Neal Wiggermann

Risk factors for lower extremity fatigue among assembly plant workers

BACKGROUND Work-related fatigue of the lower extremities is a known cause of lost productivity and significant employer costs. Common workplace solutions to reduce fatigue levels include anti-fatigue matting, shoe orthoses, or sit/stand work stations. However, assessment of these anti-fatigue measures within the workplace has been limited. METHODS This was a cross sectional study in an automotive assembly plant on employees with at least 6 months tenure. Subject data were collected via questionnaires including Likert-scale questions to define fatigue severity. Jobs were evaluated for lower extremity ergonomic exposures via videotaping, pedometers, interviews, and industrial engineering records. RESULTS Lower extremity fatigue at the end of the work day was associated with a higher prevalence of smoking, rheumatoid arthritis, job dissatisfaction, use of shoes with firmer outsoles, and increased time on the job spent standing or walking. Supervisor support and increased time spent on carpet were protective. Lower extremity fatigue that interfered with activities outside of work had additional risk factors including higher BMI, prior diagnosis of osteoarthritis, and increased hours per week spent working. CONCLUSIONS While these results identify carpet as being protective against lower extremity fatigue, no similar relationship was identified for anti-fatigue mats. No adverse relationship was found between hard surfaces such as concrete and lower extremity fatigue. Given the high costs associated with work-related fatigue, future areas for potential intervention include smoking cessation, specific shoe recommendations, and enhancing psychosocial aspects of work such as supervisor support.

Inter-Worker Variability in Lower Body Postures During Assembly Line Work: Implications for Exposure Assessment

This study evaluated inter-worker variability in lower body posture and work activity during highly-structured assembly line work. Data were collected from 79 unique assembly line workstations in an engine manufacturing plant. Because the plant utilized work teams, 4–8 workers rotated through each workstation. At least 30 min of videotape was collected from at least three workers at each workstation. A computer-assisted work sampling procedure randomly selected 200 video “freeze-frames” for each worker. Lower body posture/movement (e.g., sit, stand, walk, etc.) was determined for each frame and used to estimate the percentage of time the worker spent in various postures and activities. Chi-square analyses were performed for each workstation to assess the significance of inter-worker differences. Due to variations in individual work methods, significant differences (p <.05) were found at 57 out of 79 workstations (72%). The greatest differences occurred when workers had the option to choose between standing and sitting (significant in 8 of 8 cases; in extreme examples, sit time ranged between 0–100% on one job, and 6.5–98% on another). Studying a single worker (or “proxy”) can contribute to substantial error when estimating exposures in workplace studies of ergonomic stressors, since the proxy may not be representative of all workers who perform the job. Individual measurements are preferable, particularly for jobs where workers have substantial latitude to develop individualized work methods.

Risk factors for foot and ankle disorders among assembly plant workers

BACKGROUND Jobs that necessitate prolonged standing and walking activities are commonly associated with workers complaints of foot and ankle pain. The objective of this study was to determine the relative contributions of work activity (time spent standing, walking, or sitting), floor surface characteristics, weight, BMI, age, foot biomechanics, and other demographic and medical history factors to the prevalence of foot and ankle disorders. METHODS A cross-sectional observational study design was used to evaluate employees of an engine manufacturing plant. The main outcome variable was foot or ankle disorders defined by pain and a positive physical examination. The independent variables included baseline demographics, medical history, ergonomic exposures, psychosocial factors, shoe characteristics and foot biomechanics. RESULTS Twenty-four percent of the cohort met the case definition of foot/ankle disorder with 10% defined as new cases. Fifty-two percent had symptoms of foot/ankle. An increased risk of presenting with foot/ankle disorders was associated with high metatarsal pressure on gait assessment, increased time spent walking, female gender, reported high job dissatisfaction, a history of rheumatoid arthritis, osteoporosis or vascular disorder. For the truck/forklift drivers, an increased number of times getting in and out of the vehicle was associated with a higher prevalence of ankle/foot problems. CONCLUSIONS An increased risk is associated with higher metatarsal pressure and increased time spent walking. These findings suggest several options for primary and secondary prevention strategies. The use of shoe orthoses with a medial longitudinal arch and metatarsal pad as well as including optional sit/stand workstations may be helpful.

