Exercise

October 2, 2010

What Causes Muscles to Quiver When Lifting

I’m commonly asked why muscles tend to quiver on the last few reps of an intense strength training set. You know, that shakiness you get in your arms or legs while struggling to finish off a set of presses or squats. Actually, the phenomenon is caused by your golgi tendon reflex (GTR). Here’s how it works. Within muscles are proprioceptors (i.e. sensors) called golgi tendon organs (located at the junction of a muscle and its tendon). Their purpose is to monitor neuromuscular overload and hence protect muscles from ripping or tearing from bone. They accomplish this task by sending an impulse to your muscles that causes them to relax when there is a perceived threat to their safety.

But while such proprioceptors are beneficial if, say, you try to lift your refrigerator in a moment of unbridled impulse, from a training perspective it can hamper your efforts. The issue with the GTR is that it in certain instances, such as during intense weight training, it tends to kick in long before there is an actual safety threat. So while your quads are pushing to finish off that last rep of squats, your golgi tendon organs are sending impulses for them to relax, causing that awkward quivering sensation.

The good news is that the GTR is nothing to be concerned about. Assuming you are lifting within your own capabilities, there is no danger to your muscles in trying to push past ‘the shake’. For advanced trainees, doing so may be necessary to reach true muscular fatigue and thus optimize body composition. Just make sure that you have a contingency plan in case your muscles completely give out (read: spotter, power rack, etc)—you certainly don’t want to get stuck under the weight of a loaded barbell at the end of an intense set.

Stay Fit!

Brad