Muscle Adaptations (And Why They're Not Just About Getting Bigger!)

Written by Ben Bunting: BA, PGCert. (Sport & Exercise Nutrition), British Army Physical Training Instructor.

If you're hitting the gym regularly but not seeing the results you expect, it might be time to understand the science of muscle adaptations.

These intricate changes are what turn regular workouts into results you can see and feel.

Ready to learn all the ins and outs of muscle adaptations? Let's break it down.

Key Takeaways

Muscle adaptations are a major aspect of the benefits that exercise-training produces.

They are the result of a series of coordinated changes in genes and proteins that occur within the muscle.

These changes are driven by a number of transcription factors such as MEF2, GLUT-4 enhancement factor and PGC-1 alpha. They also involve small non-coding RNAs called micro RNAs.

Increased Muscle Size

The body responds to exercise-training by increasing the size (hypertrophy) of muscle cells. This process is dependent on dietary protein intake and hormones.

The hypertrophy of muscle cells occurs due to the increased concentrations of actin and myosin in muscle fibers.

This process can be enhanced by a variety of training techniques that increase the frequency and intensity of repetitions performed with the proper weight.

High-intensity resistance exercise, such as those performed with weights above 85% of your one-repetition maximum (1RM), is the most effective type of training for muscle growth and strength increases.

It also has the added benefit of improving cardiovascular fitness.

Another option is to perform low-intensity resistance training with blood flow restriction with cuff inflation (BFR).

This technique induces a similar response in muscle hypertrophy as traditional high-intensity resistance training.

Several studies have reported the effect of LIT-BFR on muscle growth, including in the elbow flexor muscles, upper arm muscle, and biceps brachii muscles.

Researchers found that LIT-BFR induced a significant increase in skeletal muscle mass and strength in healthy young men who participated in a 12-session training program.

The average increase in skeletal muscle mass was 7% over the course of the study, which is similar to the hypertrophy observed in aerobic exercise training protocols.

In addition, the % change in muscle mass per session was comparable to traditional high-intensity training (0.1 to 0.5% per session).

The LIT-BFR training regimen induced no signs of muscle damage as blood levels of creatine kinase, myoglobin and interleukin-6 remained unchanged during the trial.

It is important to keep in mind that the muscles need time to recover and grow after each workout. This means that you need to rest at least 48 hours between workouts.

A good rule of thumb is to choose a weight or resistance level that you can easily do 12 to 15 repetitions with controlled form.

Lifting too heavy a weight can result in injury and can prevent you from seeing the results that you are seeking.

Variation in your workouts will help you push past a plateau and achieve the gains that you want.

It can also encourage your muscles to fire up different or multiple muscle fibers during the same workout.

Increased Strength

If you're looking to build up your muscles or even if your fitness goal isn't just to get big but also to feel strong, strength training can be the best way to achieve those goals.

Studies show that doing strength training at least twice a week can help you build muscle mass, boost your resting metabolic rate and improve bone health.

Muscle strength is the ability to lift and move heavy objects. You'll develop strength by doing resistance exercises, which use weights and other forms of resistance to make a muscle contract or push against something.

This increases your overall strength, because you can lift more weight and perform more reps without feeling fatigued. You'll also develop power, or the ability to create force quickly.

The strength of your tendons and bones also increases, especially if you perform more repetitions of weight-bearing exercise than usual.

This is because it stimulates the growth of collagen fibrils, which strengthen tendons and reduce your risk of injury.

You can use a variety of exercises to increase your strength, such as weighted pull-ups, squats, push-ups and other bodyweight movements.

You can also do exercises that target specific muscle groups, such as the chest, legs or back.

A key part of any strength-training program is a gradual progression, which means gradually increasing the amount of weight you lift over time.

This is because it's important to keep the muscle-tendon tear-down and repair process going.

Another important part of a good strength-training routine is a proper warm-up and cool-down.

For example, you'll want to do some cardiovascular exercises like walking or running before a workout and some stretching afterward.

Some strength-training programs include exercises that don't require the use of weights, such as yoga, which can be a great way to build up your muscles and increase flexibility.

This type of exercise can also have a positive effect on your mood, because it stimulates the release of endorphins, which are natural chemicals that help you feel good about yourself.

The US Department of Health and Human Services recommends that adults do at least two days of muscle-strengthening exercises each week.

This can include weightlifting, exercises like push-ups and sit-ups, and some types of yoga.

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Improved Body Composition

Many people have a difficult time stepping on the scale and seeing their weight stay the same.

