How Long Does it Take the Human Body to Adapt to a New Exercise?

The physiological adaptations that your body undergoes when you exercise help protect you against chronic diseases such as cancer, high blood pressure, diabetes and heart disease. Your body systems undergo both immediate and long-term adaptations in response to exercise.

For a timeline of these adaptations, it is hard to give hard and fast rules about how any individual will adapt to exercise over time. It will depend on the frequency, duration and intensity of your exercise. Here are some generalizations for you to consider.

After about one week of exercising you will start to experience changes mentally and physically, including on the cellular level, with an ability to produce more energy as discussed above.

After two to four weeks of exercising regularly, improvements in strength and fitness will start to be noticeable. If you've been eating healthily, you may also begin to see a reduction in weight if that has been your goal. Much depends on whether you have been maintaining a caloric deficit, which is needed to produce weight loss.

After four weeks or more of regular exercise, you may be able to see improvement in your physical health, as well as in other areas of your life, such as productivity, less sick days and improved mood.

There are two ways that the human body adapts to exercise: acute physiological response and chronic physiological response. Acute responses refer to changes in the body systems in reaction to exercise that occur immediately, such as an increase in heart rate.

Long term adaptation to exercise is a chronic response and refers to how the body changes over time in reaction to an exercise habit, such as metabolic changes, increases in endurance and better utilization of muscle glycogen and blood glucose, among others.

These changes will help you to regulate your blood sugar, maintain a healthy weight and increase your ability to function in everyday tasks.

Each change that your body makes is an attempt to make your body more efficient. How you train, and how often, will influence these adaptations and will determine how long they take.

The intensity and duration of your training sessions, as well as the force or load used, will determine how your body changes, and how quickly these changes occur. Your level of fitness when you begin exercising will also influence how fast or how much your body adapts within a specific time frame.

In turn, if you stop your training, then you will lose this efficiency that you garnered while exercising. This loss of adaptations is called detraining. This is why it is important to make exercise a life-long habit.

Read more: What Really Happens to Your Body When You Start Exercising?

Any physiological responses to exercise will occur both immediately and over the long term if you keep up your exercise habit. Adaptations occur in your muscles, cardiovascular system, hormones and metabolism.

When you are exercising, moving and generating force with your body, your skeletal muscle fibers go to work. They can contract and become shorter, or extend to become longer, or counteract force when static. When this generation of force occurs, your skeletal muscle fibers are activated and consequently need energy in the form of adenosine triphosphate (ATP), according to the Centers for Disease Control and Prevention (CDC).

Skeletal muscle force can be generated when your muscles remain static (isometric) — when the weight that you are using is causing an external resistance that is equal to the force produced by your muscles. A great example of this is when you are holding a heavy box and resisting dropping it. Or with weight lifting, when you hold weight over your head in a locked position for an isometric hold.

Read more: What is Concentric Exercise?

Dynamic muscle actions consist of concentric and eccentric action. During the concentric movement, the muscles need to overcome external resistance by producing enough force to counteract it. Concentric actions are used to move the body during exercise, such as running or when lifting weights.

The opposite of concentric action is called eccentric muscle action. Eccentric action occurs when external resistance is applied during the lengthening phase of the muscle movement, which is an essential training stimulus, according to a November 2012 article published in PM&R.

Eccentric movements are known to cause more muscle damage and soreness, so if you are relatively new to exercise, limiting eccentric movements can help reduce muscle soreness as part of your adaptation to exercise, says the PM&R study. An excellent example of this is when you are lowering a dumbbell after a biceps curl.

Three types of muscle fibers work during exercise, some more than others, depending on the kind of training. These are type I, type IIa and type IIx. Type I muscle fibers are used for more endurance-type exercise as they are slower and more fatigue resistant.

Type IIx is used for more quick and powerful movements because they are very fast at contracting and fatigue quickly. Type IIa fibers are more in the middle of the other two in that they contract rapidly but fatigue more slowly than type IIa.

If you wish to get better at more powerful and quick movements, then you need to train the appropriate muscle fibers to adapt to this specific type of action. Exercise that uses the ATP phosphocreatine system and anaerobic (without oxygen) glycolysis will help you accomplish this.

To put it in layman's terms, anaerobic activity such as HIIT will work well. Any exercise that requires intense muscle activity for a short length of time, like two to three minutes, will provide benefit from this type of training. Examples include 100 to 800 meter track races, golf or tennis swings or throwing events in track and field.

Read more: How to Build the Best HIIT Workout for You

Many activities that are longer than two to three minutes use oxidative metabolism, meaning that they need a more slow and long-lasting energy source. These types of activities are called aerobic activities.

Many exercise activities use a blend of anaerobic and aerobic metabolism, however. If you would like your body to adapt to be able to function optimally in sports such as basketball and tennis, then training to produce adaptations in both aerobic and anaerobic activities is your best bet.

Your aerobic metabolism will adapt in several ways, according to a July 2019 article published in the Journal of Science in Sport and Exercise. If you are training for more prolonged durations, then your body will adapt by becoming better at sending blood to your skin to cool you through sweat.

Your body will also become better at buffering hydrogen ion accumulation, which causes muscle acidity that leads to fatigue. Your body will better be able to sustain exercise after training in this way for some time. The amount of time will depend on how often and intensely you train.

The enzymes that produce ATP aerobically will increase their activity to help create more ATP to fuel you. This adaptation will aid the capacity and endurance of the aerobic energy system so you can work out for more extended periods at more intense levels without getting tired. Your muscle cells will also adapt by helping to remove lactate buildup and reduce muscle acidosis so that you can train at higher intensities for longer.

When it comes to anaerobic physiological adaptations, your body will get better at storing phosphocreatine and carbohydrates in your muscles so that you can generate ATP to use for energy without oxygen. Once you can better store this ATP, then you'll be able to work at higher intensities.

The enzymes in your body that help to break down phosphocreatine and synthesize and break down ATP, as well as glucose to form lactate, will have an increased ability to work. This better ability will help increase your power, speed and strength during anaerobic activity.

Other interesting physiological adaptations that occur in your cardiovascular system, according to the CDC, are:

• Increase in heart wall thickness for more powerful contractions and larger left ventricle size.
• A decrease in resting heart rate and an increase in stroke volume.
• Improved endurance performance as your cardiac output increases during high-effort exercise.
• A reduction in blood pressure if you have hypertension in response to how much exercise you do. The conditions of the muscles in your blood vessel walls improve with consistent exercise — one of the most beneficial adaptations to exercise that your body undergoes, helping to prevent cardiovascular disease.

Several hormonal changes also occur with exercise, including increases in catecholamines, which helps to increase your muscle's and liver's use of glycogen as well as increase fat burning. An increase in growth hormone, cortisol, testosterone, estrogen and others is also seen. These increases can help to produce better fat burning and help to manage blood sugar levels.