Biomechanical Effects of a Passive Back-Support Exosuit During Simulated Military Lifting Tasks-An EMG Study

Abstract

Military operators performing vehicle maintenance work are at times subject to onerous tasks such as lifting and transporting heavy loads, potentially in confined spaces. As this presents a risk for developing musculoskeletal injury, it is of interest to evaluate if a passive back-support exosuit could help reduce back muscle load. This study used wireless electromyographic (EMG) sensors to evaluate the biomechanical effects of exosuits during lifting tasks. Ten male participants performed military-relevant lifting tasks with and without wearing the exosuit in randomised orders. The lifting tasks included (1) vertical lifts of different weights (15 and 25 kg) onto different platform heights (0.5 m and 1.2 m) and (2) a lateral walk task across 4 m in a confined space while carrying a 39 kg weight. EMG activities of three back muscle groups (longissimus, iliocostalis, and multifidus) were measured and normalised to maximal isometric back extension tasks. The results showed no significant differences in muscle activation between conditions in most lifting tasks, except for a reduction in longissimus muscle activity when using the exosuit during lateral walking. Individual responses varied substantially, with some participants showing reduced muscle activity, while others did not. These findings highlight the challenges in implementing exosuits in reducing back muscle load during military lifting tasks. While passive back-support exosuits may provide benefits to some users, their effectiveness varies among individuals and may be task-dependent.

Keywords: Auxivo; electromyography; exoskeleton; load; muscle activity; spine.

Figure 1

Key elements of the Auxivo LiftSuit 2.0 back-support exosuit from the front and back views.

Figure 2

Markings were drawn on the participant’s back to guide EMG sensor placement for wireless data acquisition of muscle activity during lifting tasks.

Figure 3

A maximal isometric back extension task was used as a reference for normalisation of EMG data to allow between-day comparisons.

Figure 4

Participants were tasked to lift a load from the ground and place it onto a raised platform positioned 50 cm in front of them.

Figure 5

(a) A vehicle battery weighing 39 kg. (b) A participant executing the lateral walk task in a confined space (1.2 m × 1.4 m × 4 m) while carrying the load. The yellow arrow indicates the direction of travel.

Figure 6

Normalised %MVC averaged across all participants for the (A) iliocostalis, (B) multifidus, and (C) longissimus muscles during vertical lifting tasks. P1: Lowering Phase; P2: Lift and Forward Phase; and P3: End Phase. Error bars represent 1 standard deviation. %MVC is displayed across different loads (columns) and lifting heights (rows) under two conditions: exosuit-assisted (blue) and non-exosuit (red) conditions for each muscle.

Figure 7

Normalised %MVC in all participants (S01–S10) across different lifting heights (0.5 m represented by circles; 1.2 m represented by triangles), loads (15 kg represented by solid lines; 25 kg represented by dashed lines), and muscles (iliocostalis in red; longissimus in green; multifidus in blue) in the vertical lifting tasks. Exo and Non-Exo refer to the use of an exosuit and no exosuit, respectively.

Figure 8

Time to completion for lateral lifting tasks, with each dot representing a single participant. Trend lines shown indicate comparative performance between conditions: green lines indicate faster completion time with the exosuit compared to the non-exosuit condition, while red lines indicate the opposite.

Figure 9

Group mean (SD) of normalised %MVC for the iliocostalis, multifidus, and longissimus muscles during lateral lifting tasks, separated by side (left in blue; right in red).

Figure 10

Normalised %MVC in all participants (S01–S10) for each muscle (iliocostalis in red; longissimus in green; multifidus in blue) and sides (left represented by circle; right represented by triangle) in the lateral lifting tasks.

Figure 11

Participants used a wide range of techniques to perform lifting tasks.