Effect of verbal encouragement on quadriceps and knee joint function during three sets of knee extension exercise

BACKGROUND: Although the common practice of verbal encouragement is scientifically supported, its effect on the maintenance of force output in fatiguing exertions is unknown. OBJECTIVE: To examine the effects of verbal encouragement on exercise-induced quadriceps and knee joint function during three sets of knee extension exercise. METHODS: Sixty-five healthy males (23.3 years, 175.8 cm, 75.3 kg) underwent testing using the administration of verbal encouragement (n = 32) or not (n = 33) during assessment of quadriceps and knee joint function. Assessments were performed at baseline and times 1, 2, and 3. The knee concentric isokinetic extension at 60 degrees/s, was performed between the time points. For quadriceps function, maximal isometric strength and activation (central activation ratio) were recorded. Absolute error values on knee flexion replications at 15 degrees or 45 degrees were recorded for knee joint function. RESULTS: There was no verbal encouragement effect over three sets of exercise in quadriceps strength (condition x time: F-3,F-189 = 1.71, p = 0.17) and knee flexion replication (condition x time for 15 degrees: F-3,F-189 = 0.11, p = 0.96; 45 degrees : F-3,F-189 = 0.63, p = 0.6). However, subjects who had received verbal encouragement maintained quadriceps activation (condition x time: F-3,F-189 = 5.49, p = 0.001). Specifically, quadriceps activation in the verbal condition was 3.0% higher at time 2 (p = 0.01) and 4.7% higher at time 3 (p = 0.0003) versus in the non-verbal condition. CONCLUSIONS: Verbal encouragement appears to be effective in maintaining central activation, but is insufficient for promoting strength. This supports the idea that peripheral contributing factors play a larger role in force production when performing multiple sets of exercises.