TABLE 1.

Summary of MRI studies investigating the brain myelin content in humans.

References	Study design	MRI sequences	Conclusion
Boa Sorte Silva et al., 2023	Cross-sectional study: older adults with cerebral small vessel disease and mild cognitive impairment	The myelin water fraction was defined as the fraction of signal with T2 < 40 ms over the entire T2 distribution	Greater physical activity was linked to a higher myelin content in the whole-brain white matter, in the sagittal stratum, the anterior corona radiata and the genu of the corpus callosum
Kirby et al., 2022	Longitudinal study: 2-week motor-training in healthy subjects	The water myelin fraction was obtained using a 32 echo gradient and spin echo (GRASE) sequence T2 scan	Higher myelin content induced by physical exercise augments axonal transmission efficiency in the cortico-spinal tract
Greeley et al., 2022	Cross-sectional study: chronic stroke (>6 months) patients vs. older healthy controls	The water myelin content was defined as the sum of the amplitudes within a short T2 signal (15–40 ms) divided by the sum of the amplitudes for the total T2 distribution	More physically active patients showed less myelin asymmetry in brain regions responsible for movement
Shao et al., 2022	Cross-sectional study: elite golf players compared with control participants	Maps of macromolecular tissue volume and quantitative T1 for each participant were generated from spoiled gradient echo images and spin-echo inversion recovery images	Golf players showed higher myelin content in the left temporal pole than non-players
Tobiume et al., 2022	Case study: an alcohol-dependent man who recovered from central pontine myelinolysis	Abnormality detected in the central pons in diffusion-weighted images as a relatively high-signal area resembling a piglet sign but not clear in T2- and T1-weighted images, 1.5 T MRI	Physical exercise therapy is important for improving the prognosis of central pontine myelinolysis
Mendez Colmenares et al., 2021	Longitudinal study: 6-month aerobic walking and dancing interventions in older adults	Calibrated T1- to T2-weighted images	White matter plasticity is induced by aerobic walking and dance in the late myelinating regions containing association and commissural fibers: the genu and the splenium of the corpus callosum, the forceps minor and the cingulum
Rowley et al., 2020	Longitudinal study: 12 weeks of exercise three times a week on a stationary bike in healthy subjects	Quantitative T1 and proton density maps with B1 correction for cortical segmentation and R1 images calculated as R1 = 1/T1	Exercise may upregulate myelination in the motor regions of the cerebral cortex
Casella et al., 2020	Longitudinal study: 2 months of drumming training in patients with Huntington disease	Changes in white matter microstructure were investigated with DTI-based metrics, the restricted diffusion signal fraction from the composite hindered and restricted model of diffusion and the macromolecular proton fraction from quantitative magnetization transfer imaging	Significantly greater change in the macromolecular proton fraction in patients with Huntington’s disease relative to controls in the CCII and CCIII segments of the corpus callosum, and the right white matter pathways linking the putamen and the supplementary motor areas post-training
Bracht et al., 2016	Cross-sectional study: young healthy subjects	Multicomponent driven equilibrium single pulse observation of T1 and T2	Higher physical activity is associated with greater myelination of the right parahippocampal cingulum