Type 1 – Low-Intensity Exercise
Type 1 muscle fibers are your slow-twitch fibers, which have a very low force output and are highly resistant to fatigue
They are red in color due to the presence of large volumes of myoglobin and oxygen and high numbers of mitochondria – this is why they are very resistant to fatigue and are capable of producing repeated low-level contractions by producing large amounts of ATP
Those who engage in prolonged low-intensity exercise such as marathon runners, type 1 fibers are dominantly used – fat is the predominant fuel utilized by type 1 fiber, which utilizes the aerobic pathway
Aerobic exercise increases your need for oxygen, such as long distance running – once the exercise intensity increases, Type 2 fibers will gradually be recruited
Type 2a – Moderate-Intensity Exercise
Your Type 2a muscle fibers are your intermediate fast twitch fibers (also known as fast oxidative fibers and are a hybrid of type I and II fibers) – meaning that Type 2a fibers can use both the aerobic and anaerobic pathways, making both carbs and fat the predominant fuel
These fibers 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 fibers
Unlike aerobic, anaerobic exercises are short-duration and do not require oxygen – Type 2a fibers produce high force output for longer periods of time
Type 2b – High-Intensity Exercise
Type 2b muscle fibers are your fast twitch glycolytic fibers – these strictly utilize the anaerobic pathway, making carbs the predominant fuel source
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 – results in short, fast bursts of power and rapid fatigue
They are recruited for activities involving very short-duration with high-intensity burst of power such as sprints or near-maximal lifts – due to their ability to fire rather quickly, they excel at producing powerful bursts of speed
But, due to the rapid firing of all the muscle fiber types, they have very low resistance to fatigue
A study published in the Journal of Strength and Conditioning Research looked at how the effects of training affected muscle fiber type shifting
Researchers concluded that one cannot change inherent fiber types I to II, only within the I or II subtypes (can only change 2a to 2b and vice versa)
In other words, type 1 stays type 1 and type 2 stays type 2, although 2A and 2B can interconvert based upon how you train.
See you next time,
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