Wave Kurtosis: A Novel, Specific Parameter for TUG-Turn Quantification

The Timed Up and Go test (TUG) is widely used in both research and clinical settings. The most common parameter for quantification of functional decline is the duration of a performed TUG. Analysis of the turn part of the TUG could provide valuable information about functional decline. Notwithstanding, there are only a few studies that deals with the TUG turn processing. This study proposes a novelty parameter—wave kurtosis (WK) that provides quantitative metrics for describing and comparing turn patterns. The WK is designed to evaluate the shape of the signal waveform. The WK quantifies the peak of the signal, its position and tails. The TUG-turn angular rate was analysed. Intra-class correlations (ICC) of WK and the strength of a linear association between WK and established turn parameters (turn duration, peak angular rate, and mean angular rate) were calculated. The reliability of WK about the vertical axis was moderate (ICC > 0.50), while reliabilities of the frontal axis and sagittal axis varied according to the subject group. The WK about the vertical axis was moderately correlated with turn duration, mean value and peak value. Utilization of waveform parameters opens a new area of TUG turn analysis and may allow for a more sensitive determination of movement disorders or fall risk assessment. Therefore, future studies utilizing turn movement may benefit from the use of the wave kurtosis.