Selected movement and force pattern differences in rail- and rung-climbing of fire apparatus aerial ladders at 52.5° slope.

This study compares human climbing performance, including climbing speed and movement and force patterns, between rail- and rung-climbing styles for a moderate aerial ladder slope (52.5°). Hand and foot movements and forces were recorded for 9 male and 10 female firefighters as they ascended and descended a 3.4-m ladder using elevated handrails (rail-climbing) or rungs (rung-climbing) for hand support. The results indicated that climbers used three or more points of contact 54% of the time for rung-climbing and 100% of the time for rail-climbing. Furthermore, rail-climbing was 10% faster than rung-climbing. In rail-climbing, the lateral hand forces were mostly directed away from the body; while during rung-climbing, they were alternated in lateral and medial directions. Overall, the results suggested that rail-climbing provides better control over body positioning and faster climbing speed. Furthermore, the continuous contact of both hands in rail-climbing may reduce the fall risk by facilitating the recovery from a slip or perturbation.

Impact of the seated height to stature ratio on torso segment parameters.

Ergonomic modelling programmes such as the Three Dimensional Static Strength Prediction Programme (3DSSPP) are valuable tools for assessing strength capabilities and risk assessment. These tools rely on accurate, representative inputs in the form of body segment parameters (BSPs). The upcoming version of 3DSSPP will employ BSPs for the torso, split into thoracic, lumbar and pelvis segments in order to more precisely determine spinal forces and injury risks. This study determines the impacts of age, body mass index and the estimated seated height to stature ratio (SHS) on these full and split torso parameters in a sample of working American adults. The results show that all of these metrics have significant relationships with the BSPs of interest, indicating that they must be accounted for when determining these parameters. A sensitivity analysis performed in 3DSSPP demonstrates that varying the parameters inputs will have large effects on L5/S1 compression force calculations. Practitioner Summary: Current anthropometric data sets for ergonomic applications do not account for wide ranges of age, BMI and overall body shape on segment parameter calculations. This study quantifies the associations of age, BMI and the seated height to stature ratio on full and split torso segment parameters. Abbreviations: 3DSSPP: Three-Dimensional Static Strength Prediction Program; BMI: body mass index; BSP: body segment parameter; BW: body weight; COM: centre of mass; DXA: dual energy x-ray absorptiometry; RG: radius of gyration; SHS: seated height to stature ratio; SL: segment length.

Effects of aerial ladder rung spacing on firefighter climbing biomechanics.

This study investigated the effects of aerial ladder rung spacing on firefighter climbing biomechanics. Ten female and 9 male firefighters ascended and descended instrumented ladders with rungs spaced at 356 mm (current design) and 305 mm in a laboratory setup. The climbing tests were performed at five ladder slope and handrail conditions: 30° with low (305 mm) and high (914 mm) handrails, 52.5° with and without a low handrail, and 75° without a handrail. Foot and hand forces and body movements were recorded and used to calculate joint moments of the upper and lower body. Reduced rung spacing resulted in reduced foot forces, reduced hand forces, and reduced ankle transverse moment. It was also associated with increased climbing speed for female climbers, and increased ankle vertical overshoot. The results indicate that reduced rung spacing on aerial ladders may lead to lower biomechanical stress; better climbing efficiency and safety; and reduced climbing speed disparity across sexes.

Maximum hand-rung coupling forces in children: the effects of handhold diameter.

OBJECTIVE: To quantify the effect of handhold size (diameter) on the maximum breakaway strength between a hand and handhold for children. BACKGROUND: Falls from playground equipment are a major cause of childhood injury and death. It is unclear if recommendations for handholds on playground equipment are too broad. METHODS: Breakaway strength was defined as the maximum quasistatic force that can be exerted on a grasped object before the object is forcibly pulled from the grasp. Hand anthropometry, grip, and breakaway strengths were measured for 397 children between the ages of 6 and 11 years. Three cylindrical handhold diameters were tested. RESULTS: Breakaway strength was significantly affected by handhold size, gender, and hand dominance. Significant covariate predictors for breakaway strength included grip strength, age, and hand breadth. Breakaway strength was reduced for the largest diameter (3.81 cm) for children of all ages. CONCLUSION: Handhold design factors significantly affect the breakaway strength of children. APPLICATION: The results can be used as a basis for design recommendations for hand rungs used by children to reliably support their bodyweight.

