Thread by @Gareth_Sandford

Endurance performance focuses on:

• VO2max
• Lactate threshold
• Efficiency/economy

But what else impacts oxygen supply and delivery?

Here are 4 muscle characteristics that may be limiting your endurance performance ⬇️

1. Skeletal muscle fiber type

Slow fibers are for low intensity continuous activity

Fast fibers are made for explosive actions

Endurance athletes have 70-80% slow fibers

Sprinters have 20-30% slow fibers

https://twitter.com/eline_lievens/status/1442809593684504577?s=20

2. Skeletal muscle fiber size

Fast fiber muscle is larger in size

But has lower aerobic capacity

Slow fiber muscle is smaller in size

But has higher aerobic capacity

3. Muscle capillary networks

Capillaries are the train lines that deliver oxygen

Slow fibers have:

• More capillaries per fiber

• Deliver more oxygen

• Show strong relationships with critical power ⬇️

https://twitter.com/Gareth_Sandford/status/1275868674809720832?s=20

4. Myoglobin

Myoglobin acts like an escalator within a train station

Transporting oxygen within the fibers

Train lines (capillary network) + escalators (myoglobin)

= Station transport capacity (muscle oxygen supply)

Do not forget how effectively people leave the train

(oxygen extraction)

https://twitter.com/Gareth_Sandford/status/1270057680497827840?s=20

For middle distance and team sport athletes

To compensate for low aerobic capacity of fast fibers

We can improve delivery of oxygen

By⬆️number of train lines to the muscle (capillaries)

But how do we target this?

Use principles of a polarized model (e.g. ⬇️)

Execution of intensity becomes important

You can get the volume component using intervals

A 20 min tempo in an endurance profile

Can be 12-20 *1 min on/1 min off in a speed profile

https://twitter.com/Gareth_Sandford/status/1359598458391334912?s=20

For full text on skeletal muscle determinants of endurance performance see:
frontiersin.org/articles/10.33…

For more on developing the qualities underpinning aerobic capacity see ⬇️

https://twitter.com/Gareth_Sandford/status/1294311494113308674?s=20