Insomnia, a prevalent sleep disorder characterized by difficulty initiating or maintaining sleep, is particularly common among older adults. Current treatments, such as psychological/behavioral therapy and pharmacological interventions, have limitations in efficacy, side effects, and cost. Exercise has emerged as a potential alternative treatment for insomnia, with numerous studies demonstrating its positive impact on sleep quality, efficiency, and duration. While animal studies suggest exercise promotes beneficial morphological and functional brain changes, the specific neural mechanisms underlying exercise-induced sleep improvement in older adults with insomnia remain unclear. This study aimed to investigate the effects of a 12-week exercise program combining Tai Chi and resistance training on sleep quality and brain functional connectivity (FC) in middle-aged and older adults with insomnia, hypothesizing that exercise would improve both subjective and objective sleep quality and restore FC within the motor network. The motor network was chosen as a focus given its documented deficiency in insomnia patients. Resting-state functional connectivity (rsFC) analysis, using fMRI, was used to examine temporal correlations among brain regions, providing insights into brain organization and function and offering potential biomarkers or therapeutic targets for improving insomnia.

Existing literature supports the beneficial effects of exercise on sleep in older adults. Studies have shown improvements in sleep quality, efficiency, and duration following various exercise interventions, including aerobic exercise, resistance training, and Tai Chi. Tai Chi, a mind-body exercise, has gained attention for its potential in alleviating sleep problems in older adults due to its gentle, balanced nature. Resistance training also demonstrates positive effects on sleep. Combining both may offer synergistic benefits. While the effects of exercise on sleep are well-documented, the underlying neural mechanisms remain less understood. Animal studies reveal exercise-induced changes in brain regions including the motor cortex, cerebellum, striatum, and hippocampus. In humans, aerobic exercise has been linked to restoration of prefrontal cortex function and gray and white matter volume changes, mainly in motor, prefrontal, and temporal cortices. However, the impact of exercise on functional connectivity in the context of insomnia in middle-aged and older adults requires further investigation. This study addresses this gap by examining the effects of a combined Tai Chi and resistance training intervention on brain FC.

This study employed a randomized waitlist-controlled trial design. 169 middle-aged and older adults (45-80 years old) were recruited, with 85 having insomnia and 84 serving as healthy controls (HCs). Insomnia participants were randomly assigned to either a 12-week exercise intervention group (EX) or a waitlist control group (WL). The exercise intervention consisted of a 12-week program combining Tai Chi and resistance training, conducted three times a week for approximately 90 minutes per session. Baseline assessments included demographic information, Mini-Mental State Exam (MMSE), body mass index (BMI), International Physical Activity Questionnaire (IPAQ), Insomnia Severity Index (ISI), Pittsburgh Sleep Quality Index (PSQI), Self-Rating Anxiety Scale (SAS), and Self-Rating Depression Scale (SDS). Objective sleep measures were obtained using a wearable sleep recorder (LumiSleep) which assessed sleep stages (wakefulness, light sleep, deep sleep, REM sleep). Resting-state fMRI data were acquired using a 7 Tesla Prisma scanner to assess functional connectivity. Data were preprocessed using AFNI and MATLAB, including motion correction, spatial normalization, and nuisance covariate removal. Seed-based FC analysis with the motor cortex (M1) as the seed was performed. Statistical analyses included independent samples t-tests, paired samples t-tests, mixed-model ANOVA, and Pearson's correlation analysis. The primary outcome was improvement in sleep efficiency, assessed via subjective and objective measures. Secondary outcomes were changes in motor network FC. Sensitivity analysis was conducted including depression scores as covariates.

Insomnia patients demonstrated significantly worse sleep quality (higher ISI and PSQI scores) and increased negative emotion (higher SAS and SDS scores) compared to HCs. Objectively, insomnia patients had longer wake after sleep onset (WASO) and REM sleep onset latency (RSOL). At the brain circuit level, insomnia patients showed decreased connectivity in the motor network. Following the 12-week exercise intervention, the EX group experienced significant improvements in both subjective (lower ISI and PSQI scores) and some objective (shorter WASO, although not statistically significant for the interaction) sleep measures. The EX group also showed a significant increase in functional connectivity between the left M1 and bilateral cerebellum. Crucially, improvements in sleep quality were significantly correlated with increased connectivity within the primary motor network and between the right M1 and the superior parietal lobule. These correlations remained significant even after controlling for depression scores.

The findings support the effectiveness of exercise interventions in improving sleep quality in middle-aged and older adults with insomnia. The study utilized both subjective and objective sleep measures, providing a more comprehensive assessment of sleep improvement. The demonstration of changes in brain functional connectivity, specifically increased connectivity in the motor network following exercise, provides novel insights into the neural mechanisms underlying these improvements. The correlations between sleep improvement and changes in brain connectivity suggest that the observed benefits are not solely subjective but are reflected in altered brain function. This study contributes to our understanding of the therapeutic potential of exercise in treating insomnia and highlights the brain plasticity that can occur in later life. The improved motor network connectivity may contribute to improved sleep by enhancing the coordination of motor activity during sleep, thereby preventing sleep disturbances and promoting more efficient sleep.

This study demonstrates that a 12-week exercise program improves sleep quality and restores functional connectivity within the motor network in middle-aged and older adults with insomnia. The findings highlight the therapeutic potential of exercise for insomnia treatment and underscore the importance of considering brain plasticity when developing interventions for sleep disorders in older adults. Future research should investigate longer-term effects, explore the use of sham exercise controls, and examine the influence of different exercise types and intensities on sleep and brain connectivity. Further investigation into the specific neurobiological mechanisms underlying the observed effects is also warranted.

The study had several limitations. A significant number of participants dropped out of the study, which might impact the results. The study used a waitlist control group rather than a sham exercise condition, making it difficult to completely isolate the effects of exercise. The study primarily focused on a specific age range, which might restrict the generalizability of the findings. Future studies should incorporate larger sample sizes, control for confounding factors such as baseline depression levels more rigorously, and incorporate longer follow-up periods.