Active sitting with backrest support : is it feasible?

Ergonomics science recommends office chairs that promote active sitting to reduce sitting related complaints. Since current office chairs do not fulfil this recommendation, a new chair was developed by inverting an existing dynamic chair principle. This study compares active sitting on the inverted chair during a simulated computer based office task to two existing dynamic office chairs (n=8). Upper body stability was analysed using Friedman ANOVA (p=.01). Additionally, participants completed a questionnaire to rate their comfort and activity after half a working day. The inverted chair allowed the participants to perform a substantial range of lateral spine flexion (11.5°) with the most stable upper body posture (≤11mm, ≤2°, p≤0.01). The results of this study suggest that the inverted chair supports active sitting with backrest support during computer based office work. However, according to comfort and activity ratings, results should be verified in a future field study with 24 participants.ZHAW Zurich University of Applied SciencesAccepte

Towards the development of a novel experimental shoulder simulator with rotating scapula and individually controlled muscle forces simulating the rotator cuff

A preclinical analysis of novel implants used in shoulder surgery requires biomechanical testing conditions close to physiology. Existing shoulder experiments may only partially apply multiple cycles to simulate postoperative, repetitive loading tasks. The aim of the present study was therefore the development of an experimental shoulder simulator with rotating scapula able to perform multiple humeral movement cycles by simulating individual muscles attached to the rotator cuff. A free-hanging, metallic humerus pivoted in a polyethylene glenoid is activated by tension forces of linear electroactuators to simulate muscles of the deltoideus (DELT), supraspinatus (SSP), infraspinatus/teres minor and subscapularis. The abductors DELT and SSP apply forces with a ratio of 3:1 up to an abduction angle of 85°. The rotating scapular part driven by a rotative electro actuator provides one-third to the overall arm abduction. Resulting joint forces and moments are measured by a 6-axis load cell. A linear increase in the DELT and SSP motors is shown up to a maximum of 150 and 50N for the DELT and SSP, respectively. The force vector in the glenoid resulted in 253N at the maximum abduction. The present investigation shows the contribution of individual muscle forces attached to the moving humerus to perform active abduction in order to reproducibly test shoulder implants

Active sitting with backrest support : is it feasible?

Ergonomics science recommends office chairs that promote active sitting to reduce sitting related complaints. Since current office chairs do not fulfil this recommendation, a new chair was developed by inverting an existing dynamic chair principle. This study compares active sitting on the inverted chair during a simulated computer based office task to two existing dynamic office chairs (n = 8). Upper body stability was analysed using Friedman ANOVA (p=.01). Additionally, participants completed a questionnaire to rate their comfort and activity after half a working day. The inverted chair allowed the participants to perform a substantial range of lateral spine flexion (11.5°) with the most stable upper body posture (≤11mm, ≤2°, p≤0.01). The results of this study suggest that the inverted chair supports active sitting with backrest support during computer based office work. However, according to comfort and activity ratings, results should be verified in a future field study with 24 participants. Practitioner Summary: This experimental laboratory study analyses the feasibility of active sitting with a backrest support during common office work on a new type of dynamic office chair. The results demonstrate that active sitting with a backrest support is feasible on the new but limited on existing chairs

Experimental shoulder testing under in-vivo anatomy and physiology

Simulating arm abduction using a n experimental shoulder simulator which matches physiological conditions would be of highest interest in shoulder bio-mechanics, e.g. to study the influence of shoulder anomalies on joint reaction force and muscular activity levels, to simulate rotator cuff tears to analyse different surgical treatment approaches, or to investigate primary stability of newly developed implants. For this purpose, we developed an experimental shoulder simulator. However, previous conducted studies revealed that the increase of the joint reaction force while abduction is considerably decreased compared to in vivo measurements, and cranial subluxation was already observed at very low shear reaction force levels. We therefore advanced the existing shoulder simulator by adapting anatomy and physiology to in vivo human shoulder condition by tilting the force action line of the rotator cuff muscles according to anatomical observations 15° caudally, and introduced primary antagonists: the Pectoralis Major and Latissimus Dorsi. The aim of this study was to compare compressive joint reaction force to literature data, to introduce a novel approach to study humeral head migration to detect cranial subluxation, and to analyse maximum shear joint reaction force of stable shoulders

Towards the development of a novel experimental shoulder simulator with rotating scapula and individually controlled muscle forces simulating the rotator cuff

A preclinical analysis of novel implants used in shoulder surgery requires biomechanical testing conditions close to physiology. Existing shoulder experiments may only partially apply multiple cycles to simulate postoperative, repetitive loading tasks. The aim of the present study was therefore the development of an experimental shoulder simulator with rotating scapula able to perform multiple humeral movement cycles by simulating individual muscles attached to the rotator cuff. A free-hanging, metallic humerus pivoted in a polyethylene glenoid is activated by tension forces of linear electroactuators to simulate muscles of the deltoideus (DELT), supraspinatus (SSP), infraspinatus/teres minor and subscapularis. The abductors DELT and SSP apply forces with a ratio of 3:1 up to an abduction angle of 85°. The rotating scapular part driven by a rotative electro actuator provides one-third to the overall arm abduction. Resulting joint forces and moments are measured by a 6-axis load cell. A linear increase in the DELT and SSP motors is shown up to a maximum of 150 and 50 N for the DELT and SSP, respectively. The force vector in the glenoid resulted in 253 N at the maximum abduction. The present investigation shows the contribution of individual muscle forces attached to the moving humerus to perform active abduction in order to reproducibly test shoulder implants