Adaptation of bilateral coordination of gait during split belt walking as reflected by the phase coordination index.

BACKGROUND: The Split belt treadmill (SBTM) has recently been used in research and rehabilitation to study and utilize gait adaptations. The Phase coordination index (PCI) is useful in assessing bilateral coordination of gait by quantifying the consistency and accuracy in generating the anti-phased left-right stepping pattern. Recently we proposed that 23 strides are sufficient to reliably characterize PCI values from regular over ground and treadmill walking RESEARCH QUESTION: Can we detect the effect of SBTM on PCI using only 23 gait cycles also from SBTM walking? METHODS: Young healthy participants (n = 13) with right side motor dominance performed SBTM walking trials. Experiment protocol began by walking in tied belt (TB) mode, followed by an incremental speed increase of one of the belts by 50 % - split belt (SB) mode. This was performed for each side. Two 1-minute segments were analyzed per participant, TB and SB. PCI analysis was carried out upon fewer strides (n = 23) and compared to PCI that was obtained based on all available strides (n = 56 ± 5). RESULTS: Clear SBTM walking effects on PCI were seen in both experiments, for example, PCI increased from 4.46 ± 1.5 % (TB) to 10.07 ± 3.6 % (SB) for left belt speed increase. Twenty three strides from each trail were sufficient to demonstrate the effect. SIGNIFICANCE: PCI can be a useful metric to characterize changes in bilateral coordination of gait during SBTM gait adaptations. The fact that 23 strides are sufficient for its reliable estimation, contribute to the continued monitoring through the adaptation process (i.e., by using time windows).

Novel methodology for assessing total recovery time in response to unexpected perturbations while walking.

Walking stability is achieved by adjusting the medio-lateral and anterior-posterior dimensions of the base of support (step length and step width, respectively) to contain an extrapolated center of mass. We aimed to calculate total recovery time after different types of perturbations during walking, and use it to compare young and older adults following different types of perturbations. Walking trials were performed in 12 young (age 26.92 ± 3.40 years) and 12 older (age 66.83 ± 1.60 years) adults. Perturbations were introduced at different phases of the gait cycle, on both legs and in anterior-posterior or medio-lateral directions, in random order. A novel algorithm was developed to determine total recovery time values for regaining stable step length and step width parameters following the different perturbations, and compared between the two participant groups under low and high cognitive load conditions, using principal component analysis (PCA). We analyzed 829 perturbations each for step length and step width. The algorithm successfully estimated total recovery time in 91.07% of the runs. PCA and statistical comparisons showed significant differences in step length and step width recovery times between anterior-posterior and medio-lateral perturbations, but no age-related differences. Initial analyses demonstrated the feasibility of comparisons based on total recovery time calculated using our algorithm.

How many strides are required for a reliable estimation of temporal gait parameters? Implementation of a new algorithm on the phase coordination index.

BACKGROUND: The Phase coordination index (PCI), a temporal gait measure that quantifies consistency and accuracy in generating the anti-phased left-right stepping pattern, assesses bilateral coordination of gait in various cohorts (e.g., Parkinson's disease, post stroke). As PCI is based on mean values calculated across a series of gait cycles, individuals are required to perform lengthy walking trials, prolonging gait assessments which cause discomfort to some of them. This study introduces an algorithm to identify the required number of strides to obtain a reliable, characteristic PCI value. METHODS: Simulated data sets, as well as physiological data (obtained from healthy elderly and young persons, from over ground and treadmill trials) were used in this research. A series of N-1 PCI values was calculated for i = 2,3,4…N gait cycles for each participant. There is a value i = k, representing certain number of cycles, for which no significant change in PCI occurs as additional cycles are added, termed point of stabilization (POS). The algorithm presented here uses a 2-stage iterative process to determine POS. Stage 1 searches for the gross location of the interval of PCI values containing the POS. In stage 2, the algorithm performs a high-resolution recursive, iterative process within this interval to find the exact point. The criterion for defining stability within a window of PCI values is a coefficient of variation (CV) of ≤ 5%. RESULTS: Our recursive, iterative algorithm indicates that ~23 strides on average should be captured to attain a characteristic PCI. CONCLUSIONS: Gait trials with at least 23 strides on average should suffice to obtain a reliable estimation of PCI in healthy young adults. While this methodology may be considered generic, future studies should obtain POS values based on additional cohorts (e.g., disabled participants, fixed walking speeds).