There’s no disputing that cardio is an essential component of any total-body fitness regime. It boosts metabolism, strengthens the heart and lungs, improves endurance, promotes lean muscle,and burns excess fat like few other activities can.
But (and yes, there’s always a but)... over-dedication to cardio can do more harm than good... it comes in the form of sore joints, stress fractures, chronic fatigue, metabolic issues and a number of related side effects. How is it that something so good can be so bad for you? The answer lies in the way in which our bodies create energy. Fat is how the body stores energy for future use. We eat calories in the form of food. We process them. We use what we need and store the rest as fat. Later, when we need energy and are not actively feeding ourselves, fat comes to the rescue to fuel whatever activity is occurring. It is in this way that cardio helps people lose weight. The demand for energy exceeds that which is already in the metabolic cycle so fat reserves are tapped (and depleted) to supply needed energy. However, engaging in cardio to such an extent that the body cannot burn fat effectively causes it to burn muscle instead. When the body doesn’t get enough oxygen (from too long or strenuous activity in a single instance) or when the body doesn’t have adequate stores of fat (from long term cardio excess), muscle becomes the only fuel available to answer the body’s needs. The end result is a feeling of weakness or lack of strength despite excellent cardiovascular conditioning.
Another drawback of too much cardio is decreased metabolic function. The body treats exercise in a way that is very similar to any physical stressor... which means it releases many of the same hormones it does for other stressful situations. The primitive portion of our brain involved with regulatory body functions says, “Ok, we’re running. We must be running from something. We should conserve our fat stores in case we’re unable to devote time to a proper meal.” Obviously, if you’re running for 30-90 minutes a day, the body realizes that the “threat” is gone and allows metabolic function to mirror the caloric balance needed for an increase in regular activity. However, if you’re on the run for 2 or more hours a day, every day, or if you regularly participate in two-a-day cardio workouts, you can see why your caveman brain might think it needs to safeguard against some sort of attack. This can be exceptionally challenging for those who have picked up cardio specifically to lose weight. They see minimal results, and so press that much harder, only to perpetuate an undesirable metabolic rate. Besides weight, the body also releases hormones and neurotransmitters during vigorous activity. The constant flood and/or depletion of these bio-chemical compounds can lead to emotional and psychological conditions such as depression, paranoia, psychosis, eating disorders and body dysmorphic disorder to name a few.
Lastly, cardio is generally hard on the body... which is part of why it’s so effective. However, the constant impact of feet against concrete or treadmill, the constant grinding of knees on an elliptical or bike, and the ceaseless rotation of shoulders during swim laps begin to take their toll. Little by little, cartilage and protective cushioning is worn away and replaced by pain. As well, the force of the exercise on the body starts moving outward from joints into other nearby parts of the body, causing such injuries as stress fractures (most commonly in feet and ankles), bone spurs, tendonitis, and more.
Unless you’re training for an event like a marathon or triathlon, most of us can get optimal cardio benefit from 2 to 5 miles of jogging at a moderate pace. Walking, biking and swimming should also be taken on in conservative distances, especially when starting out. If you find that your weight loss is tapering off, the answer may not be more cardio – it may be more intensity. Begin by raising inclines or adding resistance in the form of stairs, reverse current, or by carrying additional weight before you automatically add more distance and time. And always make sure you’re supplying your body with an adequate amount of nutrition to fuel your workouts and help your heart, lungs and muscles with the post-workout recovery process.