Nancy Black

Muscle force prediction: can we rely on musculoskeletal model estimations? A case study on push force exertions with the upper limb

Muscle force prediction: can we rely on musculoskeletal model estimations? A case study on push force exertions with the upper limb S. Duprey, L. Savonnet, N. Black & X. Wang a Université de Lyon, Lyon, France b Université Claude Bernard Lyon 1, Villeurbanne, France c LBMC Laboratoire de Biomécanique et Mécanique des Chocs, IFSTTAR, Bron, France d Département de génie mécanique, Faculté d’ingénierie, Université de Moncton, Moncton, Canada Published online: 20 Aug 2015.

Isometric Pull and Push Strengths of Paraplegics in the Workspace: 1. Strength Measurement Profiles

The isometric strength profiles of male and female paraplegics were determined for pull and push strengths in the normal, maximum, and extreme working reach envelopes. A computerized isometric strength measurement system was designed and constructed for the purpose. The strongest pull location was at extreme reach vertically above the shoulder and the strength values for males and females were 473 and 318 newtons (N), respectively. The strongest push location was at maximum reach, at vertical (ϕ) angle of 45° and at horizontal (θ) angle of 45° for males and at 0° for women and the strength values were 235 and 172 N, respectively. The nature of the strength profiles was found to be similar for both the sexes. The pull and push strengths of the female were 77 and 68% that of the male, respectively.

Isometric Pull and Push Strengths of Paraplegics in the Workspace: 2. Statistical Analysis of Spatial Factors

The effect of reach levels, horizontal angles, and vertical angles on isometric pull and push strengths of male and female was determined. Highly significant increases in men’s push strength were found between extreme to maximum reaches, and from extreme to normal reaches. However, for women’s push strength, a significant increase was found only between extreme to maximum reach. Significant or highly significant increases were found in men’s and women’s pull strength between the horizontal angle (θ) sagittal through the active shoulder (90°) and other angles (0, 45, and 135°). However, for men’s push strength, highly significant increases were found between the horizontal angle 45° from the frontal plane, and other angles. For women’s push strength, significant or highly significant increases were found between the horizontal angles 0° and angles of 90 and 135°. For men’s and women’s pull strength, significant or highly significant increases were found between the vertical angle (ϕ), 90°, and other angles (–20, 0, and 45°). Similar increases were found for women’s push strength between the 45° angle and other angles. In the design of a workstation for paraplegics that requires pull and push forces, consideration must be given to the spatial factors.

Postural and Perception Variations When Using Manually Adjustable and Programmable Sit–Stand Workstations in an Emergency Call Center

OCCUPATIONAL APPLICATIONS Two styles of sit–stand workstations were tested in an emergency (911) call center to quantify postural stress and perception variations. The usual manually adjusted electrically controlled sit–stand workstation was compared with a programmable workstation that automatically changed between seated and standing heights, made forward–backward adjustments, and rotated around the user regularly during a 20-minute cycle. Over 2 working days, neck and seated trunk postures improved with the programmable workstation. Manually controlled sit–stand workstations were not adjusted with the regularity recommended to minimize musculoskeletal discomfort. While seven perceptual measures did not significantly vary between workstations, two others worsened with the programmable workstation: general discomfort and back pain. Participant comments suggested opportunities for design refinements. User training was not included here but would normally further improve results. The programmable workstation improved posture over the manually adjusted workstation, although design refinements and user training in office ergonomics are recommended to maximize benefits. TECHNICAL ABSTRACT Background: Call center workers have high musculoskeletal discomfort, and emergency (911) center workers are among the most affected. Despite many centers including manually controlled sit–stand workstations that facilitate postural changes, these are not typically adjusted with the regularity recommended to minimize musculoskeletal discomfort. Thus, underuse or improper use may be barriers to preventing musculoskeletal disorders and discomfort. Purpose: This study investigates posture and perception of physical factors when using a powered dual-surface manually adjustable workstation and a powered programmable adjustable workstation. Methods: Twelve 911 call-center operators participated. For each workstation, postures were recorded using video cameras over a working day. Nine perception factors were captured at the end of each day using a visual analog scale. Results: Programmable workstation use resulted in significantly lower incidence of at-risk postures in the neck and back and more frequent standing. Perception did not vary significantly between workstations except for an increase in back pain and general discomfort with the programmable workstation. Conclusions: This limited sample exposure to a programmable moving workstation concept should be pursued, though with refinements in larger populations to improve musculoskeletal health of workers in high-stress sedentary environments and should be combined with training. Current observations may be applied to improve programmable workstation aspects that are contributing to perceived discomforts.

