NMES Before and After ACL Surgery: Protecting Your Quadriceps at Every Stage
The quadriceps muscle, designed by God to absorb enormous force with every step, run, and jump, is often the first casualty of an ACL injury — and it can start weakening before you've even had surgery. Neuromuscular electrical stimulation (NMES) is one of the most effective tools we have to prevent this, which is why it's part of Phase 0 prehab at NUH, not just post-op rehab.
The Problem: Quadriceps Weakness Starts Early
After an ACL injury, the knee reflexively "switches off" some of the nerve signal to the quadriceps — a protective response called arthrogenic muscle inhibition.¹ This begins immediately, well before surgery, and continues afterward. Left unaddressed, quadriceps atrophy can exceed 20%, and strength loss can exceed 30%, within three months of surgery — with deficits persisting for years.⁶ Weak quadriceps at return to sport is one of the strongest predictors of reinjury, and is linked to earlier knee osteoarthritis.¹
This is why quadriceps protection needs to start in prehab, not wait until after surgery.
What Is NMES and How Does It Help?
NMES uses small electrical currents through skin electrodes to directly stimulate the quadriceps to contract — bypassing the inhibition signal from the injured knee.¹ It's used as an adjunct to exercise, not a replacement, and is valuable at two distinct stages:
- Before surgery (prehab): maintains muscle activation and limits atrophy while you're waiting for surgery, so you go into the operating theatre with a stronger baseline.
- After surgery: counters post-op inhibition when pain and swelling make voluntary quad activation difficult.
Does It Work? What the Research Shows
A 2025 meta-analysis of nine randomised trials found NMES plus standard physiotherapy produced significantly better quadriceps strength recovery than physiotherapy alone — with earlier NMES (within a week of surgery) outperforming later starts.¹ An earlier meta-analysis found similar results for both strength and function.²
At the cellular level, a sham-controlled trial found early NMES reduced muscle fibre atrophy and preserved fibre contractility, giving a biological basis for these clinical results.³ Other trials combining NMES with functional movement — like sit-to-stand exercises in the first weeks post-op — found better strength recovery and better left-right symmetry than exercise alone.⁴
Backed by Clinical Practice Guidelines
NMES isn't experimental. The 2017 clinical practice guidelines for ACL rehabilitation graded the evidence for NMES an "A" — strong evidence.⁵ Yet many clinicians still underuse it or dose it below a therapeutic level.⁵ Getting the timing and dosing right — starting early, both before and after surgery — is what makes the difference.
How We Do It at NUH
NMES is part of our standard ACL protocol at both stages:
- 2-3x daily, 15 minutes per session, 5-7 days a week
- 6–8 weeks before surgery (Phase 0 prehab), and again for 6–8 weeks after surgery
Patients are guided to actively contract the thigh muscle with each stimulation, pairing voluntary effort with the electrical signal.
References
- Li Z, et al. Effects of NMES on Quadriceps Femoris Muscle Strength and Knee Joint Function in Patients After ACL Surgery: A Systematic Review and Meta-analysis. Orthop J Sports Med. 2025;13(1).
- Hauger AV, et al. Neuromuscular electrical stimulation is effective in strengthening the quadriceps muscle after anterior cruciate ligament surgery. Knee Surg Sports Traumatol Arthrosc. 2018;26(2):399-410.
- Toth MJ, et al. Utility of Neuromuscular Electrical Stimulation to Preserve Quadriceps Muscle Fiber Size and Contractility After ACL Injuries and Reconstruction. Am J Sports Med. 2020;48(10):2429-2437.
- Labanca L, et al. Neuromuscular Electrical Stimulation Superimposed on Movement Early after ACL Surgery. Med Sci Sports Exerc. 2018;50(3):407-416.
- Arhos EK, et al. Who's Afraid of Electrical Stimulation? Let's Revisit the Application of NMES at the Knee. J Orthop Sports Phys Ther. 2024;54(2):1-6.
- Hasegawa S, et al. Effect of early implementation of electrical muscle stimulation to prevent muscle atrophy and weakness in patients after anterior cruciate ligament reconstruction. J Electromyogr Kinesiol. 2011;21(4):622-630.