Inter-limb Asymmetry of Equilibrium Regulation in the Legs of 10-11-Year-Old Boys during Overground Sprinting.

Short-distance running at top speed is important in field sports. Previous studies have analyzed kinematic and kinetic properties of sprinting in adults, but equivalent knowledge in children is underexplored. Quantifying relevant aspects of children's sprinting is useful for classifying their running skills and providing effective coaching based on motor control theory. This study aimed to clarify differences in equilibrium regulation in more- and less-skilled boy sprinters. Five 10-11-year-old boys regularly participating in lessons at the Mizuno running school performed 30-meter and 50-meter field track sprints, and the kinematic and electromyography findings were recorded. Equilibrium-point-based synergy analysis was then applied to estimate their respective virtual trajectories. The virtual trajectory is an equilibrium time sequence that indicates how the central nervous system controls a skeletal system with multiple muscles. The results suggested that: (1) the equilibrium of the right and left legs was regulated differently, although together the legs showed similar kinematics; (2) in the first type of virtual trajectory (type-I) in one leg, the equilibria after foot-strike were regulated intermittently during the early swing phase; (3) in the second type of virtual trajectory (type-II) in the other leg, the equilibria after foot-strike were continuously regulated during the early swing phase; and (4) the less-skilled child runners showed a slow equilibrium action response in both types of virtual trajectory during the early swing phase. These findings provide insights for "tailor-made" coaching based on the type of leg control during sprinting.Clinical relevance-Information on gait asymmetry would be beneficial not only for coaching to improve sprint training but also from clinical and injury perspectives.

Bimanual digit training improves right-hand dexterity in older adults by reactivating declined ipsilateral motor-cortical inhibition.

Improving deteriorated sensorimotor functions in older individuals is a social necessity in a super-aging society. Previous studies suggested that the declined interhemispheric sensorimotor inhibition observed in older adults is associated with their deteriorated hand/finger dexterity. Here, we examined whether bimanual digit exercises, which can train the interhemispheric inhibitory system, improve deteriorated hand/finger dexterity in older adults. Forty-eight healthy, right-handed, older adults (65-78 years old) were divided into two groups, i.e., the bimanual (BM) digit training and right-hand (RH) training groups, and intensive daily training was performed for 2 months. Before and after the training, we evaluated individual right hand/finger dexterity using a peg task, and the individual state of interhemispheric sensorimotor inhibition by analyzing ipsilateral sensorimotor deactivation via functional magnetic resonance imaging when participants experienced a kinesthetic illusory movement of the right-hand without performing any motor tasks. Before training, the degree of reduction/loss of ipsilateral motor-cortical deactivation was associated with dexterity deterioration. After training, the dexterity improved only in the BM group, and the dexterity improvement was correlated with reduction in ipsilateral motor-cortical activity. The capability of the brain to inhibit ipsilateral motor-cortical activity during a simple right-hand sensory-motor task is tightly related to right-hand dexterity in older adults.