You can only take so many whacks to the head before it starts to show...

In addition to vision and the vestibular system, proprioceptive information is gathered by primarily 2 sources: The peripheral joint mechanoreceptors left (type 1, type 2, type 3, and type 4 ), as well as the muscle mechanoreceptors: Muscle spindles and golgi tendon organs. This information is transmitted to the cortex via the dorsal column and spinocerebellar pathways. The information is then integrated in the parietal lobe (for information in the dorsal columns) and cerebellum. The information is then relayed to the motor cortex, basal ganglia, and vestibular system. The interplay of these 3 systems, vision, the vestibular system, and the joint/muscle mechanoreceptors is what allows us to keep our bodies up right and functioning in the gravitational field. When integration is compromised, at either a peripheral or cortical level, proprioception suffers.

" Measures of cumulative subconcussive head impacts during a men’s lacrosse season are associated with decreases in balance scores from pre- to postseason, according to findings from Sacred Heart University in Fairfield, CT, that could have implications for lower extremity injury risk. The findings suggest that, even in the absence of a concussion, repetitive subconcussive impacts can negatively affect an athlete’s balance, which in turn can increase the risk of lower extremity injury"

Miyashita TL, Diakogeorgiou E, Marrie K. Correlation of head impacts to change in balance error scoring system scores in Division I Men’s lacrosse players. Sports Health 2017 Jan 1. [Epub ahead of print]

Plisky PJ, Rauh MJ, Kaminski TW, Underwood FB. Star Excursion Balance Test as a predictor of lower extremity injury in high school basketball players. J Orthop Sports Phys Ther 2006;36(12):911-919.