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].

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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Shultz, R., Silder, A., Malone, M., Braun, H., & Dragoo, J. (2014). Unstable Surface Improves Quadriceps:Hamstring Co-contraction for Anterior Cruciate Ligament Injury Prevention Strategies Sports Health: A Multidisciplinary Approach DOI: 10.1177/1941738114565088