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There are 2 main muscle fibre types, Slow twitch (Type I) and Fast twitch (Type II). Fast twitch fibers can then be split into 2 sub categories, Fast-oxidative (Type IIa) and Fast-glycolytic (Type IIb). Type IIa fibres have a greater potential for prolonged activity than type IIb fibres which tire very rapidly but produce the greatest power, as required in sprinting, jumping and throwing. Athletes with predominantly type I fibres are ideally suited to long distance events, 1/2 marathon +. Athletes with predominantly type II fibres are ideally suited to sprinting, jumping and throwing, and athletes with a mix of both types are better suited to races between 1500 and 10,000m.

So how do you determine what composition of fibres you have? Well, there are various methods, the most accurate, and least appealing is to have a muscle biopsy taken and analyzed. This is a rather invasive method so you may want to try a less accurate test that you can do yourself in the gym. It should be noted before I continue that the composition of muscles can vary greatly between muscle groups in a single individual.

The following test should help give an indication if there is a balance in favour of type I or type II fibres.

For the test you will need a dumbell, barbell, or machine with small weight increments.

During the test rest for 2 minutes between trials to rebuild your energy stores

To keep the test uniform: lift for 2 seconds, pause, and lower for 4 seconds


  1. Warm up by doing 10 light repetitions of you chosen exercise (e.g. bench press, leg extension)
  2. Do 5 repetitions with a moderate weight
  3. Do 1 repetition with a heavier weight
  4. Repeat part 3, increasing the weight in increments of 1-4Kg, until you reach a maximum weight you can lift at one time. This represents your 1 repetition maximum (1RM). To avoid exhaustion, try to determine this in less than 8 trials.
  5. Rest for 5 minutes
  6. Multiply your 1RM by 0.75
  7. Lift this weight (75% 1RM) as many times as possible


bullet1-8 repetitions with 75% 1RM = predominantly type II muscle fibres
bullet9-11 repetitions with 75% 1RM = combination muscle fibres
bullet12+ repetitions with 75% 1RM = predominantly type I muscle fibres