# Binanual Movements and Chronic Stroke Rehabilitation: Looking Back and Looking Forward
## 3 Bimanual Kinematic and Kinetic Functions in Chronic Stroke  
Motor impairments on one side of the upper body such as muscle weakness, spasticity, and loss of motor skills in the affected arm typically appear in patients with stroke [3]. Further, the increased asymmetrical motor functions between paretic and non-paretic arms interfere with bimanual movement control capabilities (e.g., bimanual performances and coordination) required for successful execution of activities of daily living [60; 61]. For example, common post-stroke motor impairments include movement initiation and control on command as well as coordination problems during bimanual arm/hand reaching, moving objects, hand drawing, and finger tapping tasks [62; 63; 64; 65]. According to motor control theory, movement kinetics are the primary components involved in activating motor actions [67; 68; 69; 70]. As individuals post-stroke initiate or attempt to initiate arm movements, generating forces in the paretic arm are imperative. One way to facilitate this process or system is to require the non-paretic arm to initiate the same movement. Symmetrical motor performances are easier to execute than asymmetrical movements. [PERSON] and colleagues suggested that estimating interlimb coordination is crucial for stroke motor rehabilitation because less cooperative upper limb movements post-stroke can increase motor reliance on the non-paretic arm compromising the efficiency of motor actions requiring both arms (e.g., opening the drawer with the non-paretic arm) [66]. Thus, investigating potential motor rehabilitation protocols for improving bimanual coordination functions is useful for facilitating progress toward motor recovery. A recent meta-analysis study summarized specific patterns of bimanual movement and coordination deficits post-stroke [71]. Patients with stroke showed more interlimb kinematic and kinetic coordination impairments than age-matched healthy controls while executing asymmetrical movements with more difficult task goals such as asymmetric movement with independent goals and asymmetric parallel movements with a common goal for each hand [63; 72]. These impairments were additionally observed in symmetric movement tasks when two hands targeted a common task goal. Bimanual movement tasks consisting of more challenging task constraints typically require more interactive behavioral communications between two arms with increased motor-related cortical activation across the primary motor area and supplementary motor areas [73; 74]. Thus, unbalanced cortical activation and interhemispheric inhibition levels between hemispheres post-stroke may cause more impairments in bimanual movement and coordination with more difficult task goals [75]. Interestingly, meta-regression results indicated that deficits in bimanual coordination were significantly associated with increased time since stroke onset [71]. These findings indicate that despite relatively rapid recovery progress within six months post-stroke [76], bimanual movement control capabilities continue to be compromised in the chronic stage of motor recovery. In addition to bimanual kinematic dysfunctions post-stroke, impairments in bimanual kinetic functions often appeared in patients with stroke. [PERSON] and [PERSON] [77] conducted a comprehensive literature review that demonstrated potential deficits in bimanual force control capabilities in post-stroke individuals. While processing visual feedback displaying isometric forces produced by both hands and a targeted submaximal force level, stroke groups revealed less force accuracy (e.g., root mean squared error) and variability (e.g., coefficient of variation), indicating more erroneous and inconsistent force generation patterns during bimanual wrist extension and gripping force tasks [78; 79; 80; 81].