The TUG is a widely used clinical assessment for measuring fall risk and functional mobility. The test begins with participants sitting with their spines against a chair back and their hands on their laps. Upon verbal cue, subjects stand up, walk around a cone placed three meters from the front edge of the chair and then return to their seated position. The participants will be timed as they complete the task as quickly as possible. Each participant will perform one familiarization trial and two test trials, with at least a one-minute recovery between trials.

Three-dimensional movement analysis of subjects gait patterns during a 10-meter walk.

The Biodex 4 Dynamometer will be used for all isokinetic testing. Subjects will be asked to perform an isokinetic warm-up of 10 repetitions of leg extension at 270 deg/s, be given a three-minute recovery, and then perform three maximal isokinetic quadriceps extensions at 90, 180, and 300 degrees/second using 2-minute recoveries in between sets. All results will be recorded. The repetitions producing the highest peak torque among the three efforts, and the average power for the repetitions will be used for statistical evaluation. Given the nature of isokinetic testing the resistance is at the speeds we have chosen, far below maximum.

Ultrasound images of the quadriceps femoris muscle (vastus medialis, vastus lateralis, vastus intermedius, rectus femoris) will be taken on the thigh at the two-thirds and midpoint of the length between the anterior superior iliac spine and the upper border of the patella. A LOGIQ P9 R3 Ultrasound System (GE Healthcare, Buckinghamshire, UK) and 3-12 MHz linear array transducer probe will be used, and testing will be conducted on a padded treatment table. Care will be taken to maintain the same standardized body positions and probe locations for all participants. Minimal pressure will be applied by the researcher to reduce any tissue compression that would artificially influence the results. Before acquiring measurements, subjects will rest on the examination table for five minutes to avoid any potential movement-induced stiffness. To improve acoustic contact between the probe and skin, a water-soluble transmission gel will be used on the head of the probe.

ower testing will begin with a warm-up of 10 repetitions at 30% 1RM, followed by a 1-minute recovery period. A second warm-up of 5 repetitions at 30% 1RM will then be performed as rapidly as possible. Peak muscle power will then be assessed at 8 relative intensities (40, 50, 60, 70, and 80% 1RM) on the same resistance machines used for strength testing. The percentages will be randomized to reduce any order effect. For each repetition, the concentric phase will be performed as fast as possible, and the eccentric phase will be performed over 2-3 seconds. Each repetition will be verbally cued "3.2.1. Go!" This testing protocol is commonly used for power testing.34,35 Any repetition not performed properly will be repeated after a 1-minute break. Power output will be recorded from the display of each machine and cross-referenced with the electronic spreadsheets.

The Stroop color word test is another commonly used neurophysiological assessment which evaluates the participant's ability to inhibit cognitive inference. This cognitive domain is associated with EF and involves the processing of a stimulus where one feature of a previous stimulus may affect the simultaneous processing of a new stimulus. Typically, the test requires an individual to name the color of ink of color words printed in incongruent colors (incongruent condition), for example, the word "red" is printed in green ink. Participants must also complete a control task, where they read a color name printed in black ink and identify colored rectangles that correspond to that color as quickly as possible (congruent condition).

The TMT is yet another frequently used neurophysiological assessment which examines visuospatial abilities, working memory and task switching abilities associated with executive function domains. The test is separated into two different assessments, part A and part B. Both tasks incorporate 25 circles distributed across a white sheet of paper. In part A, the circles are numbered from 1 to 25. In part B, the participant is presented with alternating numbers and letters. Both tasks require the participant to connect the circles with lines in ascending order as quickly as possible. It has been shown that TMT Part A is associated with EF domains of visuospatial abilities, whereas part B is associated with working memory and response inhibition. Those with PD have demonstrated decreased scores on both the TMT part A and B indicating executive function decrements.

Study participants will have a home sleep study using the NoxA1 system that allows for monitoring of sleep (i.e., EEG) along with respiratory effort and oxygen saturation. The goal of the home sleep study is to exclude other respiratory-related sleep disorders.

An actigraph will be worn on the wrist for seven consecutive 24-hour periods, to collect data on habitual sleep duration. Wrist actigraphy is a technique for measuring movement over an extended recording period (days to weeks). Data garnered from wrist actigraphy will be used to derive variables such as habitual total sleep time, number and duration of awakenings per night, and napping behavior.