Biomechanical analysis of different dynamic sitting techniques: an exploratory study

Postural shifts and body perceived discomfort during 1-hour sitting when leaning and sitting on an air-filled seat cushion among healthy office workers

This study compared the number of postural shifts and perceived discomfort while leaning and sitting on an air-filled seat cushion for 1 hour. Sixty office workers typed a standard text while leaning on a cushion placed behind the low back, sitting on a cushion placed under the buttocks, and sitting without a cushion (a control condition). The number of postural shifts was collected using a seat pressure mat device. Low back discomfort was assessed using the Borg CR-10 scale. Leaning on a seat cushion (22 shifts/h) led to a significantly higher number of postural shifts than sitting on a seat cushion (18 shifts/h) and the control condition (20 shifts/h). Leaning or sitting on a seat cushion significantly decreased low back discomfort compared to the control condition (p < 0.05). Leaning on a seat cushion placed behind the low back may be an effective means of preventing low back pain among office workers.

Steering-by-leaning facilitates intuitive movement control and improved efficiency in manual wheelchairs

BACKGROUND

Manual wheelchair propulsion is widely accepted to be biomechanically inefficient, with a high prevalence of shoulder pain and injuries among users. Directional control during wheelchair movement is a major, yet largely overlooked source of energy loss: changing direction or maintaining straightforward motion on tilted surfaces requires unilateral braking. This study evaluates the efficiency of a novel steering-by-leaning mechanism that guides wheelchair turning through upper body leaning.

METHODS

16 full-time wheelchair users and 15 able-bodied novices each completed 12 circuits of an adapted Illinois Agility Test-course that included tilted, straight, slalom, and 180° turning sections in a prototype wheelchair at a self-selected functional speed. Trials were alternated between conventional and steering-by-leaning modes while propulsion forces were recorded via instrumented wheelchair wheels. Time to completion, travelled distance, positive/negative power, and work done, were all calculated to allow comparison of the control modes using repeated measures analysis of variance.

RESULTS

Substantial average energy reductions of 51% (able-bodied group) and 35% (wheelchair user group) to complete the task were observed when using the steering-by-leaning system. Simultaneously, able-bodied subjects were approximately 23% faster whereby completion times did not differ for wheelchair users. Participants in both groups wheeled some 10% further with the novel system. Differences were most pronounced during turning and on tilted surfaces where the steering-by-leaning system removed the need for braking for directional control.

CONCLUSIONS

Backrest-actuated steering systems on manual wheelchairs can make a meaningful contribution towards reducing shoulder usage while contributing to independent living. Optimisation of propulsion techniques could further improve functional outcomes.

Differences in oscillometric blood pressure readings between unsupported and supported back conditions

Appropriate body posture is important for accurate blood pressure (BP) measurement. However, the impact of an unsupported back on BP readings is currently controversial. This study included 224 subjects (18-86 years old, 54.5 ± 15.5 years old, 105 males). BP was measured with an oscillometric BP device randomly following one of two protocols for back support conditions: (1) supported-unsupported-supported-unsupported, or (2) unsupported-supported-unsupported-supported. The average of the two systolic BP (SBP) and diastolic BP (DBP) readings in the same position was recorded as the final BP value. The differences in BP between the unsupported and supported back conditions were calculated as delta BP. Moreover, the percentage variation in BP (PV) was calculated with the formula delta BP/BP with an unsupported back. Multivariable regression analysis evaluated the impact of age, sex, hypertension history and supported BP level on PV. The SBP/DBP levels measured with an unsupported back were slightly higher than those when the back was supported (132.7 ± 19.5/79.6 ± 12.9 mmHg vs. 130.3 ± 20.0/78.5 ± 14.3 mmHg), and the delta SBP (2.3 mmHg) was statistically significant. The multivariable regression analysis showed that age was a positive factor but supported SBP level as a negative factor for systolic PV, while age and supported DBP level were positive factors, but hypertension history was a negative factor for diastolic PV. For a group participant, the mean difference in oscillometric SBP/DBP in the unsupported back position was 2.3/1.0 mmHg higher than that in the supported back position.