Effects of transcutaneous electrical nerve stimulation on quadriceps function in individuals with experimental knee pain
Son SJ, Kim H, Seeley MK, Feland JB, Hopkins JT. Scand J Med Sci Sports. 2015: 1-11. Accessed October 4, 2015 doi: 10.1111/sms.12539
Take Home Message: Sensory transcutaneous electrical nerve stimulation may help reduce knee pain and increase quadriceps function among people with knee pain.
Knee pain inhibits muscule function. Unfortunately, we don’t know if a disinhibitory modality such as sensory transcutaneous electrical nerve stimulation (TENS) can increase motor function of inhibited muscles. The purpose of this research study was to see if sensory TENS had an influence on quadriceps muscle activation before and after the treatment. A total of 30 healthy volunteers (~24 years old) with no recent lower extremity injuries were placed into 2 groups (TENS, placebo). The placebo group was matched to the TENS group based on gender, age, mass, and height. This is important since this study is not a randomized trial. Everyone attended three sessions where they randomly received hypertonic saline infusion (pain inducing infusion), isotonic saline infusion, or no infusion (control). Participants had 2 days between sessions. At each session the researchers assessed quadriceps maximum voluntary contraction (MVC) and central activation ratio at 4 times: 1) baseline, 2) infusion, 3) treatment, and 4) post-treatment. Knee pain was recorded every 2 minutes throughout the infusion and treatment using a 100-mm visual analog scale (VAS). Two different sensory TENS channels were used to cross the knee joint. The TENS protocol was a continuous, asymmetric biphasic square-pulse wave with a pulse width of 120ms and a pulse rate of 180Hz. The intensity was set by increasing the machine until there was a visible contraction of the vastus medialis and then the intensity was decreased until the contraction was no longer seen or felt. Contact points were set 5-7cm apart surrounding the knee joint with intersecting currents. Both groups (TENS and placebo) had similar changes in MVC and CAR from baseline to hypertonic infusion recording times, but the TENS group had better quadriceps performance during the treatment and post-treatment recordings as seen by their increased MVC and central activation ratio. As for knee pain, scores peaked at 40mm during hypertonic saline infusion and remained steady in the placebo group, whereas the TENS group showed a gradual decrease on the VAS to 12mm.
Overall, sensory TENS decreased pain and increased the activation of the quadriceps muscles when compared to the placebo group. TENS is used to as a disinhibitory modality, meaning that muscle function can be improved while the muscle being inhibited. The importance and significance of these findings is that sensory TENS can be used as an immediate modality to help reduce pain and restore normal motor function in healthy individuals with knee pain. It is important to consider that TENS can be used to reduce the pain as well as helping to improve quadriceps function. However, we need to keep in mind that this was induced knee pain and so it is unclear if sensory TENS will be as effective among patients with knee pain due to injury or among patients with pain at different joints. Regardless, there is evidence to support the use of sensory TENS to reduce pain and promote muscle activation when the quadriceps are inhibited due to pain. This could potentially lead to quicker and more effective rehabilitation and help preserve joint health. Clinically, these findings should encourage clinicians that TENS may help decrease knee joint pain and facilitate better quadriceps activation among knees with pain-induced quadriceps inhibition.
Questions for Discussion: Do you think that motor or noxious TENS prove to be more effective than sensory TENS in relieving pain and increasing muscle activation? Would there be a difference in results of the effects of TENS in acute or chronic injuries?
Written by: Damian Pulos, Ashley Schuster
Reviewed by: Jeffrey Driban