Analysis of human knee flexion-extension during gait, in a laboratory and a non-laboratory based environment

Abstract

The two major aspects with which the current thesis was concerned were firstly, validating a wireless inertial measuring unit (IMU) based motion capture system against an optical motion capture system and secondly, testing the IMU motion capture system in a non-laboratory based environment. While there are a number of protocols for IMU motion capture available in the literature to our knowledge, hitherto, the vast majority of studies merely compared this technique to optical motion capture without actually completely validating the proposed techniques against the reference system. For the purpose of this study, the flexion-extension angle of the knee during gait was measured during two sessions, using IMU and optical motion capture in a laboratory and only IMUs in an outdoor environment, for 10 healthy non-athlete male participants, aged 22-30 years, with a weight of 69-93kg and a height of 169-193cm. When comparing data from the two motion capture systems, variability of ΔROM = 0.2° to 16.3°, RMS = 2.9° to 6.1°, σ = 2.5° to 7.9°, CV = 3.3% to 10.3% and correlation of CMC = 0.977 to 0.994, r = 0.958 to 0.995, were discovered. Furthermore, a two sample t-test revealed that despite such high correlation statistically significant differences (p < 0.04(*) to p < 0.0008(***)) were present between percentages 17 and 56, and 69 and 94 of the average knee flexion-extension angles recorded during a gait cycle with the two systems. Therefore, in order to validate the IMU motion capture protocol against the reference system, calculations were made and a vector, comprising a correction factor for the knee flexion-extension angle computed from the IMU data at every percentage of the gait cycle, was generated. Once the correction vector was applied to the IMU data, no statistically significant differences were found between the average knee flexion-extension angles of the gait cycle recorded with the two systems. When comparing laboratory to outdoor IMU motion capture variability of ΔROM = 0.1° to 14.3°, RMS = 1.8° to 6.1°, σ = 1.5° to 5.1°, CV = 2.3% to 7.8% and correlation of CMC = 0.974 to 0.998, r = 0.966 to 0.996, were discovered. Despite such large variability measures, two-sample t-tests showed no statistically significant differences between the average knee flexion-extension angles recorded during a gait cycle in the two venues. The findings of the current study show that the IMU system and data processing protocol presented in the thesis can be used for the purpose of indoor as well as outdoor motion studies. However, for studies involving human knee flexion-extension during gait, the proposed correction factor should be applied in order for the data to be comparable to the currently accepted gold standard. For studies involving other motions further testing needs to be carried out.

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