Perturbation-based balance training for individuals with freezing of gait
In the current study, we conducted a randomized controlled clinical trial to assess the effect of a multisession training program based on sudden AP or ML perturbations of body balance on immediate and persistent postural response gains in individuals with PD+FoG. In addition, individuals with PD+FoG receiving muscular resistance training (RT) were employed as controls for possible gains not associated specifically with PBT, like physical activity leading to gains in muscular function and social interaction. We hypothesized that a multisession program of PBT through varied and unpredictable perturbations leads to persistent stability gains of reactive postural responses as reflected by decreased values of center of pressure (CoP) amplitude/velocity and decreased numbers of experimental near-falls. In an exploratory approach, we also tested the generalization of reactive postural responses to a context of reacting to perturbations while involved cognitively with mental operations or responding to a perturbation of higher magnitude than those experienced during training. As the main findings, PBT led to balance stability gains in reactive responses, as indicated by decreased CoP (a) ML displacement amplitude, (b) AP/ML peak velocity, and (c) AP/ML time to peak displacement in response to perturbations. Performance gains in ML perturbations persisted over the rest interval of 30 days. PBT also led to reduced numbers of near-falls in responses to platform perturbations. Results showed no transfer either to a cognitive-motor dual-task or to faster-than-trained support base displacements. Conclusions. A training program based on sudden balance perturbations led to persistent stability gains in reactive postural responses to different unpredictable perturbations applied when standing on a moveable platform. PBT also led to lower numbers of falls, better scores in qualitative global evaluation of body balance and reduction of fear of falling. No evidence of generalizability of performance gains to dual tasking or increased perturbation magnitude was found. Therapeutic applicability. From a therapeutic perspective, we showed that a PBT program can lead to gains in the ability to recover body balance following an unpredictable perturbation. This increased resilience to perturbations threatening upright stance could potentially reduce the risk of falls in individuals with PD+FoG. Lack of drop-outs during the program and no cases of adverse effects are positive aspects favoring the adoption of this therapeutic strategy in clinical practice.
Steps to reproduce
PD+FoG were pseudorandomly assigned either to a PBT (n = 9) or to a RT (n = 10) group. PBT was implemented through balance perturbations varying in kind, direction, side, and magnitude of support base displacements. Both groups were exercised with progressive difficulty/load activities twice a week for 4 weeks. Primary outcomes were variables derived from the center of pressure (CoP) displacement in response to unpredictable platform displacements. Specific gains and generalization to dual-tasking and to faster-than-trained support base displacements were evaluated 24 h after the end of the training, with retention evaluated after one month of rest. Eligibility criteria were as follows: (1) diagnosis of idiopathic PD confirmed by a movement disorders specialist by UK Parkinson’s Disease Society Brain Bank diagnostic criteria 13, (2) FoG confirmed if they answered affirmatively item 1 of the NFoG-Q 14 and/or if FoG was observed during the 2-minute turning task during ON medication status; 15 (III) Hoehn and Yahr stage range 2-4; (IV) Mini Mental State Exam score (MMSE) > 23; 16 (V) absence of orthopedic or neurological disorders other than PD that might affect performance in the experimental task. Participants were assessed in the clinically “on” state (about 45 min. after taking their dose of dopaminergic medication), and all assessment sessions were performed individually at about the same daytime at the laboratory. The experimental protocol for the main evaluation was performed on a custom-made moveable platform, having as the support base a force plate (AMTI, model OR6-WP), controlled through a LabView computer interface (National Instruments). That equipment was used to generate sudden support surface displacements leading to balance perturbations while measuring ground reaction forces for balance recovery. The aim was to evaluate the ability to recover body balance under full unpredictability of perturbations. Participant’s initial posture was upright, barefoot, feet parallel 5 cm apart (between the medial malleoli), arms relaxed beside the trunk, and gazing at a frontal spot 2 m away at the eyes height. The reduced support surface in the ML direction was used to increase the challenge of the perturbations. Participants were verbally instructed that if unable to keep the feet position for balance recovery, they should recover balance through spontaneous limb movements. Perturbations were applied separately in the AP and ML directions. Variability of platform displacements in each direction was performed in three dimensions, as follows: (a) two perturbation modes, translation and combined rotation-translation; (b) two sides, right and left (ML direction perturbations), or backward and forward (AP direction perturbations); and (c) two (peak) velocities: low, 20o/s-20 cm/s and high, 40o/s-40 cm/s. Displacement amplitude (7o and/or 7 cm) and peak acceleration (500o/s2 and/or 500 cm/s2) were constant across perturbations.