A particular type of exercise therapy has been developed at the Movement Disorders Research and Rehabilitation Centre (MDRC) in Waterloo, Canada, which has been found to improve symptom severity in people with Parkinson’s Disease. The programme encourages greater utilisation of proprioceptive information by reducing the reliance on vision and drawing greater attention to body awareness, and was thus termed sensory attention focused exercise, or PD SAFEx for short. Despite the success of PD SAFEx, it hadn’t been determined if the exercise programme positively impacted balance in participants.
And this is where the Lefaivre and Almeida’s 2015 study comes in. They also attempted to provide support for the theory that PD SAFEx worked by stimulating depleted populations of dopaminergic neurons in the basal ganglia Â to cause an adaptation, as opposed to bypassing the dysfunctional basal ganglia with a cortical pathway. This is important as the former process is more likely to give rise to better long term improvement in motor symptoms, as Sage and Almeida (2010) found only the PD SAFEx group (vs the non-SAFE group) maintained symptom alleviation following a six week washout period.
As with the programmes at MDRC, 12 weeks of one hour exercise sessions, three times a week were performed by participants. Sessions were broken up into 30 mins of gait exercises, and 30 mins of resistance band exercises, all intended to increase attention to non-visual sensory input by being performed with eyes closed.
The researchers hypothesised that PD SAFEx would improve the utilisation of proprioception, and thus improve balance. They also predicted that improved proprioception would not have an effect on the balance tests in the eyes open conditions. Two balance tests were performed: a generic postural stability test (PST), and a modified clinical test of sensory integration of balance (thankfully this test also has an abbreviation – m-CTSIB). Each test was performed one week before the programme onset, and one week after its cessation.
The PST provided a measure of overall postural stability as well as scores in the medial-lateral and anterior-posterior directions. Three trials of 30 seconds with vision available on a force platform measuring centre of pressure generated a stability index.
The m-CTSIB attempts to quantify sensory organisation, using the standard deviation of postural shifts from a central reference point on the platform. This test was performed using four different conditions, laid out as 1-4 in the matrix below.
|Somatosensory feedback – |
|Somatosensory feedback –|
Results and discussion
A repeated measures ANOVA revealed balance control improved in the m-CTSIB, but only in the eyes closed condition (sway index improved 12.7%). As the PST was only performed with vision available, no significant difference was found between the pre- and post-test scores. During online control of movement, presence of vision likely decreases the use of proprioceptive input. Vision can thus be used as a compensatory mechanism to overcome proprioceptive deficits by those with PD, supported by the finding that no change in balance was found in the eyes open conditions. Only when proprioceptive information becomes the primary sensory input (eyes closed), are improvements found.
The lack of difference in eyes open condition might lead to the reader being tempted to render the findings meaningless as no one needs to frequently walk around with their eyes closed. However, the tests are performed in simple and undemanding conditions, with both feet on the ground. Conditions in real life become much more demanding in real life when one is walking and taking in their surroundings. Indeed, as I discussed in one of my presentations, people with PD appear to have limited capacity to process sensory information and to integrate it into ongoing movements. So while it might be easy to rely on vision in a standing balance test, proprioception likely becomes more important in more complex movements with more visual information in the surrounding environment.
Improving balance control then, should be a preventative in reducing the risk of falls in people with PD, which is the leading cause of hospitalisation for those living with the disease. People with PD display a reduction in limb and trunk position awareness, which may be accompanied by an increased threshold for detection of body movements in space. An inability to adapt to perturbations or initiate early compensatory steps are feasible implications of poor body awareness, then. Better utilisation of proprioception, therefore, should decrease the likelihood of falls, improving quality of life. Research needs to be done to measure the effects of a sensory integration exercise programme on actual fall risk measures, though.
The authors highlight a couple of extra key points. Firstly, no difference was found between firm and foam surface conditions in the m-CTSIB, meaning the contribution by the vestibular system cannot be ruled out. Secondly, to the study’s credit, the exercises performed by participants are dynamic and not done while standing still. This rules out the possibility of the results being due to practice effects, instead pointing to a more central adaptation, likely at the level of the basal ganglia.