Two by Twenty - Take 2

Way back I posted about a workout known as the 2 x 20. It's pretty simple. Ride for 20-minutes at around your time trial pace/effort/power, have a short break and then do it again. Combined with a warm up and cool down, it makes for a nice tight one-hour workout that's exceptionally effective at developing one's aerobic engine.

On a power meter chart - it looks a bit like this:


The squiggly yellow line denotes power output and was around 200 watts for two efforts lasting around 20-minutes. The horizontal dashed line shows 200 watts.

In between efforts I stopped and hopped off the ergo bike to remove my leg and dry the liner and leg, and replace so I could go again. It's a challenge I face at the moment as the leg liner tends to fill with perspiration making it a little weird to pedal. Imagine pedalling in loose gumboots with water in the bottom of them.

Of course there is nothing magical about 20-minutes. Overall it's about getting enough time at these levels. Some do 3 x 20-min. Others 3 x 15-min. Some ride the hour straight at that power. Typically though we break up efforts into smaller duration "chunks" (known as intervals) so that we can maintain perhaps slightly higher power than we may otherwise have the motivation to do all in one go.

So what's actually happening when I train at this level? Well lots of good things. The main physiological changes that are brought about by riding at these intensities include:

- increasing my muscle glycogen storage capacity. Glycogen, along with free fatty acids are key sources of chemical energy which is converted by our muscles into mechanical energy (and heat). Basically this means I develop the ability to ride hard for longer.

- increasing muscle mitochondral enzymes - these are the "mini power plants" inside our muscles, which use the available oxygen for the conversion of chemical energy to mechanical energy (as well as heat). The greater the number and density of these suckers we have the better

- increased lactate threshold - which is another way of saying one can go harder for longer. Blood lactate concentration is one way of determining how effectively our working muscles are performing at various intensities.

Now you gain these benefits by riding at lower intensity levels as well but the rate at which improvements occur is greatest at these intensities, which is an effort level equivalent to how hard you could maximally sustain riding for about an hour.

They are also effective at increasing my blood plasma volume, increasing my heart stroke volume (amount of blood moved per beat) and maximal cardiac output (maximum amount of blood I can pump per unit time) and for increasing the amount of oxygen I am capable of both delivering to my working muscles and actually utilising (my VO2 Max).

There are other funky things too, like increasing the density of blood carrying capilliaries inside the muscles - which enables a greater and faster transfer of oxygen to the working cells. On top of that, our (slow twitch) muscles fibres also grow.

The body is an amazing thing. It knows how to adapt when it is provided with a training stimulus. The trick is to keep providing that stimulus in the right doses.