We recently reviewed the results of the Stand More AT (SMArT) Work trial in edition 251 of BC Disease News (here).
SMArT tested an assumption that prolonged periods of occupational sitting increases the risk of cardiovascular mortality, cardiovascular disease, musculoskeletal disorders and type II diabetes, by allowing 77 out of 146 NHS Trust employees the opportunity to use height-adjustable workstations (sit-stand desks).
However, more recently, experts have discovered that back pain (a musculoskeletal condition) is better avoided through ‘perching’, a ‘hybrid sit-stand posture’. Compared with binary, conventional posture types, i.e. ‘sitting’ or ‘standing’, ‘perching’ induces a ‘neutral spine’, which is the optimal lumbar posture.[i]
In the latest study, published in the Ergonomics journal, researchers at the University of Waterloo and Western Washington University examined how muscle activation and ground reaction forces differed at 3 distinct ‘postural phases’ of knee bend, i.e. ‘sitting’, ‘perching’ and ‘standing’.[ii] The results may assist chair designers with the development of improved ergonomic furniture.
To calculate the male and female ranges of ‘perching’ phase, 24 participants completed one-minute static testing at 19 sequential ‘trunk-thigh angle increments’, starting with ‘sitting’ (90°) and ending with ‘standing’ (180°). The indicator for ‘perching’ posture was the point at which ‘lumbopelvic and pelvic angles deviated’. Male participants exhibited a wider ‘perching’ phase than females (see the table below):
Having identified the 3rd ‘postural phase’, the researchers remarked that tension and stress levels in the back muscles were lowest during the ‘perching’ phase.
They went on to observe the physical demands on lower limbs in each phase.
For both sexes, knee extensor activity was lower during the ‘standing’ phase, compared with ‘perching’ or ‘sitting’ phases. What is more, anterior-posterior forces were highest in ‘perching’ individuals, requiring 15% body-weight, on average.
In view of these lower limb findings, which were ultimately ‘draw-backs’, the researchers deduced that:
‘Chair designs aimed at reducing the lower limb demands within 115–170° trunk-thigh angle may improve the feasibility of sustaining the perched posture’.
Put simply, without enhanced ‘perching’ support, any reported improvement of lumbar posture, or decreased prevalence of cumulative back disorders, will be compromised by additional stress on the lower limbs.
[i] Jeremiah Rodriguez, ‘Perching could reduce lower back pain more than sitting, standing: new study’ (20 February 2019 CTV News) <https://www.ctvnews.ca/health/perching-could-reduce-lower-back-pain-more-than-sitting-standing-new-study-1.4305447> accessed 28 February 2019.
[ii] Mamiko Noguchi et. al, Are hybrid sit-stand postures a good compromise between sitting and standing? Ergonomics (14 Feb 2019) 10.1080/00140139.2019.1577496> accessed 28 February 2019.