JMIR Publications

ABSTRACT

Background:

Chronic low back pain (CLBP) is characterized by pain-induced motor inhibition, reduced trunk muscle strength, and disturbances in body perception, which can constrain voluntary muscle activation. Virtual reality (VR) enables the real-time modulation of body representation, and the Proteus effect suggests that embodying a stronger avatar may influence perceived bodily capability and behavior. Although preliminary CLBP studies have reported short-term improvements in pain and beliefs, it remains unclear whether avatar-based embodiment can acutely modify objective muscle strength or how such changes relate to subjective embodiment.

Objective:

We aimed to examine whether embodying a progressively muscular avatar during a VR-based squat task produces immediate changes in muscle strength and pain in individuals with CLBP and to explore the associations between strength changes and subjective embodiment.

Methods:

In this proof-of-concept pre–post study, 16 individuals with CLBP and 16 age- and sex-matched healthy control participants performed a VR-based squat task while observing a sex-matched avatar whose muscularity gradually increased. Muscle strength (handgrip, trunk extension, knee extension) was assessed before and after VR. Pain and task-specific fear were measured in CLBP only. Subjective embodiment was assessed using a Virtual Embodiment Questionnaire (VEQ). Group × time effects were analyzed using repeated-measures analysis of variance, and associations were examined using Spearman correlations with false discovery rate (FDR) correction.

Results:

Significant main effects of time were observed for trunk extension, knee extension, and handgrip strength (all P < .005), with no group × time interactions. Healthy controls showed significant pre–post increases in trunk and knee extension strengths, whereas individuals with CLBP showed significant gains in knee extension strength and a nonsignificant trend in trunk extension strength. The handgrip strength did not change. In the CLBP group, pain decreased during VR (P = .015) but returned to baseline thereafter. Changes in trunk extension strength were strongly correlated with the VEQ Change subscale in CLBP (ρ = .76, FDR = .006), with no significant correlations in controls.

Conclusions:

Embodying a progressively muscular avatar is associated with immediate, task-relevant increases in trunk and knee extensor strength, consistent with the Proteus-effect–related modulation of motor output. In CLBP, greater trunk strength gains coincide with stronger momentary changes in the embodied self, suggesting that visually driven modulation of body representation may acutely facilitate voluntary motor output. Although causal inference is limited by the single-session design and the absence of a neutral-avatar control, these findings provide proof-of-concept evidence supporting avatar-based embodiment as a potential adjunct to exercise in CLBP. Clinical Trial: the UMIN Clinical Trials Registry (UMIN000056456)