Functional Muscle Function

by Andrew Gorecki, DPT

One of the most important concepts that makes Superior Physical Therapy unique is the understanding of how muscles actually function.  Now this may sound like an arrogant statement but let me explain.  Most health and fitness professionals have learned some degree of anatomy and have knowledge of muscle origins and insertions, textbook muscle function, and exercises to increase muscle mass and strength.  Functional muscle function is the understanding of biomechanics, human function, and proprioception (neuromuscular control and feedback of muscles and joints-movement memory some may say).  There are a few basic rules that dictate the understanding of how muscles function during function.  First of all the functional movement must be identified.  For example running is different than throwing a baseball and muscles function differently during these movements.  Second, muscles function in three planes of motion always.  There may be a dominant plane of motion but there are always three sagittal ( front to back), frontal  (side to side), and transverse(rotational) planes of motion.  Thirdly never forget about gravity and ground reaction forces as these play an integral role in the function of muscles.

Now lets talk specifically about functional muscle function.  One of the easiest topics to discuss is walking as most people understand walking is a very important function.  Even more specifically lets discuss the function of the hamstrings during walking.  Our textbooks have taught us over the years (decades) that the hamstrings flex the knee joint.  This is to some extent true because I can stand here right now at my standing work station writing this blog and lift my foot off the ground and begin to flex my knee and feel my hamstring activating.  Now thinking about what happens when walking using the basic principles of function I realize that gravity actually flexes my knee.  In fact my quadriceps are activated a majority of the time in order to not flex my knee so that I don't fall onto the ground.  I also know that flexion is a sagittal plane of motion movement and even if true there are three more planes of motion to think about.  Now I will tell you that the hamstrings do not flex the knee during walking.  The functional muscle function of the hamstrings in the sagittal plane is to decelerate or slow down the pelvis and trunk when the foot hits the ground as we take a step.  The hamstrings in the frontal plane decelerate the pelvis while it moves laterally as the foot hits the ground.  Finally the hamstrings decelerate lower extremity internal rotation when the foot hits the ground and eccentrically create lower extremity external rotation as the body moves over the foot on the ground and heel off begins and we take another step.

Nowhere in that sequence did the hamstrings flex the knee. In fact the hamstrings as they decelerate the pelvis and trunk flexion actually extend the knee in the sagittal plane during walking by building up tension eccentrically.  So the question of the day is why do we train our hamstrings to flex the knee??  Think about it.  We have seated knee flexion machines, or we have people lay on their backs with their feet on a ball and tell them to flex the knees.  This doesn't make sense.  We are training the brain proprioceptively the wrong function of the hamstrings.  Proprioceptors are responsible for letting the brain know where the body is in space and what movements are safe and which ones to avoid.  Therefore if we train the proprioceptors incorrectly we are setting the person up for injury and poor movement patterns.  Lets think about the purpose of our exercises and develop exercises that look like the activity we are trying to get the person to improve.

Just some food for thought today.....

Cheers,

Andrew Gorecki, DPT