Sports Medicine

Carbohydrates and The Glycemic Index: Quick, Slow, or Confusing

Once upon a time, carbohydrates were classified as sugars or starches. Today, carbs such as fruits, vegetables and grains are classified by their glycemic effect: that is, their ability to elevate blood sugar. The Glycemic Index (GI) ranks carbs according to their ability to elevate blood glucose. It was originally developed as a tool to help people with diabetes. Today, several popular diet books and magazines have expounded upon the virtues of avoiding carbs such as carrots, potatoes, and white bread because they have a high glycemic effect. Supposedly, they quickly elevate blood sugar, stimulate the body to secrete too much insulin, and this, in turn is said to promote fat storage.


Should I stop eating bagels and pasta? I’ve heard they are fattening because they quickly digest into sugar, which raises insulin and encourages fat storage. Is that true?


No. Sounds plausible, but the bottom line is: excessive calories promote fat storage, not excess insulin. If you lose weight after you stop eating bread or pasta, you do so because your are eating fewer calories, not because these foods are inherently fattening.

The Glycemic Index and Exercise

Exercise scientists, fascinated by the way different carbohydrates affect blood glucose, have explored the idea that low glycemic foods might enhance endurance performance by providing a slow release of glucose into the blood. One of the first studies to look at low glycemic pre-exercise foods reported that cyclists who ate (low glycemic) lentils before they exercised to exhaustion were able to pedal hard for 117 minutes, as compared to only 97 minutes when they ate (high glycemic) potatoes a significant difference!


Should I eat slowly digested carbohydrates like lentils before I exercise because they provide sustained energy? If I were to do so, I’d end up with intestinal distress.


The answer depends on the situation. Choosing foods based on GI is particularly important for endurance athletes who cannot take in fuel, such as sports drinks or gels, during exercise. But if you exercise for more than an hour and can consume energy while exercising, that is the best way to enhance endurance. Hence, you need not choke down lentils or bran cereal, thinking they will help you, when they actually might only create problems. If you cannot take in fuel during exercise, you may benefit from low glycemic pre-exercise carbs. Experiment during training.

High glycemic foods (sugary beverages, bagels, watermelon) are good recovery choices if you exercise hard more than once in a day (such as at a track meet or soccer tournament). High glycemic carbs can most rapidly refuel the glycogen stores depleted during the first exercise bout.

Note: If you are sensitive to sugar and easily experience sugar “lows”, experiment with eating more low glycemic foods. You may be better off choosing (low glycemic) yogurt as compared to the same amount of calories of (high glycemic) rice cakes. Take heed and make wise food choices!

The Pros and Cons of Stretching

There have always been questions and controversy over whether it is good or bad to stretch. Runners are often concerned about “over-stretching”. They worry if they have stretched enough or too much.

First, why stretch?

Many coaches and trainers create pre-game or pre-sport warm-ups. They understand that a few minutes spent stretching before an activity can help prevent many common injuries such a sprains, strains and tears. This preparatory activity stimulates circulation to the muscle, connective tissue areas and joints, increasing flexibility and improving range of motion. In short, stretching helps prepare the body for activity.

Watch a dog as he arises from bed, and lets you know he’s ready for exercise. The first movement he engages in is his long stretch. You’ve seen many other animals practice the same ritual, and yet no one told them to do it! It’s a natural experience to prepare the body for quick, propulsive action. Think how you spend your day: sitting at a desk, standing in one position, driving and watching television, sometimes for hours at a time. After maintaining these positions so long, the flexor muscles tighten and shorten, while the extensor muscles require strengthening. Women who wear high heel shoes all day have a similar problem, with calf muscles and Achilles tendons tightening and shortening. Stretching is imperative for them prior to activity.

After muscles have been stretched to 110% of their resting length, they function much more efficiently. Moving joints help to improve the flow of synovial fluid within the joints. By performing exercises which increase flexibility and strengthen muscles, improved function follows.

However, stretching has to be done properly. Either the participant or a trainer must be familiar with muscle groups, their origins, and their insertions. Certain exercises are recommended for particular sports, and they usually help to work specific muscle groups.

The rule of thumb when exercising and stretching is to start distally (towards the ends of the body) and work proximally (towards the core of the body). Muscles to pay attention to are the triceps in the upper body and the hamstrings in the lower extremity. The calf muscles and Achilles tendon need extra attention, since they are usually the first muscles to tighten during the course of the day. Stretching these muscle groups will aid your heel strike, which, in turn, will help with deceleration on the running stride, and allow for a better, more stable, push-off. Other muscle groups that need attention are the adductors (internal rotators) and abductors (external rotators) of the hip. In long-distance running, as well as in in-line skating and cycling, they are very important.

Since the anterior muscle groups (quadriceps) are usually much more dominant than the posterior (hamstring, gastroc-soleus) muscles, it is imperative to strengthen both muscle groups equally. Otherwise, the outweighing muscle group will cause the weaker group to work harder, and will usually cause a pull or strain. This happens frequently in the latter miles (18-20) of a marathon. Many runners will start to “cramp-up”‘ an indicator they are overusing weaker muscle groups. As a result, racing times that were excellent midway through the race begin to sour.

Do’s and Don’ts

The cardinal rule of proper stretching is: “don’t bounce”. Ballistic stretching will only cause the muscle receptors to fire, and, rather than stretch, will cause the stretch reflex mechanism to instantly contract.

The stretch should be performed slowly, and each side should be repeated, holding the stretch for 10 seconds. It is recommended that the stretch be repeated 10 to 15 times.

Whereas ice is the remedy for muscles and joints after an activity, heat is the prescription for muscles prior to activity. By heating the muscles (warm shower, bath or hot tub) for approximately 10 minutes, muscles will have increased blood supply when they are needed to stretch or fire quickly. If a runner has a pre-existing overuse injury such as tendonitis or muscle strain, the heat will help tremendously. A light massage will also offer beneficial results. This warm-up makes the beginning of the run go smoother, and decreases stiffness at the end or after the run.

So you’re probably asking yourself, can stretching be harmful, or can I overstretch?

The answer is a definite yes!!!

Bouncing or overstretching can be counter-productive. It can cause micro-trauma or tears in the muscles or connective tissue. As a result, this can create a weakness that may surface later in the run. Stretching should be performed for a prescribed period of time, generally not to exceed 5 to 10 minutes. Keeping the body in proper alignment when performing the stretch is important to keep in mind. Stretch adequately as many of the muscle groups as will be involved in the activity.

In the summer months, stretching is not as necessary as it is in the winter. However, it is still recommended as opposed to a slow trot warm-up during the first mile. Running slowly in the beginning of the run in hot climates is often recommended to avoid increased lactic acid build-up and cramps. In cold weather, there is no substitute for good stretching to warm up muscles and prepare them for the run ahead. This help prevents tightness due to the cold, and helps to avoid injury.