Differential effects of sex on upper body kinematics and kinetics during fatiguing, Asymmetric lifting.

This study quantified sex-specific biomechanical adaptations to fatigue in asymmetric lifting. Twenty-one females and fifteen males performed a prolonged asymmetric lifting protocol while upper body, trunk and pelvis kinematics were collected. Features of movement identified with principal component analysis, and peak joint angular velocities and moments were calculated. Sex-specific kinematic adaptations to fatigue included females adopting a 'stoop-like' lifting strategy to a greater extent than males. Additionally, females exhibited higher vertical elbow positions during load rotation, moved their body toward the destination for load deposit, and did not reduce peak right shoulder flexion velocities, in contrast to male participants. Females also had greater low back and shoulder peak normalized joint moments. When fatigued, females adopted an asymmetric lifting strategy that minimized metabolic demand as supported by smaller decreases in maximum voluntary contractions. However, females' fatigue-related adaptations increased biomechanical exposures associated with injury risk.

The biomechanical benefits of active sitting.

This cross-sectional study examined the biomechanical effects of two active chairs (AC1: had the feature to pedal and slide forward on the seat pan; AC2: a multiaxial motion seat pan) compared to a traditional office chair and standing workstation. Twenty-four healthy participants worked at each of the workstations for 60-min. The following equipment was used: Motion Capture, Electromyography, Ratings of Perceived Discomfort Questionnaire, and Exit Survey. The active protocol had positive effects on the body, including increased neuromuscular activity in the gastrocnemius, increased overall movement, and a more open trunk-thigh angle. Greater discomfort in the buttocks due to the lack of seat pan contour was reported for the AC1 which identified a need for a design modification. While standing, participants' shoulders were less flexed than when sitting in any of the three seats, however, greater discomfort was reported in the lower legs after 1 h of computer work. Practitioner summary: A comparison of four different workstations was conducted to further understand the use of active workstations. Active sitting was found to have positive effects on the body, such as allowing sitters to increase movement while sitting without the high activation of muscular activity. Standing can also provide a positive break from sitting.

Does active sitting provide more physiological changes than traditional sitting and standing workstations?

This cross-sectional study examined the physiological effects of two active chairs (AC1: had the feature to pedal and slide forward; AC2: was a multiaxial chair) compared to a traditional office chair and standing workstation. Twenty-four healthy participants computed at each of the workstations for 60 min. The active protocol was to alternate between a pedalling/side-to-side motion and sliding forward/front-to-back motion to the sound of a metronome operating at 40 bpm. The participants' physiological effects were recorded using near-infrared spectroscopy (NIRS); electrodermal activity (EDA) and a heart rate (HR) monitor for each collection period. Statistical analysis was conducted using a repeated measures analysis of variance for within-task and between-workstation comparisons. A Tukey's post hoc analysis was calculated for significant findings. Both active chairs significantly increased oxygenated blood in the gastrocnemius and participants' heart rate and EDA (stress) levels were affected slightly by task and time. However, participants felt more "productive" sitting in the control chair than in either of the active chairs.

A biomechanical analysis of active vs static office chair designs.

The objective of this study was to provide a biomechanical comparison of two different types of active chairs (AC1 & AC2) versus a static chair (NAC). Thirty healthy participants were recruited: fifteen healthy females and fifteen healthy males. Participants worked at a computer workstation (1-h per chair). Equipment included: Pressure pads, Electromyography, Near-Infrared Spectroscopy, and Questionnaires (rate of perceived discomfort, seating discomfort questionnaire and exit survey). A significant increase in anterior-posterior postural sway was found on the seat pan with the use of the AC1. An increase in neuromuscular activity of the external obliques and an increase change in total oxygen index (%TOI) values in the gastrocnemius were also found using the AC1, however the difference was not much higher than the NAC and AC2. Lower discomfort scores in the gluteal area were found with the use of active chair AC1 compared to the NAC. Preliminary findings suggest that having an office chair with a split seat pan design shows potential to yield biomechanical and physiological benefits for the sitter, however further research is needed to better understand the ergonomic benefits of active sitting.