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)

POSTECHHuman System Design Laboratory

Ground reaction forces on Ground reaction forces on stairs:stairs:

effects of stair inclination and effects of stair inclination and ageageAlex Stacoff et al. (2005, Switzerland)

Gait and Posture

2009. 7. 14. Tue.Heo, Jiyoon


ContentsContents

1. Introduction2. 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

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1. Introduction1. 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.

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1. Introduction1. 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

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2. Materials and methods2. 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)

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Force plates were installed


2. Materials and methods2. 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

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3. Results3. Results

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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



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Effects of stairs Slightly changed from level gait to ascent Considerably changed from level gait to descent.

Fz3, Fz4, and en were not apparent



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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%


4. Discussion4. Discussion

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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.



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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 ambulationCV (5~10%), ASI (5~15%), loading rate (10~15%), unloading rate (10~20%)



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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


5. Conclusion5. Conclusion

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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.


Appendix _ tablesAppendix _ tables

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Documents

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)