Current researches of the HBL has been expanded to investigate how the CNS optimizes solutions when the peripheral system involves mechanical redundancy, and how motor variability is compatible with optimality in human motor actions. We have expanded this line of research by examining central and peripheral adaptations in human movements to internal (e.g., aging, fatigue, injury, movement disorder, etc) and external changes (e.g., environment-related changes such as zero-gravity environment in space) in optimality and motor variability. Answering this question is critical not only because it has been a century-long question in robotics and human motor control but also because the advent of brain-computer interfaces (BCI) in modern times has made answering this question more imperative. For example, one of the main objectives in BCI is to reduce the amount of redundancy in both the neural and mechanical systems for effective processing of recorded neural signals from the CNS and efficient control of artificial limbs, respectively. Additionally, We are currently conducting several studies on musculoskeletal mechanisms and mathematical modeling of optimization on end-effector forces or muscle activities, as well as their applications for people with movement deficit and disorder such as patients with Parkinson’s disease, cerebellar disorders, stroke, cerebral palsy, essential tremor, etc. In particular, new clinical research suggests that workers exposed to welding fumes and pesticides may be at risk for developing brain damage in an area of the brain affected in Parkinson’s disease. The studies with the cohorts of welders and farmers provide an exciting opportunity for early detection of Parkinson’s disease and for tracking its progression and effects of treatment. They also suggest that the newly invented experimental paradigms may be used in other cases of impaired coordination in neurological patients.