Mechanisms of Strength Adaptation – Morphological Adaptations.
As we mentioned in our previous blog post, improving your strength is primarily dependant on improving the muscles ability to generate force. This can be done in either by triggering adaptions in the muscle tissue itself, or by neurological adaptations.
Adaptations in the muscle tissue are referred to as morphological adaptations, and these occur in the muscle tissue itself. These adaptations include things such as muscle fibre type, the cross-sectional area of the muscle, and something known as the angle of pennation of the muscle fibres. In this blog post we will talk about each of these three things in a bit more detail.
Muscle fibre type –
It is well known that muscle fibres come in three main types. Type 1, Type 2a and Type 2B, each with different physiological properties and force development characteristics. Type 1 muscle fibres or slow twitch muscle fibres contract with less force than type 2a or type 2b muscle fibres, but can maintain that level force production for multiple reps. As a result a high proportion of type 1 muscle fibres are found in endurance athletes.
Type 2a and type 2b muscle fibres can produce 3-4 times more force than type 1 fibres but fatigue much quicker. They have a lower number of mitochondria and can therefore produce less ATP to drive muscle contraction via aerobic processes. This means the muscle fibres are dependant on anaerobic energy production which produces more lactate and leads to a faster rate of fatigue. Type 2 muscle fibres have a much shorter contraction time than type 1 muscle fibres, allowing them to produce more force quickly, just what we need when we want to improve our maximal lifts.
There is some debate as to whether it is possible to change muscle fibre type through training, or whether it is inherited, but there is some research to show muscle fibre type can change following periods of training or detraining suggesting there is some degree of plasticity in fibre type composition. High volume strength training is thought to lead to the hypertrophy of type 2a muscle fibres at the expense of type 2b fibres which may improve peak force, but at the consequence of peak power.
Cross sectional area of muscle fibres –
Regardless of fibre type, the amount of force a single muscle fibre can produce is proportionate to its cross sectional area (CSA). Increases in CSA of muscle fibres are brought about by increasing both the size and number of myofibrils within the muscle and are as a result of hypertrophic responses to strength training. The increase in CSA of muscle fibres is dependant on the intensity, volume and frequency of the strength training and the level of adaptation has been shown to diminish as training age increases.
In order for improvements in force production to occur following training, the training period must have included training that utilised loads heavy enough to elicit this adaptation. Whilst performing high rep light load resistance training may lead to muscle hypertrophy, the low loads used during this kind of training do not lead to increases in maximal strength. Instead protocols that use heavy loads (75%+) and low to medium reps (3-8) have been shown to be most effective at increasing the cross sectional area of the muscle fibres and facilitating increases in force production.
Angle of Pennation –
The angle of pennation of a muscle fibre refers to the way muscle fibres are aligned in relation to the joint they pull on. Muscle fibres are either aligned in series or in parallel. Think of them as been arranged like a train - lots of carriages attached in a straight line (in series), or all lined up next to each other ready to pull on a single joint (in parallel). The more muscle fibres that are aligned in parallel, the greater the angle of pennation, and the more force is produced in each contraction. The angle of pennation can be increased through heavy resistance training.
As you have probably picked up on through this article, resistance training can lead to adaptations in muscle fibre type, CSA and the angle of pennation. All three adaptations are also all beneficial, and work in conjunction with each other to allow muscle fibres to produce the maximum amount of force possible. But, whilst these three factors are important in improving your force production there are also a number of neurological adaptations that occur that are just as important, which we will discuss in our next post!