Table 2. Methods and outcomes of biomechanical measurements in the reviewed articles.

Author (Year)	Measurement	Instrument (methods)	Manufacturer	Biomechanical measurement outcome
Chen et al. (2014)	Body-mattress contact pressure Sleep quality/polysomnography Subjective feedback	ABW body pressure measurement system ALICELE PSG polysomnograph Questionnaire, yes/no questions on hardness, comfortability, and difficulty to fall asleep	NS Philips Co., Andover, USA NA	Max pressure, min pressure, total stressed area
Denninger, Martel & Rancourt (2011)	Body dimensions Body mass distribution Force-compression curve of foam cubes loaded with body volume slice Spinal curvature	POWERSHOT A610 camera Custom-made apparatus with load cells ANSYS, finite element method Optotrak 3020 optical measurement system	Canon, Ontario, Canada NS Ansys Inc., Pittsburgh, USA Northern Digital Inc., Ontario, Canada	Location of vertebra, mass of each body volume slice, force-compression curve of individual mattress cubes
Deun et al. (2012)	Body surface contour Sleep quality/polysomnography Spinal curvature Subjective feedback	IKÉLO optical measurement system Dream system, polysomnograph Indentation sensors embedded in Dynasleep mattress (Spinal curvature was simulated and estimated by indentation using a human model personalized based on the results of body contour measurements) Questionnaires:Karolinska sleepiness scale, profile of mood state, stress/arousal adjective checklist, activation/deactivation adjective checklist	Custom8, Leuven, Belgium Medatec, Brussels, Belgium Custom8, Leuven, Belgium NA	NA (The results of biomechanical measurement were not included)
Esquirol Caussa et al. (2017)	Body dimensions Body-mattress contact pressure	Kinect camera and tape Surface with integrated pressure capacitive sensors	Microsoft, Washington, USA NS	Number of pressure points exceeded the threshold level in head and body regions
Lee et al. (2015)	Body-mattress contact pressure Subjective feedback	Body pressure measurement system Questionnaires: pain score using visual analogue scale, faces pain rating scale, Iowa pain thermometer	Tech Storm, DaeJeon, Korea NA	Mean pressure in different body regions (head, shoulder, right/left arm, lower back, pelvic girdle, right/left leg)
Lee et al. (2016)	Body-mattress contact pressure Subjective feedback	Body pressure measurement system Questionnaires: pain score using visual analogue scale, faces pain rating scale, Iowa pain thermometer	Tech Storm, DaeJeon, Korea NA	Mean pressure in different body regions (head, shoulder, right/left arm, lower back, pelvic girdle, right/left leg)
Leilnahari et al. (2011)	Spinal curvature	(1a) DCR-TRV356E cameras (1b) BRG.LIFEMOD2007, musculoskeletal modeling(spinal curvature was simulated and estimated by modeling and validated by captured images)	(1a) Sony Co., Tokyo, Japan (1b) LifeModeler, San Clemente, US	Location of vertebra centreπ-P8: angle between the thoracic spinal line and the lumbar spinal line
López-Torres et al. (2008)	Mannequin-mattress contact pressure Subjective feedback	PLIANCE 19 P body pressure measurement system Questionnaire: perceived firmness with hands, buttocks, in supine/lateral posture; difficulties in rolling over and getting up; four-point grading in comparing overall comfort	Novel, Munich, Germany NA	Max pressure; average pressure; average contact area
Low et al. (2017)	Body-mattress contact pressure	TEKSCAN 5400N pressure mapping sensor	Tekscan, South Boston, USA	Peak body contact pressure and contact area in back torso and buttocks for supine; side torso (inclusive upper arm and shoulder) for lateral; front torso (chest and stomach) for prone
Palmero et al. (2017)	Body surface contour Body-mattress contact pressure	Kinect camera In-house built capacitive pressure-sensitive mattress sensor	Microsoft, Washington, USA NS	Number of pressure points exceeded the threshold level in head and body regions
Park, Kim & Kim (2009)	Body-mattress contact pressure Subjective feedback	Self-assembled force-sensing resistor matrix Questionnaire, five-point scale of comfortability in nine body regions (neck, shoulder, back, elbows, lumbar, hand/wrist, hip/thigh, knee, ankle)	NS NA	Fraction of body pressure on eight transverse bed sectors
