Ever wonder why some people are able to flop into pretzel-like poses on their first attempt and others spend years or sweat and tears trying to master the same poses ? Why some people are more flexible and find it difficult to strengthen and others are strong as an ox but can’t touch their toes? The answer is : Morphology. Our genetic constitution gives us our postural disposition, which is linked to what is called our ‘dosha‘ in Ayurveda, and this determines, to a large degree which muscle fibres are dominant in our bodies and what type of yoga practice we are therefore most suited to ….. Lets have a look at the science of it all….  

Humans are born with a specific amount of muscle fibres; this amount does not change; we leave with the same amount of muscle fibres that we were born with (seemingly cats are the only animal with the capacity to split fibres, thereby increasing their numbers and this theory is also debated). However exercise and yoga can bring about changes in skeletal muscle fibres. There are two distinct types of muscle fibres in humans. These are Slow Twitch and Fast Twitch fibres. Everyone possess and use both types of fibres. For example, if you are going to lift a light object like a bag or rice off a table, a weak muscle contraction is needed and therefore only type 1 muscle fibres will be activated. If you increase the load however, type 2 muscle fibres will also be activated.

MORPHOLOGY AND DOSHA The relative ratio of fast-twitch and slow-twitch fibres in each muscle is genetically determined by our parents and our morphology. Different morphological types vary in either slow twitch or fast twitch muscle fibre dominance. For example Ectomorphs, relating to Vata dosha in Ayurveda, has more type 1 muscle fibres. Mesomorphs, relating to Pitta dosh in Ayurveda, has more type 2A muscle fibres and Endomorphs, relating to Kapha dosha, has more type 2B muscle fibres. However these are not all mutually exclusive categories. No one is all Vata, pitta or Kapha and similarly everyone possesses type 1 and 2 fibres. 

MUSCLE IMBALANCES Type 1 slow twitch muscle fibres constitute our Postural anti-gravity muscles, which shorten on contraction. Type 2 fast twitch muscle fibres are considered to be Phasic muscles and lengthen on contraction. (Once again these categories should not be defined as being completely exclusive. Research has proven that muscles that usually operate posturally, can also operate phasically in certain conditions). When your muscles are placed under faulty, imbalanced, repetitive loading, the postural muscles will shorten and the phasic muscles will lengthen and weaken. This creates muscle imbalance which in turn creates dysfunctional postural holding patterns, which displace the soft tissues and the skeletal system.

MUSCLES FIBRES, YOGA AND MOVEMENT Different types of exercise and different styles of yoga recruit difference muscle fibres. The muscle fibre relationship with our morphology. as outlined above, helps account for individual differences in physical performance generally and why certain people are suited to different styles of yoga. For example, people with a higher proportion of fast twitch type 2 fibres often excel in activities that require periods of intense activity such as weight lifting, sprinting or core strengthening asana.. People with higher percentages of slow twitch type 1 fibres are better at activities that require endurance such as long distance running or Vinyasa yoga. 

TYPE 1 SLOW TWITCH FIBRES, VINYASA AND LONG HOLDINGS

Slow twitch fibres are the smallest in diameter and thus are the least powerful type of muscle fibres. Type I fibres are used in endurance training and low-intensity exercises such swimming, rowing and other exercises. Endurance training also trains the aerobic system and involves controlling and conditioning the breath. Focus is another important aspect of endurance exercises and endurance athletes are often encouraged ‘to centre in the present’. We see all of these characteristics, breath, focus and low intensity movement in vinyasa yoga; therefore we can deduct that vinyasa primary activates type 1 fibres. 

Slow twitch fibres are also activated in Hatha yoga for a different reason. Because Type 1 muscle fibres are also used in prolonged, sustained contraction, they are also recruited in long holdings of yoga asanas. 

TYPE 2 A FAST TWITCH FIBRES AND STRENGTH BUILDING DRILLS

Fast-twitch or type 2 muscle fibres has two primary divisions – type 2a and type 2b. The type 2a fibres possess somewhat higher aerobic capacity than the 2b type. Both however are associated with strength training, which involves muscular contraction, anaerobic endurance and increasing the size of skeletal muscles. Strength training provides significant functional benefits and improvement in overall health and well being, including increased muscle, tendon, ligament strength and toughness, improved joint function, increased bone density, increased metabolism, improved cardiac function, and elevated HDL (good) cholesterol. Strenuous bursts of core strengthening yoga asanas or sequences of strengthening asana drills combined with controlled breathing will activate type 2A muscle fibres.

