PT on the Net Research

Muscle Fatigue


Question:

I thought Jason Anderson’s recent Research Corner Q&A regarding Spot Reduction for Glutes was fantastic; however, there is one issue that confuses me. When we work a muscle, will other muscles take over, as in his example of fatiguing the legs, causing the glutes to handle the load during squatting comfortably and not respond by growing? Wouldn't the muscles working on their own like this cause them to grow? And where does this leave us in response to muscle activation such as stretching the adductors and working abductors before squatting or lunging?

Answer:

Many thanks for your feedback and your question.

In the example of the “upright” squat, the angle of the femur and therefore the knee placement has moved further from our center of gravity, subsequently placing greater emphasis onto the quadriceps to control the increased forces at knee (work = force x distance). This is ever present in the deceleration of running or walking down steps.

So the performance of this exercise, whether we have pre-exhausted the quadriceps or not, is as always dependant on the weakest link in the chain. We will only lose the ability to perform the task at hand due to fatigue in quads, while the glutes are still relatively fresh, which is why their adaptation will be far less than the response gained by the fatigued and therefore “stimulated” quads.

The only way the glutes will take over and allow us to continue with the exercise is if we alter our position and bend forward more during the performance of the squat, something that is often seen at the end of a set of squats when the trainer is attempting to extend the set beyond the quads’ ability to overcome the same resistance.

Furthermore, we can take a look at your example of stretching out the adductors to de-sensitize them, therefore reducing their force output and subsequently reducing their inhibition potential on the opposing abductors. This is a practice adopted by many fitness professionals to manipulate the neural drive, allowing us to maintain better knee control in the squat and lunge by facilitating a greater activation from the often suppressed and weaker lateral glutes.

There is a big difference between pre-exhaust where we want to completely fatigue the muscle with an isolation exercise just before a compound one and pre-exercise facilitation where we only want to “awaken” a dormant muscle to get it a little more involved in the performance of a movement to maintain better control or positioning.

So you could say that pre-exercise facilitation is about giving the muscle a “shake” and not completely annihilating it!

I hope this is of some help.