Bimanual multijoints coordination: A brief review

Walking upright freed the hands for carrying and manipulating tools. This complex bimanual coordinative ability may have been an essential step to lead our ancestors' brains to grow. The current review aims to tackle the state-of-the-art control mechanisms in kinematics and motor control perspectives during performing bimanual multijoints coordinative movements. The endeavor is to delineate possible principles from task goals, manipulations and modules, related brain activation and connectivity perspectives, and benefits and limits of considered modules to apply these principles to improve the life quality of people with movement disorder diseases and people who want to be healthier. About six million years ago, Sahelanthropus may have walked on two legs. Becoming bipedal, walking upright freed the hands for carrying and manipulating tools. This complex bimanual coordinative ability may have been an essential step to lead our ancestors' brains to grow. In daily life, the ability to master objects such as weapons, tools, stationaries etc. by strong and agile upper limbs is revolutionary throughout the human evolution. The hierarchy of constraints in bimanual coordination: Bimanual multijoints coordinative activities have been studied at many levels of the cognitive and motor systems. Three paradigms, including drawing tasks with direct objectives using pens or styluses in both hands, e.g., circle [1-6], star-line, etc. [7-12], bimanual tasks with abstract temporal and spatial objectives employing manipulanda [13] and joy sticks [14], and freehand bimanual multijoints coordinative tasks have been utilized to study the representation of bimanual actions [15-17]. As a unique evolutional landmark, writing and drawing are mostly a unilateral task. Therefore, intensive training of non-dominant hand to handle a pen or stylus is often needed to minimize the unequal motor capability as compared to the skillful dominant hand. The other two paradigms well compromise the unequal skillfulness of both hands by applying unified devices or focusing on pure joint/limb movements. In the past few decades, research findings in bimanual coordination suggest a coalition of constraints in bimanual coordination. The identified constraints cover from cognitive or perceptual to neuromuscular level, which are centered by network-level perception-action interactions of the CNS [18]. Among these bimanual coordination constraints, the neuromuscular constraint is defined as the relative timing of homologous muscle activation. Relative phase (Φ), subtraction of the phase angle of each limb at each measurable time point during cyclic movement, serves as a measure of two-limb-coordination. In-phase motion (IN, Φ = 0°) refers to moving the fingers, wrists, or forearms inwards and outwards from the body midline simultaneously activate homologous muscle groups. Anti-phase motion (AN, Φ = 180°) means that homologous muscle groups are activated in alternation. In-phase is more stable than anti-phase in bimanual coordination. The higher the movement speed goes, the more differential stability between both coordination modes becomes [19,20]. These coordination modes are generic as they are evident across different movement effectors. *Correspondence to: Yong Li, Neurologische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675 Munich, Germany, E-mail: yong.li@lrz.tu-muenchen.de