Missing periods can also put women at risk for developing osteoporosis and cardiovascular problems. It seems counterintuitive that exercise can reduce bone density, but without nutrition and estrogen -- another hormone that can get depleted -- bones can become weak, even with physical activity.
Fitness proponents urge people to feel the burn and love the pain, but what if an exercise routine could actually kill you? For some, that fear can be a reality.
Exercise-induced anaphylaxis (EIA) is a condition in which, during physical exertion, the body's mast cells release histamine, the molecule responsible for the swelling and itching associated with an allergic reaction, according to a 1992 paper in the Clinical Journal of Sports Medicine.
People with EIA can have an allergic reaction, including hives, trouble breathing, nausea and wheezing, to even small amounts of exercise.
Dr. Thomas Casale, chief of allergy and immunology at Creighton University in Omaha, Neb., and executive vice president of the American Academy of Allergy, Asthma & Immunology, studied the phenomenon in the 1980s. He found that EIA is often associated with certain foods, such as celery, shellfish and peanuts that, when eaten on their own, pose no problem, but if eaten before a workout can trigger an allergic reaction.
Despite the seriousness of an anaphylactic reaction to exercise, small amounts of regular exercise can build the body's tolerance for physical activity. In addition, avoiding food triggers and using antihistamines can help those with EIA stick to their exercise regimes.
Think pumping extra iron or running 20 miles is uber-masculine? Think again.
"With shorter bouts of activity, hormones that strengthen us (like testosterone) can be increased," Goldberg said. "However, with excessive exercise, testosterone drops."
While hormonal imbalances due to excess exercise is not a huge problem, it can result in problems, including loss of bone density, decreased sex drive and feeling weaker or less energetic. Goldberg said this probably affects a small group of people with a specific, likely obsessive, personality type.
Lack of nutrients is the underlying problem of a hormonal imbalance as intense exercise can deplete the body of the raw materials necessary to make hormones.
Goldberg supposes the use of synthetic steroids can be a way to combat this imbalance.
"They depleted their own and they know it," he said.
Women can experience hormonal imbalances, as well, losing estrogen if they do not fuel themselves with calories during intense exercise, which puts them at risk for osteoporosis.
Sore muscles and aching feet after a workout is one thing. But a splitting headache is altogether different. And, for some, a bad headache is just part of their exercise routine.
"The physiology of exercise can promote the physiological changes in the brain that cause a migraine headache," said Dr. Joel Saper, founder and director of the Michigan Headache and Neurological Institute.
This can be true of almost any kind of physical exertion, from aerobic exercise to weight lifting to sex.
Beyond the exertion of exercise, straining muscles, particularly in the neck, are a classic trigger for a migraine or other headache. Pain in the neck muscles, joints and nerves can all translate to an intense headache.
But a post-workout headache can signal a more serious, even dangerous problem.
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.
Increased blood pressure from exercise can, in rare cases, put someone at risk for aneurysms or intracranial bleeding.
But, Saper said, most of these headaches occur in people who are predisposed to headaches for some reason. If, for example, someone has a history of migraines or has low blood sugar because of diabetes, then they will be at risk for headaches after exercising.
"Common sense prevails on those kinds of things," said Saper, adding that if headaches are deemed benign by an expert, people can head them off by taking anti-migraine drugs or other pain medication.