Fitness, Glucose Homeostasis, and Brain Morphology in Twins
Fitness, Glucose Homeostasis, and Brain Morphology in Twins
The characteristics of our twin participants are shown in Table 1, and the intrapair differences, in Table 2. By definition, the past 3-yr-LTMET index, the 12-month-LTMET index, and Baecke sport index, all three of which characterize leisure time physical activity level, differed between the members of the twin pairs discordant for physical activity (Table 2). According to our retrospective interviews covering year by year the time 1–6 yr before the outcome measurements, there was a pairwise difference in leisure time physical activity during past 3 yr, but no difference was seen 4–6 yr before the examinations. Among these pairs, there was no pairwise difference in leisure time physical activity according to the questionnaire data collected from the cohort at the mean age of 24.5 yr or during their late adolescence, on the basis of questionnaire data from ages 16 to 18.5 yr (see Table, Supplemental Digital Content 2, Intrapair differences in leisure time physical activity among FITFATTWIN study participants, http://links.lww.com/MSS/A424). This means that we investigated the effects of physical activity differences during the 3-yr period before outcome measurements.
As expected, active twins had higher cardiorespiratory fitness (P < 0.001) compared with their inactive co-twins. Active twins tended to have higher exercise enjoyment (P < 0.06), with a moderate effect size (Cohen d = 0.75) compared with their inactive co-twins (Table 2). To establish more personal reasons for engaging or not engaging in leisure time physical activity, the co-twins were asked to describe in their own words their reasons for their physical activity behaviors. Six of the inactive co-twins reported that work and/or family commitments were the primary reasons for physical inactivity.
The active twins had a lower body fat percent (P = 0.029) compared with inactive co-twins, but there was no pairwise difference in lean mass (Table 2). The Matsuda index was higher (P = 0.021) and the HOMA index was lower (P = 0.031) among active twins compared with those among their inactive co-twins, indicating better insulin sensitivity/lower insulin resistance among the more active individuals (Table 2).
Segmentation of brain MR images revealed that total GM, WM, and cerebrospinal fluid volumes were similar between co-twins (P > 0.60 for all comparisons). However, the VBM analysis indicated regional GM volume differences in the nondominant striatum and prefrontal cortex between active and inactive members of the pairs. Specifically, the putamen (peak voxel coordinates 18, 6, −6; peak T = 8.8; 395 voxels in cluster) in the nondominant hemisphere showed larger GM volume in the active twins compared with their inactive co-twins (Fig. 2). In addition, nondominant prefrontal cortex (subgyral and inferior frontal gyrus (IFG), peak voxel coordinates 34.5, 33, 18; peak T = 6.6; 99 voxels in cluster) showed larger GM volume in active members than that in inactive members of the pair (Figs. 2 and 3).
(Enlarge Image)
Figure 2.
Axial MRI slices extending from the inferior tip of putamen (–10) to the superior tip of the caudate nucleus (+18), illustrating increased GM volume in yellow and red in the nondominant hemisphere of active versus inactive members of twin pairs (nine pairs). D, dominant hemisphere; ND, nondominant hemisphere.
(Enlarge Image)
Figure 3.
Coronal MRI slices demonstrating the extent of significantly differing GM volumes in the striatum in the nondominant hemisphere (+4) and in the subgyral prefrontal region in the nondominant hemisphere (+32). The same regions are shown in axial slices in Figure 2. D, dominant hemisphere; ND, nondominant hemisphere.
Results
The characteristics of our twin participants are shown in Table 1, and the intrapair differences, in Table 2. By definition, the past 3-yr-LTMET index, the 12-month-LTMET index, and Baecke sport index, all three of which characterize leisure time physical activity level, differed between the members of the twin pairs discordant for physical activity (Table 2). According to our retrospective interviews covering year by year the time 1–6 yr before the outcome measurements, there was a pairwise difference in leisure time physical activity during past 3 yr, but no difference was seen 4–6 yr before the examinations. Among these pairs, there was no pairwise difference in leisure time physical activity according to the questionnaire data collected from the cohort at the mean age of 24.5 yr or during their late adolescence, on the basis of questionnaire data from ages 16 to 18.5 yr (see Table, Supplemental Digital Content 2, Intrapair differences in leisure time physical activity among FITFATTWIN study participants, http://links.lww.com/MSS/A424). This means that we investigated the effects of physical activity differences during the 3-yr period before outcome measurements.
As expected, active twins had higher cardiorespiratory fitness (P < 0.001) compared with their inactive co-twins. Active twins tended to have higher exercise enjoyment (P < 0.06), with a moderate effect size (Cohen d = 0.75) compared with their inactive co-twins (Table 2). To establish more personal reasons for engaging or not engaging in leisure time physical activity, the co-twins were asked to describe in their own words their reasons for their physical activity behaviors. Six of the inactive co-twins reported that work and/or family commitments were the primary reasons for physical inactivity.
The active twins had a lower body fat percent (P = 0.029) compared with inactive co-twins, but there was no pairwise difference in lean mass (Table 2). The Matsuda index was higher (P = 0.021) and the HOMA index was lower (P = 0.031) among active twins compared with those among their inactive co-twins, indicating better insulin sensitivity/lower insulin resistance among the more active individuals (Table 2).
Segmentation of brain MR images revealed that total GM, WM, and cerebrospinal fluid volumes were similar between co-twins (P > 0.60 for all comparisons). However, the VBM analysis indicated regional GM volume differences in the nondominant striatum and prefrontal cortex between active and inactive members of the pairs. Specifically, the putamen (peak voxel coordinates 18, 6, −6; peak T = 8.8; 395 voxels in cluster) in the nondominant hemisphere showed larger GM volume in the active twins compared with their inactive co-twins (Fig. 2). In addition, nondominant prefrontal cortex (subgyral and inferior frontal gyrus (IFG), peak voxel coordinates 34.5, 33, 18; peak T = 6.6; 99 voxels in cluster) showed larger GM volume in active members than that in inactive members of the pair (Figs. 2 and 3).
(Enlarge Image)
Figure 2.
Axial MRI slices extending from the inferior tip of putamen (–10) to the superior tip of the caudate nucleus (+18), illustrating increased GM volume in yellow and red in the nondominant hemisphere of active versus inactive members of twin pairs (nine pairs). D, dominant hemisphere; ND, nondominant hemisphere.
(Enlarge Image)
Figure 3.
Coronal MRI slices demonstrating the extent of significantly differing GM volumes in the striatum in the nondominant hemisphere (+4) and in the subgyral prefrontal region in the nondominant hemisphere (+32). The same regions are shown in axial slices in Figure 2. D, dominant hemisphere; ND, nondominant hemisphere.
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