By Dr. Mercola
Whether fitness newbie or seasoned athlete, you may have experienced some puzzling physical sensations in the midst of your exercise routine.
Do your muscles quiver when holding your body in plank? Do you start itching midway through your high-intensity interval routine, making you wonder what's going on with your body?
Many of those physical symptoms are normal—or at least benign—and you're not alone. The good news is, science continues to shed new light on some of these unusual exercise-induced phenomena.
We'll explore a few in this article, including how to tell if there might be something for which you really should see your doctor.
Quivering, Shaking Muscles
Quivering or shaking muscles are a normal result of muscle fatigue. But why does your body quiver instead of collapsing altogether when your muscles get tired? Exercise scientist Len Kravitz, PhD, of the University of New Mexico, says it has to do with the communication between your muscle fibers and nerve cells:1
"Challenging exercise depletes the chemical messengers that carry signals between nerve and muscle cells. This causes some of the nerves and their corresponding fibers to drop out of service.
And since your cells don't all fire at once — some are contracting as others are relaxing — your body shakes like a car sputtering on a low gas tank."
Holding your muscles in a high-stress position, such as holding your body in a plank or a squat, or holding a dumbbell still mid bicep curl, is more likely to induce muscle fatigue.
Shaking muscles are linked to fast muscle contraction. Your muscles are smart—they divvy up the workload between fast and slow fibers, some working while others are allowed to rest, until your body says, "Switch!"
So, quivering is not a bad thing and can be one of the signs of an effective workout. However, pay close attention to form when your muscles begin to shake, as it's typically a sign of increasing fatigue and impending failure.
If your muscles are shaking earlier than expected in your workout, then other factors might be at play such as inadequate sleep, insufficient rest days since your last workout, not enough fuel, doing too much too soon, or possibly dehydration.2
If none of those factors seems to apply, you may just need to scale back on your intensity that day and lighten up the weights a bit.
Generally speaking, as your muscles get stronger and more accustomed to an exercise, the shaking will improve. But this is highly individual, and if it persists, it's not something that warrants much concern.
Dehydration and Electrolyte Imbalance
Dehydration can contribute to muscle shaking, muscle cramps, and nausea. According to Dr. Kravitz:
"Muscle proteins contract in a fluid environment, and sometimes if a person is dehydrated it will disrupt the muscle contraction signals. So make sure you are hydrated when you exercise."
When your body becomes low on fluids, your electrolytes may get a little off kilter, causing your connective tissue to be less smooth in transmitting signals from your brain to your muscle fibers. Muscles quiver when they receive a "garbled message" about when to contract.3
Making sure you're hydrated before, during, and after a workout will help keep your tissues juicy, so the signals to your muscle fibers won't get lost in translation.
Water is important with exercise because your body releases toxins, and you need water to flush them out. You may be surprised to learn that exercise actually increases your hydration, at least in the long run. This is because muscle holds much more water than fat, according to dermatologist and cellular hydration expert Dr. Howard Murad. Muscle tissue is 70 percent water but fat is only 10 percent.4 So as your fitness increases, so will your body's ability to stay hydrated.
Do You Get Itchy When You Exercise?
If you begin itching when you exercise, you aren't losing your mind! Your itching is likely an exercise-induced histamine response. A Japanese study5 recently showed that histamine may be released during exercise to help protect your body from exercise-induced fatigue or exhaustion. Unfortunately, histamine also sends itchiness signals to your brain.
Histamine is also a vasodilator. An older theory about itching is that when your blood vessels dilate during exercise to increase oxygen and carbon dioxide exchange, the surrounding nerves mistakenly register the sensation as itchiness. However, according to Stanford exercise physiologist Dr. Anne Friedlander, there's never been much scientific evidence to support this theory.6
Exercise-induced itching may occur by a mechanism similar to water-induced itching, a known phenomenon called aquagenic pruritus,7 (also see aquagenic urticaria and cholinergic urticaria). Both are histamine responses. People with aquagenic pruritus experience intense, prickling-like itching when exposed to water, such as after a shower, and sometimes after exposure to sweat.8
Exercise dilates the blood vessels throughout your body, including those in your head. For some this may trigger a headache, especially in high heat, high humidity, or at higher elevations. Blood vessel dilation can excite branches of your trigeminal nerve—the nerve that carries painful sensations from within the skull outward.
You are more likely to develop exercise-induced headaches if you are already prone to headaches. If you're diabetic, exercise-related blood sugar fluctuations can also trigger a headache. Make sure you're getting plenty of magnesium, as magnesium deficiency is a known factor in headaches and migraines,9 along with dozens of other health issues.
If you experience headaches only with resistance training, your posture might be the culprit. For example, rounding your shoulders forward can cause excessive muscle contractions in your neck, generating spasms that can result in a headache. Be sure to keep your posture tall and your shoulders back, and try to stay as relaxed as possible when you exercise.
