Why Your Muscles Shake During a Hard Workout

Do shaking muscles mean you're really working it or that you might be overdoing it? An expert weights in.

woman shaking muscles during workout doing push-ups
Photo: gradyreese/Getty Images

Pushing yourself during a workout is rarely a bad thing, and going so hard that your muscles start to shake is certainly a sign that you're at your max—but your body may also be trying to tell you something. While many people pass this off as a simple sign that they're out of shape, and a majority of my fitness colleagues would agree that this trembling is not a great cause for concern, it could also lead to injury if you're not careful to use proper form. (See: Warning Signs You're Pushing Yourself Too Hard In the Gym)

Let's explore why your muscles may shake during a barre class, Pilates, strength workout, or other type of exercise—and what to do about it.

1. Inadequate sleep. If you are heading into a cardio or strength training session feeling lethargic or lacking a good night's rest, you will probably experience tremors at some point in your routine. The body continues to grow and heal when it gets the proper amount of sleep, and disrupting this can cause your muscles to stay locked in a catabolic-like state. If you've been skimping on sleep, I recommend you skip the gym and stay in bed (if you work out in the morning) or head to bed early (if you're a p.m. exerciser).

2. Going to extremes. With fitness crazes like CrossFit and endurance events like Tough Mudder becoming the staple in mainstream fitness, people are really pushing themselves to the extremes these days. However, take caution and implement mandatory rest days into your fitness routine. Learn how to take a proper rest day so that you can maintain a sustainable workout routine and stop the shakes for good.

3. Too new, too much, too soon. If you try a new fitness class or jump into a new routine, at some point during your workouts you may feel your body start to wobble because working different muscles than you're used to may be too much, too soon. While it may not be a cause for great alarm, it's probably best to lighten up. You could place stress on other parts of your body in order to compensate for weaker muscles, which may cause injury. For example, if it's your first time performing burpees, by the fourth or fifth one your legs may start to shake. Instead of resting, you decide to continue but with bad form, which can strain your lower back. Bad idea.

4. Dehydration. Your workout can be one of the best indicators of whether or not you are hydrated. When your body is low on water, your muscles and connective tissues have difficulty performing what they are meant to do, as improper hydration can cause an imbalance of your electrolytes, which are involved in muscle contraction. I recommend drinking half of your body weight in ounces daily. Remember, if you're thirsty, you're dehydrated.

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