Physical inactivity is a major concern and poor adherence to exercise programs is often reported. The aim of this paper was to systematically review published reviews on the study of adherence to physical exercise in chronic patients and older adults and to identify those adherence-related key factors more frequently suggested by reviews for that population. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed. Results were classified considering the target population and participants’ characteristics to identify the most repeated factors obtained for each condition. Fifty-five articles were finally included. Fourteen key factors were identified as relevant to increase adherence to physical exercise by at least ten reviews: (a) characteristics of the exercise program, (b) involvement of professionals from different disciplines, (c) supervision, (d) technology, (e) initial exploration of participant’s characteristics, barriers, and facilitators, (f) participants education, adequate expectations and knowledge about risks and benefits, (g) enjoyment and absence of unpleasant experiences, (h) integration in daily living, (i) social support and relatedness, (j) communication and feedback, (k) available progress information and monitoring, (l) self-efficacy and competence, (m) participant’s active role and (n) goal setting. Therefore, adherence to physical exercise is affected by several variables that can be controlled and modified by researchers and professionals.

Paired-pulse transcranial magnetic stimulation (TMS) has been applied as a probe to test functional connectivity within distinct cortical areas of the human motor system. Here, we tested the interaction between the posterior parietal cortex (PPC) and ipsilateral motor cortex (M1). A conditioning TMS pulse over the right PPC potentiates motor evoked-potentials evoked by a test TMS pulse over the ipsilateral motor cortex, with a time course characterized by two phases: an early peak at 4 ms interstimulus interval (ISI) and a late peak at 15 ms ISI. Activation of this facilitatory pathway depends on the intensity of stimulation, because the effects are induced with a conditioning stimulus of 90% resting motor threshold but not at lower or higher intensities. Similar results were obtained testing the ipsilateral interaction in the left hemisphere with a slightly different time course. In control experiments, we found that activation of this facilitatory pathway depends on the direction of induced current in the brain and is specific for stimulation of the caudal part of the inferior parietal sulcus (cIPS) site, because it is not observed for stimulation of adjacent scalp sites. Finally, we found that by using poststimulus time histogram analysis of single motor unit firing, the PPC conditioning increases the excitability of ipsilateral M1, enhancing the relative amount of late I wave input recruited by the test stimulus over M1, suggesting that such interaction is mediated by specific interneurons in the motor cortex. The described facilitatory connections between cIPS and M1 may be important in a variety of motor tasks and neuropsychiatric disorders.

The left dorsal premotor cortex (PMd) is thought to play a dominant role in the selection of movements made by either hand. We used transcranial magnetic stimulation to study the functional connectivity of the left PMd and right primary motor cortex (M1) during an acoustic choice reaction time (RT) task involving contraction of the thumb and forefinger. The facilitatory and inhibitory pathways that can be demonstrated between left PMd and right M1 at rest were suppressed during most of the reaction period. However, they were activated briefly at the start of the reaction period, depending on whether the cue indicated that the forthcoming movement had to be made with the left or the right hand. The facilitatory pathway was active at 75 ms in those trials in which the subjects were required to move the left hand, whereas the inhibitory pathway was active at 100 ms in trials in which the subjects had to move the right hand. These changes in excitability did not occur in hand muscles not used in the task. There were no significant changes in the excitability of intracortical circuits [short intracortical inhibition (SICI) and intracortical facilitation (ICF)] in the right M1. Interhemispheric interactions between the right PMd and left M1 were mainly inhibitory at rest and showed the same temporal profile of interhemispheric inhibition as for left PMd–right M1, although no evidence was found for facilitatory interactions. The results illustrate the importance of PMd not only in facilitating cued movements but also in suppressing movements that have been prepared but are not used.