On the Cause of Experienced Care Workers’ Lower Back Pain:

Considering Posture and the Strength of Back Muscle

Ryuichi ITOi.ryuuichi@gmail.comProduction Engineering of Advanced Engineering CourseNiihama National College of Technology

Japan-Taiwan symposium In 2012, In Taiwan

BackgroundIn Japan, 70 ％ of people in the care

workers have complained of lower back pain.

　　　　　　　　　　　　　　 but

　

• People who are involved in care workers for many years is not that always cause lower back pain.

• Some care workers continue to work even if they have lower back pain.In other words: There are points unlikely to be lower back pain.

Experimental Method

Examinee （ 18 pairs in total ）• Care workers, and students of college of welfare make 9 pairs within each group.

Patient （ 1 person ）• We assumed patient who requires full support.• Bathing care by two-persons• She is female student who is weight about 48 kg.After the experiment, the patient evaluatesthe care level of comfort in five point scales.

Three-Dimensional Motion Analysis System

Infrared camera

Infrared marker

Model of marker

front back

20 points in total

Operation of Bathing Services There are four patterns.

　　 From wheelchairto edge of bathtub

From edge of bathtubto bottom of bathtub

from bottom of bathtub to edge of bathtub

from edge of bathtub to wheelchair

Task2Task1

Task3 Task4

The Patient Evaluates the Care Level of Comfort in Five Point Scales

5care workers

Ｃ

4

care workers A

care workers B

care workers Ｅ

3

care workers Ｆ

care workers Ｇ

care workers Ｉ

students ｇ

2

care workers Ｄ

care workers Ｈ

students a

students h

students i

1

students b

students c

students d

students e

students f

3

care workers Ｆ

care workers Ｇ

care workers Ｉ

students g

Exce

llent

gro

upM

iddl

e gr

oup

Fair

grou

p

Definition of Waist Angle (θ)

　

　

　　　　　　　　　　 model of waist angle 　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　

neck

waist

θ

vertical direction

Moment Round the Waist of Care Worker

L

F

ＬS

WP ・Ｌ S ・Sin(θ) 　　

F ・Ｌ S ・Sin(θ) 　

WC ・Ｌ g ・Sin （ θ’ ）　

θ‘

Ｌg

WC

WP

（θ）

θ

Strength of back muscle : F necessary in caring posture

　　 F ＞ WP+0.3 ・ W c total

F ・Ｌ S ・　　　　 ＞ WP ・Ｌ S ・ 　　　 +

WC ・Ｌ g ・

H=height LS ＝ 0.28 ・ H Lg ＝ 0.14 ・ H WC=0.6 ・ W

c total

F 　　　＞ WP ・ 　　　　　　　　　　　　　　　　　　　　 + 　 WC ・ Lg / LS

F 　＞　 WP + 　 0.6 ・ W c total ・（ 0.14H ） / （ 0.28H ）

Sin（ θ ）

Sin （ θ）

Sin（ θ）

LS / LS

Moment of F ＞　 Moment of WP 　＋　 Moment of

WC

Assuming as follows;

• F ＞ WP + 0.3 ・ WC

Care worker : weight is 60 (kg)Patient : weight is 50 (kg)

F : Strength of back muscleF > 50 + 0.3 ・ 60 = 68 (kg)

If strength of back muscle of him is value less than 70 (kg), he has higher risk of lower back pain.

Definition of Roundness of the back (τ)

back1

back2

waist

τ

Model of roundness of the back

Correlation Diagram of Strength of Back Muscle and Roundness of the Back

50 60 70 80 90 100 130

140

150

160

170

180

task3　

Excellent

Excellent

Fair

Fair

Back muscle strength [kgf]

Roun

dnes

s of

the

Back　

[deg

]

Strength of Back Muscle [kgf]

Conclusion

• The risk of the lower back pain increases.

1. When expert care workers’ strength of back muscle is less than “Wp+0.3*Wc”,

even if he has not had lower back pain.

2. When care workers have the posture oflarge roundness of the back.