Effects of Anti-Fatigue Mats on Perceived Discomfort and Weight-Shifting During Prolonged Standing:

Objective: The aim of this experiment was to investigate the effects of anti-fatigue mats on perceived discomfort and behavioral responses (weight-shifting between the feet) during prolonged standing. Background: Prolonged standing is a common requirement in the workplace and is a well-known cause of discomfort. Anti-fatigue mats have been shown to reduce discomfort resulting from standing, but no study has identified a particular mat that performs better than others or examined the relationship between discomfort and weight-shifting. Methods: Participants stood for 4 hours on four commercially available “anti-fatigue” mats and a hard surface (control condition). Subjective ratings of discomfort were measured, and in-shoe pressure was recorded and used to evaluate weight-shifting during standing. Results: Compared to the control condition, after 4 hours of standing discomfort was reduced by three of the four mats, but discomfort ratings did not significantly differ among mats. However, significant differences among mats were found in the frequency of weight-shifting, and weight-shifting was positively correlated to discomfort. Conclusion: These results suggest that subjective reports of discomfort were not sufficiently sensitive to detect differences among mats for the experimental conditions tested. Behavioral responses, specifically weight-shifting between feet, may provide a more sensitive alternative to subjective reports.

Quantification of patient migration in bed: catalyst to improve hospital bed design to reduce shear and friction forces and nurses' injuries.

Objective: The study objective was to quantify the movement of hospital bed occupants relative to the bed in typical bed articulations. Background: Movement of a patient in bed results in two common adverse events: (a) increase in shear and friction forces between the patient and bed, which are extrinsic pressure ulcer risk factors, and (b) musculoskeletal injuries to nurses, resulting from repositioning patients who have migrated down in bed. Method: The study involved 12 participants who lay supine in three hospital beds, which were articulated to common positions. Body movement relative to the bed was quantified with the use of motion capture. Cumulative movement, net displacement, and torso compression (shoulder to trochanter distance) were calculated for different bed types and bed movements. Results: Bed design and bed movement had a significant effect on most of the dependent variables. Bed design (e.g., type) influenced cumulative movement by up to 115%, net displacement by up to 70%, and torso compression by about 20%. Bed movement (e.g., knee elevation) reduced cumulative migration by up to 35%. Conclusion: The quantification of patient migration provides a metric for evaluating the interaction between body and bed surfaces. Overall, the measures were sensitive to design changes in bed frames, bed articulations, and mattress inflation. Application: Documentation of the cumulative movement, net displacement, and torso compression provides hospital bed designers quantifiable measures for reducing migration and potentially shear and friction forces when designing bed frames, bed articulations, and mattresses. Optimization of these metrics may ultimately have an impact on patient and caregiver health.

Ergonomic evaluation of brake pedal and push handle locations on hospital beds

Transporting patients in hospital beds is a physically demanding activity performed by healthcare workers and bed design may moderate the risk of injury. Nine healthcare workers participated in a study to investigate how brake pedal location affected maximal voluntary exertion (MVE) force and the level of acceptable force for engagement. Preferred and acceptable push heights when maneuvering a bed were also evaluated. The method of limits was used to determine acceptable forces and push heights. Results demonstrated that pedal depth, clearance above, and clearance behind the pedal significantly affected MVE force and acceptable force. Preferred push height was approximately at elbow level and a single height would not accommodate the user population. These findings provide important considerations for hospital bed design. The method of limits was a valid and reliable approach for evaluating user acceptance of design inputs characterized by continuous variables and may be useful in other design evaluations.

Biomechanical Evaluation of a Bed Feature to Assist in Turning and Laterally Repositioning Patients.

