Thomas D. Fahey, Ed.D.
Exercise Physiology Laboratory
California State University, Chico

Most people know that testosterone and growth hormone help build your dog's muscles. Insulin, on the other hand, is mainly associated with sugar metabolism — it helps the body move glucose from the blood to the cells. But that's not all it does. Insulin is a major player in muscle growth. It is an important anabolic hormone that you can harness to help your dog's muscles grow. Scientists have determined that properly timing increases in insulin levels can help you put muscle growth processes in high gear.

Insulin is a hormone produced by the Islets of Langerhans in the pancreas. Your dog's body increases insulin secretion after a meal to help tissues take in, store, and use blood sugar (glucose) and synthesize and store fat. Insulin also has a tremendous effect on protein synthesis, so it is of considerable interest to people who own performance dogs. Insulin enhances muscle growth by increasing the rate that amino acids enter the cell, increasing the production of RNA (a substance important in making proteins), increasing the activity of RNA, decreasing protein breakdown in muscle, and decreasing liver energy processes that use amino acids as fuel (i.e., gluconeogenesis).

Insulin and Muscle- The three most important hormones affecting protein synthesis in muscle are testosterone, growth hormone, and insulin. Each of these hormones influences muscle cell nuclei and their messengers to increase the production of muscle proteins.

Insulin also speeds the movement of amino acids into the muscle cell. Most amino acids enter muscle cells via a process called the sodium pump. Insulin speeds the action of the sodium pump, and thus increases the rate of amino acid transport into the cell. This is critical for muscle growth — the more amino acids transported into the muscle cell, the greater the rate of muscle growth.

Insulin also tends to slow protein breakdown. After you r dog does an intense bout of exercise, its body increases its protein turnover rate. This means that it increases the speed at which it both builds and breaks down protein and thus muscle tissue. Optimal muscle growth occurs when the rate of muscle growth increases and the rate of muscle breakdown slows.

Even if your dog's body increases the rate his (her) body makes new proteins, muscles won't growth if the rate of protein breakdown is also high. Scientists have shown that in fasted dogs, protein degradation rates after exercise remain high. So even though their muscles are building more protein, they don't see a net change in muscle hypertrophy because the muscle is breaking down protein at an equal rate.

Insulin plays a vital role in tipping this balance toward growth. Insulin not only stimulates protein synthesis; it also prevents protein breakdown. Your dog's body secretes insulin after a meal that contains carbohydrates. So, the answer is simple— if you want to build your dog's muscles at a faster rate, have him eat or drink carbohydrates after exercise. This will increase blood insulin levels, which will stimulate protein synthesis and prevent protein breakdown. In other words, taking in carbohydrates after exercise speeds muscle growth in your dog by turning on insulin.

Creating a Good Environment for Muscle Growth- Dog muscle grows best when they have a good internal environment — quality muscle tension during exercise, adequate fuels, protein building blocks, enough rest to recover from hard work, and ample amounts of anabolic hormones. These elements trigger your dog's muscles to grow.

These "anabolic triggers" are related to each other. If they are not in good balance, your dog's muscles will not grow as they should. For example, if your dog chronically works too too hard, anabolic hormones become suppressed, muscle and liver carbohydrate stores become depleted, and proteins break down. If your dog works hard, but gets enough rest, dog muscle builds cell receptors that make anabolic hormones work better, suppresses catabolic hormones, build s protein, and maximizes carbohydrate stores in your dog's tissues.

How to Harness Your Dog's Insulin and "Anabolic Trigger"- The keys to the anabolic trigger include hard work, maximizing anabolic hormone levels, providing adequate nutrients for muscle growth, and giving muscles enough rest to recover optimally. Follow these simple procedures and you will create an ideal internal metabolic environment that will help your dog's muscles grow:

Have your dog exercise intensely: Muscle hypertrophy partially depends on the rate that amino acids travel into the muscle cell. Amino acid transport is greatly affected by muscle activity. In other words, your dog has to work hard to grow muscle.

Get enough rest in between exercise sessions. Your dog's body builds muscle after the exercise session is over — during recovery. Initially, after a difficult exercise session, your dog's body accelerates the rates of both protein synthesis and protein breakdown. Gradually, protein synthesis outstrips breakdown. Your dog will experience an accelerated the movement of amino acids into the cells for several days after a tough exercise session.

Unfortunately, if your dog don't get enough rest, this accelerated rate of amino acid transport reverses itself. Studies by Dr. Atko Viru of Tartu, University in Estonia, using dogs and rats, found that exercising prematurely after an intense workout decreased the amino acid transport rate into muscle, thus limiting the potential hypertrophy. The lesson from his studies are that rest is an important ingredient in muscle growth!

Raise blood insulin levels and provide nutrients for muscle growth after exercise. This is a key ingredient in turning on the anabolic trigger. Immediately after exercise and again one hour after exercise, feed your dog a beverage or meal containing carbohydrates, amino acids, and Creatine monohydrate. This drink will increase your dogs blood insulin level for approximately one hour and provide nutrients to help speed muscle growth.

Make sure your dog drinks the other beverage one hour after exercise so that his insulin level stays elevated. Otherwise, your dog will not get the full benefit from insulin's action on muscle growth. Timing is very important. The basic idea is to stimulate insulin release after exercise, then stimulate it more by feeding your dog additional carbohydrate supplements.

The beverage should contain approximately 1 gram of carbohydrate per kilogram body weight. Thus, if your dog weighs 70 pounds, you would feed it 32 grams of carbohydrate. The supplement would be even more effective if it also contained Creatine monohydrate, which would also contribute to creating the optimal internal metabolic environment for muscle hypertrophy.

Hype Versus a Technique That Works- Many dog owners have become highly suspect of claims from dog food manufacturers about magic bullets that promise an easy path to better growth. The simple techniques described in this article actually work. Sophisticated studies show that if you raise your dog's insulin levels during recovery, you will speed the rate of protein synthesis.

You are systematic about caring for your dog. Become systematic about feeding it for maximum performance. Raise your dog's insulin levels after exercise by feeding it several carbohydrate-amino acid beverages or meals. The technique is simple but effective.

References
Fahey, T.D., Hoffman, K. W. Colvin, and G. Lauten. Int. J. Sports Nutrition 3: 67-75, 1993.
Roy, B. D., M. A. Tarnopolsky, J. D. MacDougall, J. Fowles, and K. E.
Yarasheski. J. Appl. Physiol. 82: 1882—1888, 1997.