The relationship between physical workload and the position of tipping lever of wheelchair while accompanied helper lift up and down wheelchair front

Masaki Tauchi PhD, Kazuya Kuro-oka, Takabun Nakamura PhD

Okayama Prefectural University, Japan

INTRODUCTION Because of ‘Aged Society,’ the use of manual

wheelchairs for physically disabled is rapidly increasing. Many of the elderly persons who use wheelchairs are not able to maneuver freely by themselves but need assistance of care workers.

One of the major problems when they encounter in the mobile environment in the town is to clear differences in heights on floor or road surface.

For this problem, tipping levers are equipped in the rear of the wheelchair to lift up the front of wheelchair. But the shape and position may not be appropriate for the assistance by less powerful persons.

The shape and the position of typical tipping lever

PURPOSE

The tipping lever of manual wheelchair to lift up and down the casters is not always easy to use because of the present shape and/or position.

To find out appropriate position of the tipping lever, we investigated the relationship between the power needed to lift up and down casters and positions of the tipping lever in this study.

For this purpose, an introspection of the effort on upper and lower limb and load on lumber area when the subjects lift up the front of wheelchair at the various tipping lever position was measured.

METHODS SUBJECTS Eleven subjects having certain skill for wheelchair

assistance participated. Four of them were males and 7 were women, mean age 27.6 +/- 3.8yrs, body weight 57.8 +/- 10.9kg and height 165.8 +/- 10.2cm

SETTING OF EXPERIMENTAL TIPPING LEVER On both sides of the tip of the tipping levers, the experimental tipping lever holders aligned to the perpendicular to the direction of travel were attached.

17.5

Distance from wheel axis (cm)

19.0

7.5

10.0

12.5

15.0

15.011.

0

23.0

Heig

ht fr

om fl

oor (

cm)

Wheel axis

The tip of TPL position of control

floor

THE SHAPE OF TIPPING LEVER HOLDER (Large)

The tipping lever holders, Large, were made allow to search wider range in the lower posterior part of the wheelchair In total 17 positions were examined.

10 ㎝EXPERIMENTAL PROCEDURE① Lift up the front of the loaded wheelchair and step forward to put caster on the of 10cm high platform slowly② Ask ‘how heavy it was’ for the work③ Lift up front again, then land on floor stepping backward slowly④ Ask ‘how heavy it was’ for the work

10 ㎝

THE LOAD ON THE WHEELCHAIR 　 The concrete slab was used as a dummy load of wheelchair user. The weight placed on the seat was as much as 70% of the weight that the individual subjects can manage to lift up the front.

Result 1 The spatial distribution of the average effort of upper and lower limbs and load on lumber area

11.0 23.019.015.0

Distance from wheel axis (cm)

17.5

15.0

12.5

10.0

7.5

Heig

ht fr

om fl

oor (

cm)

control

Effort or load

Small

Large

THE SHAPE OF TIPPING LEVER HOLDER (S) The tipping lever holders S allow to take 14 different positions in total including two control positions at foremost and rearmost locations. The pits for four different heights and three distances were installed on the holder.

Distance from wheel axis (cm)

floor

17.520.0

22.5

15.0

27.5

15.017.513.75The shape of TPL holder used in Experiment 1 He

ight

from

floo

r (cm

)

Wheel axis

The tip of TPL, control position 1

Control position 2

12.5

EVALUATION

1) Effort on lower limb and upper limb

Need very small power (1pt)

~Need large power (5pts)

The effort of position 1 (the tip of tipping levers) was set at 5 points and the position 2 at 1pt. The subjects answered their effort by taking numbers at intervals of 0.5.

2) Load on lumber area

Feel very small load( 1pt) ~ Feel large load (5pts) Measurement was the same as lower and upper limbs

15.0 17.5 20.0 22.5 1.00

2.00

3.00

4.00

5.00

15.0 17.5 20.0 22.5 (cm)Distance from wheel axis

1

3

5

Phys

ical

effo

rtSm

all

Larg

e

Result 2 Effect of distance from wheel axis to physical effort on lower limb

** ** p<0.001****

Position 1

12.513.7515.0

17.5

17.5 20.0 22.515.0

12.00 14.00 16.00 18.00 1.00

2.00

3.00

4.00

5.00

12.00 14.00 16.00 18.00 1.00

2.00

3.00

4.00

5.00

12.00 14.00 16.00 18.00 1.00

2.00

3.00

4.00

5.00

Distance from wheel axis 17.5 cm

Phys

ical

effo

rt/lo

adSm

all

Larg

e

1

3

5

13.0 15.0 17.0

Distance from wheel axis 20.0 cm

Distance from wheel axis 22.5 cm

13.0 15.0 17.0

Height from floor (cm)

