Investigation of Differences in Phasic Patterns During a Multicyclic Fatiguing Task
MetadataShow full metadata
This research examined the phasic differences of the lower extremities for a repetitive lifting task using two relative phase techniques, Discrete Relative Phase and Continuous Relative Phase. Both were calculated using the knee and hip angular positions along with their angular velocities in the sagittal plane. Further investigation was carried out using Vector Coding and Principal Component Analysis of the knee and hip angular positions. Discrete relative phase displayed information of the coupling relationship between the two joints when the distal joint was assessed relative to the proximal joint. The results showed that up to and including the 4th lift the coupling angle of the participants executed an ideal lifting posture where the hip extension leads the knee extension for the entire lifting cycle. For lifts 5 to 21, the participants displayed a distinct phasic difference. From approximately 50% to 100% of the remaining lifting cycle, the knee extension leads the hip extension for the remainder of the cycle. Continuous relative phase analysis used the angular positions and velocities, which was performed using the raw values or normalizing (+/-1) the raw values. It was found that in normalizing the raw values, temporal information was lost compared to using the raw values. The analysis of raw values showed information consistent with the discrete relative phase analysis, but the continuous relative phase is considered as a higher-order interpretation due to the addition of assessing both angular position and velocity of the two joints of interest. The results from continuous relative phase analysis showed that participants performed what could be referred to as an ideal lifting posture from lift 1, up to and including lift 4, where the hip extension leads the knee extension for the entire lifting cycle. From lifts 5 to 21, continuous relative phase displayed a phasic shift from approximately 50% of the lifting cycle to 100%. The knee extension would then lead the hip extension during the lifting cycle. Vector coding procedure was used to compute relative phase plots of both the knee and hip joint angular positions. Vector coding procedure displayed unsatisfactory results relating to the assessment of fatigue, due to the results outputting the direction and magnitudes of frame-to-frame vectors, and therefore, valuable temporal information for the entire cycle is lost. The Principal Component Analysis used the correlation matrix, which produced similar results to discrete relative phase and continuous relative phase. A comprehensive prediction can be made about the two principal-components, which makes up approximately 85% of the variation of the participant's knee and hip angular positions across the 21 lifting cycles. Although the results for one participant yield tangible outcomes, further analysis will be required when applying principal component analysis to several participants and would likely include cluster analysis of the results. In summary, both relative phase methods yielded the best results for the interpretation of differences in phasic patterns relating to fatigue in multicyclic behaviour. Continuous relative phase provides a higher-order analysis of the results, which provided both continuous spatial and temporal information relating to the two joints of interest.