Keywords

1 Introduction

Due to the rapid improvement of economy, living standard and health care in Japan from “After World War II”, Japanese longevity has boosted into a 80 years old “super ageing” era. In recent years, falling born ratio has resulted in a sharp reduce tendency of young population, on the contrary, the elderly population percentage accounts for total population has become larger and larger. By the end of 2014, the elder population over 65 years old has accounted for 26.8 % of total population, in which 13 % elders are over 75 years. According to the elderly population demographic and estimation reported in Japanese Ministry of Health, Labour and Welfare, current ageing situation is becoming serious year after year. Until 2035, elderly population over 65 years old will increase to 33.4 %, in other words, one elder must be contained in three citizen for imbalanced population structure. It is worth noting that the late over 75 age population proportion also reach for 20 %, in which more bedridden, dementia and elder required high nursing care level number are increasing.

Under such a crisis ageing issue, social factors such as generation size reduction, the improvement of women’s employment opportunity and elderly care consciousness transition from family to social welfare facilities still brought some developing challenge and opportunities for Japanese nursing industry. Therefore, urgent requirement and demand of related elder nursing care welfare facilities and professional caregivers is increasing to a large scale significantly. In general, transfer care from wheel chair to port toilet was found to be an extremely toughness and frequent job among all of the nursing care works that had substantial danger of causing a low‐back pain whether with multiple caregivers or assistant device [1]. Low back pain is a universally occupational disease troubling caregivers in nursing care industry, which may affect caregiver’ s care work efficiency and elder care service quality, moreover it leads to limitation and negative effect on shortening occupational year [2, 3]. In Japan, 60 %– 70 % of caregivers in elderly nursing care industry have low back pain disease, which has become a realistic reason of the industry’ s turnover rate, even expert caregiver also has the same issue. Thus, in order to conduct safe transfer care process and prevent caregiver’ s low back pain situation in a long‐term occupational period, it is very important to master proper nursing care gesture/technology and knowledge for beginner and non‐expert caregivers.

By far, some researchers have reported some body loading comparison between assistant device and manual work in general. However, there is little paper focusing on the cause of low-back pain issue, limitation solution for the low back pain problem other than device substitution, quantitative description of expert and non-expert’s waist motion effect on body burdening. In our previous study, expert and non-expert caregiver’s lower limb utilization during transfer care process were investigated. It is clarified that expert’s knee and joints angular acceleration is small and stable compared to non-expert, which resulted in little body loading for expert’s transfer care process. As well known, up and down motion impact force for caregiver’s head caused caregiver himself/herself body fatigue, and stable and slipping lifting transfer care process directly reflects head motion style. Referring to head movement, we also investigated expert and non-expert’s motion characteristic in our previous research. It was considered that little impact power loaded for expert’s head during whole transfer care process, which reflected a kind of care with small body burden. In general, low back pain symptom is origin from incorrect care gesture and concentrated force loaded in waist location. In this paper, continuing with previous study, waist movement track of caregivers with different experience years were focused. Afterwards, expert’s waist movement characteristic was visual analyzed by waist moving velocity, accelerated velocity, waist bending angle and roundness discussion and comparison between expert and non-expert. In a word, this paper was aimed to give the feedback to elder nursing care occupational site, improve non-expert’s awareness of correct care gesture and optimize their care skill finally.

2 Experiment

2.1 Participants

Two caregivers employed in the same Japanese nursing home (Asokaen) were considered as subjects for the whole study. One caregiver is 34 years old with 9 experience years for elder nursing care occupation referred as “Expert”; And the other one caregiver is 23 years old with only 4 month working experience referred as “Non-expert”. Both of them have similar body weight and height with 50 kg and 161 cm respectively. A ‘hypothesis’ elder (a 80 kg co-operative female with 15 years of care occupation experience, assumed that the lower half body is paralyzed) was employed in both expert and non-expert caregiver’s handling tasks. Additionally, the current study represented an “ideal” case scenario since the ‘hypothesis’ elder is a super expert (guider) could master good care motion skill with relatively heavy body. Thus, it is more conductive to evaluate both two caregiver’s care gesture difference by guider’s own comfort perception and get good knowledge of caregiver’s body loading level during heavier object elder care task.

2.2 Experimental Preparation

Transfer care work from wheel chair to port toilet was predetermined for expert and non-expert’s care job investigation process. One main and one assisted caregiver totally two caregivers (experts or non-experts) in a group were cooperated to carry out transfer care work for the same “hypothesis” elder, but only main caregiver was focused in this research. Prior to experimental process, both expert and non-expert caregiver subjects were required to attach 20 reflection markers throughout body positions as head top, head front, head left, head right, neck, back1, back2, waist, shoulder (left and right), elbow (left and right), hand (left and right), daitenshi (left and right), knee (left and right), ankle (left and right) and foot (left and right). And the whole process of caregiver’s motion was recorded by infrared camera three-dimensional (3D) capture system with an interval of 100 frames per second.

2.3 Post Process

Firstly 20 detected markers on caregiver’s body were fetched in coordinate by post process of cortex motion analysis system. Afterwards, all markers were jointed into human model to simulate and review caregiver’s real care motion track in three-dimensional space. And next low back bending angle, waist joint angle (marker points back2-waist-knee) and waist roundness (marker points back1-back2-waist) were calculated and exported, which illustrated in Fig. 1. Due to the smooth movement could result in small physical JERK value with little impact of human perception, waist acceleration change (JERK) was also deduced by acceleration derivative with respect to time additionally. Furthermore, in order to discuss effective value of acceleration and JERK value of waist movement, both acceleration and JERK’s root of mean square (RMS) were calculated.

