Many bodybuilders have phenomenal leg muscle development in the off-season. Thick quads, bulging hamstrings, and some swollen calves. Yet after they complete their 8 to 12 weeks of dieting, their legs shrink drastically. Their upper body didn’t shrink much, so why would the lower body lose so much muscle size. The answer lies in the fact that so many bodybuilders perform cardio at too high an intensity level, which leads to losses in muscle size in the legs.

Any intermediate to advanced level bodybuilder who has been guilty of carrying too much body fat in the off-season – and therefore been required to crash diet for a show – will tell you that a lot of time must be spent doing cardio in order to achieve low body fat levels. Walk into any gym in America and you’ll likely see overweight and underweight (in terms of muscle) people who are absolutely killing themselves on cardio – running, sprinting, or just speeding along. They burn some fat, but they also burn valuable muscle. Their fast-twitch muscle fibers – those which do the most work during super-intense, low-repetition weight training – are recruited to assist with this insane level of intensity.

Professional bodybuilders, on the other hand, are very rarely seen doing cardio at such an intense pace. They know how many years it took them to build such a level of muscle, and they know that elevating the heart level above 60 to 80% doesn’t really affect fat storage levels. Rather, it causes the body to burn up carbohydrate stores. This is fine if one is on a high-protein, near-zero carb diet requiring the body to use body fat once all carbohydrates are burned. But for most people on a balanced pre-contest diet, whose bodies will have plenty of carbs available for energy purposes, it just isn’t practical.

In order to preserve your muscle – particularly leg muscle which is often burned by bodybuilders who use too high an intensity level for cardio – cardiovascular exercise should be done at a slow, controlled pace. The minutes might climb, but that is acceptable. Thirty to forty-five minutes of low-intensity cardio, completed first thing in the morning on an empty stomach, is usually enough to burn stored body fat levels and achieve optimal conditioning for a show with ample time remaining for tweaking the physique in the last week or two. If the fat isn’t peeling away fast enough, bumping the cardio training to two daily sessions, the second being performed just after the day’s weight session and also on an empty stomach, is the way to go. It’s important for bodybuilders to remember that low-intensity cardio, performed for more minutes, will allow them to preserve leg muscle while losing body fat.

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