Title: Assessing lower limb proprioception with a novel mechatronics device
Thesis Supervisors: Dr. Jean-Sébastien Blouin
Committee members: Dr. Calvin Kuo, Dr. Martin Héroux
Defence Chair: Dr. Shannon Bredin
Abstract:
Awareness of our body position and movement is fundamental to how we interact with the world. Proprioception, the sense we use to perceive our physical self, is vital for tasks of daily living such as balancing upright and coordinating motor actions. Current proprioception tests, however, focus on simple movements occurring at single joints or require participants to be immobilized. These reductionist approaches fail to capture the functional application of proprioception in real-world contexts. This limitation emphasizes the need to develop functionally relevant proprioception tests. In this thesis, I propose a novel proprioception test assessing the perception of stance width adjustments during standing balance. The test integrates stance width, a key variable for the neuromechanical control of balance, with the natural context of free balancing to create a functionally relevant proprioception test.
I investigated three psychophysical methods (2-interval detection, single interval discrimination and detection at 1 mm) and two stance width displacements (1 mm and 2 mm) to develop preliminary parameters for my test. In detection experiments, participants identified the presence of a stance width change, while in discrimination experiments, they determined the direction of the change. Thresholds were defined by varying platform movement velocities across all experiments. Given that no established standards exist for this test, these explorations were necessary to identify effective approaches for proprioception threshold measurement. The experiments were accomplished with custom-developed mechatronic platforms capable of precise stance width adjustments (errors < 0.1 mm) with minimal mechanical vibrations. In a 2-interval detection protocol, participants (N = 19) exhibited smaller detection thresholds (1.7 ± 1.3 vs 2.6 ± 1.2 mm/s) as the displacement increased from 1 to 2 mm (p < 0.001). Thresholds from the single interval discrimination experiment (N = 9) were lower compared to the 2-interval detection protocol (2.2 ± 0.8 to 1.4 ± 1.1 mm/s, p = 0.030), differing from previous literature. Also, single interval detection (N = 10) thresholds were higher (3.0 ± 1.4 to 4.0 ± 0.9 mm/s, p = 0.006), also diverging from reported findings in the literature.
I found proprioception thresholds more than 10-fold lower compared to previous research, highlighting the importance of testing thresholds during functional tasks. The lower discrimination thresholds compared to detection thresholds were unexpected, suggesting that sway and load-bearing during standing balance may enhance sensory acuity and alter decision making, opening avenues for future research. These findings support the potential of my novel proprioception test as a valuable tool for both laboratory and clinical applications for its functional relevance.