Objective: This study investigated the effects of hospital bed features on the biomechanical stresses experienced by nurses when turning and laterally repositioning patients. Turn Assist, a common feature in ICU beds that helps to rotate patients, and side rail orientation were evaluated. Background: Manual patient handling is a risk factor for musculoskeletal injury, and turning patients is one of the most common patient handling activities. No known studies have evaluated bed attributes such as the Turn Assist feature and side rail orientation that may affect the stresses experienced by the nurse. Method: Nine female nurses laterally repositioned and turned a 63-kg and 123-kg subject on an ICU bed while motion capture, ground reaction forces, and hand force data were recorded. Loading of the spine and shoulder was modeled using 3D Static Strength Prediction Program (3DSSPP). Results: Spine compression and shear forces did not exceed recommended limits when turning or laterally repositioning. However, the mean pull forces required to manually laterally reposition even the 63-kg subject was 340 Newtons, more than 50% greater than limits established in psychophysical testing. Turn Assist considerably reduced spine loading and pull forces for both turning and laterally repositioning. Lowering side rails reduced spinal compression by 11% when turning patients. Conclusion: Laterally repositioning patients as part of turning may pose an injury risk to caregivers. Turn Assist reduces physical loading on nurses when turning and repositioning patients. Application: Caregivers should consider using Turn Assist and other aids such as mechanical lifts or sliding sheets especially when turning patients requires lateral repositioning.

Risk Factors for Hip Problems Among Assembly Plant Workers

Objective The objective of this study was to determine the relative contributions of work activity (time spent standing, walking or sitting), floor surface characteristics, weight, BMI, age, foot biomechanics, and other demographic and medical history factors to the prevalence of hip disorders. Methods A cross-sectional observational study design was used to engine assembly plant workers. The main outcome measure was the finding of a hip disorder. The independent variables included baseline demographics, medical history, ergonomic exposures, psychosocial factors, shoe characteristics and foot biomechanics. Results Logistic regression revealed that increasing age, female gender, pes planus, smoking, history of a knee or hip injury, and a history of rheumatoid arthritis were significant risk factors while time on carpeted surfaces was protective. Conclusions Hip disorders are associated with a history of biomechanical trauma to the hip but also from gait abnormalities such as pes planus.

Effect of Flooring on Discomfort and Behavioral Responses to Prolonged Standing

Prolonged standing is a common requirement in the workplace and is a well-known cause of discomfort. This experiment investigated the effect of material properties of flooring surfaces on perceived discomfort during prolonged standing. Behavioral responses to prolonged standing such as fidgeting (or weight-shifting between feet) were also analyzed. Participants stood for four hours on each of four “anti-fatigue” mats and a hard surface (control condition) while discomfort ratings and in-shoe pressures on the feet were recorded. Results showed that discomfort ratings did not significantly differ among mats, but all mats were more comfortable than the hard floor during the fourth hour of standing. The frequency of fidgeting was affected by flooring surface and was correlated to discomfort. The results indicate that if differences in discomfort between these mats exist, they require a longer standing duration to be observed. The behavioral results provide a possible proxy measurement for discomfort, as well as information that can be used to direct future physiological and biomechanical research.

The Effect of Patient Migration in Bed on Torso Elevation

BackgroundElevating the hospital head of bed (HOB) to at least 30° is recommended practice to reduce the risk of ventilator-associated pneumonia (VAP) in mechanically ventilated patients. However, this common practice prescribes the position of the bed and not of the patient, which could be significantly different. ObjectiveThe aim of this research was to determine the relationship between patient migration in bed and anatomic torso angle. MethodsTen healthy participants were positioned in a hospital bed that was raised from flat to 30° and 45° HOB elevations. Prior to bed movement, participants were aligned to different locations along the length of the bed to represent different amounts of migration. A motion capture system was used to measure torso angle and migration toward the foot of the bed. The relationship between torso angle and migration was estimated by linear regression. ResultsPatient migration resulted in lower torso angles for both 30° and 45° HOB articulations. A migration of 10 cm resulted in a loss of 9.1° and 13.0° of torso angle for HOB articulations of 30° and 45°, respectively (for 30° articulations: &bgr; = −0.91, R2 = .96; for 45° articulations: &bgr; = −1.30, R2 = .98). DiscussionMigration toward the foot of the bed flattens the torso. To maintain a torso angle that is likely to protect against VAP, healthcare providers need to manage both HOB angle and migration. Protocols and equipment that minimize patient migration will help support effective clinical practice. Future research on patient migration, as it relates to VAP or other outcomes, should measure patient torso angle to allow accurate translation of the results to care practice.