Deficits in task-specific modulation of anticipatory postural adjustments in individuals with spastic diplegic cerebral palsy

Abstract

We examined whether individuals with spastic diplegic cerebral palsy (SDCP) have the ability to utilize lower leg muscles in anticipatory postural adjustments (APAs) associated with voluntary arm movement while standing, as well as the ability to modulate APAs with changes in the degree of postural perturbation caused by arm movement. Seven individuals with spastic diplegia (SDCP group, 12-22 yr of age) and seven age- and sex-matched individuals without disability (control group) participated in this study. Participants flexed both shoulders and lifted a load under two different load conditions, during which electromyographic activities of focal and postural muscles were recorded. Although the timing of anticipatory activation of the erector spinae and medial hamstring (MH) muscles was similar in the two participant groups, that of the gastrocnemius (GcM) muscle was significantly later in the SDCP group than in the control group. An increase in anticipatory postural muscle activity with an increase in load was observed in MH and GcM in the control group but not in GcM in the SDCP group. The degree of modulation in MH was significantly smaller in the SDCP group than in the control group. An additional experiment confirmed that these differences in APAs between the two participant groups were unlikely to be attributable to their differences in initial standing posture before load lift. The present findings suggest that lower leg muscles play a minor role in APAs in individuals with spastic diplegia. In addition, it is likely that these individuals have difficulty modulating anticipatory postural muscle activity with changes in the degree of postural perturbation.

Deficits in anticipatory inhibition of postural muscle activity associated with load release while standing in individuals with spastic diplegic cerebral palsy

“…This finding suggests that individuals with SDCP have the ability to modulate anticipatory activation of ventral postural muscles with changes in the degree of perturbation. This is a surprising finding, since our previous study on APAs in the load-lifting task revealed that insufficient modulation of anticipatory activation of postural muscles is a primary constraint on APAs while standing in individuals with SDCP (Tomita et al 2011). In addition, an inability to modulate postural muscle activities to fit task conditions in these individuals has been reported for voluntary forward reach while sitting (van der Heide et al 2004) and compensatory postural adjustments (CPAs) to backward translation of a support surface while standing (Roncesvalles et al 2002).…”

“…This is a surprising finding, since our previous study on APAs in the load-lifting task revealed that insufficient modulation of anticipatory activation of postural muscles is a primary constraint on APAs while standing in individuals with SDCP (Tomita et al 2011). In addition, an inability to modulate postural muscle activities to fit task conditions in these individuals has been reported for voluntary forward reach while sitting (van der Heide et al 2004) and compensatory postural adjustments (CPAs) to backward translation of a support surface while standing (Roncesvalles et al 2002). Since the internally or externally induced postural perturbations in these previous studies are in the forward direction, activation of dorsal postural muscles is needed to maintain postural equilibrium.…”

“…In the heavy condition, the weight was set at 4%BW for female participants and 6%BW for male participants. Since muscle strength of the upper and lower limbs is generally lower in women than in men, many previous studies using a load-lifting task have adopted different percentages of BW based on the participant's sex (Fujiwara et al 2009;Maeda and Fujiwara 2007;Tomita et al 2011). We therefore used a similar method in this study to examine APAs associated with load release.…”

“…APAs thus probably play an important role in adequately performing various voluntary movements while standing (Bouisset and Do 2008;Massion 1992). Recently, we examined APAs associated with voluntary arm movement while standing in individuals with SDCP (Tomita et al 2010(Tomita et al , 2011. These studies demonstrated that although anticipatory activation of postural muscles is observed in individuals with SDCP, these individuals exhibit several deficits in APAs, including a delayed onset of activation of lower leg muscles, insufficiently smaller anticipatory activation of postural muscles, and a lack of adequate modulation of anticipatory postural muscle activity with changes in the degree of postural perturbation.…”

“…These studies demonstrated that although anticipatory activation of postural muscles is observed in individuals with SDCP, these individuals exhibit several deficits in APAs, including a delayed onset of activation of lower leg muscles, insufficiently smaller anticipatory activation of postural muscles, and a lack of adequate modulation of anticipatory postural muscle activity with changes in the degree of postural perturbation. These deficits in APAs in individuals with SDCP are likely to be related to a larger disturbance of postural equilibrium during voluntary arm movement (Tomita et al 2010(Tomita et al , 2011.…”