NEUROMUSCULAR ELECTRICAL STIMULATION TIMING IN ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION REHABILITATION: A SCOPING REVIEW
Background
Quadriceps weakness and arthrogenic muscle inhibition are persistent barriers to functional recovery after anterior cruciate ligament reconstruction (ACLR). Neuromuscular electrical stimulation (NMES) is commonly used to facilitate early quadriceps activation, yet clinical practice varies widely regarding when NMES is initiated ranging from immediate postoperative use to delayed initiation weeks after surgery. Timing may influence neuromuscular recovery and subsequent function. This study aims to systematically map evidence on NMES timing, outcomes, and clinical application following ACLR.
Objectives
To map the existing literature on NMES initiation timing after ACLR, summarize how “early” versus “delayed” initiation is defined, describe reported timing outcome relationships, and identify evidence gaps to guide future comparative studies.
Study design
A scoping review was conducted in accordance with PRISMA-ScR. Scopus and PubMed were searched from inception to January 2026 using ACLR-related terms combined with NMES-related terms. Two independent reviewers screened titles/abstracts and full texts. Studies were eligible if they included adults undergoing ACLR, applied NMES as part of rehabilitation, and reported sufficient protocol detail to classify NMES onset. Non-English publications and conference abstracts without full text were excluded. Data extraction captured study design, NMES onset definitions, intervention features, and outcomes (quadriceps strength and activation, muscle morphology, functional performance, and gait/biomechanics).
Results
Nine studies published between 2021 and 2025 met inclusion criteria (six original studies, two systematic reviews, and one meta-analysis). NMES initiation timing was inconsistently defined and was grouped into three pragmatic windows: immediate (24–48 hours postoperatively; 2 studies), early (within the first postoperative week; 3 studies), and delayed (>2 weeks; 4 studies). Across studies, NMES was most commonly integrated with active quadriceps training rather than applied as a stand-alone intervention. Early initiation (immediate-to-first-week) was more frequently associated with superior early quadriceps outcomes (strength and/or activation-related measures) and improvements in selected functional tasks compared with delayed initiation, although direct head-to-head comparisons of timing strategies were limited. Protocol reporting varied, with inconsistent documentation of stimulation parameters and adherence. Longer-term outcomes, including return-to-sport measures, were assessed inconsistently across studies.
Conclusions
Preliminary evidence suggests that initiating NMES within the first postoperative week may support early quadriceps recovery after ACLR, particularly when combined with structured quadriceps training. This scoping review provides a comprehensive evidence map of NMES timing strategies to inform clinical decision-making, highlight inconsistent timing definitions and protocol reporting, and identify key research gaps for future trials comparing immediate, early, and delayed NMES initiation with longer-term functional and return-to-sport outcomes.
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