Verhaert et al. (2011)	Body dimensions Body surface contour Spine curvature Sleep quality/polysomnography Subjective feedback	Calliper and tape IKÉLO optical measurement system 3D Vario rasterstereograph (Spinal curvature was estimated using an algorithm based on body dimension and surface measurements) Dream System, polysomnography Questionnaire: Karolinska sleepiness scale, arousal scale of Cox’s stress, arousal adjective checklist, profile of mood states.	NS Custom8, Leuven, Belgium Vialux, Chemnitz, Germany Medatec, Brussels, Belgium NA	P1: angle between the VP-DM line and the horizontal axis; P2: mean distance between the spinal curvature line and its least square line; P3: angle between the least square line and the horizontal axis; P4: angle between thoracic and lumbar least square lines.
Verhaert et al. (2012a)	Body dimensions Body surface contour Spinal curvature	Calliper and tape IKÉLO optical measurement system Indentation sensors embedded in Dynasleep mattress. (Spinal curvature was simulated and estimated by indentation using a human model personalized based on the results of body contour measurements)	NS Custom8, Leuven, Belgium Custom8, Leuven, Belgium	P1: angle between the pelvis-shoulder line and the horizontal line; P2: angle between the least square line of the spine curvature and the horizontal line; P3: angle between thoracic and lumbar least square lines.
Verhaert et al. (2012b)	Body surface contour Body surface contour (for validation) Spinal curvature	IKÉLO optical measurement system zSnapper 3D scanner Spinal curvature was simulated and estimated based on the mass distribution of body portions and the human model personalized by body surface measurements and validated by 3D scanning	Custom8, Leuven, Belgium Vialux, Chemnitz, Germany NA	Least square line of spinal points (α); angle between lumbar and thoracic parts of the spine (γ). The score (EBS_L) featured a weighted combination of α and γ
Verhaert et al. (2013)	Spinal curvature	Indentation sensors embedded in Dynasleep mattress. (Spinal curvature was estimated using indentation data and a personalized human model)	Custom8, Leuven, Belgium	P1: angle between the horizontal line and the line connecting starting and ending points of the spine; P2: mean unsigned distance from the spine to its least square line; P3: angle between the horizontal line and the least square line; P4: angle between the thoracic and lumbar least square line; P5: RMSD between the spine curvature and the reference spine; P6: difference between the lordotic angle of the spine curvature and the reference spine; P7: difference between the kyphotic angle of the spine curvature and the reference spine; P1–P4 for lateral posture; P5–P7 for supine posture.
Wu, Yuan & Li (2018)	Back surface contour Spinal alignment/mattress indentation Body-mattress contact pressure	3D body scanning system ANSYS finite element model Tactilus body pressure measurement system	NS; ANSYS Inc., Pennsylvania, US; Sensor Products Inc., Madison, US	Max pressure, total pressure and the contact area of thoracic, lumbar and buttock regions;LLT, LLB: thoracic-lumbar and lumbar-buttock distances between standing and supine lying; similarity of back surface contour between measured upright standing and predicted supine lying.
Yoshida, Kamijo & Shimizu (2012)	Internal stress, head & chest displacement Subjective feedback	ANSYS finite element model Questionnaire, seven-grade scale on the feeling of firmness, mattress preference, firmness preference, sinking preference, comfort for different regions of the body	ANSYS Inc., Pittsburgh, USA; NA	Von Mises stress of cervical vertebra; sinking displacement of the head and chest
Zhong et al. (2014)	Spinal curvature	Custom-made indentation measuring bar embedded in the mattress (Spinal curvature was estimated by fitting a curve on the indentation points)	NA	Back-inclination line: line joining the lower points of the curve at the upper back and the hip; back-hip inclination angle (β): angle between the back-inclination line and the horizontal axis; CTh, ThL, LS (angle between the region line and the back-inclination line); depth of lumbar lordosis (DL)

Note:

NA, not applicable; NS, not specified; VP, vertebral prominens; DM, the midpoint of the dimples of the posterior superior iliac spine; RMSD, root mean square distance; CTh, cervicothoracic angle; ThL, thoracolumbar angle; LS, lumbosacral angle.