Build a Body that's Engineered like a Ferrari 458
Is your goal to lose body fat, build muscle, and improve your health?
If so, you must train for strength and limit the endurance (cardio) training.
I love cars so I will use a car analogy to explain.
When you train for strength, you are in essence trying to build the physical equivalent of a Ferrari 458. The 458 is a marvel of engineering; it is a beautiful, agile, and extraordinarily powerful machine that performs well beyond the comfort level of the average driver. The biggest drawback, aside from the ridiculous price-tag, is the rate at which this car burns fuel. A Ferrari 458 averages about 14 mpg (miles/gallon); it is built for performance but energy expensive.
A well designed strength program has a similar effect on the human body, and this is primarily due to an increase in fast-twitch muscle. As you gain muscle and strength, not only does your appearance and performance improve, your energy requirements increase. Fast-twitch muscle tissue is metabolically expensive and requires a lot of fuel to build and maintain. And over time, even a small increase in muscle tissue can result in the loss of excess body fat.
On the other hand, when you train for endurance, you are building a Toyota Prius. The Prius is a much lighter and very efficient (48 mpg) vehicle. It burns less fuel and can travel long distances using minimal resources.
Engaging in low-intensity long-duration cardio(marathon training) will create a very efficient muscular system due to the preferential adaptation that occurs in the slow-twitch muscle; this is great for the endurance athlete but counterproductive for those trying to build an impressive physique. There is no doubt that chronic endurance training will increase your ability to travel long distances, but it achieves this adaptation by discarding energy expensive fast-twitch muscle. Since fast-twitch muscle is the primary storage site for muscle glycogen(glucose), loss of this tissue will decrease your ability to store energy and burn fuel(food). This is not conducive to maintaining a lean, strong body.
"Well, what about your heart?" you ask. Almost any form of dedicated exercise will improve health markers. Yoga, Pilates, strength training, rock climbing, kick boxing, jogging, etc... will improve general health markers when performed consistently, but they are not equally effective for building a Ferrari-like body.
Take home message.
If you want to build a lean body that turns heads, train to build a Ferrari. Intermittent bouts of intense muscular work is what builds muscle and transforms you into an energy guzzling machine.
Before you start an exercise regimen, ask yourself, "Do I want to build a Ferrari 458 or a Toyota Prius?"