An experimental investigation on push force and its perception during a flexible hose insertion task encountered in a truck assembly line

The push force and its perception when inserting a flexible hose laterally into a connector were investigated. Effects of hose diameter, glove, target position and obstacle condition were studied. Maximum voluntary insertion forces (MVFs) under similar working conditions were also measured. The larger the diameter, the higher the force required. The peak axial forces for the hoses of 6, 12 and 16 mm in diameter were on average respectively 94, 122 and 184 N, representing 45%, 61% and 93% of MVF. Glove condition, target position and obstacle did not significantly affect the axial insertion force and moment, but they did affect effort perception. Lower effort was perceived with gloves and high and near position. High intra- and inter-individual variability in insertion force for a given hose may suggest that feedback of successful insertion was insufficient. The recognition of a successful insertion must be ensured to avoid unnecessary extra force exertion. Practitioner summary: The effects of glove, hose diameter, target location and obstacle on push force and its perception were studied when inserting a flexible hose. Solutions for improving the recognition of a successful insertion and the hose/connector system design must be found to reduce force exertion to safe levels.

Observed postural variations across computer workers during a day of sedentary computer work

Sedentary computer work is widespread and typically occurs at a fixed-height seated workstation. Both neutral and at-risk postural classes of the back and neck were observed among 11computer-intensive workers using such workstations who had reported high discomfort levels. Four video recordings of approximately 1 hour each over the working day were analyzed to determine the percent duration and number of observations of each body and neck posture. Risky slouching (32.3% ±17.3%) and neck forward postures (16.9% ±12.3%) varied significantly by participant but not by time of day. Absence from video field of view of the workstation was not negligible, occurring 23.8%±14.8%. Postural changes of slouch and neck forward occurred several times during each recording (4.8±1.9 and 2.5±0.9, respectively) and varied significantly by participant but not over the day. Despite these postural adjustments, the prevalence of risky postures suggests that static workstations are fundamentally problematic.

Human Factors/Ergonomics Education and Certification: The Canadian Experience

The Canadian College for the Certification of Professional Ergonomists (CCCPE) is responsible for ensuring certificants (CCPE and AE) meet minimum educational levels and at least four years work practice (for CCPE). The Association of Canadian Ergonomists – Association canadienne d’ergonomie supports the CCCPE but each educational institution determines the number and scope of ergonomics course offerings. Relevant courses exist at institutions across Canada, with the exception of the full-time programs in the Prairie provinces, but in limited number. Only four programs are designed currently to ensure graduates qualify for AE, two in Ontario in English for Kinesiology students and two in Quebec in French open to various undergraduate degree holders. Nineteen post-secondary institutions offer some ergonomics courses but their number and focus varies, most frequently offered within kinesiology or movement science programs. The number of qualified, certified human factors and ergonomics practitioners is growing well, but could improve with more courses for those in the Prairie region and those with non-kinesiology backgrounds outside of Quebec.

Postural Deviation Gestures Distinguish Perceived Pain and Fatigue Particularly in Frontal Plane

Office workers frequently report discomfort in the neck, back and shoulders. Extreme and prolonged static postures are known risk factors. Sit-stand workstations encourage regular postural changes and tend to reduce discomfort. Head and upper back deviations were recorded for ten adults entering data using a seated desk and two sit-stand desks following three twenty-minute cycles with 6 or 9 min standing. Participants reported their perceived back pain, neck pain and fatigue following each recording.

Assessing ergonomic and postural data for pain and fatigue markers using machine learning techniques

Ergonomic data obtained from trials with human participants at a number of workstations are evaluated in terms of whether different workstations elicit different fatigue and pain responses. Data is analyzed using a pair of simple machine-learning based classifiers in order to identify activities associated with the workstations that lead to or avoid pain and fatigue. Results indicate that information content sufficient to predict pain and fatigue is present in this data, with evidence of information increase consistent with postures held for a period of time. Additional analysis will be performed to isolate postures associated with fatigue and pain in follow-up work.