Feasibility of a Biomechanically-Assistive Garment to Reduce Low Back Loading During Leaning and Lifting

Abstract

Goal: The purpose of this study was: 1) to design and fabricate a biomechanically-assistive garment which was sufficiently lightweight and low-profile to be worn underneath, or as, clothing, and then 2) to perform human subject testing to assess the ability of the garment to offload the low back muscles during leaning and lifting.

Methods: We designed a prototype garment which acts in parallel with the low back extensor muscles to reduce forces borne by the lumbar musculature. We then tested eight healthy subjects while they performed common leaning and lifting tasks with and without the garment. We recorded muscle activity, body kinematics, and assistive forces.

Results: The biomechanically-assistive garment offloaded the low back muscles, reducing erector spinae muscle activity by an average of 23-43% during leaning tasks, and 14-16% during lifting tasks.

Conclusion: Experimental findings in this study support the feasibility of using biomechanically-assistive garments to reduce low back muscle loading, which may help reduce injury risks or fatigue due to high or repetitive forces.

Significance: Biomechanically-assistive garments may have broad societal appeal as a lightweight, unobtrusive, and cost-effective means to mitigate low back loading in daily life.

Fig. 1.

(a) During lifting or leaning, the lumbar (low back) extension moment is the result of large muscle and ligament forces (F_M) acting at short moment arms (r_M) about the spine. This extension moment counterbalances flexion moments from the weight of the head-arms-trunk (F_HAT) and carried weight (F_W), which act at larger moment arms (r_HAT and r_W). (b) The large muscle and ligament forces constitute the majority of loading experienced by the intervertebral discs. Excessive and/or repetitive loading can lead to degeneration or injury of the lumbar tissues (muscles, ligaments, vertebrae, and intervertebral discs).

Fig. 2.

Biomechanically-assistive garment prototype. The prototype distributes forces over the shoulders and thighs via the upper- and lower-body interfaces. Elastic bands connect these two interfaces and act in parallel with muscles and ligaments to support the lumbar extension moment. Slack length of the elastic bands was set via adjustable clasps.

Fig. 3.

(a) The biomechanically-assistive garment stretches during lifting and leaning. (b) Forces borne by the elastic bands are expected to offload the extensor muscles, and to reduce intervertebral disc loading by increasing the extensor moment arm (Δr). Analytically, from the moment balance equation, F_E + F′_M < F_M from Fig. 1.

Fig. 4.

Mean normalized EMG for a representative subject. (a) EMG for lifting task with vs. without the biomechanically-assistive garment prototype. Trials were parsed into cycles; a cycle began with the subject standing upright, next the subject squatted down, and then stood back upright to complete the cycle. (b) EMG for leaning task with vs. without the prototype. Mean EMG was calculated over the middle of the trial, during which the subject was leaning statically.

Fig. 5.

Mean EMG of the erector spinae muscles was reduced during leaning when wearing the biomechanically-assistive garment prototype (dark blue) vs. not wearing it (light green). Reductions were statistically significant for all leaning angles tested (p<0.05, denoted with asterisks). Intersubject means and standard deviations are depicted.

Fig. 6.

Mean and peak EMG of the erector spinae muscles were reduced during lifting when wearing the biomechanically-assistive garment (dark blue) vs. when not wearing it (light green). All reductions were statistically significant (p<0.05, denoted with asterisks). Intersubject means and standard deviations are depicted.

Fig. 7.

Theoretical reduction in lumbar disc compression force when wearing a biomechanically-assistive garment. Disc force reduction increases as a function of increasing elastic cable force (F_E) and increasing moment arm (Δr).