Effects of age, gender, and target location on seated reach capacity and posture

Alterations in Physical Demands During Virtual/Augmented Reality-Based Tasks: A Systematic Review

The digital world has recently experienced a swift rise in worldwide popularity due to Virtual (VR) and Augmented Reality (AR) devices. However, concrete evidence about the effects of VR/AR devices on the physical workload imposed on the human body is lacking. We reviewed 27 articles that evaluated the physical impact of VR/AR-based tasks on the users using biomechanical sensing equipment and subjective tools. Findings revealed that movement and muscle demands (neck and shoulder) varied in seven and five studies while using VR, while in four and three studies during AR use, respectively, compared to traditional methods. User discomfort was also found in seven VR and three AR studies. Outcomes indicate that interface and interaction design, precisely target locations (gestures, viewing), design of virtual elements, and device type (location of CG as in Head-Mounted Displays) influence these alterations in neck and shoulder regions. Recommendations based on the review include developing comfortable reach envelopes for gestures, improving wearability, and studying temporal effects of repetitive movements (such as effects on fatigue and stability). Finally, a guideline is provided to assist researchers in conducting effective evaluations. The presented findings from this review could benefit designers/evaluations working towards developing more effective VR/AR products.

Age-Dependent Control of Shoulder Muscles During a Reach-and-Lift Task

Aging affects fatigability and is a risk factor for incurring a fatigue-related injury in the neck/shoulder region. Age-related changes in the electromyographical features of motor control may be partly responsible. Young (N = 17) and older (N = 13) adults completed a reach-and-lift task at their self-selected speed, before and after a fatiguing task targeting the neck/shoulder. Electromyography amplitude (root mean square), amplitude variability (root mean square coefficient of variation [CV]), functional connectivity (normalized mutual information [NMI]), and functional connectivity variability (NMI CV) were extracted from several muscles and analyzed for effects and interactions of age using general estimating equation models. Root mean square CV and deltoid NMI CV increased from pre- to postfatigue (ps < .05). Upper trapezius-deltoid NMI decreased for young, but increased for older adults, while the opposite response was found for lower trapezius-deltoid NMI (ps < .05). Older adults seem to adapt to fatigue in reach-and-lift movement with a cranial shift in control of the scapula.

Trunk Compensation During Bimanual Reaching at Different Heights by Healthy and Hemiparetic Adults

The authors explored how trunk compensation and hand symmetry in stroke survivors and healthy controls were affected by the distance and height of virtual targets during a bimanual reaching task. Participants were asked to reach to 4 different virtual targets set at: 90% of their arm length at shoulder, xiphoid process, and knee height, and 50% of their arm length at xiphoid process height. For the stroke group, for all targets, the hands' movements were more asymmetrical than those of the healthy group, with more asymmetry observed in the direction of gravity, and trunk forward displacement values were larger and more variable. The knee targets had the largest trunk displacement values; index of curvature and trunk displacement were strongly correlated with participants' impairment scores. A strong correlation was found between the hands' asymmetry in the anterior or posterior direction for the shoulder targets, and the impairment scores. The results suggest that target height influences the degree of trunk compensation and hand symmetry during bimanual reaching by hemiparetic participants.

The manipulability: a new index for quantifying movement capacities of upper extremity

In this work, it is proposed to evaluate the upper-limb movements through a global index of performance borrowed from the field of robotics: the manipulability. For a given posture, this index quantifies the set of velocities that can be achieved at the wrist in all the Cartesian directions. The manipulability can be represented by an ellipsoid from which the volume and shape related parameters can be derived. During a reach to grasp movement, the ellipsoid obtained from experiment presented a flattened shape along the forearm longitudinal axis and an increased volume as the arm was extended. From this study, it is concluded that: (1) the ellipsoid volume reflects well the ability to generate speed at the wrist which is effectively maximal for an extended posture; (2) if maximal velocity is an important parameter it might be advisable to primarily move the hand perpendicularly to the forearm longitudinal axis.

PRACTITIONER SUMMARY

The interest of manipulability indices is that they evaluate globally a posture of the upper-limb in relation to a given task. This original parameter could help to design environments or devices in order that the adopted postures maximise one particular aspect of the performance, i.e. the velocity of the hand.

Effects of target location, stature and hand grip type on in-vehicle reach discomfort

In order to improve car interior design, data of perceived discomfort and reach posture were collected for 75 different target locations. Altogether, 24 males and females of different statures participated in the experiment. In addition to three-finger grip, index fingertip reach and five finger grip were also compared. The effects of target location, stature and hand grip on reach discomfort were analysed. Predictive regression equations were provided. In addition to the confirmation of target location effects, the results showed that seat back and steering wheel affected discomfort. Their effects differed according to the subject's anthropometry. A detailed analysis of possible interference between the car interior and reach movement showed that short females were more likely impeded by the seat back when a target was close to the body. A significant difference between three hand grip types could be explained by the change of hand reach distance when changing hand grip type. STATEMENT OF RELEVANCE: The present study analysed the effects of target location, stature and hand grip type on reach discomfort, based on the statistical analysis of subjective ratings when reaching a target in a vehicle. The results would help to optimise the location of automotive controls for improving car interior design.