This can be frustrating, but it doesn't necessarily mean that their exercise and diet efforts aren't working.

Body composition is the percentage of fat, bone, muscle, water and other tissues in your body.

It's a better measure of health and fitness than simply stepping on the scale, because it takes into account the total mass of your body and its various components.

The body is divided into two compartments: fat mass (or adipose tissue) and fat-free mass, which consists of muscles, organs, bones, nerves, hair, nails and tendons.

Generally, your body fat percentage is the easiest way to gauge your overall body composition, but other measures like your lean body mass and water weight can also be useful.

In addition, the amount of calories burned during exercise can affect how much body fat you have.

For example, if you do more aerobic exercises, your body will compensate by burning more calories than it would if you did less cardio.

This can result in a "diet-induced negative energy balance," or the state when you expend more calories than you consume.

To improve body composition, it's essential to sustainably decrease caloric intake while increasing your physical activity.

This will help reduce excess body fat, build muscle and improve metabolic health parameters like blood sugar and insulin resistance.

However, while many research studies show that exercise-training can lead to a positive body composition change, they're observational in nature and tend to focus on overweight or obese populations.

These studies are important for public health research, but they're not practical for everyone looking to lose body fat and gain muscle.

That's why scientists from The University of Arizona, George Washington University, and University of Southern California used a new method called Mendelian randomization to study the effects of exercise on body composition in overweight and obese subjects.

Using this method, the researchers found that exercise-training significantly decreased body fat levels in overweight and obese subjects without affecting their body weight or body mass index.

They also found that the amount of body fat reduction was significantly greater in the group that performed an aerobic-based exercise program than a more traditional strength-training program.

Increased Endurance

A key benefit of exercise is the increased stamina it provides, so it's important to include some endurance training in your workout routine. Incorporating endurance activities into your fitness routine is essential for every aspect of your life.

It is recommended using low-intensity high-rep exercises as an endurance builder.

The body is able to normalize continuous motion when you train with these low-intensity and high-rep sets, so it's easier for the muscles to adapt.

Endurance training has been shown to increase the amount of oxygen available in the blood. It can also help the body burn more calories because of its heightened oxygen intake.

The body can also use more fuel during endurance activity because of a boost in fuel mobilisation and utilisation, which reduces fatigue. In addition, exercise increases the levels of growth hormone, insulin sensitivity, and testosterone in the body.

This has the effect of reducing the risk of developing diseases and other health problems. For example, exercising regularly can help prevent type 2 diabetes and heart disease.

Other benefits of exercising can include improved glycemic control, lower blood pressure, and reduced risks of certain cancers. In addition, exercise can improve the way your brain works, which can lead to higher concentration and memory skills.

Lastly, exercise can increase your metabolism and nutrient absorption. This can help keep your energy up and aid in weight loss.

In order to achieve these benefits, you should eat healthy foods and get plenty of rest.

It's especially important to get adequate sleep if you're training for an endurance event, as less than seven hours of sleep can negatively affect your performance and appetite.

Another way to build your endurance is by using intervals in your cardio routine. Sprint interval training, for example, can be a great endurance builder because it trains your cardiovascular system and helps you build strength and speed at the same time.

The increased endurance that occurs with exercise-training can help you perform longer, more intense workouts and reduce the risks of injury while you're exercising.

It's also a good idea to incorporate more strength-training into your fitness routine to further enhance the benefits of exercise.


Aerobic exercise training improves aerobic energy metabolism by improving the capacity for oxygen extraction from the blood supply.

This capacity is accompanied by increased skeletal muscle mitochondrial content, capillary density and improved cellular control of energy metabolism.

Other factors such as increases in maximal stroke volume, cardiac output and blood volume also contribute to the positive effect of training on skeletal muscle (Blomqvist & Saltin, 1983).

Exercise-induced skeletal muscle adaptations are induced specifically in the muscles used in the exercise task; these adaptations are lost after prolonged rest periods.

Moreover, the intensity of training sessions is important for determining the magnitude and duration of these changes.

In addition to changes in skeletal muscle biochemistry, these adaptations can affect the structure of muscle fibers.

For example, a shift from type IIb to type IIa/x fibers is a common result of training.

This change is associated with an increase in hexokinase II and AMPK activity. It has been shown that individuals with insulin resistance and type 2 diabetes have a higher proportion of glycolytic type IIx fibers than healthy subjects (Zierat & Hawley, 2004; Zierath et al., 2011).

These findings indicate that training-induced fiber type changes may be of clinical significance.


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