Most caregivers have low back pain which results from frequent care activities such as assistance motion that supports transfer and standing-up. Various parameters are associated with the caregiver’s lumbar load. In this study, we focus on the foot position of the caregiver as one of the subjective adjustable parameters. This study aimed to analyze the relationship between foot position and stresses of the L4–L5 joint as lumbar load during supporting standing-up via musculoskeletal simulation. The musculoskeletal model was tasked with simulating supported standing-up motions based on a specific pelvic position and angular variation of each joint. The anterior foot (left foot) was fixed, and the posterior foot (right foot) was moved to three backward positions and three rightward positions, thus obtaining nine posterior foot positions. Compressive, anteroposterior shear, and lateral shear stresses of the L4–L5 joint were compared for nine foot positions. The results showed that as the anteroposterior distance and lateral widths between both feet increased, the average value of compressive/shear stress of the L4–L5 joint during motions decreased. From our findings, we hypothesized that the foot position may reduce the lumbar load and prevent low back pain.

Caregivers experience low back pain because of patient handling such as supporting standing-up. The lumbar load of a caregiver depends on the required force for patient handling motions. If the relationship between the required force and the lumbar load is quantitatively clarified, it may be useful for preventing low back pain in caregivers. In this study, we investigated the quantitative relationships between the required force and lumbar loads such as vertebral stress and muscle activity in supporting standing-up by computational musculoskeletal simulation. First, a musculoskeletal model of a caregiver was prepared, and then the model performed simulated supporting standing-up motions. The vertical load used as the required force was placed on the upper limb of the model. The compressive/shear stress of the vertebral (L4–L5) and muscle activities of spinae erector muscle group were recorded as the lumbar load. The results showed that there are highly significant correlations between the required force (r > 0.9, p < 0.01). In addition, regression equations for predicting each lumbar load by the required force with highly determination coefficients (R2 > 0.9) were obtained from these relationships. Furthermore, we found that when the required force was more than 120 N, the compression stresses of the vertebral exceeded injury threshold (3400 N) by the regression equation. These regression equations contribute to quantitatively consider lumbar loads of caregiver during patient handling based on injury thresholds and the required force.

We used musculoskeletal simulation to estimate abduction of the shoulder and lateral bending of the spinal column during crutch walking, and investigated the relationship between lateral bending of the spinal column and abduction of the shoulder during double-crutch walking. [Participants and Methods] The participants were five healthy young males. Data of movement during crutch walking was measured using a 3D motion analysis system. Based on the obtained data, shoulder joint abduction and lateral bending of the spinal column during doublecrutch walking was estimated using a musculoskeletal simulation. [Results] A significant correlation between the lateral bending angle of the spinal column and abduction angle of the shoulder was found during the crutch stance phase. [Conclusion] A relationship between lateral bending of the spinal column and abduction angle of the shoulder was found, and it was considered that the axillary pad slipping out of the axilla during double-crutch walking was a possible factor.

To clarify the reason why the axillary pad often deviates from the axilla during doublecrutch walking using a musculoskeletal simulator. [Participants and Methods] The subjects were five healthy young males without orthopedic disease. Movement during crutch walking was measured using a 3D motion analysis system. Based on the obtained data, muscle activity related to the shoulder joint during double-crutch walking was modeled using a musculoskeletal simulation. [Results] The shoulder joint was abducted in the crutch stance phase of all subjects. [Conclusion] The results suggest that crutch walking with the shoulder blades rotated downward may suppress the activity of the abductor muscle of the shoulder joint and the activity of the shoulder joint adductor muscle.