Context: Knee pain is a common symptom in knee pathology and is associated with alterations in quadriceps activation and movement patterns. Reducing pain through intervention may help reestablish neuromuscular function. The independent effects of knee pain are difficult to examine and unclear. Objective: To investigate the effects of transcutaneous electrical nerve stimulation (TENS) on quadriceps activation and vertical ground reaction force (VGRF) during walking. Design: Crossover. Setting: Laboratory. Subjects: 15 in the TENS group (10M and 5F, 23.5 ± 2.8 yrs, 70.5 ± 12.5 kg, 178.1 ± 7.4 cm), and 15 in the sham group (10M and 5F, 22.5 ± 2.0 yrs, 72.1 ± 13.7 kg, 177.5 ± 9.3 cm). Interventions: Subjects underwent three experimental conditions (pain, sham, and control). Measurements were recorded across four time points (preinfusion, infusion, treatment, and posttreatment). Hypertonic or isotonic saline, respectively, was infused into the infrapatellar fat pad for 48 minutes (total 7.7 mL). The TENS group received a 20-minute treatment. A sham treatment was administered to the sham group. Main Outcome Measures: Perceived knee pain on a 10-cm visual analog scale, knee extension maximum voluntary isometric contraction (MVIC) normalized to body mass, knee extension central activation ratio (CAR), and VGRF. Results: Knee pain peaked at 4 cm during infusion and remained consistent across time in the sham group (F2,28 = 49.90, P < 0.0001), while knee pain gradually decreased to 1.5 cm following TENS treatment (F2,28 = 23.11, P < 0.0001). A group x condition x time interaction was detected for both the MVIC (F6,168 = 2.92, P < 0.01) and CAR (F6,168 = 3.03, P < 0.008) measurements. Post hoc analysis revealed that the infusion of hypertonic saline reduced knee extension MVIC by 29% in the TENS group, and by 26% in the sham group (P < 0.05). However, while the MVIC remained depressed by 26% following sham treatment, the MVIC was found to improve by 12% following TENS treatment (P < 0.05). Similarly, a 10% decrease in CAR was detected in both sham and TENS groups prior to treatment. This 10% deficit held, with a 9% deficit following sham treatment, while the deficit of CAR was improved by 4% following TENS treatment (P < 0.05). For the TENS group, infusion of hypertonic saline changed VGRF at initial loading, midstance, and push-off phase. VGRF was only different at initial loading and push-off phase following TENS treatment. For the sham group however, sham treatment did not restore VGRF, showing alterations in initial loading, midstance, and push-off phase (α = 0.05). Conclusions: Infusion of hypertonic saline increased perceived knee pain, reduced knee extension MVIC, reduced CAR, and altered VGRF over some of stance phase. TENS lessened the deficits in MVIC, CAR, and VGRF, suggesting decreased muscle inhibition and improved movement function.



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Life Sciences; Exercise Sciences



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