BACKGROUND: Poor postural control has been reported in people with Parkinson\'s disease, which could be explained by the changes in muscular activation patterns related to antigravitational muscles. This study aims to measure the muscle activation of antigravitational muscles during balance tasks in individuals, with and without Parkinson\'s.
METHODS: Sixteen (16) participants (9 with Parkinson\'s), aged ≥65 yrs., performed 2 × 30-s trials of 4 balance tasks (bipodal and semi-tandem opened eyes and closed eyes) on a force platform (center of pressure measurement); while surface electromyography measurements were obtained bilaterally on the multifidus at L5, biceps femoris and medialis gastrocnemius. Electromyography amplitude analysis was processed by the Root Mean Square (250 ms window epochs) and normalized by the peak of activation during the balance task, to determine each muscle\'s activity level.
RESULTS: The Parkinson\'s group reported lower muscle activation than control across tasks (in mean for multifidus = 8%, biceps femoris = 16%, gastrocnemius = 7%), although not statistically significant. Parkinson\'s reported significantly poorer postural control than control, mainly for the center of pressure sway ellipse area (p = 0.016) from challenge balance tasks such as semi-tandem.
CONCLUSIONS: Poor postural control was confirmed in the Parkinson\'s group, but not significantly associated by the changes from muscle activation of trunk and lower limbs, during balance performance.

Adults with late-onset Pompe disease (aLOPD) are characterized by muscular contractile tissue deterioration. However, their neuromuscular performances are poorly known. We aimed to compare maximal muscle strength, activation, explosive strength and neuromuscular fatigue between aLOPD and controls. We studied 20 aLOPD and 20 matched controls. Isometric maximum voluntary contraction (MVC) torque was obtained for the hip, knee and ankle muscles. The voluntary activation level (VAL) during knee extensor MVC was assessed using interpolated twitch technique. Explosive strength was evaluated for knee and ankle muscles through the rate of torque development (RTD) during fast contractions. Neuromuscular fatigue was measured during a 30-second contraction of knee flexors and extensors. All muscle MVC torques were significantly lower in aLOPD than controls (p <0.05). The weakest muscles were the hip extensors followed by hip abductors and abductors. Raw value of RTD was lower in aLOPD for the majority of muscles (p <0.05). No intergroup differences were reported for normalized RTD, VAL and neuromuscular fatigue (p-values> 0.05). Our study shows that maximal strength was the only neuromuscular characteristic affected in aLOPD with a proximal-distal intensity gradient. This suggests that the surviving muscle tissue of aLOPD is as functionally efficient as that of control individuals.

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