First, let’s quickly cover the energy systems of the body so we know what we’re measuring. Adenosine triphosphate (ATP) is the energy compound that provides fuel to the working muscles, and there are three main systems that use ATP in order for you to propel your bike forward, the ATP-PC System, the Lactic Acid System, and the Aerobic System.
The ATP-PC system uses ATP already stored in the muscle for an immediate energy source. When the stored ATP is depleted (within seconds), the body breaks down phosphocreatine (PC) which is found in muscle tissue, into ATP for further energy.
This process lasts for 10-15 seconds, then the body kicks into another system.
Lactic Acid System
The lactic acid system uses sugars (glycogen-glucose) stored in the muscle tissue. When inadequate oxygen is available, the body converts glucose into ATP with a series of reactions that result in lactic acid being produced.
The lactic acid system can only fuel a period of intense exercise for a few minutes, and the accumulation of lactic acid in the muscles results in a burning sensation and fatigue.
The aerobic, also known as the oxygen system, supply’s the body with most of it’s ATP. The fuel source is glucose and fatty acids, and it relies on the circulatory system to transport oxygen to the working muscles and tissues to make the process work.
As a result, it’s a slower acting system than the ATP-PC and lactic acid system, however it is the system that allows ong periods of work or endurance activity.
Image: Climbing hills with Mitchelton-Scott (Premax a proud sponsor and supplier)
The systems don’t change suddenly, rather gradually transitioning between each other, and this is where the term threshold (lactate or anaerobic) comes in. Let’s use lactate threshold for the rest of this blog. Your lactate threshold represents an aerobic exercise intensity that can be maintained without a significant contribution from the anaerobic systems.
Workloads above this threshold will result in clearly identifiable increase in blood lactate (due to anaerobic metabolism) and you will not be able to continue the effort. This why lactate threshold becomes one of the most important determinants of endurance performance.
Sedentary people may have a lactate threshold of 50% of maximum heart rate, whilst some of the guys and girls on the World Tour can maintain 90-95% for an hour or so.
Image: One of them seems to be hitting their lactate threshold. Team Tibco-Silicon Valley Bank in action (Premax a proud sponsor and supplier)
So how do you measure your lactate threshold?
There’s lab-based tests, where every few minutes the resistance is increased and a technician pricks your finger for a drop of blood, analysing lactic acid levels in your blood. Results are entered into a computer and it plots when your system switches from aerobic to anaerobic.
The lab-based tests are great, however most don’t have access to these, so you can still work out yours via a standardised protocol at home.
Functional Threshold Test
One well known test performed on a Wattbike or home trainer with a power metre is the Functional Threshold Test (FTP). This test is an all-out effort for either 20 or 40 minutes with average power the measure.
The reliability of the FTP test has been questioned as most cyclists have difficulty sustaining a steady state for 20 or 40 minutes. And, unless you’re addicted to pain for prolonged periods, who really wants to do that? Even if you do perform the FTP test is it something you can or want to repeat on a frequent basis in order to measure your progress?
Introducing the 2-Bout Exercise Test…
2-Bout Exercise Test
This test, also known as the 2 x 4-min mean power test (2 x 4MMP) is a protocol designed and tested by the Australian Institute of Sport as a highly reliable and repeatable method for monitoring cycling performance and for investigating factors that affect performance in cycling events (Driller et. al 2014).
The 2 x 4MMP involves two 4-minute maximal efforts completed 42 minutes apart, with a controlled warm up for each maximal effort, and a 30-minute recovery in between each effort. Average power output is measured for both 4-minute efforts.
It could easily be combined as an indoor training session and testing session in one.
Here’s the 2 x 4MMP protocol;
Warm Up 1
6 minutes at 60% HRmax,
6 minutes at 80% HRmax,
3 minutes at 90% HRmax,
2- minute stationary recovery
2 minutes at 70% peak power output
1-minute setup for test T1
T1: 4-minute maximal effort
Recovery: 30-minute seated recovery
Warm Up 2
6 minutes at 80% HRmax
3 minutes at 90% HRmax
2-minute stationary recovery
1-minute setup for test
T2: 4-minute maximal effort
Image: Testing at the Victorian Institute of Sport (Premax a proud sponsor and supplier)
In the study on this testing protocol, published in the International Journal of Sports Physiology and Performance, the testing was performed on a Wattbike however, you can perform this on your own bike. Ensure that everything is the same between testing sessions to ensure reproducibility and an accurate comparison of results.
The authors of the test and study concluded that the 2 x 4MMP can detect small meaningful changes in performance in cyclists, and is highly reproducible in elite cyclists.
The 2 x 4MMP can be easily and frequently used to effectively measure changes in performance for interventions such as nutrition, training, recovery, gym/resistance training as well as help design more effective training programs.
Give it a go!
I hope this helps! Whilst you’re here, please check out performance skincare products for cyclists formulated in collaboration with some of the best cycling teams and athletes in the world.
Driller, M.W., Argus, C.K., Bartram, J.C., Bonaventura, J., Martin, D.T., West, N.P. and Halson, S.L. (2014) Reliability of a 2-Bout Exercise Test on a Wattbike Cycle Ergometer. International Journal of Sports Physiology and Performance. 9, 340 -345