13.0 15.0 17.0

Result 3 Effect of height from floor to physical effort on lower limb

12.513.7515.0

17.5

17.5 20.0 22.515.0

12.513.7515.0

17.5

17.5 20.0 22.515.0

12.513.7515.0

17.5

17.5 20.0 22.515.0

Result 4Comparison of physical effort on upper and lower limb and load on lumbar area to the distance from wheel axis

15.0 17.5 20.0 22.5 1.00

2.00

3.00

4.00

5.00

15.0 17.5 20.0 22.5 1.0

2.0

3.0

4.0

5.0

15.0 17.5 20.0 22.5 1.0

2.0

3.0

4.0

5.0

12.513.7515.0

17.5

17.5 20.0 22.515.0

Upper limb

Lower limb

Lumber

1

Distance from wheel axis

5

3

15.0 17.5 　 20.0 22.5 Distance from wheel axis

5

3

15.0 17.5 　 20.0 22.5 (cm)

5

3

Phys

ical

effo

rt

Larg

e

15.0 17.5 　 20.0 22.5 (cm)

1

Smal

l

1

1

Phys

ical

effo

rt

Larg

eSm

all

Phys

ical

load

La

rge

Smal

l

15.0 22.520.017.517.5

13.8

15.0

12.5Heig

ht fr

om fl

oor (

cm)

Distance from wheel axis (cm)

Position 1

Mapping of total average physical effort and load of tipping lever

Total average physical effort and load: mean value of physical effort on upper and lower limbs and load on lumber

Small

Large

Result 5

SUMMARY• The amounts of effort of subject’s lower and upper limbs and

physical load on lumber area decreased linearly toward lower distal direction from the present tipping lever position.

• The effort and the load decreased when the height of the tipping lever decreased, though the relationship was not linear.

• The effort and the load were almost the same for both for both lifting up and lifting down wheelchair front.

• By searching the appropriate space for tipping levers behind wheelchair, it was found that the area around 12.5cm height and 22.5cm distance from the axis of rear wheel fulfill the purposes.

CONCLUSION

• By elongating and lowering the tipping levers of the manual wheelchair certain amounts, to lift up or down the casters become much easier for assistance with low physical strength persons.

Thank you for your attention

・現状のティッピングレバー位置を、やや低く、水平位置を介助者側により近づけることで、車いす前輪上げ動作時における介助者の身体的負荷を軽減することが可能であることが分った。・実用化には、ティッピングレバーの踏む部分の形状に関する検討が必要である。

8. 　結　論

ティッピングレバーを鉛直線から θ の角度で踏むと仮定するM ：回転モーメント、 F ：ティッピングレバーを踏む力　M = F ・ L ・ sin(θ +θ1 ）　 － (1) 　(1) 式を展開し、 F について整理するF = M / （ L2 ・ sinθ + L1 ・ cosθ ） － (2)

Stevens の式に従い、力の感覚量で表すJ ：力の大きさ感覚J = k ・ FP 　 k ：定数、 P ：重さの場合は 1.5J = k ・（ M/ （ L2 ・ sinθ + L1 ・ cosθ ） P

K=k ・ MP = 定数とし、 L2 を h で表し整理する

L1

L2

H

h

LF

θ1

θ

A

O

B

θ

床面J = K ・（（ H － h ）・ sinθ + L1 ・ cosθ ）－ P

　 = K ・（（ 27.7 － h ）・ sinθ + L1 ・ cosθ ）－1.5

5. 力学モデル

L ・ sin(θ+θ1)

TL

車軸

コントロール

負荷量

非表示部分

小

大15.0

22.5

20.0

17.5

後輪軸からの水平距離（㎝）

床面から

の高さ（

㎝） 17.5

13.8

15.0

12.5

4-4. 結果 　ティッピングレバー位置と負荷 * の分布＊負荷量は下肢・上肢・腰それぞれの負荷の平均とした

0.005

0.01

0.015

15 17.5 20 22.5

17.515.0 13.812.5

0.005

0.01

0.015

12 14 16 18

17.52022.5

後輪軸からの水平位置（ cm ）

力の感覚

床面からの高さ (cm)

（ A ）水平位置と足への負荷の関係の シミュレーション

床面からの高さ（ cm ）

力の感覚

（ B ）床面からの高さと足への負荷の関係のシミュレーション

6. 負荷のモデルによる理論値

水平距離（ cm ）

Distance from wheel axisHeight from floorPhysical load on handPhysical load on footPhysical load on waist