Most exercise headaches are benign, albeit unpleasant. However, if the pain lasts for several days or is accompanied by other symptoms, you should stop your workout and see a doctor, as it could be a sign of something serious.
Too much or too little fluid in and around the brain can cause high-pressure or low-pressure headaches, respectively. These could signal spinal fluid blocks or leaks, which can be dangerous. If you experience any of the following in conjunction with your headaches, please stop exercising immediately and see your doctor:
- Loss of consciousness
- Double vision
- Neck rigidity
Blurred Vision, Seeing Stars, and Swollen Hands
What do brief visual disturbances and swollen hands have in common? They both signify circulatory issues and blood pressure fluctuations and adjustments. If you see spots or stars during heavy full-body weightlifting moves, such as dead lifts, this is normal. You're moving from a low to a high-body position, which results in blood pressure changes, forcing your heart to pump more blood to your brain.
It's normal to see stars for a second or two while that shift occurs—like when you suddenly stand up after sitting for a while. Positional changes sometimes cause you to see sparkly spots due to a momentary reduction in the blood perfusion of your retina, which causes it to fire off abnormal signals.10
If you see a major shower of spots, particularly if accompanied by light flashes, then you should seek immediate medical attention. Or, if the spots occur excessively and persistently when stretching or exercising, you should consult your physician to rule out an underlying medical problem such as a migraine or even a stroke. It is also not normal to have your vision go completely white or black, especially if accompanied by other symptoms like dizziness or fainting. If this occurs, you are better off stopping exercise until you consult your doctor.
Swelling in your hands or feet after exercise is most often a result of increased blood flow. If your veins aren't effectively returning the blood to your heart and lungs, it will collect in your periphery and produce swelling. This can happen after exercise, or after a day of shopping or any other activity.
Of course, your hands and feet can also swell from insufficient activity. Here is a test: push your finger into the swollen area with your thumb. If the indentation lasts for more than one second, it's a sign that the flow of blood and fluids beneath your skin is poor, but not an emergency. Just be sure to mention it to your physician.11
Do Your Feet Go Numb on the Elliptical?
This one is easy! The nerve that runs along the top of your foot can get pinched if your shoelaces are too tight, resulting in too much pressure from the top of your shoe. The remedy is just loosening your laces. You can even skip a loop or two in the middle to give your feet some extra room. Stretching your feet and calves may also help. For a great foot stretch: Sit in a chair in socks or bare feet. Bend your foot so that the tops of your toes touch the floor. Gently press into the floor enough to feel tension in the top of your foot. Stretch each foot for 20 to 30 seconds.12
Are You Allergic to Exercise?
While this may sound more like a comedic byline, the "exercise allergy" phenomenon actually does exist. These unusual allergic reactions generally depend on cofactors, such as a particular food or drug that triggers the allergic reaction with exertion.13 Medical News Today14 tells the story of a 33-year-old mother of four, Kasia Beaver, who reported that when she exercises, her heart beats too rapidly, her eyes swell shut, her throat closes off, and she breaks out in hives. Working up a sweat places her at risk for a potentially fatal anaphylactic reaction.
People initially didn't believe her reports and accused her of being lazy, until her symptoms were undeniable as she was transported to the ER. Mrs. Beaver was diagnosed with Exercise-Induced Angioedema (EIA), also referred to as Exercise-Induced Anaphylaxis, which typically occurs when exercising within a few hours of eating a certain food. Besides foods, other factors that can precipitate this reaction include alcohol, drugs (especially non-steroidal anti-inflammatories or NSAIDS), humidity, seasonal changes, and hormonal fluctuations.15 EIA has also been linked to hypothyroidism.
Fortunately, stopping physical activity usually results in immediate improvement of symptoms. This really seems to be more of a food allergy than an exercise allergy—so don't stop exercising. Fitness is simply too important to your overall health. It would also be wise to consider improving your diet by removing grains, sugars and dairy to see if it improves. The most likely answer for EIA is to exercise while fasting—which is a good idea for other reasons, such as improved fat burning. If you have allergies, it's a good idea to always carry emergency injectable epinephrine, and a med alert bracelet is not a bad idea either. Until you know you can exercise successfully, it's best to avoid exercising alone.
Keep on Exercising!
Exercise has profound effects on just about every system of your body, so you may at times experience some unexpected physical symptoms. Exercise places your body under stress, and most of the time this is "good stress" that promotes positive changes. Most exercise-induced reactions are benign, but occasionally it may exacerbate signs of a more serious problem that warrants medical attention. Don't ignore your intuition—please see your doctor if you are concerned, and remember, you know your body best. The good news is that exercise also has many unanticipated positive effects, such as clearer skin, improved mood and sleep, increased creativity, improved sexual function, and a wide range of other bonuses! So keep on exercising, as it's well worth your efforts in the long run.