Muscle Adaptation During Exercise

iStockbyte/Stockbyte/Getty Images

For most exercisers, the first step for adding strength and improving fitness is developing a reasonably consistent workout routine. Your muscles will adapt to the new workload and should grow stronger. But muscle adaptation can cut both ways. If you’re too consistent in your workouts, you may find that your progress levels off at a certain point. If you hit this exercise plateau, it’s time for Step 2.

The Overload Principle

You must continually challenge your muscles if you want them to grow. For example, if you can bench press 100 pounds eight times fairly easily, add sufficient weight so your muscles are fatigued after eight reps. As long as you don’t overload your muscles and cause an injury, your muscles will adapt to the heavier load by growing larger, thereby increasing your strength. To make further gains, however, you must continue to challenge your muscles by increasing the weight load.

What Happens to Overloaded Muscles

Your body reacts in a variety of ways when you begin to overload your muscles. As your training begins, improved neural pathways to the trained muscles help muscles generate more force, so you can handle heavier weights. Progressively overloading your body also stimulates bone growth and strengthens the ligaments that link your bones together and the tendons that attach muscles to bones. At the same time, your muscles absorb and synthesize more protein, while losing less, so you gain muscle fibers, causing your muscles to grow larger.

The Exercise Plateau

If you stop challenging your muscles, they won’t continue to grow and you hit what’s known as an “exercise plateau.” The solution is to increase your workload to further challenge your muscles. However, muscles may adapt so well and become so used to a specific exercise, or group of exercises, that simply increasing the weight load doesn’t result in improvements. In these cases, try performing different exercises, or doing your workout in a different order. You can also examine your daily routine outside the gym. Eating a healthier diet or getting more rest may help your body push through the plateau.

Aerobic Muscular Adaptation

Muscle adaptation to aerobic exercise is similar to strength-training adaptation. Performing aerobic exercise increases the number of mitochondria -- which convert fuel into energy in a form your muscles can consume -- in your muscle cells. Cardiovascular training also increases the number of capillaries that bring oxygen to the mitochondria. The overall result is an improvement in each muscle’s capacity to absorb energy. With more fuel, your muscles can endure longer periods of exercise. But the adaptation has its limits. Depending on the duration and intensity of your training, you may reach your peak efficiency in as little as four to five weeks.