Understanding postural control requires considering various mechanisms underlying a person's ability to stand, to walk, and to interact with the environment safely and efficiently. The purpose of this paper is to summarize the functional relation between biomechanical and neurophysiological perspectives related to postural control in both standing and walking based on movement efficiency. Evidence related to the biomechanical and neurophysiological mechanisms is explored as well as the role of proprioceptive input on postural and movement control.

Objective: To analyse the relation between contralesional and ipsilesional limbs in subjects with stroke during step-to-step transition of walking.Design: Observational, transversal, analytical study with a convenience sample. Setting:Patients from a physical medicine and rehabilitation clinic in Portugal (Braga). Participants:Sixteen subjects with post-stroke hemiparesis with the ability to walk independently and twenty-two healthy controls.Interventions: Not applicable. Conclusions:The findings obtained suggest that the lower performance of the contralesional limb in forward propulsion during gait is not only related to contralateral supraspinal damage but also to a dysfunctional influence of the ipsilesional limb.

one composed by ten healthy subjects and the other by ten subjects with history of stroke and increased H-reflex. Electromyographic activity (EMGa) of SOL and TA was analyzed during SitTS and StandTS in the ipsilateral (IPSI) and the contralateral (CONTRA) limb to the side lesion in stroke subjects, and in one limb in the healthy subjects. A force plate was used to identify the movement onset. Results: In both sequences, in the stroke group SOL activation timing occurred prior to movement onset, contrary to the pattern observed in the healthy subjects. Statistical significant differences were found in SOL activation timings between each lower limbs of the stroke and healthy groups, but no significant differences were found between the IPSI and the CONTRA limb. The TA activation timing seems to be delayed in the CONTRA limb when compared to the healthy subjects and showed also a better organization of TA timing activation in StandTS when compared to SitTS. Conclusion: Compared to healthy subjects, APAs seems to be altered in both limbs of the post-stroke subjects, with the SOL activation timing being anticipated in both SitTS and StandTS.

1Background: Anticipatory postural adjustments during gait initiation have an 2

The purpose of this study was to analyze the change in antagonist co-activation ratio of upper-limb muscle pairs, during the reaching movement, of both ipsilesional and contralesional limbs of post-stroke subjects. Nine healthy and nine post-stroke subjects were instructed to reach and grasp a target, placed in the sagittal and scapular planes of movement. Surface EMG was recorded from postural control and movement related muscles. Reaching movement was divided in two sub-phases, according to proximal postural control versus movement control demands, during which antagonist co-activation ratios were calculated for the muscle pairs LD/PM, PD/AD, TRIlat/BB and TRIlat/BR. Post-stroke's ipsilesional limb presented lower co-activation in muscles with an important role in postural control (LD/PM), comparing to the healthy subjects during the first sub-phase, when the movement was performed in the sagittal plane (p<0.05). Conversely, the post-stroke's contralesional limb showed in general an increased co-activation ratio in muscles related to movement control, comparing to the healthy subjects. Our findings demonstrate that, in post-stroke subjects, the reaching movement performed with the ipsilesional upper limb seems to show co-activation impairments in muscle pairs associated to postural control, whereas the contralesional upper limb seems to have signs of impairment of muscle pairs related to movement.

Purpose: To analyse the interlimb relation and the influence of mechanical energy on metabolic energy expenditure during gait. Methods: 22 subjects were monitored as to electromyographic activity (EMG), ground reaction forces (GRF) and VO 2 consumption (metabolic power) during gait. Results: A moderate negative correlation was observed between the activity of tibialis anterior (TA), biceps femoris (BF) and vastus medialis (VM) of the trailing limb (TRAIL) during mid-stance to double support transition (MS-DS) and that of the leading limb (LEAD) during DS for the same muscles, and between these and gastrocnemius medialis (GM) and soleus (SOL) of the TRAIL during DS.TRAIL SOL during MS-DS was positively correlated to LEAD TA, VM and BF during DS. Also, the TRAIL centre of mass (CoM) mechanical work was strongly influenced by the LEADs, although only the mechanical power related to forward progression of both limbs was correlated to metabolic power. Conclusion: A consistent interlimb relation was observed in terms of EMG and CoM mechanical work, being the relations occurred in the plane of forward progression the more important to gait energy expenditure.

Introduction: Lesions at ipsilateral systems related to postural control at ipsilesional side, may justify the lower performance of stroke subjects during walking. Purpose: To analyse bilateral ankle antagonist coactivation during double-support in stroke subjects. Methods: Sixteen (8 females; 8 males) subjects with a first isquemic stroke, and twenty two controls (12 females; 10 males) participated in this study. The double support phase was assessed through ground reaction forces and electromyography of ankle muscles was assessed in both limbs. Results: Ipsilesional limb presented statistical significant differences from control when assuming specific roles during double support, being the tibialis anterior and soleus pair the one in which this atypical behavior was more pronounced. Conclusion: The ipsilesional limb presents a dysfunctional behavior when a higher postural control activity was demanded.

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