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The purpose of this study was to characterize quadriceps femoris muscle fatigue of both lower extremities in patients with knee osteoarthritis (OA). Sixty-two subjects (mean age 68.2 years, standard deviation [SD] ± 7.9 years) with knee OA participated in the study. Significantly higher knee pain was reported in the involved knee than in the contralateral knee, as determined by a visual analog scale. Significant differences were demonstrated between the lower extremities in terms of maximal voluntary isometric contraction, in favor of the less involved leg (P = 0.0001). In contrast, the degree of fatigue of the quadriceps femoris muscle, as measured by the decrement in force production following ten repeated contractions, was significantly higher in the contralateral leg (P = 0.0002). Furthermore, normalization of the fatigue results to the first contraction yielded a similar result (P < 0.0001). Similar results were noted when analysis was performed separately for subjects whose involvement was unilateral or bilateral. The results indicate that, irrespective of the initial strength of contraction, the rate of muscle fatigue in the contralateral leg is significantly higher than in the involved leg. Hypotheses for these unexpected results are suggested. Rehabilitation of patients with knee OA should focus on increasing quadriceps muscle strength and endurance for both lower extremities.

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OBJECTIVE: To determine whether neuromuscular electrical stimulation applied to the quadriceps femoris muscle will enhance the effectiveness of an exercise programme in patients with knee osteoarthritis. DESIGN: A randomized trial with parallel intervention treatment groups. SETTING: Outpatient physical therapy clinic. SUBJECTS: Fifty participants (mean age (SD) 68.9 (7.7) years) with symptomatic idiopathic knee osteoarthritis and radiographic evidence (grade ≥ II Kelgren's classification). INTERVENTIONS: Participants were randomized into one of two groups receiving 12 biweekly treatments: An exercise-only group or an exercise combined with neuromuscular electrical stimulation group (biphasic pulses, at 75 Hz and 250 µs phase duration). MAIN MEASURES: Knee pain intensity; maximal voluntary isometric contraction and voluntary activation of the quadriceps femoris muscle; measures of functional performance. RESULTS: A significant interaction effect (P = 0.01) indicated greater improvement in pain for the electrical stimulation group. The mean (SD) change in pain intensity was from 7.5 ± 2 to 5 ± 2.2 and from 7.4 ± 1.9 to 3.3 ± 2.4 in the exercise and electrical stimulation groups, respectively. A significant treatment effect was also noted for the voluntary activation of the quadriceps femoris, which increased by 22.2% in the electrical stimulation group and by 9.6% in the exercise group (P = 0.045). Significant improvements were observed in both groups in all remaining measures, with no differences between groups. CONCLUSIONS: Electrical stimulation treatment to the quadriceps femoris enhanced the effectiveness of an exercise programme in alleviating pain and improving voluntary activation in patients with knee osteoarthritis, but did not enhance its effect on muscle strength or functional performance.

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Background. There is no consensus regarding gender-related differences in pain intensity and functional abilities among patients with knee osteoarthritis (OA). Objective. Determine gender-related differences in pain intensity and functional ability among subjects with knee OA, as assessed by a self-report questionnaire and by performance-based tests. Methods. Sixty-three subjects with symptomatic knee pain due to OA were included in this study. The outcome measures were self-reported knee pain intensity and physical function (WOMAC), as well as three performance-based functional assessments: time up and go test, a 10-meter walk test, and stair negotiation. Independent sample t-tests were performed to determine gender differences. Level of significance was set at P ≤ 0.05. Results. Female subjects reported higher levels of knee pain and lower functional performance. In contrast, no significant gender-related differences were determined in any of the performance-based measures. Conclusion. The results indicate that the two types of functional ability measures may address different constructs of functional ability. Self-reported ability, particularly in the female subjects, may be influenced by psychological aspects associated with chronic pain. Rehabilitation programs should consider the underlying mechanisms of the patients' performance limitations in order to address the specific needs of each individual patient.