POSTECH H uman S ystem D esign Lab oratory Ground reaction forces on stairs: effects of stair inclination and age Alex Stacoff et al. (2005, Switzerland) Gait and Posture Tue. Heo, Jiyoon

POSTECH H uman S ystem D esign Lab oratory Contents 1. Introduction 2. Materials and methods Subjects Experimental setup Definition and detection of parameters of the vertical GRF Coefficient of catiation and gait symmetry 3. Results Patterns of vertical GRF curves during level gait and stair ambulation Detection of parameters Effects of stairs Effects of age Gait velocity and stair inclination Trial-to-trial variability Variability and age Gait symmetry 4. Discussion Limitaions Level gait Variability and left-right symmetry Stairs Variability and gait symmetry on stairs Gait velocity and age on stairs 5. Conclusion 2

POSTECH H uman S ystem D esign Lab oratory 1. Introduction  Stairs are often considered as an obstacle and are a major cause for falls and accidents in the elderly population(Archead(1985), Startzell JK(1998)).  However, research on stair ambulation is limited and is rare with respect to GRF(ground reaction force) measurements during stair ascent and descent. 3

POSTECH H uman S ystem D esign Lab oratory 1. Introduction  Literature survey  Too short (less than 5 stair cases) test stairs ∵ Without considering “transition” phase  Besser et al.(1993), Kaufman et al.(2001), etc.  Not report GRF data  Christina and Cavanagh(2002), Lobo da Costa and Amadio(1995), etc.  Independently measured left and right steps(not two consecutive steps)  Objectives  To provide comparisons of vertical GRF data with patient data  To test whether selected parameters of the vertical GRF of stair ambulation differ with respect to stair inclination, age and test-to-test variability  To test left-right symmetry 4

POSTECH H uman S ystem D esign Lab oratory 2. Materials and methods  Subjects  20 healthy subjects  Subdivided into 3 categories(young(33.7 years) / middle(63.6 years) / old(76.5 years))  Experimental setup  Data capture system(VICON) – kinematic, kinetic and EMG data  Force plates(Kistler)  Step prototype(below) – dimensions from SUVA(1995) 5 Force plates were installed

POSTECH H uman S ystem D esign Lab oratory 2. Materials and methods  Experiment design  7 conditions (level gait, [up, down] × [flat, standard, steep])  8~10 repetitions  considering only trials with two correct consecutive steps  With normal street shoes, but high heels  With natural walking speed  Measurements  Normalized force parameters (Fz2, Fz3, Fz4) – Stussi and Debrunner (1980) Fz2: force in phase of weight acceptance after touchdown Fz3: minimum force between Fz2 and Fz4 Fz4: force in phase of push-off  “intensity” (bn, en) – Stussi Debrunner (1980) Bn: loading rate En: unloading rate  CV (coefficient of variation): SD/mean × 100  ASI (absolute symmetry index, force) (%):  Gait velocity 6

POSTECH H uman S ystem D esign Lab oratory 3. Results 7  Patterns  Ascent pattern is slightly different with the level gait pattern  Descent pattern is considerably different with the level gait pattern  Parameter detection - with the routine by Stussi and Debrunner (1980)  Level gait: 100%  Ascent gait: 96~100 %  Descent gait: 60~90% Fz3, Fz4, and en were excluded

POSTECH H uman S ystem D esign Lab oratory 3. Results 8  Effects of stairs  Slightly changed from level gait to ascent  Considerably changed from level gait to descent.  Fz3, Fz4, and en were not apparent

POSTECH H uman S ystem D esign Lab oratory 3. Results 9  Effects of age  On ascent: young group marked higher values of Fz2, Fz4, and bn.  On descent: differences between age groups were not found to be significant  Gait velocity  Gait velocity dropped significantly from level gait to stair ascent and descent.  The steeper, the slower (both ascent and descent)  Trial-to-trial variability  Level gait: 2~5%  Ascent and descent gait: 10~15%  Bn and en Level gait: 5~10% Stair ascent: 10~15% Stair descent: 15~20%  Variability and age  There is not systematic increase from the young to the middle the data age group  Gait symmetry (ASI)  Level gait: 2~5%  Ascent and descent gait: 5~15%

POSTECH H uman S ystem D esign Lab oratory 4. Discussion 10  Limitation  Data loss of Fz3, Fz4, and unloading rate en in descent gait ∵ during descent, take-off maximum (Fz4) was not apparent.  Loading rate bn and unloading rate en have the greatest trial-to-trial variability (hard to detect and repeat)  the definitions of these parameters should be improved.  Level gait  Level gait GRF curve: regular, repetitive, and left-right symmetry  Some investigators reported smaller values for the GRF parameters. (Perry J. (1992), McCrory FL et al. (2001), etc) ∵ This discrepancy may be explained by the differences in gait velocity (faster than previous) of young group. Middle and old group of this study compared well with previous findings.

POSTECH H uman S ystem D esign Lab oratory 4. Discussion 11  Variability and left-right symmetry (in level gait)  CV of vertical GRF parameters in this study: 2~5% 7~15%: reported for normal children by White R et al. (1999) 12.5%: considered as acceptance level by White R et al. (1999) 3~4%: reported for young adults by Masani et al. (2002)  the result of this study is representative  ASI of vertical GRF parameters in this study: 3~5% This study is the first to describe ASI of two consecutive step in level gait and on stairs  ASI in level gait above 5% may be used as an indicator for asymmetry  Variability and gait symmetry on stairs  From level gait to stair ambulation, the CV and asymmetry of most parameters increased significantly. This study is the first to publish CV and symmetry data on stairs, therefore cannot be compared  the results of this study can be used as indicators for an increased gait variability and asymmetry during stair ambulation CV (5~10%), ASI (5~15%), loading rate (10~15%), unloading rate (10~20%)

POSTECH H uman S ystem D esign Lab oratory 4. Discussion 12  Stairs  The vertical GRF pattern was changed slightly from level gait to stair ascent, but considerably to stair descent ↔ Riener et al. (2002) said that vertical GRF pattern on ascent or descent is almost same on level gait There are differences among the results of many studies related with vertical GRF  the amount of available normative data on vertical GRF parameters during stair ambulation is diverse and still limited  Age effects Young group had larger Fz2, Fz4, and bn in the majority of the comparisons with the middle and old age group. But no significant age effects were found on stair descent  support previous findings by Christina and Cavanagh (2002)  Gait velocity and age on stairs  Gait velocity dropped significantly from level walking to stair ascent and descent Comparing flat to standard stair, the decrease in velocity was not associated by an increase in stance time. ∵ differences in stance and swing phase proportions, depending on stair inclination  supported by Archea (1985), Yu et al. (1997), and Christina and Cavanagh (2002).  Old age group showed significantly slow walking in two conditions of level gait and flat stair up.  the selection of the age group may have to be considered when intending to compare normative data with patient data

POSTECH H uman S ystem D esign Lab oratory 5. Conclusion 13  The parameterization procedure for level walking cannot be reliably applied on stair descent data.  During level walking the vertical GRF curves were found to be regular and repetitive. The trial-to-trial variability and left-right asymmetry of defined test parameters being 2~5% and 3~5%.  The vertical GRF pattern was found to change slightly from level walking to stair ascent and considerably during stair descent.  The steep stair descent condition was the most demanding test which showed the largest variability and asymmetry. Thus, it is the least stable gait pattern.  Age was found to be a factor which should be considered. The young age (33.7 years) group walked faster and produced larger vertical GRF than the middle (63.6 years) and old (76.5 years) age group.

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