Brian Wiseman and J. Ty Hopkins, Exercise Sciences
More than ten million people in the U.S. suffer from knee pain, and one in every two people may develop chronic knee pain by age 85.3 Knee pain is also 1 of 5 leading causes of disability among adults, and alters muscle function and walking mechanics, which in turn, decreases quality of life.6 To alleviate the effects of knee pain and its consequences, transcutaneous electrical nerve stimulation (TENS) is often used to decrease perceived pain5 and increase quadriceps activation.7 However, it is unclear whether these benefits could offer potential improvement for walking mechanics. Therefore, the purpose of this study was to examine the effects of TENS on quadriceps motor function and walking mechanics in patients with pathological knee pain. We hypothesized that knee pain patients will show decreased quadriceps maximum voluntary isometric contraction (MVIC), quadriceps central activation ratio (CAR), and (3) altered walking mechanics. However, compared to placebo treatment, TENS will effectively mitigate the aforementioned variables.
This study was a randomized controlled laboratory trial. Subjects were randomly assigned to either the TENS or placebo groups. Treatment was blinded to subjects. Independent variables were time (baseline, treatment, post-treatment) and group (TENS, placebo). Dependent variables were quadriceps MVIC, quadriceps CAR, and walking mechanics. Sample size was calculated using previous experimental knee pain data.4 Using an alpha level of 0.05 and a beta of 0.2 (80% power), the power analysis, α priori, estimated that 15 subjects in each group are necessary. Subjects were provided the same pair of Nike shoes (T-Lite VRX), a spandex short, and shirt. Subjects performed quadriceps MVIC for 3 sec on the Biodex (System Pro 4, Shirley, NY, USA) with the knee and hip secured at 90° and 85° of flexion. When MVIC plateaued approximately 2 sec later, a superimposed burst (SIB) was manually transmitted to two electrodes on the anterior thigh. Three trials of MVIC and CAR were collected at three different time points (baseline, treatment, post-treatment). CAR was calculated by dividing the MVIC by the torque generated by the SIB plus the MVIC: CAR = (MVIC) / (MVIC + SIB). Walking trials were recorded using 3-D motion analysis system (Vicon, Oxford, UK), and a force-sensing tandem treadmill (AMTI, Watertown, MA, USA) at a self-selected walking speed. A 2 × 3 (group × time) mixed model ANOVA with repeated measures was used to detect differences between groups over time for quadriceps MVIC and CAR. Tukey’s HSD tests was performed for post hoc comparisons. A functional data analysis of variance (FANOVA) was used to determine differences between groups and times for walking mechanics (α = 0.05) during the stance phase of walking. A FANOVA allows us to compare treatment effects as polynomial functions rather than only discrete time points. As the means for inference, any difference between factors (effects), which is not equal to zero (no effect) at 95% confidence intervals, is deemed statistically and clinically significant.1
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- Andriacchi TP, Mundermann A. The role of ambulatory mechanics in the initiation and progression of knee osteoarthritis. Curr Opin Rheumatol. 2006;18(5):514-518.
- Lawrence RC, Felson DT, Helmick CG, et al. Estimates of the prevalence of arthritis and other rheumatic conditions in the United States. Part II. Arthritis Rheum. 2008;58(1):26-35.
- Park J, Hopkins J. Induced anterior knee pain immediately reduces involuntary and voluntary quadriceps activation. Clin J Sport Med. 2013;23:19 – 24.
- Robinson AJ. Transcutaneous electrical nerve stimulation for the control of pain in musculoskeletal disorders. J Orthop Sports Phys Ther. 1996;24(4):208-226.
- Seeley MK, Park J, King D, Hopkins JT. A novel experimental knee-pain model affects perceived pain and movement biomechanics. J Athl Train. 2013;48(3):337-345.
- Son S, Kim H, Seeley M, Feland B, Hopkins J. Effects of Transcutaneous Electrical Nerve Stimulation on Quadriceps Function in Individuals with Experimental Knee Pain. Scand J Med Sci Sports. 2015;In press.