Why Do My Legs Shake On Leg Press? (3 Things You Need to Know)

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I remember the first time my legs were shaking uncontrollably when I came off the leg press machine.

My first thought was to panic, but I soon discovered this isn’t as bad as you may initially believe.

Here’s what you need to know.

The main reason that your legs shake when you leg press is because the muscles are depleted of oxygen. This is nothing to worry about on a neural or physiological level. It simply means that you have pushed the muscles very hard, which in the gym environment is typically a good thing. If a muscle is short on oxygen, which can often happen during intense exercise, it will spasm or twitch. This is completely harmless and the muscle will return to “normal” once rested adequately.

Your Leg Muscles Are Depleted of Oxygen

A Woman on the Leg Press Machine

If you find that your legs start to shake when you use the leg press machine this is a sign that the muscles are low on oxygen.

Now I know that probably sounds a little scary, but it’s actually not, and it’s not something that you need to overly worry about.

Obviously, you’ll be able to tell the difference between general shaking, feeling “the burn” from exercise, and a genuine painful injury.

Basically, what has happened here is that your leg muscles have been worked very hard and therefore they’re no longer receiving an adequate oxygen supply.

This most commonly occurs when the muscles are unaccustomed to the intensity.

Now, you may even experience this “shaking” sensation with an upper-body push or pull-based exercise.

However, it seems to happen more often with lower-body exercises.

And this is especially true of the leg press.

The main reason for this is because the lower body houses the largest muscles in the body.

Therefore, you can typically produce far more force with these “bigger” muscles.

Additionally, due to the position of your body your legs are more likely to shake during leg presses, as opposed to barbell squats.

Plus, you generally press a lot more weight with your legs than you squat with a barbell.

In fact, I know from personal experience that I can more than double (even treble) the amount of weight on the leg press machine compared to barbell squats.

And I generally perform twice as many reps.

The twitching of your leg muscles does not have any neural or physiological effect on the body.

It’s simply a sign that you’ve exerted a lot of effort, worked hard, and the muscles have been depleted of oxygen.

Your Legs Haven’t Yet Adapted to Leg Press (Intensity)

Something I mentioned above was that your legs haven’t become accustomed to the intensity of the exercise.

Please note, I said “intensity” there.

I know that the very first time you try the leg press machine that this “shaking” may occur.

This may also be true if you haven’t performed leg presses in quite a while.

And many so-called “experts” will tell you that this will stop once you become used to the exercise.

However, I’m sure I’m not the only one who looks to progressively overload an exercise on a regular basis (as you should be doing if you want to get bigger and stronger).

So, in effect your intensity is increasing week-on-week.

Therefore, you could say that your legs won’t get a chance to adapt to a particular intensity.

I see this as a good thing.

What you may notice is if you use the same weight on the leg press machine every week then your muscles will definitely adapt to this weight.

You’ll probably notice that the shaking has stopped.

This is literally a sign to add more weight and get your legs shaking once more.

Basically, don’t be scared of the “leg shakes” when you leg press.

As I say, it’s a sign that you’re working hard, with good intensity, and this will of course lead to growth.

The Leg Muscles Are Fatigued

I guess many of us notice the leg shaking during the actual exercise.

More often than not this occurs at the top of the movement once you’ve pushed the foot plate to extend your legs.

Just a quick side note – be sure not to fully extend the legs whenever you leg press.

If you fully lock out the knees this could actually lead to an injury.

Plus, in a way it keeps constant tension on the muscles, which once again is great for muscle and strength development.

Anyway, back to the point, shaking legs.

Sometimes you may notice that this actually occurs after your set of leg presses.

So, you make your way through your allotted set of reps.

You lock the foot plate in place, and either stay seated or stand up to rest before your next set.

And then you notice that legs are twitching and spasming uncontrollably.

If this happens after your set this is typically a sign that the muscles are fatigued.

Basically, you have either hit failure or are very close to the point of failure.

Yet again, this can be viewed as a good thing.

I know there are many opposing views on whether or not you should train to failure.

And I will say that you probably shouldn’t train to absolute failure on the leg press machine.

Okay, it’s far safer than training to failure with barbell squats, but there’s still a hint of danger with the leg press machine.

Once you hit failure, and especially if this is mid-rep, you’re going to struggle to push the foot plate back up.

Depending on your height, and the length of your limbs, this can of course be very dangerous.

In fact, this can cause a lower back injury while leg pressing.

For me, I prefer to train (irrespective of the exercise) to just before failure.

So, I typically have a rep or two left in the tank.

This will still fatigue the muscles plenty, particularly if I’m performing more sets.

So, the leg shaking that you experience once you’ve actually finished your set on the leg press machine is a sign that you’re near to muscular failure.

Therefore, you simply need to rest up, allow the twitching to stop, and you should be ready to go again.

Key Learning Points

  • If your leg muscles are depleted of oxygen they will shake when activating them through an exercise such as leg press. This isn’t something to worry about, but rather appreciate that you’ve hit the movement with proper intensity.
  • If your legs shake afterwards this is also a sign that you’re nearing muscular fatigue (failure).
  • “Shaking” when nearing muscular fatigue more commonly occurs in the lower body, as it houses larger muscles than the upper body.

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