇O2max, maximal oxygen consumption in exercise; V̇O2sum, maximal oxygen consumption in thermogenesis.
Regressions were performed across all ages. Regression coefficients (r) and P values for fat and lean tissue content were computed from absolute tissue mass and as fractions of whole body mass; in the latter case, regressions also included whole body mass (r and P values not shown). P values significant after Bonferroni correction are indicated with an asterisk (adjusted α=0.0038 for all ages combined).
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- Table 7.
Effects of age and body composition (lean tissue and fat) on V̇O2max and V̇O2sum in deer mice younger and older than the `breakpoint' age of 485 days
Young mice (<485 days) Old mice (>485 days) Variable Fat and lean (absolute values) Fat and lean (fractions of body mass) Fat and lean (absolute values) Fat and lean (fractions of body mass) V̇ O2max Fat r=0.509, P=0.013 r=0.237, P=0.289 r=0.481, P=0.0096 r=0.152, P=0.449 Lean r=0.397, P=0.060 r=0.174, P=0.439 r=0.346, P=0.0708 r=0.231, P=0.245 Age r=0.207, P=0.344 r=0.055, P=0.808 r=0.264, P=0.174 r=0.425, P=0.027 V̇ O2sum Fat r=0.360, P=0.091 r=0.155, P=0.491 r=0.121, P=0.582 r=-0.225, P=0.259 Lean r=0.466, P=0.025 r=0.132, P=0.557 r=0.065, P=0.767 r=-0.289, P=0.143 Age r=0.113, P=0.608 r=0.003, P=0.989 r=-0.370, P=0.083 r=-0.399, P=0.039 -
V̇O2max, maximal oxygen consumption in exercise; V̇O2sum, maximal oxygen consumption in thermogenesis.
Regressions were performed on animals younger and older than the `breakpoint' age of 485 days determined from the complete data set. Regression coefficients (r) and P values for fat and lean tissue content were computed from absolute tissue mass and as fractions of whole body mass; in the latter case, regressions also included whole body mass (r and P values not shown). No P value is significant after Bonferroni correction (adjusted α=0.0023 for young and old mice).
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