Form Follows Function

"It is the pervading law of all things...that form ever follows function. This is the law."
- Louis Sullivan

From: sixpackfactory.com

It's understandable that you want to look good in a bathing suit.  I want to look good with my shirt off too.  Jack Lalanne is one of the greatest health and wellness advocates even used standing in front a mirror naked as a better indicator of health than weighing in on a scale.  Striving for a lean body is not pure vanity but also a great way to improve your overall self-esteem and sense of self.

That being said, physique based diet and exercise plans don't necessarily lead to developing a "capable" body--one that can perform a broad range of physical feats.  I argue that a capable person has even greater self-esteem than one who is merely lean and muscular.  Confidence comes from knowing that you can handle life's curve balls and that you can respond to unpredictable situations where a weaker, slower or less nimble person wouldn't be able to avoid tragedy and failure.

Free running is an excellent mix of real world physical skills

Fortunately beauty does not need to be sacrificed for effectiveness and vice versa.  A functionally adept person is very likely shapely and visually pleasing in form.  The reverse is seldom true however.  How many body builders can swim a mile?  How many triathletes are capable of chinning themselves more than 5 times?  How many marathoners could pick up and carry someone their own size?  Some but not many.

I'm with Jack Lalanne in that a fit body should be a shapely one. Don't just focus on bigger arms and a smaller butt though.  Replace isolation weight training movements with compound ones (i.e. pull-ups over bicep curls).  Stand up when you workout versus laying down.  Use your own body weight and awkwardly shaped items for resistance training.  Run, swim and walk with a weight frequently. Working to develop real world physical skills will build an attractive body but more importantly you will acquire physical capabilities that will serve you throughout your life.

Competence leads to confidence.