Quantification Of Rapid Repetitive Movements By Manual Counting And Force Platform Analysis: 2461 Board #208 May 29, 11

Rapid, repetitive movements, such as foot tapping, are used in clinical settings for evaluating individuals with altered central motor drive. Traditionally, tapping has been measured manually by counting the number of taps in a defined period of time. However, manual counting introduces investigator error and provides only the number of taps as an outcome variable. Therefore, we investigated the use of a force platform to count the number of rapid foot taps and provide information about additional performance variables. Additionally, a 90-s foot tapping task was used to examine how performance changes during prolonged rapid tapping. PURPOSE: compare manual and force platform methods, and use the platform to quantify Inter-Tap-Interval (ITI, ms), standard deviation (SD) of the ITI, and changes in rapid tapping during the 90s trial. METHODS: 10 participants (mean±SD, 21.7±1.1 years, 5F, 5M) sat comfortably in a standard lab chair (seat height 45cm) with the knee and hip of the right leg at ∼90°. The ball of the right foot rested on the force platform (Advanced Mechanical Technology Inc, Watertown MA) and the heel was off the platform. After a brief practice, participants performed three 10-s trials, with 60s rest between trials, followed by one 90-s trial. One researcher indicated the beginning and end of the task verbally while another counted the number of times the foot made contact with the force platform. A custom Matlab (Mathworks Inc, Natick MA) program was used to determine the number of taps from the force data by identifying a tap as a local maximum of the force, and average, SD and coefficient of variation (CoV) for ITI were calculated. RESULTS: For all trials, the number of taps was higher for the manual vs. force platform method (55.8±9.2 vs. 51.1±7.1 per 10s, respectively, p=0.025), as was the highest count of the 3 trials for each individual (p=0.011). Average ITI was 20.2ms (range =17.4 - 25.5ms) and average SD of ITI was 4.57ms (range = 2.49 - 7.87ms). Tapping speed was slower during the final 10s than the first 10s of the 90-s trial (47.9±6.7 vs 31.4±5.9, p<0.001, n=7), whereas the CoV of ITI did not change (p=0.48). CONCLUSION: Performing rapid foot tapping on a force platform may reduce interpreter bias and can provide information on dynamic movement variables related to the variability of motor performance.