How can one person beat everyone in a marathon, but be left in the dust in a sprint?
Strength, power and endurance may be due, in part, to the distribution of the two different types of muscle fibre in a person’s muscles. Muscles are a mixture of two basic types of fibres – fast twitch and slow twitch.
Fast twitch fibres can:
- develop greater forces
- contract faster
- contract without needing oxygen (anaerobic)
Slow twitch fibres:
- develop force slowly
- maintain contractions longer
- have greater aerobic capacity (with oxygen)
It’s in the genes
It appears that your genes determine the percentage of each type of muscle fibre you have. Someone born with a greater percentage of slow twitch muscle fibres would, in theory, be more suited to endurance events like triathlons, long distance cycling and marathons. In contrast, a person born with a greater percentage of fast twitch fibres would be genetically more suited to anaerobic events like weightlifting or sprinting.
Muscle biopsies (samples taken from the muscle) show that sprinters tend to have more fast twitch fibres, whereas marathon runners would have more slow twitch fibres. The rest of us have a more equal distribution of each. More research needs to be done to find out if training can change the percentages of each fibre type a person has.
Those super athletes!
These differences could also help explain the differences in sporting abilities across some ethnic groups.
At Otago University’s Anatomy Department, Professor Phillip Houghton has spent 10 years studying Polynesian people’s evolution. His muscle biopsies have shown that although most skeletal muscles are a mixture of slow twitch and fast twitch muscle fibres, Polynesians have a predominance of fast twitch muscle fibres.
Nature of science
The explanations that scientists provide are their best explanations at that time. Over time, new data can be gathered or existing data can be re-examined, and the explanation may change. This is the strength of science - it doesn't mean that scientists can't make up their minds.
Since these fibres are anaerobic (don’t need much oxygen to work), they enable people to have short bursts of energy in high athletic performance, and then rest while the body reoxygenates. This is particularly suitable for sprinting, netball, rugby, weightlifting and boxing. This may help explain the make-up of our All Blacks, Silver Ferns and other elite sporting teams in New Zealand.
Houghton’s theory is that their muscle comes from their ancestors enduring extremely cold temperatures while exploring and settling the Pacific hundreds of years ago, and that today’s Polynesians have inherited their body types from those early navigators.
Aerobic and anaerobic exercise
Different types of exercise use mostly different types of muscle fibres. Aerobic exercise (for example, running a marathon) involves low levels of exertion over a long period of time. All the muscles are being used at well below their maximal contraction strength, but for long periods of time.
This aerobic exercise:
- relies mainly on the aerobic (with oxygen) system
- uses more of the slow twitch muscle fibres
- uses fat, protein and carbohydrates for energy
- uses huge amounts of energy
- produces little lactic acid
On the other hand, anaerobic exercise (like weightlifting or sprinting) involves short bursts of higher intensity contractions at a much greater percentage of their maximum contraction strength.
This anaerobic exercise:
- uses predominantly fast twitch muscle fibres
- relies mainly on ATP or glucose for fuel
- consumes only a little oxygen, protein and fat
- produces large amounts of lactic acid
- can not be sustained for as long a period as aerobic exercise
Read about Professor Phillip Houghton’s research.