Cardiovascular exercise is critical for good health, improving heart and lung functions over time. You have your choice of steady-state cardio (aerobic exercise where you maintain the same intensity through your workout session) or varied-state cardio (aerobic exercise where you allow your intensity to shift up or down through your workout session). Most fitness gurus now advise people looking to slim down against too much steady-state cardio, recognizing that it has the following problems.
Cortisol is a hormone the body naturally produces during periods of stress. It suppresses triiodothyronine (T3), a thyroid hormone necessary to keep your metabolism humming at a quick pace. At the same time, it stimulates the production of excess glucose. The end result is that you don’t burn as many calories and store fat more easily. Adding insult to injury, cortisol also reduces levels of leptin, a hormone that helps keep your appetite in check, and increases levels of ghrelin, a hormone that makes you want to eat. This response is simply your body’s way of protecting itself and ensuring you have enough energy to survive what it perceives as a rough time, but when you want the number on the scale to go down, it can work against you. Cortisol doesn’t just affect your waistline, either. It contradicts the muscle-building influence of another hormone, testosterone, inhibiting protein synthesis so it’s hard to repair muscle damage and gain strength. Muscle burns more calories to maintain, too, so if you can’t bulk up, you won’t be able to maximize how many calories you could torch. Excess cortisol also is linked to decreased immunity, increased oxidative stress and osteoporosis, increasing your odds of getting sick or experiencing a training injury.
Understanding the negative effects too much cortisol has on the body, all exercise raises cortisol levels to some degree. Higher-intensity exercise, however, results in a higher production of anabolic or building hormones, such as human growth hormone (HGH), which will counteract cortisol to some degree. If you lower your intensity so you can get through your endurance-based, steady-state cardio routine, you don’t get this benefit.
The Fat Burning Zone
When you exercise at a low- to moderate-intensity level such as you need for steady-state routines, your body burns a higher percentage of