Neuromuscular fatigue has been implicated as a significant problem for individuals returning to sport following an anterior cruciate ligament (ACL) injury and reconstruction. Due to the high rate of re injury in those that have had an ACL reconstruction, one hypothesis is that neuromuscular fatigue will negatively impact strength performance, postural stability (single leg balance), and biomechanics during jumping and landing. It blows my mind that a female athlete with an ACL tear is 16 times more likely than a healthy female athlete to tear an ACL again.
The interplay between a previous injury, the resulting changes to the input to the brain, modified motor planning, and re injury is an interesting development in research. Today I wanted to dive a little more into fatigue, the impact on biomechanics, and how physical therapy and strength training can start to augment the problem.
Neuromuscular fatigue is a decrease the ability of an athlete to produce voluntary force in a muscle or group of muscles (McLean), which is combination of central and peripheral fatigue. Peripheral fatigue is a related to muscle damage and metabolic factors distal to the connection between the motor neuron and muscle fiber. Central fatigue can occur anywhere prior to the connection between the muscle and motor neuron (Figure 1). On the surface, quantifying or even getting a clear view of central fatigue seems impossible to examine in detail with any moving or jumping test. When I was reading over all the information on fatigue, I kept imagining when I ran a 400 meter race in track (just a horrible experience). The first two hundred meters felt fine but by the final curve, my ability to run and pick my legs up was basically gone. This fatigue was due to the metabolic byproducts produced from all out effort along with bumping against a central governor.
This physical therapy review is dedicated to the knee and the brain. While this is not a common connection, there are direct implications in how any peripheral joint injury should be approached with physical therapy and strength training in a well designed program.
Neuroplasticity following anterior cruciate ligament injury: a framework for visual-motor training approaches in rehabilitation
Grooms D, Appelbaum G, Onate J. Neuroplasticity following anterior cruciate ligament injury: a framework for visual-motor training approaches in rehabilitation. J Orthop Sports Phys Ther. 2015;45(5):381-393.
This past year and half, I have been working with an anthropologist from the University of Arizona, Dr. Jim Watson. The process has been fascinating and opened my eyes to the role of mismatched diseases in my practice. Dr. Jim Watson, Brianna Herndon (an honors student), and I have been looking specifically at the development of the knee and the impact of culture, sex, topography, and activity on its morphology.
Brianna was able to present some of our findings at the WeBIG conference this past year. As a student, she has done a great job diving into the research arena. Congrats Brianna!!
A Test of Sexual Dimorphism in Morphology of the Femoral Intercondylar Fossa.