Immediate Effects Of Verbal Encouragement On Fatigued Quadriceps Strength, Activation, And Knee Joint Position Sense

Abstract

PURPOSE: To examine the effects of verbal encouragement on quadriceps maximal voluntary isometric contraction (MVIC), central activation ratio (CAR), and knee joint position sense (KJPS). METHODS: Sixty eight active healthy male adults (age: 23.3±2.6) randomly underwent either condition (verbal: “kick, kick, harder, harder” or control: non-verbal encouragement during MVIC). Measurements were assessed at time-0 (baseline), -1, -2, and -3. Superimposed burst was delivered to the quadriceps during MVIC assessments (knee locked at 90°) for CAR calculations. For KJPS, subjects flexed their knees and stopped when they thought that their knee flexion angle was 15° or 45° (in a randomised order), then absolute error scores were calculated. Each assessment was performed on a dynamometer and assessed three times at time-0 and twice for other time intervals. Between assessments, muscular fatigue protocols (continuous knee extensions at 60°/s until three consecutive torque values dropped below 50% of the averaged MVIC value recorded during the previous assessments) were implemented. To test effects of verbal encouragement on quadriceps muscle and knee joint function over time, we performed mixed model ANOVAs and Tukey-Kramer post hoc tests (p<0.05) and calculated between-time effect sizes (ES). RESULTS: Our fatigue protocol immediately decreased both group’s MVIC (F3,198=4.42, p=0.005; verbal: a 24% reduction, ES: 1.13; control: a 27% reduction, ES: 1.44) and CAR (F3,198=10.91, p<0.0001; verbal: a 2.1% reduction, ES: 0.33; control: a 3.2% reduction, ES: 0.73) at time-1. While subjects in the control group showed a 6.8% and a 3.3% further decrease in MVIC (p=0.03, ES=0.30) and CAR (p<0.0001, ES=0.49), respectively, subjects in the verbal group did not change both values at time-2. Regardless of the conditions, absolute error scores in KJPS at 15° were began to alter at time-2 (F3,198=7.74, p<0.0001, a 17% reduction, ES=0.28) while those in KJPS at 45° were immediately altered at time-1 (F3,198=11.76, p<0.0001, a 29% reduction, ES=0.49), from the baseline values. CONCLUSIONS: (1) verbal encouragement may delay reduction of force output and activation, (2) fatigued muscle may affect adjacent joint position sense, and (3) less knee flexion, 15° appears to be more fatigue resistance.