Determining the sites of neural adaptations to resistance training: A systematic review and meta-analysis.

Background: To investigate the relative contributions of cerebral cortex and basal ganglia to movement stopping, we tested the optimum combination Stop Signal Reaction Time (ocSSRT) and median visual reaction time (RT) in patients with Alzheimer’s disease (AD) and Parkinson’s disease (PD) and compared values with data from healthy controls. Methods: Thirty-five PD patients, 22 AD patients, and 29 healthy controls were recruited to this study. RT and ocSSRT were measured using a hand-held battery-operated electronic box through a stop signal paradigm. Result: The mean ocSSRT was found to be 309 ms, 368 ms, and 265 ms in AD, PD, and healthy controls, respectively, and significantly prolonged in PD compared to healthy controls (p = 0.001). The ocSSRT but not RT could separate AD from PD patients (p = 0.022). Conclusion: Our data suggest that subcortical networks encompassing dopaminergic pathways in the basal ganglia play a more important role than cortical networks in movement-stopping. Combining ocSSRT with other putative indices or biomarkers of AD (and other dementias) could increase the accuracy of early diagnosis.

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Purpose: Cross-education (CE) increases strength of both the trained and untrained limb, with emerging evidence, suggesting CE could be used to attenuate muscle strength and thickness following periods of limb immobilization. This study examined the available evidence for the clinical efficacy of CE to attenuate muscle strength, thickness and neural activation during limb immobilization. Methods: We performed a systematic review and meta-analysis on the effects of CE on muscle strength, thickness and activation of an immobilized limb.  The evidence from randomized controlled trials (RCTs) were pooled to assess effect estimates for changes in strength, muscle thickness and neural activation of the untrained immobilized limb. Results: CE attenuated muscle strength in 5 RCTs (n= 78) which reported a SMD of 1.60 (95% CI 0.62, 2.59; P = 0.001) and muscle thickness, with an SMD of 1.52 (95% CI 0.22, 2.81; P = 0.02) compared to control. There was no difference in muscle activation (SMD of 0.08; 95% CI -0.34, 0.50; P = 0.72), regions of cortical activation (MD 31.8; 95% CI -22.71, 86.31; P = 0.25) or corticospinal excitability (MD 5.2; 95% CI -2.38, 12.78; P = 0.18) compared to control.    Conclusions: These results show that strength training the free limb via cross-education maintains muscle strength and muscle thickness of the immobilized limb compared to control (immobilization only). Because there was no effect on muscle activation, but a large mean difference in cortical activation, it is likely that the attenuation of muscle strength is due to neural adaptations at a cortical level.

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