The effect of handhold orientation, size, and wearing gloves on hand-handhold breakaway strength.

OBJECTIVE: The aim of this study was to quantify the effect of handhold orientation, size (diameter), and wearing a glove on the maximum breakaway strength between a hand and handhold. BACKGROUND: Manual breakaway strength is known to be greatly reduced for vertical compared with horizontal handholds, but oblique orientations have yet to be studied. METHOD: For this study, 12 young adults (6 female) attempted to hold on to fixed overhead cylindrical handholds with one hand in low-speed simulated falls as forces on the handhold were recorded in two experimental designs. Breakaway strength was measured for (a) three different-sized cylinders in four orientations while the participants were using the dominant hand and (b) a single-sized cylinder in four orientations while the participants were bare-handed or wearing a glove on the nondominant hand. RESULTS: Handhold orientation (p < .001), handhold diameter (p < .001), and wearing gloves (p < .001) significantly affected breakaway strength. Breakaway strength increased 75% to 94% as the orientation of the handhold was moved from vertical to horizontal. Breakaway strength decreased 8% to 13% for large-diameter (51-mm) handholds as compared with smaller diameters (22 mm to 32 mm), depending on orientation. Gloves may increase or decrease the ability to hang on depending on interface friction; greater friction increased breakaway force. CONCLUSION: Handles oriented perpendicular to the pull direction and high-friction gloves provide the greatest breakaway strength. Smaller handhold diameters than predicted by grip strength afford greater capability in these orientations. APPLICATION: These insights can be used to design handholds that increase the ability to support one's body weight and reduce the effort needed to pull or lift heavy items.

The effect of visualization method on the performance of simulated microsurgery tasks.

The operating microscopes may be a significant cause of fatigue and discomfort in surgeons. The need for the microscope to be placed over the operating field forces surgeons to remain at the microscope's eyepieces at an uncomfortable posture for the entirety of the surgery. This study compared the effects on microsurgical task performance for four visualization methods: a monocular microscope, a binocular microscope, a three-dimensional (3D) flat-panel television display and a two-dimensional (2D) flat-panel television display. Eleven subjects each performed two microsurgical tasks and their performance was documented by video camera. The statistical analysis performed indicated utilization of the microscope as a visualization method increased subject performance. No significant difference in performance between the 2D and stereoscopic visualization methods.

Quantification of hand grasp force using a pressure mapping system.

The goal of this study was to use a pressure sensor to measure the force distribution and contact area of the hand when gripping, pushing, and pulling a cylinder. Data was collected from 10 subjects with no hand impairments and from 1 subject with rheumatoid arthritis (RA). Subjects grasped an aluminum cylinder wrapped with a Tekscan pressure sensor and performed each trial at 25%, 50%, and 100% maximum voluntary exertion. A relationship was found between increasing exertion and increasing hand area with increasing hand contact area. The force distribution maps showed the thenar region of the hand exerts the most force during pushing while the metacarpal joint line exerts the highest force during pulling. The third and fourth phalange were found to exert the highest phalange force during gripping. The force distribution maps from the RA subject showed higher thumb forces and distal phalange forces, relative to the entire phalange, compared to the non-impaired subjects. This suggests that the RA subject compensates for the lack of phalange function with the regions of the hand that still function. Future studies should sample individuals with a larger hand area range and sample more individuals with RA.

Quantitative posture analysis of 2D, 3D, and optical microscope visualization methods for microsurgery tasks.

