Voluntary activation of the ankle plantar flexors following whole-body vibration

This study investigated the effect of whole-body vibration (WBV) on the voluntary activation of the ankle plantar flexors. Twelve healthy young adults were randomly exposed to two treatments on separate occasions. The first (non-WBV) involved stretching of the plantar flexors at end range of dorsiflexion for five 1-min bouts. The second involved the same stretch with WBV (26 Hz) for five 1-min bouts. Attempted maximal voluntary contractions (AMVCs) of the plantar flexors were performed on an isokinetic dynamometer (30 degrees s(-1)) before and after each treatment. A twitch interpolation technique was used to investigate voluntary activation. Post-treatment data were normalised against pre-treatment data. Subjects were classified as maximally (n = 6) or sub-maximally (n = 6) activated using the pre-treatment twitch interpolation data. The effects of WBV were assessed by repeated measure (RM) MANOVA. After WBV, the group of subjects classified as sub-maximally activated increased peak voluntary torque and rate of voluntary torque production (P < 0.05), whereas angular displacement to peak torque reduced (P < 0.05); i.e. peak torque was produced at a longer muscle length. No significant non-WBV treatment effects were found for this group. No significant WBV effects were found for the group of subjects classified as maximally activated. This study found that the response to WBV was dependent on the level of voluntary activation of the ankle plantar flexors during a set of AMVCs.