Build Muscle Fast | Which Muscle Fibres Should I Be Training?

Written by Callum Melly

How To Build Muscle Fast

When it comes to exercise there is one key factor that often gets overlooked and it really is as simple as “TRAIN” towards your goals.


For example, if you want to run a marathon, then you would work on improving your VO2 max to better perform at a higher intensity, for a further distance and longer duration; if you were looking to increase strength or power, then you would be best to focus on multi-joint and muscle compound exercises, working in a range of 1-6 repetitions and taking 3-5 minutes’ recovery for your ATP and creatine phosphate (ATP-PCr) system to recover.


Far too many people over complicate things and buy into a “trending” fitness programme or routine that won’t actually help them reach their individual goals; the best thing you can do is take a step back, have a good think about what you want to achieve and then focus on training towards that goal.


How Can We Build More Muscle?


We can increase the size, endurance and strength of a muscle by training each fibre specifically. For example, if you stick to the same amount of sets, reps and rest when you train then it is likely you are only training one muscle fiber type and likely to reach a plateau fairly quickly and as a result, you would limit your progress and restrict the potential results you could achieve if you trained all three fibres.


Each muscle fibre will compliment each other, by training a different muscle fibre each week, you can move more load, for longer and recover faster, in order to promote more lean muscle growth and improved performance.


For example, if you build a combination of strength, endurance, power and lean muscle over a 1-4 week period, then by theory, in weeks 4-8 you should be able to move more load, for longer and recover faster, with more power and again, promote more lean muscle growth and improved performance.

beginner weight lifters

Type I (Slow Twitch)


Type I fibres are also known as slow twitch fibres. They are red in colour due to the large volumes of myoglobin and mitochondria, thus extremely oxygen efficient. Due to this fact they are very resistant to fatigue and are capable of producing repeated low-level contractions by producing large amounts of ATP through the aerobic metabolic cycle. Athletes such as marathon runners have a high number of this type of fibre, partly through genetics, partly through training.


We can specifically target this muscle fibre by using a higher rep range such as 15-30 reps. By completing a higher amount of sets, reps and taking a shorter rest/recovery period, we will promote improved muscular and cardiovascular endurance by an increase in blood flow to the muscle, an increase in oxygen supply & therefore, increased muscular endurance. This type of training can also cause micro tears to the muscle, as so much blood is flushed into the muscle to supply the aerobic/oxygen demand that is causes cell tears in the muscle and thus can promote further lean muscle growth.

mind muscle connection

Type IIa (Fast Twitch)


Type IIa fibres are also sometimes known as fast oxidative fibres and are a hybrid of type I and type II fibres. These fibres also contain a large number of mitochondria and myoglobin, hence their red colour. They manufacture and split ATP at a fast rate by utilising both aerobic and anaerobic metabolism and so produce fast, strong muscle contractions, although they are more prone to fatigue than type I fibres. Resistance training can turn type IIb fibres into type IIa due to an increase in the ability to utilise the oxidative cycle.


We can specifically target this muscle fibre by completing a more hypertrophy based rep range between 8 and 12 reps. As mentioned above, type IIa fibres are a hybrid of type I and II; this allows us to move more load for fewer reps but also take advantage of using our aerobic and anaerobic energy and thus promoting a combination of power, strength, endurance, to promote lean muscle growth.


Type IIb (Fast Twitch)


Often known as fast glycolytic fibres, they are white in colour due to a low level of myoglobin and also contain few mitochondria. They produce ATP at a slow rate by anaerobic metabolism and break it down very quickly. This results, in short, fast bursts of power and subsequently, rapid fatigue. As mentioned above, this type of fibre can be turned into type IIa fibres as a result of resistance training. This is a positive change due to the increased fatigue resistance of type IIa fibres. These fibres are found in large quantities in the muscles of the arms.


We can specifically target this muscle fibre by completing a more strength and power based rep range between 4 and 8 reps. As mentioned above, these muscle fibres primarily work in fast bursts and fatigue quickly, therefore we want to move more load for fewer reps or move load quickly, which will ultimately develop increased power and strength.


So, if your end goal is to change your body composition and achieve a lean, shaped and toned body, then I would highly recommend training a different muscle fibre each week; that way you can improve your all round performance and thus improve your athletic ability.

Our articles should be used for informational and educational purposes only and are not intended to be taken as medical advice. If you’re concerned, consult a health professional before taking dietary supplements or introducing any major changes to your diet.

Chris Appleton

Chris Appleton

Writer and expert

Chris is an editor and a level 3 qualified Personal Trainer, with a BA honours degree in Sports Coaching and Development, and a level 3 qualification in Sports Nutrition. He has experience providing fitness classes and programs for beginners and advanced levels of clients and sports athletes. Chris is also a qualified football coach, delivering high-level goalkeeping and fitness training at a semi-professional level, with nutritional advice to help maintain optimal performance. His experience in the sports and fitness industry spans 15 years and is continuously looking to improve. In his spare time, Chris likes to dedicate it to his family while training in the gym.

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