Here is an example of a core strengthening drill that will work type 2B fibres: Chaturanga, Upward Dog, Chaturanga, knee to nose, one legged Chaturanga, 1 legged Dolphin Plank, Downward Dog, Child’s pose. Repeat.            

TYPE 2B FAST GLYCOTIC FIBRES AND STRENGTH BUILDING DRILLS

Fast glycolytic fibres are the largest in diameter. Anaerobic exercise activates type 2B fibres and is typically used to promote strength and build muscle mass. Anaerobic exercise involves short duration; high-intensity activities, which involves triggering lactic acid fermentation.

Because ATP production is generated from anaerobic glycolysis, which is fast but not sustainable due to the lack of aerobic respiration involved, muscle fatigue occurs sooner. As breath is always used in yoga asana, even in core strengthening asana work, type 2b muscle activation is less prominent. This is why the typical yogi body is lean and strong, sometimes demonstrating incredible muscular strength and yet exhibiting little muscle bulk. 

CAN WE CHANGE OUR MUSCLE FIBRES AND MORPHOLOGY WITH YOGA?

The characteristics of muscle fibres alter to some extent with exercize and yoga. Various types of exercises can bring about changes in a skeletal muscle. Research suggests that endurance type exercise like vinyasa yoga can cause a gradual transformation of some fast glycolytic fibres  (2B) into fast oxidative glycolytic fibres (2A). However, this is debated. It may well be that the type 2B fibres show enhancements of the oxidative capacity after high intensity exercise, which brings them to a level at which they are able to perform oxidative metabolism as effectively as slow twitch fibres. This would be brought about in the increase in the number of mitochondria, blood supply and strength. Endurance activities like vinyasa yoga also result in cardiovascular and respiratory changes that cause skeletal muscles to receive better supplies of oxygen and nutrients but do not increase muscle mass. Type 1 muscle fibres will never transform into type 2 muscle fibres. Type 2A muscle fibres may increase the size and strength of type 2B fibres, creating bigger muscles, but traditional yoga is not the ideal practice for creating muscle bulk. Some western styles of yoga combine yoga with weights to activate type 2B muscle fibres and many practitioners do other type 2B activities in addition to yoga. However while they may create bulk, look good in a bathing suit, and help in some yoga asanas, the extra bulk may also prevent yoga students from advancing in their practice. For example rectus abdominus activation using machines in a gym with fire the type 2B muscle fibres and create the 6 pack muscles that look so good in a bikini. However over activation of the rectus abdominus muscles may create too much front body muscular contraction for deep backbending, which requires the front body myo-fascia to release.

As you can see from the morphological relationship to muscle fibres as outlined above, the type of yoga asana you choose to practice can create some changes in muscle fibre, however the morphology determined by your genetics cannot be changed. When you know your dosha, or ayurvedic constitution, you will be able to enhance your physical health through yoga asana in relation to your morphology, but not change it. In ayurveda, this is called the difference between the prakriti, which is the morphology you were born into and your vrkriti, which is the element in the body that is out of balance in the moment, creating health issues. Your prakriti never changes; your vrkriti does change.

Therefore someone with type 2B fibres (kapha) will benefit from the practice of vinyasa yoga, which activates type 1 muscle fibres. By contrast, people with primarily type 1 and 2A fibres (vata-pitta) who wants to strengthen will benefit from practicing core strengthening yoga asana to build strength.

MUSCLE FIBRES AND VARYING YOUR PRACTICE Varying your practice and alternating vinyasa style practice with practices that focus on strengthening drills and longer holdings will help activate both type 1 and 2 muscles fibres to balance aerobic endurance and muscular support. If you practice only vinyasa, especially with set sequencing, you may find yourself stuck at a limitation for a long time, wondering where the strength will come from to move forward. In this situation, alternating vinyasa practice with core strengthening asana drills can really help create the balance you are looking for.

Similarly if you regularly combine vinyasa and strengthening in the same practice, you may find yourself drained, feeling weak and not able to give the strengthening work the full attention it deserves. Yoga strengthening work is best suited to 60 min practices, as type 2 muscle fibres exhaust themselves faster than type 1. Using intelligence to focus on problem areas on some of your practice days will short cut a lot of time spent on the mat. This allows you to work on areas of your practice that you need to work on and maintain a degree of variation throughout your practice week.