An Electromyography-Based Constitutive Law for Force Generation in Skeletal Muscle-Part II: Model Validation on the Ankle Joint Complex.

Part II of this study evaluates the predictive ability of the skeletal muscle force model derived in Part I within the ankle joint complex. The model is founded in dimensional analysis and uses electromyography and the muscle force-length, force-velocity, and force-frequency curves as inputs. Seventeen subjects (eight males, nine females) performed five different exercises geared toward activating the primary muscles crossing the ankle joint. Motion capture, force plate, and electromyography data were collected during these exercises for use in the analysis. A constant, Km, was calculated for each muscle of each subject using four of the five exercises. The fifth exercise was then used to validate the results by treating the moments due to muscle forces as known and all other components in Euler's second law as unknown. While muscle forces cannot be directly validated in vivo, methods can be developed to test these values with reasonable confidence. This study compared moments about the ankle joint due to the calculated muscle forces to the sum of the moments due to all other sources and the kinematic terms in the second Newton-Euler equation of rigid body motion. Average percent errors for each subject ranged from 4.2% to 15.5% with a total average percent error across all subjects of 8.2%, while maximum percent errors for each subject ranged from 33.3% to 78.0% with an overall average maximum of 52.4%. Future work will examine sensitivity analyses to identify any potential simplifications to the model and solution process, as well as validate the model on a more complex joint system to ensure it still performs at a satisfactory level.

A Passive Back-Support Exoskeleton for Manual Materials Handling: Reduction of Low Back Loading and Metabolic Effort during Repetitive Lifting.

OCCUPATIONAL APPLICATIONSGlobalization and eCommerce continue to fuel unprecedented growth in the logistics and warehousing markets. Simultaneously, the biggest bottleneck for these industries is their human capital. Where automation and robotic solutions fail to deliver a return on investment, humans frequently take over handling tasks that place harmful loads and strains on the body. Occupational exoskeletons can reduce fatigue and strain by supporting the lower spine and are designed to prevent work-related musculoskeletal disorders and other injuries. They are a mid- to long-term investment for industries to improve ergonomic conditions in workplaces, with the potential for reducing absences from work, sick days logged, and workers compensation claims. To examine the effectiveness of the newly introduced Paexo Back exoskeleton, a study was completed with 10 participants who completed manual load handling tasks with and without the exoskeleton. Key findings include significant reductions in metabolic effort and low back loading when the exoskeleton is worn.

TECHNICAL ABSTRACTBackground: Work-related low back pain is a major threat to workers and society. Some new commercial and prototype exoskeletons are designed to specifically control the development of such disorders. Some beneficial effects of these exoskeletons have been reported earlier. Purpose: Determine the potential benefits of a newly introduced exoskeleton, Paexo Back, which is designed to reduce low back loading during lifting tasks. Methods: Ten healthy subjects participated in this study. To replicate a typical workplace situation, a repetitive lifting task with and without the exoskeleton was performed. For 5-min periods, the participants repeatedly lifted a 10-kg box from the floor onto a table and then placed it back on the floor. Effects of exoskeleton use were assessed using a diverse set of outcomes. Oxygen uptake and heart rate were measured using a wireless spiroergometry system. Activation levels of back, abdominal, and thigh muscles were also measured using a wireless electromyographic system. Kinematic data were recorded using an optoelectronic device, and ground reaction forces were measured with two force plates. Joint compression forces in the lower spine (L4/L5 and L5/S1) were estimated using the AnyBody™ Modeling System during the upward lifting portion of the lifting task (bringing the box to the table). Results: Using the exoskeleton resulted in significant reductions in oxygen rate (9%), activation of the back and thigh muscles (up to 18%), and peak and mean compression forces at L4/L5 (21%) and L5/S1 (20%). Conclusions: These results show that using the tested exoskeleton for a lifting task contributes to an increased metabolic efficiency, a reduction in the back muscle activation required to conduct the task, and a reduction in low back loading.