Optimizing Training Methods for Injury Prevention

Prevention is a primary focus area across the various research agendas in the Department of Exercise and Sport Science.  Our prevention efforts span across a wide spectrum, including musculoskeletal injury, cognitive decline, traumatic brain injury, ethical and legal issues in sport, disease, falls, obesity, and physical decline.  The work being done across each of these prevention areas is critical, as each of these areas directly impacts one’s quality of life.  As the mission of our department is to “discover and promote knowledge of human movement to improve quality of life“, the work being done in these areas of prevention is directly aligned with our department’s core mission.

This week we highlight the recent work of Professor Troy Blackburn, who has recently published a study entitled (click on link for copy of the article): The effect of isometric and isotonic training on hamstring stiffness and ACL loading mechanisms. The findings of this study provide insight into optimizing training methods for improving hamstring muscle stiffness, and reducing  risk of Anterior Cruciate Ligament (ACL) injury.

Why we performed this study?Blacburn & Norcross, 2014

The anterior cruciate ligament (ACL) is one of the most commonly injured ligaments in the knee.  This injury dramatically increases the risk of developing osteoarthritis, and represents a substantial burden on the US health care system.  ACL injuries incur an annual lifetime health care burden (i.e. the total cost of treatment per year over the lifetime) of $7.6 billion for those who opt to undergo surgical reconstruction and $17.7 billion who opt for non-surgical rehabilitation.  However, surgical reconstruction does not reduce the risk of developing osteoarthritis.  Therefore, additional research is necessary to identify ways to reduce the risk of ACL injury, and to improve rehabilitation following ACL injury.

Previous research from the Neuromuscular Research Laboratory in the Department of Exercise and Sport Science at UNC-Chapel Hill demonstrated that the stiffness of the hamstrings muscles might play an important role in protecting the ACL from injury.  Stiffness refers to a muscle’s ability to resist lengthening, and aids muscles in resisting knee joint motions that may injure the ACL. Individuals with greater hamstring stiffness possess more stable knees as well as biomechanics (e.g. joint motions and forces) that indicate less ACL loading during activities such as landing and jumping during which ACL injury typically occurs.

Muscle stiffness can be increased via various rehabilitation and training techniques.  As such, increasing hamstring stiffness might aid in preventing ACL injuries and improving rehabilitation following ACL injuries.  However, the best type of training for improving hamstring stiffness is unknown.  Therefore, the purpose of our study was to determine if two types of training (isometric and isotonic) influence hamstring stiffness and biomechanics related to ACL injury.

What we did in this study?Troy stiffness

We measured hamstring stiffness and landing biomechanics in thirty-six healthy individuals. Subjects then completed 6 weeks of isometric or isotonic training.  While both types of training increased hamstring stiffness, isometric training was more effective.  Landing biomechanics also improved in manners consistent with reduced ACL injury risk, but these improvements were not statistically significant.

What we found and how this impacts the public?Jan 19 blog - Movement Screening Article

These findings suggest that isometric training may be an important addition to ACL injury prevention and rehabilitation programs.  Future research using larger samples sizes and longer training periods is necessary to determine if increasing hamstring stiffness reduces ACL injury risk.

This work provides a great example of how the EXSS Department is Exercising Science Solutions for Public Impact.  By optimizing training methods for preventing musculoskeletal injuries, we can more effectively manage the associated risks associated with sport and physical activity.  In doing so, we may allow individuals to realize the benefits of being physically active across their lifespan, and prevent those negative consequences associated with a lack of exercise / physical activity (see previous blog posts: Exercise is Medicine and Re-Affirmation of EXSS Importance).  Thus, work being in the area of prevention truly impacts and improves one’s quality of life.


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  1. Pingback: Hamstring Stiffness & ACL Injury Prevention | Brian Schiff’s Blog

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