Training Mitochondria To Upgrade Your Engine
Within our cells are structures called ‘mitochondria’, which are key components of skeletal muscles, providing energy for almost all the activities of the muscle cells. Training mitochondria to upgrade your engine can be valuable – but knowing the right dose is key.
There is a close relationship between the number of mitochondria in an athlete’s muscle tissue and endurance performance. Research has demonstrated that highly trained athletes have 3-4 times the amount of mitochondria in their muscle tissue, relative to untrained individuals (1,2).
Push Harder On The Pedals For Longer
In order to push harder on the pedals for longer, we must find a way to supply more energy to the skeletal muscles by increasing the number of mitochondria in our muscle tissue, but also improve their function – the effectiveness of the mitochondria we already have.
We know that exercise is a powerful stimulus for these improvements, but little is known about the optimal training dose (3). Which is more important to up-regulate mitochondrial content and activity: training volume or intensity? In recent years, researchers have set out to answer this question.
Which Is More Important: Volume Or Intensity?
Our bodies are a complex and highly-integrated signalling system. When we train, we set off a cascade of signals that influence gene expression, driving the adaptations we are hoping to achieve.
It appears that exercise intensity is the most powerful signal to enhance mitochondrial function, whereas training volume appears to be more important for increasing the number of mitochondria we have (3).
Should You Ditch The Junk Miles?
Recent trends in the training of amateur cyclists makes these findings particularly relevant. Traditionally, the staple diet of amateur cyclists was long, low-intensity group rides with occasional racing. However, with the rise of indoor-trainers and power-meters, many time-crunched amateur cyclists are trading volume for intensity – packing multiple high-intensity interval sessions each week and disregarding the long-hours in the saddle as ‘junk-miles’.
It’s clear that a focus on high-intensity training can result in some great improvements, particularly amongst riders who have done little structured training in the past. However, at some point, riders who have limited training time often reach a plateau. This research may indicate one of the reasons why.
The highly fatiguing nature of high-intensity training means riders can only tolerate a relatively small amount each week. Once this limit is reached, improvements in mitochondrial function plateau. The most effective way to improve at this point may be to increase signalling through greater training volume at low-intensity, increasing the number of mitochondria.
This kind of training does not result in too much fatigue, so you can tolerate a lot of it, and it’s been well-documented that athletes benefit from relatively large volumes of low-intensity training (4).
When we speak about intensity, it can be helpful to summarise using a 3 zone system:
Zone 1 (Recovery/Endurance): Up to lactate threshold, Approx. 75% FTP. You would typically accumulate only 1 – 7 hours at this intensity during a session e.g. a 4 hour group ride.
Zone 2 (Temp/Threshold): Lactate threshold to lactate turnpoint. Approx. 76-104% FTP. You may accumulate as little as 10 minutes or as high as 90 minutes at this intensity during a session. E.g. 2 x 20 minutes at 90% FTP.
Zone 3 (VO2 max./Anaerobic Capacity): Approx. 105% FTP. You would typically accumulate only 12-30 minutes at this intensity during a session e.g. 6 x 3 minutes at 110% FTP.
Elite Endurance Athletes Do Little Training At Threshold Intensity
Interestingly, it appears that elite endurance athletes train surprisingly little at lactate threshold intensity (5). This evidence is reflected in anecdotes. I was recently speaking with a physiologist who has begun to work with a number of World Tour professional cyclists. One of his early observations was the phenomenal volume of low-intensity training that these riders completed, and the fact that the riders firmly believed that this was an essential, and perhaps the most important, component of their preparation.
Correlation does not necessarily imply causation, but in this case there are numerous plausible mechanisms to support the value of low-intensity training, not least the enhancements in the number of mitochondria these riders develop, to support their feats of performance in professional events.
Implications For Amateur Riders
There are a number of possible implications for amateur riders, but here are 3 to take-away:
1) If most of your training sessions are at high-intensity, and you find yourself with additional training time available, consider increasing the volume of low-intensity training, rather than adding more intensity.
2) If you’re spending a lot of training time in Zone 2, consider experimenting with a period of time where you reduce this significantly. Zone 2 training is very fatiguing, but may not provide such a potent stimulus for adaptation. Use Zone 3 training conservatively and spend a period of time focusing on Zone 1 work.
3) When coaches provide training zones, most athletes believe that they need to ride at the upper end of their zones to maximize the training effect. However, this may not be the case. Try taking a more conservative approach and ride in the middle of the ranges for both low-intensity and high-intensity sessions. Make easy rides really easy, and hard rides really hard. You may actually enhance the ‘clarity’ of the signal.
Which Is More Important: Volume Or Intensity?
So which is more important, volume or intensity? The answer is clearly ‘both.’ If you really want to improve your performance and emulate pro-rider’s preparation, the solution is likely not to ride harder, rather slower, for longer.
1) Costill, D.L., Fink, W.J., and Pollock, M.L. (1976). Muscle fiber composition and enzyme activities of elite distance runners. Med Sci Sports 8 p. 96-100.
2) Hoppeler, H. (1990). The different relationship of VO2max to muscle mitochondria in humans and quadrupedal animals. Respiration physiology 80 p. 37-145.
3) Bishop, D. et al., (2014). Can we optimise the exercise training prescription to maximise improvements in mitochondria function and content? Biochim Biophys Acta. 1840 (4) p. 1266-75
4) Seiler, K.S. (2010). What is Best Practice for Training Intensity and Duration Distribution in Endurance Athletes? International journal of sports physiology and performance 5(3) p. 276-291
5) Seiler, K.S. & Kjerland, G.O. (2006) Quantifying training intensity distribution in elite endurance athletes: is there evidence for an “optimal” distribution? Scand J Med Sci Sports.16 (1) p. 49-56
James Hewitt is Sports Scientist and Performance Coach with HINTSA Performance based in Geneva, Switzerland. In a previous life he was an Elite racer but now focusses on avoiding caffeine overdose and helping other people achieve their goals. You can contact James through twitter @jamesphewitt and find out more at his website www.jameshewitt.net