Postural control is no longer considered simply a summation of static reflexes but, rather, a complex skill based on the interaction of dynamic sensorimotor processes. The two main functional goals of postural behaviour are postural orientation and postural equilibrium. Postural orientation involves the active alignment of the trunk and head with respect to gravity, support surfaces, the visual surround and internal references. Sensory information from somatosensory, vestibular and visual systems is integrated, and the relative weights placed on each of these inputs are dependent on the goals of the movement task and the environmental context. Postural equilibrium involves the coordination of movement strategies to stabilise the centre of body mass during both self-initiated and externally triggered disturbances of stability. The specific response strategy selected depends not only on the characteristics of the external postural displacement but also on the individual’s expectations, goals and prior experience. Anticipatory postural adjustments, prior to voluntary limb movement, serve to maintain postural stability by compensating for destabilising forces associated with moving a limb. The amount of cognitive processing required for postural control depends both on the complexity of the postural task and on the capability of the subject’s postural control system. The control of posture involves many different underlying physiological systems that can be affected by pathology or sub-clinical constraints. Damage to any of the underlying systems will result in different, context-specific instabilities. The effective rehabilitation of balance to improve mobility and to prevent falls requires a better understanding of the multiple mechanisms underlying postural control.

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Postural Orientation and Equilibrium: What Do We Need to Know About Neural Control of Balance to Prevent Falls?

Falls and freezing of gait are two "episodic" phenomena that are common in Parkinson's disease. Both symptoms are often incapacitating for affected patients, as the associated physical and psychosocial consequences have a great impact on the patients' quality of life, and survival is diminished. Furthermore, the resultant loss of independence and the treatment costs of injuries add substantially to the health care expenditures associated with Parkinson's disease. In this clinically oriented review, we summarise recent insights into falls and freezing of gait and highlight their similarities, differences, and links. Topics covered include the clinical presentation, recent ideas about the underlying pathophysiology, and the possibilities for treatment. A review of the literature and the current state-of-the-art suggests that clinicians should not feel deterred by the complex nature of falls and freezing of gait; a careful clinical approach may lead to an individually tailored treatment, which can offer at least partial relief for many affected patients.

https://reylab.bidmc.harvard.edu/pubs/2004/md-2004-19-871.pdf

Falls and freezing of gait in Parkinson's disease : a review of two interconnected, episodic phenomena

We studied prospectively the epidemiology, clinical impact and prediction of falls in 59 moderately affected patients with Parkinson's disease (PD) (mean UPDRS motor score 31.5; mean age 61 years) and 55 controls (mean age 60 years). At baseline, balance and gait were evaluated extensively. The retropulsion test (response to sudden shoulder pull) was executed first unexpectedly and five more times following prior warning. All persons used standardised scoring forms to document their falls during six months. Thirty patients (50.8 %) and eight controls (14.5%) fell at least once (relative risk [RR] 6.1; 95% confidence interval [CI] 2.5-15.1, p or = 2) falls occurred in 15 patients (25.4%), but in only two controls (RR 9.0; 95 % CI 2.0-41.7; p=0.001). Recurrent falls were more common among persons taking benzodiazepines (RR 5.0; 95% CI 1.6-15.5; p 100; 95% CI 3.1-585) and asking for prior falls (RR 5.0; 95% CI 1.2-20.9). We conclude that falls are common and disabling, even in relatively early stage PD. Recurrent fallers were best predicted by disease severity and presence of prior falls. Strategies to prevent falls in PD should particularly focus at intrinsic (patient-related) factors, such as minimising the use of benzodiazepines.

Prospective assessment of falls in Parkinson's disease

Gait dynamics, fractals and falls: finding meaning in the stride-to-stride fluctuations of human walking.

Cognitive function and the performance of a secondary, dual task may affect certain aspects of gait, but the relationships between cognitive function and gait are not well understood. To better understand the motor control of gait and the relationship between cognitive function and gait, we studied cognitive function and the effects of different types of dual tasking on the gait of patients with Parkinson’s disease (PD) and controls, contrasting measures of gait automaticity and rhythmicity with other features. Patients with idiopathic PD (n ¼ 30; mean age 71.8 year) with moderate disease severity (Hoehn and Yahr Stage 2–3) were compared to age and gendermatched healthy controls (n ¼ 28). Memory and executive function were also assessed. In both groups, gait speed decreased in response to dual tasking, in a parallel fashion. For the PD group only, gait variability increased compared to usual walking. Executive function was significantly worse in the PD group, while memory was not different in the two groups. Executive function measures were significantly correlated with gait variability during dual tasking, but not during usual walking. These findings demonstrate that regulation of gait variability and rhythmicity is apparently an automatic process that does not demand attention in healthy adults. In patients with PD, however, this ability becomes attention-demanding and worsens when subjects perform secondary tasks. Moreover, the associations between executive function and gait variability suggest that a decline in executive function in PD may exacerbate the effects of dual tasking on gait, potentially increasing fall risk.

http://www.interactivemetronome.com/IMW/IMPublic/Research/Temporal%20Processing/Gait/Research_GAIT%20MATE_dual%20tasking,%20gait%20rhythmicity,%20and%20PD.pdf

Dual tasking, gait rhythmicity, and Parkinson's disease: which aspects of gait are attention demanding?

"Stops walking when talking" does not predict falls in Parkinson's disease.

Falls severely threaten the health of elderly persons and pose high costs to the public health service. Unfortunately, falls are often regarded as unavoidable and untreatable features of aging. Therefore, many clinicians merely treat the physical injuries of a fall. However, falls and gait limitations are markers of underlying (sometimes otherwise subclinical) diseases that can be amenable to treatment. Moreover, falls and gait limitations herald the onset of repeated falls, physical decline, serious psychosocial consequences and a reduced survival. We review how clinically relevant risk factors can be traced by reviewing the medical notes, by careful history taking and by physical examination. The identified risk factors can serve as a template for the design of prevention strategies, which are discussed in the companion article.

Monique Cramer

Papers

Prospective assessment of falls in Parkinson's disease

"Stops walking when talking" does not predict falls in Parkinson's disease.

Falls in the elderly. I. Identification of risk factors.