Stretching Misconceptions

Q: My daughter works out regularly and has bulky calves and shoulders. I’m convinced that it’s because she never stretches. I want to convince her to start by telling her the benefits of doing so—and the downsides to skipping flexibility exercises. Also, is Pilates or yoga better?

A: Stretching will not make a person lean, lengthen limbs or get rid of bulk. It can’t. Even though many people who practice various forms of flexibility training like Pilates and yoga often make these claims, there is no scientific proof that it is possible. And anatomically speaking, it makes no sense if you understand how muscles really work.

So, while it might be a good idea for you to encourage your daughter to stretch more, realize that she should be doing so to become more supple, but not because her body type will change.

Muscles’ Makeup

Muscles are made of two types of fibers, fast twitch and slow twitch. On average, people have a 50-50 split of both. But some muscles and some people may have varying ratios in different muscles. Muscles that have more fast-twitch fibers are more likely to bulk up because that’s one of the physical properties of this type of fiber when it gets exercised.

World-class athletes tend to excel at their chosen sport because they may have been born with more of the right type of muscle fiber (among other physical attributes) that helps them perform better. Compare a marathon runner to a sprinter: Super-fast sprint activities are driven by fast-twitch fibers, and so sprinters with more of them tend to look very buff and sculpted. Endurance running is spurred on by slow-twitch fibers, which is one of the reasons why high-level marathoners tend to be almost scrawny.

The Muscles You Inherit

As well as a person’s genetic endowment of muscle-fiber type, heredity also determines muscle shape. And some people may have more muscle fiber in specific muscles than others, allowing them to build bigger muscles. Other people may have different lengths or thicknesses of muscle tendons, or where their tendons attach to bones.

For example, calves can be skinny, thick or bulky. The main calf muscle—the gastrocnemius—attaches to the heel with the Achilles tendon. Some people have a tendon that extends farther up the leg, allowing for a thinner ankle and higher-placed calf muscle. But if the tendon is shorter, the lower leg may look thicker because there is more muscle lower down the leg. The leg may look bigger all over because the muscle is spread out, but less bulky in the calf. The underlying soleus muscle can also affect the overall look of the calf.

Short of chopping away surgically at muscles, there’s not much you can do to change a person’s natural muscle shape. Some anorexics or severely underweight people who manage to lose so much weight that they lose lots of muscle tissue may be able to lean down and appear to change their shape. Of course, this is also very dangerous and not recommended!

Although genetic research in exercise is still in its infancy, several genes have been identified that play a role in muscular development and strength. People with these genes are likely to show increased muscularity when doing the same type and amount exercise as someone without the genes.

Bone length also matters. It’s harder for a muscle to look big on a longer bone. Ever know a tall, lean person who lifted and found it difficult to bulk up? Many beefed-up body builders are short, which helps them to look bigger.

But even a person inclined to be muscular may have a limit. Bodybuilders who may be spending hours in the gym trying to build still might use steroids to trigger more muscle growth.

Women and “Leaner” Limbs

Many exercise programs targeting women make false promises that a particular exercise routine will make them longer and leaner. Any activity that merely stretches a muscle can’t make it longer. Yes, a muscle is lengthened when you stretch it. But the opposing muscle on the other side is shortened. The minute you release that stretch, the shortened muscle is lengthened and the elongated muscle shortens. So, when you stretch your quads, your hamstrings shorten. When you stretch your hamstrings, your quads shorten. Stretching is a transient activity and it is physically impossible to keep all the muscles lengthened at the same time. You’d be frozen in place.

Looking leaner, or thinner, or less bulky probably has more to do with body fat. Decreasing body fat comes from eating less and burning more calories from cardiovascular activities like running, walking and cycling. Stretching burns very few calories. So if you have thick thighs and you’re doing “lengthening” exercises in Pilates, you’re unlikely to see any change in reducing fat or slimming down. (You may feel firmer and develop increased range of motion or muscular stamina, depending upon the exercises that you do.)

Some people who do Pilates and yoga look lean, but they probably looked that way in the first place. Sure, the workouts may have helped them look firmer as any exercise can, but totally transform their body shape? Unlikely. Anecdotal claims of such changes also might be due to simultaneous dieting, ratcheting up the cardio workouts, eating disorders or any number of other factors.

Not everyone who does stretching-based workouts is lean, though. And many people who go in with the expectation that they will become so often leave frustrated. There are certainly plenty of plump and bulky body types that also do these workouts.

Stretching is relaxing and a great way to improve joint range of motion. But it’s not going to change the way your daughter looks. Perhaps, instead of trying to decide which workout will make her meet your physical preferences, you should applaud her for being fit, strong and committed to working out.

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Martica is a Manhattan-based exercise physiologist and nutritionist and an award-winning fitness instructor. She has written for a variety of publications including Self , Health , Prevention , The New York Times and others. Martica is the author of seven books, including her latest, - Cross-Training for Dummies . (Read her full bio.)