Authors (including presenting author) :
Chu KL (1)(2)
Affiliation :
(1)Department of Orthopaedics and Traumatology, The Chinese University of Hong Kong, (2) Physiotherapy Department, North District Hospital
Introduction :
The anterior cruciate ligament (ACL) remains to be one of the leading injuries in sports which impacts healthy active people from returning to sports. The prevalence of ACL injuries and cost spent on recovery is relatively high, as well as the consequences on ACL injuries leading to limitations of healthy individuals from remaining active. Injury prevention remains to be the first line of defense for ACL injuries. The hamstrings act as an important role in protecting the ACL from excessive anterior tibial translation force, which can lead to ACL injuries. However, there is yet to be a generic injury prevention exercise program that focuses on the activation of hamstrings whilst performing whole body vibration (WBV).
Objectives :
To investigate the effects of different exercise protocols on hamstrings and quadriceps activities during WBV.
Methodology :
This is a cross-sectional design study with repeated measures in which all participants performed 8 exercises while electromyography (EMG) measurements of the quadriceps and hamstrings muscles were recorded to calculate the activation ratios. Adult participants who are physically active with a Tegner score above 6 were recruited. Participants with previous injuries and contraindicated to WBV were excluded. Firstly, the maximal voluntary isometric contraction (MVIC) of bilateral knee extension and flexion was collected. Then, a selected WBV protocol was implemented to assess the hamstrings activation during single leg bridge and double leg bridges with and without WBV; and the hamstrings activation at 30°, 60°, 90° and 100° squats with WBV were assessed. Simple randomization was chosen for randomization of exercises and tests. The order of the exercises performed by each participant differs from each other. Therefore, 10 sets of 8 different exercises were randomized and allocated to the participants. EMG activation data from each muscle during each task was processed to calculate the activation of each muscle during the task when compared to its MVIC (%MVIC). One-way repeated-measures analysis of variance (ANOVA) was used to identify the differences in hamstrings activation and/or hamstrings to quadriceps (H/Q) co-activation ratios among exercises. A Bonferroni correction was used to adjust the p value in relation to the number of contrasts that were performed.
Result & Outcome :
A total of 10 subjects were recruited in the study. Single leg bridge with WBV and double leg bridge without WBV induced the highest and lowest hamstrings activation respectively (0.479 ± 0.223 %MVIC p=0.011) (0.198 ± 0.092 %MVIC p>0.05). The greatest H/Q activation ratio is noted while performing the 30° squat with WBV (0.345 ± 0.336 %MVIC p=0.021), and the least is noted while performing the 90° squat with WBV (0.164 ± 0.115 %MVIC p=0.021), a 52% increase in H/Q activation ratio. WBV enhances hamstrings activation in all of the bridging positions, and increases H/Q activation ratio in squats with WBV in contrast to all exercises without WBV. In view of clinical relevance, 30° squat with WBV should be practiced to enhance hamstring to quadriceps co-contraction, as well as practicing bridging exercises with WBV for hamstring strengthening.
