We performed an ergonomic assessment of a passive upper body exoskeleton at on-site job tasks, using surface electromyography (EMG) to quantify muscular demands at the shoulder. Six workers were assessed during cab assembly, hydraulic assembly, parts painting, parts hanging, and frame welding tasks, both with and without an exoskeleton. Workers were evaluated during consecutive job tasks, at beginning and at end of a shift. EMG amplitudes were measured and compared to recommended threshold limit values (TLVs) to determine fatigue risk values. Wearing the exoskeleton significantly reduced anterior deltoid EMG amplitudes and fatigue risk values during the consecutive job cycles, with no significant effects on the biceps brachii, superior trapezius, or lumbar erector spinae. Reduced EMG amplitudes were found at five of the six job tasks, and in three of the tasks fatigue risk values were reduced from above the TLV without the exoskeleton to below the TLV with the exoskeleton. Workers indicated that they would recommend the exoskeleton to others who perform overhead job tasks, but expressed concern that it might interfere with tasks that involve tight spaces, sitting, and bending over. We suggest evaluating specific job tasks when making decisions about exoskeleton usage.

Landing and squat tasks have been utilized to assess lower extremity biomechanics associated with anterior cruciate ligament loading and injury risks. The purpose of this study was to identify the differences and correlations in knee and hip mechanics during a single-leg landing, a single-leg squat, a double-leg landing, and a double-leg squat. Seventeen male and 17 female recreational athletes performed landings and squats when kinematic and kinetic data were collected. ANOVAs showed significant differences (p < 0.00001) for maximum knee flexion angles, maximum hip flexion angles, maximum knee abduction angles, maximum hip adduction angles, and maximum external knee abduction moments among squats and landings. For maximum knee and hip flexion angles, significant correlations (r ≥ 0.5, p ≤ 0.003) were observed between the two landings and between the two squats. For maximum knee abduction and hip adduction angles and maximum external knee abduction moments, significant correlations were mostly found between the two landings, and between the single-leg squat and landings (r ≥ 0.54, p ≤ 0.001). Individuals are likely to demonstrate different profiles of injury risks when screened using different tasks. While a double-leg landing should be considered as a priority in screening, a single-leg squat may be used as a surrogate to assess frontal plane motion and loading.

Strength and power have been identified as valuable components in both athletic performance and daily function. A major component of strength and power is the muscle mass, which can be assessed with dual-energy x-ray absorptiometry (DXA). The primary purpose of this study was to quantify the relationship between total body lean mass percentage (TBLM%) and lower extremity lean mass percentage (LELM%) and lower extremity force/power production during a countermovement jump (CMJ) in a general population. Researchers performed a DXA analysis on 40 younger participants aged 18-35 years, 28 middle-aged participants aged 36-55 years, and 34 older participants aged 56-75 years. Participants performed 3 CMJ on force platforms. Correlations revealed significant and strong relationships between TBLM% and LELM% compared with CMJ normalized peak vertical ground reaction force (p < 0.001, r = 0.59), normalized peak vertical power (p < 0.001, r = 0.73), and jump height (p < 0.001, r = 0.74) for the combined age groups. Most relationships were also strong within each age group, with some relationships being relatively weaker in the middle-aged and older groups. Minimal difference was found between correlation coefficients of TBLM% and LELM%. Coefficients of determination were all below 0.6 for the combined group, indicating that between-participant variability in CMJ measures cannot be completely explained by lean mass percentages. The findings have implications in including DXA-assessed lean mass percentage as a component for evaluating lower extremity strength and power. A paired DXA analysis and CMJ jump test may be useful for identifying neuromuscular deficits that limit performance.

Hinshaw, TJ, Stephenson, ML, Sha, Z, and Dai, B. Effect of external loading on force and power production during plyometric push-ups. J Strength Cond Res 32(4): 1099-1108, 2018-One common exercise to train upper-body strength and power is the push-up. Training at the loads that would produce the greatest power is an effective way to increase peak power. The purpose of the current study was to quantify the changes in peak force, peak power, and peak velocity among a modified plyometric push-up and plyometric push-ups with or without external loading in physically active young adults. Eighteen male and 17 female participants completed 4 push-ups: (a) modified plyometric push-up on the knees, (b) plyometric push-up without external loading, (c) plyometric push-up with an external load of 5% of body weight, and (d) plyometric push-up with an external load of 10% of body weight. Two force platforms were set up to collect vertical ground reaction forces at the hands and feet. The modified plyometric push-up demonstrated the lowest force, power, and velocity (5.4≥ Cohen's dz ≥1.2). Peak force and force at peak velocity increased (3.8≥ Cohen's dz ≥0.3) and peak velocity and velocity at peak power decreased (1.4≥ Cohen's dz ≥0.8) for the push-up without external loading compared with the 2 push-ups with external loading. No significant differences were observed for peak power among the push-ups with or without external loading (0.4≥ Cohen's dz ≥0.1). Although peak power is similar with or without external loading, push-ups without external loading may be more beneficial for a quick movement, and push-ups with external loading may be more beneficial for a greater force production.

Objective The goal of this work is to determine whether muscular fatigue concurrently reduces cognitive attentional resources in technical tasks for healthy adults. Background Muscular fatigue is common in the workplace but often dissociated with cognitive performance. A corpus of literature demonstrates a link between muscular fatigue and cognitive function, but few investigations demonstrate that the instigation of the former degrades the latter in a way that may affect technical task completion. For example, laparoscopic surgery increases muscular fatigue, which may risk attentional capacity reduction and undermine surgical outcomes. Method A total of 26 healthy participants completed a dual-task cognitive assessment of attentional resources while concurrently statically fatiguing their shoulder musculature until volitional failure, in a similar loading pattern observed in laparoscopic procedures. Continuous and discrete monitoring task performance was recorded to reflect attentional resources. Results Electromyography of the anterior deltoid and descending trapezius, as well as self-assessment surveys indicated fatigue occurrence; continuous tracking error, tracking velocity, and response time significantly increased with muscular fatigue. Conclusion Muscular fatigue concurrently degrades cognitive attentional resources. Application Complex tasks that rely on muscular and cognitive performance should consider interventions to reduce muscular fatigue to also preserve cognitive performance.