Unstable surface improves quadriceps:hamstring co-contraction for anterior cruciate ligament injury.
Shultz R, Slider A, Malone M, Braun HJ, and Dragoo JL. Sports Health. 2015. [Epub Ahead of Print].
Take Home Message: College athletes have decreased quadriceps:hamstring activation ratio, increased peak hamstring activation, and increased trunk sway when landing on an unstable surface versus a stable surface.
Proper co-contraction of the hamstrings and quadriceps muscle groups is critical in stabilizing the knee joint to reduce the risk of sustaining an anterior cruciate ligament injury. While previous literature has demonstrated a correlation between jump training on an unstable surface and a reduction in ACL injuries, no study has looked at the quadriceps:hamstring activation ratio (Q:H ratio) during these tasks, which could help clinicians gauge how important this training regime may be. Therefore, Shultz and colleagues recruited 39 female National Collegiate Athletic Association (NCAA) Division 1 college athletes and compared Q:H ratio during landing on a stable surface and an unstable surface. The authors recorded muscle activation of the vastus lateralis and lateral hamstring muscles. Participant’s biomechanics were recorded using a motion analysis system in conjunction with a floor-mounted force plate. All participants performed 3 successful, single-leg drops on a Bosu ball (unstable surface) and the floor (stable surface). Participants had to hold the landing during each single-leg drop for 2 seconds to be considered successful. All participants trained with, but did not perform single-leg drops on the Bosu ball prior to data collection. Overall, when participants landed on the Bosu ball (unstable surface) they had 20% lower Q:H ratio compared with the floor trials (stable surface). Peak hamstring activation was 18% greater in participants during Bosu ball landing compared with floor landing. Further, participant’s trials on the Bosu ball showed less quadriceps activation, less knee flexion range of motion, and more trunk sway when compared with floor single-leg drops.
The results presented in the current study are interesting because they show that athletes use different neuromuscular landing strategies on a stable and unstable surface. Landing on the unstable surface, which may be similar to some sports, led to increase hamstring activation, improved Q:H ratio, decreased quadriceps activation, less knee flexion, and greater trunk sway. Improper Q:H ratio may be associated with an inability to properly stabilize the knee joint during activity. This coupled with an increase in trunk sway, may result in an athlete being at a higher risk for orthopedic injury, including but not limited to anterior cruciate ligament injury. To prevent this, perhaps more training should be done while an athlete is on an unstable surface. By training in this environment, athletes may develop better knee stabilization techniques. This could help prepare an athlete to actively stabilize the knee joint during competition when perturbations and instability are common. However, before this can be put into widespread use more research should be done. In the current study, participants were not monitored for a learning effect; therefore, it is still unknown if participants training in this way would actually develop better knee joint stabilization. Until this question can be addressed, clinicians may include more training on unstable surfaces into their regiment but should also be cautious during such training. These results may also indicate that we may want to assess landing mechanics not just on a stable floor but also on unstable surfaces so that we can see how our athletes land during more challenging tasks. This may help us detect subtle faulty landing strategies that may occur during competition but not in the clinical setting on a stable floor.
Questions for Discussion: Do you use unstable surfaces in your rehabilitation and/or training? If so, have you seen an impact on the prevalence of knee injuries in this population?
Written by: Kyle Harris
Reviewed by: Jeffrey Driban
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