The purpose of this paper is to present a quantitative posture analysis of microsurgery tasks performed with different visualization methods. Microsurgery is traditionally performed using a binocular microscope; however surgeons are constrained by the optical eyepieces and are forced to assume joint angles that deviate away from neutral postures. This may be especially problematic for the neck and can increase surgeon discomfort and fatigue. Alternative visualization methods may improve surgeon posture by eliminating the constraints imposed by the microscope. This study examines both 2D and 3D heads-up displays as possible alternatives. Six subjects performed microsurgical tasks with each visualization methods for four hours. Quantitative posture analysis was done using Maxtraq software that tracks reflective markers on the subjects. The initial analysis of neck, upper arm, and elbow angles found significant differences between each display. A biomechanical analysis found that the differences in angles can result in loads on the neck joint that are twice as high in the microscope than the headsup displays. Although the alternative displays can result in better postures, improvements the display technology is needed to improve microsurgical task performance.

Hand-handhold coupling: effect of handle shape, orientation, and friction on breakaway strength.

OBJECTIVE: The aim was to determine the maximum force that can be exerted on an object before it is pulled or slips from the grasp of the hand ("breakaway strength") for fixed overhead handholds of varying orientation, shape, and friction. BACKGROUND: Many studies have quantified hand strength by having participants squeeze, pull on, or create torque on an object or handle, but few studies have measured breakaway strength directly. METHOD: In two experiments, hand strength was measured as both overhead breakaway strength for handholds typical of fixed industrial ladders and as maximum isometric grip strength measured using a common Jamar grip dynamometer. RESULTS: Breakaway strength was greatest for a fixed horizontal cylinder ("high friction"; 668 +/- 40 N and 691 +/- 132 N for Experiments 1 and 2, respectively), then for a horizontal cylinder that simulated low surface friction ("low friction"; 552 +/- 104 N), then for a vertical cylinder (435 +/- 27 N), and finally, for a vertical rectangular-shaped rail (337 +/- 24 N). Participants are capable of supporting only their own body weight with one hand when grasping the fixed horizontal cylinder. Breakaway strength for both the high- and low-friction horizontal cylinders was significantly greater than isometric grip strength (1.58 +/- 0.25 and 1.26 +/- 0.19 times, respectively). CONCLUSION: Results support the hypothesis that hand-handhold coupling is composed of active (isometric or eccentric finger flexion) and passive (frictional) components. Traditional isometric grip strength alone does not predict the strength of a couple between a hand and a handhold well. APPLICATION: This research shows that handhold shape, orientation, and friction are important in the safe design of grab rails or ladders.

Leg strength in peripheral arterial disease: associations with disease severity and lower-extremity performance.

OBJECTIVE: The purpose of this study was to determine relationships between lower-extremity arterial obstruction, leg strength, and lower-extremity functioning. DESIGN: The study design was cross-sectional. A total of 514 outpatients (269 with ankle-brachial index [ABI] <0.90), aged 55 and older, were identified from three Chicago-area hospitals. Individuals with history of lower-extremity revascularization were excluded. Main outcome measures Strength in each leg, 6-minute walk, 4-meter walking velocity, accelerometer-measured physical activity, and a summary performance score were measured. The summary performance score is a composite measure of lower-extremity functioning, ranging from 0 to 12 (12 = best). The leg with the lower ABI was defined as the "index" leg, and the leg with higher ABI was defined as the "contralateral" leg. RESULTS: Index leg ABI levels were associated linearly and significantly with strength for hip extension (P <.001), hip flexion (P <.001), knee extension (P =.066), and knee flexion (P =.003), adjusting for known and potential confounders. In adjusted analyses, the index ABI was also associated linearly and significantly with strength in the contralateral leg. Adjusting for confounders, including ABI, knee extension strength, was associated independently with functional measures. CONCLUSION: Among patients without prior leg revascularization, strength in each leg is highly correlated with the lower-leg ABI. Leg strength is associated independently with functional performance. Further study is needed to determine whether lower-extremity resistance training improves functioning in patients with peripheral arterial disease.