Submitted to the 2008 Annual Meeting of the American College of Sports Medicine for presentation

Peripheral Neuropathy Alters Variability but not Finite-Time Lyapunov Exponents during Treadmill Walking

Brad Manor, MS, Li Li, FACSM,

Louisiana State University, Baton Rouge, LA

Peripheral neuropathy (PN) is marked by diminished plantar cutaneous sensitivity, reduced preferred walking speed (PWS), and increased risk of falls. Predisposition to falls may result from an inability to adapt to challenging walking speeds. The purpose of this study was to compare the dynamics of treadmill walking at different speeds between individuals with PN and age-matched controls. Methods: Eleven individuals with PN (mean ± SD age = 67.0 ± 10.9 yr, height = 172 ± 11 cm, body mass = 86.8 ± 23.6 kg) and 11 healthy controls (age = 69.1 ± 10.0 yr, height = 168 ± 6 cm, body mass = 83.0 ± 18.8 kg) gave informed consent as approved by the university’s IRB. The 6-min walk test was used to determine “maximal walking speed” (100%MWS). Multiple treadmill walking trials were then completed at 100%MWS, 80%MWS, and 60%MWS. During the middle 2 min of each trial, motion analysis (60 Hz) was used to collect sagittal plane hip, knee, and ankle joint kinematics. Stride duration variability (SDvar) was calculated from 30 consecutive strides. Joint angle variability (JTvar) was calculated for each joint from the ensemble curves of the same 30 strides. Short- and long-term Finite-Time Lyapunov Exponents (ST, LT) were computed for each joint from ensemble curves of 100 consecutive strides. Factorial ANOVA with repeated measures was used for statistical analysis. Tukey’s pos-hoc tests were used wherever appropriate. Results: In general, faster walking speeds were associated with increased SDvar, JTvar, ST and LT. The PN group walked slower than the control group (100%MWS = 1.25 ± 0.17 vs. 1.45 ± 0.29 m/s, F_1,21 = 4.41, p < 0.001). Despite controlling for the variance in walking speed, the PN group exhibited increased SDvar (32.9 ± 2.2 vs. 23.7 ± 1.4 ms, F_{1, 65} = 6.77, p = .02) and JTvar (2.64 ± 0.10 vs. 1.87 ± 0.07 deg, F_{1, 65} = 29.1, p = .01). No group or group X speed interactive effects were observed for ST or LT. Conclusions: Compared to controls, the PN group exhibited increased variability (SDvar and JTvar) over and above that elicited by group differences in walking speed. However, no difference in the time dependent Lyapunov Exponents were observed. While effects were not exaggerated when walking at challenging speeds, the results nevertheless highlight the disturbed control of walking in this population.