Local dynamic stability of treadmill walking: Intrasession and week-to-week repeatability

Abstract

Repetitive falls degrade the quality of life of elderly people and of patients suffering of various neurological disorders. In order to prevent falls while walking, one should rely on relevant early indicators of impaired dynamic balance. The local dynamic stability (LDS) represents the sensitivity of gait to small perturbations: divergence exponents (maximal Lyapunov exponents) assess how fast a dynamical system diverges from neighbor points.Although numerous findings attest the validity of LDS as a fall risk index, reliability results are still sparse. The present study explores the intrasession and intersession repeatability of gait LDS using intraclass correlation coefficients (ICC) and standard error of measurement (SEM). Ninety-five healthy individuals performed 5min. treadmill walking in two sessions separated by 9 days. Trunk acceleration was measured with a 3D accelerometer. Three time scales were used to estimate LDS: over 4 to 10 strides (λ 4-10 ), over one stride (λ 1 ) and over one step (λ 0.5 ). The intrasession repeatability was assessed from three repetitions of either 35 strides or 70 strides taken within the 5min tests. The intersession repeatability compared the two sessions, which totalized 210 strides. The intrasession ICCs (70-strides estimates/35-strides estimates) were 0.52/0.18 for λ 4-10 and 0.84/0.77 for λ 1 and λ 0.5 . The intersession ICCs were around 0.60. The SEM results revealed that λ 0.5 measured in medio-lateral direction exhibited the best reliability, sufficient to detect moderate changes at individual level (20%).However, due to the low intersession repeatability, one should average several measurements taken on different days in order to better approximate the true LDS.

Could Local Dynamic Stability Serve as an Early Predictor of Falls in Patients with Moderate Neurological Gait Disorders? A Reliability and Comparison Study in Healthy Individuals and in Patients with Paresis of the Lower Extremities

“…In addition, it is very likely that LDS can differentiate among fallers and non-fallers in elderly people [11], [23]. We [24] and others [25] have very recently provided evidence that LDS can be reliably assessed with short walking tests that are suited for patients with low walking capabilities. Two of our recent studies showed that LDS could be used in clinical settings [26], [27].…”

The Maximum Lyapunov Exponent During Walking and Running: Reliability Assessment of Different Marker-Sets

“…During walking, previous studies in MLE reliability have reported good (i.e., from 0.75 to 0.88) (Portney and Watkins, 2009) intrasession (Kang and Dingwell, 2006b; van Schooten et al, 2013; Reynard and Terrier, 2014; Reynard et al, 2014; Rábago et al, 2015) and moderate (i.e., from 0.53 to 0.68) (Portney and Watkins, 2009) intersession ICC values (van Schooten et al, 2013; Reynard and Terrier, 2014). The ICCs found in our study during walking were clearly higher compared to these previous studies in both intrasession (i.e., from 0.946 to 0.980) and intersession (i.e., from 0.971 to 0.985) comparisons.…”

“…Previous studies in walking conditions reported good intrasession reliability (Kang and Dingwell, 2006b; van Schooten et al, 2013; Reynard and Terrier, 2014; Reynard et al, 2014; Rábago et al, 2015). Based on this, it was argued that differences between young and older adults (Buzzi et al, 2003; Kang and Dingwell, 2008; Terrier and Reynard, 2015; Mehdizadeh, 2017) as well as patients with moderate neurological gait disorders (Reynard et al, 2014) where instability is expected, can be discovered with the MLE.…”

“…Based on this, it was argued that differences between young and older adults (Buzzi et al, 2003; Kang and Dingwell, 2008; Terrier and Reynard, 2015; Mehdizadeh, 2017) as well as patients with moderate neurological gait disorders (Reynard et al, 2014) where instability is expected, can be discovered with the MLE. However, the reliability of the MLE is decreased between days (van Schooten et al, 2013; Reynard and Terrier, 2014). In clinical settings where the evaluation of therapies in a pre-post design is required, the reduced between days reliability provides limitations for the detection of therapy-related alterations.…”

“…Furthermore, the proof of acute changes after learning or short time adaptation (as for example while walking in different environments), needs a high degree of accuracy (Hak et al, 2012). Based on the reported reliability between days (van Schooten et al, 2013; Reynard and Terrier, 2014), detection of differences after exercise or therapy-induced adaptations might not be feasible. Using a block of measurements within several consecutive days to define a representative value of the MLE might increase the reliability, thus improving the detection ability for small alterations in the MLE.…”