Table 2.

Coefficients for the interaction term between age and fitness level on GMd in the three significant clusters from voxel-wise regression.

			Lower fitness		Higher fitness
Cluster location	Voxels	COG X, Y, Z	β	t	β	t
Left superior frontal	1146	73.2, 56.2, 49.9	−0.86**	−4.04	0.32	1.08
Right perisylvian	1318	17.8, 46.9, 39.8	−0.88**	−4.12	0.23	0.77
Temporo-cerebellar	10718	43.8, 32.7, 23	−0.6*	−2.65	0.73*	2.3

Notes: GMd = Gray matter density; AF = Aerobic fitness; COG = Center of gravity in MNI 2 mm coordinates; β = standardized beta coefficient; t = t-statistic. Statistically significant coefficient **p < 0.01, *p < 0.05. βs represent the extent and direction of the relationship between age and GMd by AF level for each significant interaction cluster (age*AF on GMd). As can be seen, for those with lower AF, greater age is associated with lower GMd in each of the significant brain regions; whereas greater age is associated with higher GMd in temporo-cerebellar regions for those with higher AF levels.