Does a ‘Back App’ ergonomic stool reduce the muscular effort of unsupported sitting?

Background: 'Back App' is a novel ergonomic stool whose seat design increases thigh-trunk angle similar to a saddle chair. It features an optional dynamic setting by means of an adjustable stability ball. To date no studies have investigated trunk muscle activity on saddle seats and studies are inconclusive as to the effect of dynamic seats. Objectives: The primary aim was to compare a 'Back App' stool with a standard stool and determine if it alters trunk muscle activity and discomfort during a typing task and if it alters trunk muscle activity during an optimal sitting posture. Secondary aim was to see if the dynamic 'Back App' setting increases trunk muscle activity. Methods: A repeated measures study design was used (n=10 subjects). Surface Electromyography of 6 superficial trunk muscles was recorded for; (i) a 10-minute typing task and (ii) a 1-minute neutral lordotic sitting posture task (O'Sullivan et al, 2010). Readings were compared for a standard stool, a stable 'Back App' stool and a dynamic 'Back App' stool. Discomfort was assessed using the Body Part Discomfort Scale (BPDS). Results: Iliocostalis Lumborum par Thoracic (ICLT) and Superficial Lumbar Multifidus (SLM) activity was reduced on both 'Back App' stools compared with the standard stool: significant for ICLT during the typing task (P=0.028) and SLM during optimal sitting posture (P=0.032). Mean discomfort did not differ significantly. Conclusions: The 'Back App' stool significantly reduces the effort of specific back muscles required for unsupported habitual and optimal sitting postures. The dynamic 'Back App' setting did not significantly alter trunk muscle activity.