Early neuromuscular electrical stimulation to improve quadriceps muscle strength after total knee arthroplasty: a randomized controlled trial. Physical Therapy. 2012 Feb;92(2):210-26. Stevens-Lapsley JE1, Balter JE, Wolfe P, Eckhoff DG, Kohrt WM.
From the study:
“Sixty-six patients, aged 50 to 85 years and planning a primary unilateral TKA, were randomly assigned to receive either standard rehabilitation (control) or standard rehabilitation plus NMES applied to the quadriceps muscle (initiated 48 hours after surgery). The NMES was applied twice per day at the maximum tolerable intensity for 15 contractions. Data for muscle strength, functional performance, and self-report measures were obtained before surgery and 3.5, 6.5, 13, 26, and 52 weeks after TKA.”
“At 3.5 weeks after TKA, significant improvements with NMES were found for quadriceps and hamstring muscle strength, functional performance, and knee extension active range of motion. At 52 weeks, the differences between groups were attenuated, but improvements with NMES were still significant for quadriceps and hamstring muscle strength, functional performance, and some self-report measures.”
“The addition of NMES treatment to the quadriceps muscles effectively attenuated loss of quadriceps muscle strength and improved functional performance following TKA. Although the effects were most pronounced and clinically meaningful within the first month after surgery, benefits persisted through 1 year after surgery.”
- Machine type: Empi 300PV ( researchers noted it was comparable to the VersaStim 380 but could be used at home)
- Wave form: biphasic symmetrical
- Duty Cycle: 15 sec on (including 3 sec ramp) 45 sec off
- Duration: 15 contractions
- Rate: 50
- Pulse Duration: 250 uS
- Intensity: maximum tolerated (up to 100 mA)
- Electrodes: Two 7.6 x 12.7 cm (96.52 square cm per pad)
- Training Frequency: 2 times per day for 6 weeks
I think this study has a lot of things worked out. The Empi unit sounds like a quality unit, but it retails for >$900, which I think is overpriced for a 2 channel unit and is more than most patients are going to want to absorb for home use. Also though it is only a 2 channel unit, they still only used one channel. The other channel could have been put on the hamstring muscles, and with a 4 channel unit they could have doubled up on both. What I have noticed and my patients have confirmed is that you can only turn up one channel so much before the contractions become intolerable, but you can add channels at equal intensity which increased muscle fiber recruitment while keeping contractions equal if not more comfortable. Such that in practice I think you may be able to get even better results than what these researchers achieved.
The researchers did stimulation on the same muscle 2 times per day daily, which while effective they gains of the patients were best in the initial 3 weeks rather than the latter 3 weeks so they may have been overtraining the muscles with the stimulation once patients worked up to higher intensities of stimulation. In most strength training studies they did not find further increases in strength when they trained more than once per day 3-4 times per week, however that was with electric stimulation applied to healthy subjects, not those with muscle inhibition post surgery. Alternatively, initially post-op is when patients have muscle atrophy, so this time period may be when EMS is more effective by preventing muscle loss in the first place compared to restoring it after it’s gone. It will be interesting to see what future research shows in this area as it seems very clear that electric stimulation increases strength and improves recovery and we have general guidelines as to parameters that are effective, but as of yet optimal parameters are still unknown.
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Chad Reilly is a Physical Therapist, obtaining his Master’s in Physical Therapy from Northern Arizona University. He graduated Summa Cum Laude with a B.S. Exercise Science also from NAU. He is a Certified Strength and Conditioning Specialist, and holds a USA Weightlifting Club Coach Certification as well as a NASM Personal Training Certificate. Chad completed his Yoga Teacher Training at Sampoorna Yoga in Goa, India.