Your weight loss workouts and muscle mass.

a study published this year in the Journal of Physical Activity & Health has found that people who participate in vigorous physical activity do not appear to compensate by avoiding other, moderate-intensity physical activity. The study concludes that clinicians should recommend vigorous activity for all its greater benefits without fearing a drop in their patients' more moderate forms of daily activity. Yet for people on a weight loss plan, moderate exercise intensity may be just as effective as vigorous. One recent study assigned 201 women to four different exercise groups of varying intensity. The participants lost between 8% and 10% of their body weight over one year, with no significant differences among the exercise intensities.

Another study assigned 173 overweight women (average age 61) to either moderate exercise in the form of recreational activity or to a stretching group. For one year, the exercisers spent only about three hours a week engaged in activity, producing differences in total body fat of -1% and weight by -3.75 pounds from the non-exercising controls. These findings suggest that a moderate approach to exercise might be the way to go if you're just starting out on a weight loss plan, and question your ability to stick with a vigorous regimen over the long haul. Just realize the results, too, will be moderate.

In addition to the increased mortality risk inherent in being out of shape (see page one), losing weight without exercising will unfortunately ensure that you lose muscle mass. This is never the goal of a weight loss plan; when we speak of weight loss goals we really mean fat loss goals. Some studies have shown, however, that exercise alone can increase fat loss, leaving lean mass alone. In one such study, 30 obese male army recruits exercised five days a week for four months, losing an average of 26 pounds. The reduced waistlines and hip circumferences indicated that the weight loss was largely from reduced abdominal fat. The recruits' fatfree muscle mass remained the same.

Yet other research has shown that lean mass goes away during a weight loss plan regardless of whether people on the plan perform aerobic exercise. There is some evidence that resistance training may minimize the reduction of lean muscle mass associated with weight loss. But research in this area, too, has yielded mixed results.

In the end, building lean muscle mass while cutting calories is desirable. Lean muscle mass burns more calories at rest than fat mass, which is the body's way of storing calories in the first place. And you certainly won't build lean muscle mass by restricting food intake alone; so move your body, even moderately, to see the best and healthiest weight loss results.

(Journ. Phys. Activity & Health, 2004, Vol. 1, No. 1, pp. 45-55; JAMA, 2003, Vol. 289, Vol. 3, pp. 323-330; Vol. 290, No. 10, pp. 1323-1330; Med. Sci. Sports & Exerc., 2003, Vol. 35, No. 2, pp. 207-213; Phys. & Sportsmed., 2003, Vol. 31, No. 9, p. 41; No. 10, pp. 17-18; No. 11, pp. 39-45)