Exoskeleton Use During Lifting Tasks May Impair Physical and Cognitive Performances among Novice Users

Abstract

Exoskeleton use may deteriorate the user’s performance on physical and cognitive tasks due to additional task demands, obstructed movement, and increased mental workload. This study examined if using unpowered exoskeletons during lifting tasks led to declines in performance on the visual attention and lifting tasks among novice users. Thirty-two participants who had no prior experience with exoskeletons completed stoop and squat lifting tasks with and without the use of back- and leg -support exoskeletons, during which they also had to detect the visual target presented in varying locations in the visual field. The results indicated that exoskeleton use led to slower lifting task performance and increased target detection errors. The findings suggest that novice users may experience physical interference, discomfort, and increased mental workload while wearing an exoskeleton.

Background

Exoskeletons can assist workers with physically demanding jobs by increasing their physical strength and endurance, leading to the increasing implementation of exoskeletons in broad industrial sectors. Despite the potential benefits, prior research suggests that using exoskeletons may adversely affect certain task performances across individual users (e.g., Leibman et al., 2022; Raveendranath et al., 2024). For instance, while some studies found minimal or no detrimental effect on attentional performance during a simple target detection task (e.g., Afzal et al., 2017), other studies showed decrements in attentional and cognitive performances associated with exoskeleton use during more complex tasks (e.g., Bequette et al., 2020). One potential cause of the adverse impact of exoskeleton use is increased mental workload due to additional task demands associated with operating exoskeletons (Zhu et al., 2021). The mixed effects observed in prior research examining mental workload or attentional performance during exoskeleton use may be due to the varying degrees of increased workload associated with specific exoskeleton systems or task demands.

Study Objective

The current study examined whether exoskeleton use affected task performances during physically demanding, repetitive lifting tasks among novice users. Novice users may experience increased mental workload due to needing to use unfamiliar exoskeletons, potentially resulting in performance decrements. Participants completed a visual target detection task while performing lifting tasks to assess if exoskeleton use could lead to decreased attentional task performance (i.e., poorer target detection) and lifting task performance (i.e., slower lifting speed).

Methods

This study used a repeated measures design to compare physical and cognitive performances with and without exoskeleton assistance (i.e., exoskeleton vs. non-exoskeleton condition) while completing two types of lifting tasks (i.e., stoop vs. squat lifting condition). During the exoskeleton conditions, passive (i.e., unpowered) leg- and back-support exoskeletons (LegX and BackX from SuitX) were used, which were combined to provide support during lifting. Thirty-two undergraduate students with no prior exoskeleton experience were recruited. Seven were excluded due to failing to complete the experiments or following task instructions. The four experimental conditions were partially counterbalanced across participants to prevent order effects.

In each of the four experimental sessions, participants performed a 20- minute lifting task involving moving a 5.5 kg kettlebell between the floor and a shelf located 61 cm off the floor, concurrently with a visual attention task (a modified, LED-based attentional visual field [AVF; Feng et al., 2016] task). Participants were asked to respond to a lighted visual target, randomly selected among the 44 small LED light bulbs placed on a 61 × 61 cm panel attached to the wall where participants were positioned to face during the lifting task. The panel contained nine breadboards in four different directions (i.e., NE, SE, NW, and SW) and three eccentricities (i.e., central, mid, and far), which were approximately in <3, 20, and 40 degrees of the visual angle, estimated based on the 60 cm distance from a participant’s position from the wall. Each breadboard contained five LED light bulbs, except for the central breadboard, which had only four LEDs. A target was presented for 20 ms, with a varying between-target interval ranging from 5 to 15 s. Participants responded to the target by pressing a left or right button attached to the kettlebell to indicate the direction of the target (i.e., left or right side from the center).

The mean time to complete each set of two lifts (i.e., each involving moving the kettlebell from the ground to the shelf and back to the ground) and the AVF target detection accuracy were measured. Participants also completed a questionnaire for demographics, prior exoskeleton experience, and self-reported mental workload.

Results

A repeated measure multivariate analysis of variance (RM-MANOVA) was administered. The results showed a significant main effect of the exoskeleton condition, F(3,22) = 9.73, p < .001, η² _p  = .57. Post hoc analyses indicated that participants had longer lifting completion time during the exoskeleton condition (M = 21.25, SD = 7.35) than non-exoskeleton condition (M = 18.94, SD = 5.55), F(1,24) = 21.63, p < .001, η² _p  = .47, suggesting exoskeletons slowed physical task performance. Furthermore, exoskeleton use led to decreased AVF accuracy (M = .91, SD = .10) compared to non-exoskeleton conditions (M = .93, SD = .05), F(1,24) = 5.48, p = .028, η² _p  = .19, indicating exoskeleton use deteriorated attentional performance. The main effect of lifting task type (stoop vs. squat lifting) was not significant, F(1,24) = 1.36, p = .280. The interaction of exoskeleton use and lifting task type was also not significant, F(1,24) = .42, p = .738, indicating the impact of exoskeleton use on task performances was not different during stoop and squat lifting.

Findings

The current results suggest that exoskeleton use may have detrimental effects on novice users’ physical and cognitive task performances, while it may still provide assistance for physically demanding tasks. Further investigation is warranted to examine changes in mental workload with exoskeleton use among novice users to investigate why exoskeletons may impair task performance and how the effects may change over time as novices become familiar with exoskeleton use and learn how to use it effectively.