Fig. 1.
figure 1

Definition of waist roundness, waist angle and waist joint angle

Full size image

3 Results and Discussions

3.1 Waist Movement Range

In Fig. 2, both expert and non-expert’s waist movement in up-down direction was indicated. The whole transfer care process was separated into “lift-up”, “turning” and “moving” three stages. It is clearly to find that expert caregiver’s waist moved more stable during “turning” period with nearly 700 mm height, and “lift-up” and “sit” stages indicated a comparable larger movement range in up-down direction than non-expert. Expert’s stable waist movement during turning stage resulted in smooth transfer care process and also able to eliminate elder’s uneasy feeling. Referring to “lift-up” and “sit” stages, expert’s waist moved owing to whole body movement with knee’s flexion and extension.

Fig. 2.
figure 2

Waist movement in up-down direction

Full size image

In Fig. 3, both expert and non-expert’s waist movement tracks during transfer care behavior in horizontal plane were illustrated. As showed in Fig. 3, it is deserved to find that non-expert caregiver’s waist moved in horizontal plane in a wider region, which showed around 3 times longer distance than expert performance in both for-backwards and right-left directions. Thus, non-expert’s transfer care process was considered to have heavier loading on her waist region which easily lead to low back pain with a larger space movement.

Fig. 3.
figure 3

Waist movement in horizontal plane

Full size image

3.2 Waist Region’s Acceleration and JERK Analysis During Transfer Care

In previous discussions, we have understood expert’s waist region narrow movement in three-dimensions. Here, waist’s moving acceleration was also compared between expert and non-expert caregiver. As showed in Fig. 4, it is notified to find that non-expert’s shake composed rotation acceleration of three-dimensions during whole transfer care process with numbers of huge large wave peaks. However, expert displayed a steady rotated acceleration inferring a continuous and smooth motion among varied stages. For further detail discussion of non-expert’s pausal transfer care process, composed acceleration of waist in horizontal plane during “turning” stage was extracted in Fig. 5. Comparing with expert’s behavior, non-expert existed a super large acceleration peak in turning moment, which means there were some difficulties in waist rotation from wheel chair to port toilet position.

Fig. 4.
figure 4

Composed rotated acceleration of waist in X, Y and Z direction

Full size image
Fig. 5.
figure 5

Composed acceleration of waist in horizontal plane during “turning” stage

Full size image

In Figs. 6 and 7, both expert and non-expert’s effective acceleration and JERK value of waist movement were computed and compared. According to Fig. 6, expert’s care process could be explained as quicker lift-up, slower turning and sit stages than non-expert, during which stable turning process and comfortable sitting process other falling feeling were also understood. JERK is the change of acceleration, where also characterize action force at minimum time interval. As showed in Fig. 7, comparing with expert’s care behavior, non-expert displayed more than 2 times of action force on waist region during whole process. Consuming energy value is a kind of indicator to define body burden or caregiver’s fatigue situation after care process. As well know that energy could be calculated by product-term of applied force and movement distance. Therefore, it could draw a conclusion that non-expert has more possibility to suffer from low back pain with larger waist energy cost during care process.

Fig. 6.
figure 6

Acceleration’s RMS value during transfer care process

Full size image
Fig. 7.
figure 7

JERK’s RMS value during transfer care process

Full size image

3.3 Waist Roundness, Bending Angle and Waist Joint Angle Discussion

In Fig. 8, expert and non-expert’s waist roundness comparison during transfer care were summarized. It is found that expert kept a comparative straight back line with nearly 170° waist roundness. However, non-expert performed a wide range of waist motion and back extension along with different stages of transfer care process. Waist angle (back bend) of caregiver was also plotted in Fig. 9. It was easy to found that expert displayed sharper increase of waist angle when lifting-up elder in shorter time duration. And comparing with non-expert’s wider range of waist extension angle, expert caregiver kept nearly vertical straight upper body gesture during turning stage in care process.

Fig. 8.
figure 8

Comparison of expert and non-expert’s waist roundness during transfer care

Full size image
Fig. 9.
figure 9

Comparison of expert and non-expert’s waist bending angle during transfer care

Full size image

Both right and left waist joint angles were compared between expert and non-expert in Fig. 10a and b respectively. It is obvious to detect that non-expert’s right and left waist joint angles were smaller than expert especially during turning stage with 20°, which visually explained non-expert’s waist fatigue loading by bending forward style.

Fig. 10.
figure 10

(a) Comparison of expert and non-expert’s right waist joint angle (b) Comparison of expert and non-expert’s left waist joint angle

Full size image

4 Conclusions

In this research, caregiver’s waist movement comparison between expert and non-expert during transfer care was studied by visually analysis based on three-dimensional coordinate system. Through comparing waist movement range, waist bending angle, roundness and waist joint angle with expert caregiver, non-expert’s waist region was found to suffer from larger force during care process in larger space movement. Consequently, it could be concluded that expert kept straight upper body gesture with less bending and stable waist motion in a smaller range during transfer care process, which was considered as effective waist movement for back pain prevention in intensive heavy care works.