Essentially yes and to understand this we need to take to take a look at our anatomy. Skeletal muscle is made up of bundles of muscle fibres called myocytes which contain many myofibrils. Myofibrils are strands of proteins (actin and myosin) that can grab on to each other and pull. This shortens the muscle and causes muscle contraction. Actin gets torn from myosin and a muscle contracts.

have two types of muscle fibres in our body:

  1. Slow twitch – Type I
  2. Fast twitch – Type II (a and b)

These differences will influence how and when muscles are activated, what they use fuel, how theyrespond to training ect.

Type I muscle fibres are:

  1. Aerobic in the nature which means they require oxygen to create energy
  2. They fire more slowly ang get can go for longer
  3. Generally, not prone to hypertrophy and they are used in activities such as mild runs, or
    other types pf LIIS.

Type II muscle fibres are:

  1. Ones that produce output quickly, which means they need to contract fast in order to generate a quick output. This would be in instances such as lifting heavy or explosive jumps, because in those instances the body needs to generate an output fast.
  2. They fatigue quickly
  3. Anaerobic (which is why they are activated in those kind of activities)
  4. Glycolytic, meaning they require glucose as they need a rapid source of energy.
  5. Prone to hypertrophy.

What this means for us and our training?
Well, different muscle groups have different % of fast and slow twitch (although this will largely depend on the individuals) so they should be trained as such.

For example:

  • Lower back – predominantly slow twich – You will train with light weight / high volume
  • Quadriceps – predominantly fast twitch – You will train moderate to high heavy / lower rep range

This is generally true, although recent research has shown that even In high repetition training, a certain muscle group will initially fire slow twitch as the loads (the requirement) isn’t that dramatic; However once we continue and these fibres star to fail, the body will activate fast twitch fibbers. This could be the reason why we are able to achieve hypertrophy, even will lighter weights, so long as we are going to failure or close to it.