Being fit matters.

New research suggests that a few extra pounds or a slightly larger waistline affects an executive's perceived leadership ability as well as stamina on the job.

While marathon training and predawn workouts aren't explicitly part of a senior manager's job description, leadership experts and executive recruiters say that staying trim is now virtually required for anyone on track for the corner office.

"Because the demands of leadership can be quite strenuous, the physical aspects are just as important as everything else," says Sharon McDowell-Larsen, an exercise physiologist who runs an executive-fitness program for the nonprofit Center for Creative Leadership.

Executives with larger waistlines and higher body-mass-index readings tend to be perceived as less effective in the workplace, both in performance and interpersonal relationships, according to data compiled by CCL. BMI, a common measure of body fat, is based on height and weight.