Does whole body vibration training affect knee kinematics and neuromuscular control in healthy people?

This study aimed to investigate the effect of whole body vibration (WBV) training on the knee kinematics and neuromuscular control after single-legged drop landings. Surface electromyographic (EMG) activity of the rectus femoris and hamstring muscles and knee and ankle accelerometry signals were acquired from 42 healthy volunteers. Participants performed three pre-test landings and after a recovery period of three minutes, they completed one set of six bouts of WBV each of one minute duration (30 Hz - 4 mm), followed by a single-leg drop landing. After the WBV intervention no significant changes were observed in the kinematic outcomes measured, although the time to stabilise the lower-limb was significantly lower after the vibration training (F(8,41) = 6.55; P < 0.01). EMG analysis showed no significant differences in the amplitude of rectus femoris or hamstring muscles after WBV training, however, significant differences in EMG frequency of the rectus femoris were found before (F(8,41) = 7.595; P < 0.01) and after toe-down (F(8,41) = 4.440; P < 0.001). Finally, no significant changes were observed in knee or ankle acceleration after WBV. Results suggest that WBV can help to acutely enhance knee neuromuscular control, which may have clinical significance and help in the design of rehabilitation programmes.

Gender differences in knee stability in response to whole-body vibration.

The purpose of this study was to determine whether there are kinematic and electromyographic (EMG) differences between men and women in how the knee is controlled during a single-legged drop landing in response to whole-body vibration (WBV). Forty-five healthy volunteers, 30 men (age 22 ± 3 years; weight 76.8 ± 8.8 kg; height 179.0 ± 6.8 cm) and 15 women (age 22 ± 3 years; weight 61.0 ± 7.7 kg; height 161.9 ± 7.2 cm) were recruited for this study. Knee angles, vertical ground reaction forces, and the time to stabilize the knee were assessed after single-legged drop landings from a 30-cm platform. Surface EMG data in rectus femoris (RF) and hamstrings (H) and knee and ankle accelerometry signals were also acquired. The participants performed 3 pretest landings, followed by a 3-minute recovery and then completed 1 minute of WBV (30 Hz to 4 mm). Before vibration, the female subjects had a significantly higher peak vertical force value, knee flexion angles, and greater H preactivity (EMG(RMS) 50 milliseconds before activation) than did the male subjects. In addition, although not significant, the medial-lateral (ML) acceleration in both knee and ankle was also higher in women. After WBV, no significant differences were found for any of the other variables. However, there was a decrease in the RF to H activation ratio during the precontact phase and an increase in the ratio during the postcontact phase just in women, which leads to a decrement in ML acceleration. The gender differences reported in knee stability in response to WBV underline the necessity to perform specific neuromuscular training programs based on WBV together with instruction of the proper technique, which can assist the clinician in the knee injury prevention.