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Start your engine: aerobic vs. anaerobic

Wesley Doyle
9 May 2016

Are you a plodder or a powerhouse? Sprinter or sportiviste? No matter, it takes both aerobic and anaerobic to power your efforts.

It’s a conundrum that’s as old as the bicycle itself: which goes first, the lungs or the legs? However, the division between the kinds of energy that power your performance isn’t as clear as it may seem at first. The notion that you’re blessed with one energy system that is more efficient than another, therefore making you better suited to short bursts or long hours in the saddle, is a myth. In fact the systems by which your body produces energy are all interconnected and whatever your goal, your training should reflect this.

So despite a familiar line being drawn between anaerobic and aerobic energy systems, the body actually has three different power pathways open to it: aerobic, anaerobic glycolysis and PCr/alactic. The first occurs in the presence of oxygen – hence aerobic – while the latter two don’t, so therefore are both anaerobic. 

‘On a cellular level the energy our bodies run on exists as a molecule called adenosine triphosphate (ATP),’ says Xavier Disley, exercise physiologist and elite coach for RST Sport, ‘and we only have about 100 grams of ATP in the body – which only lasts for around two seconds.’ 

Cycling training

It’s this store of ATP that the body turns to first when we put it under stress, using what’s known as the PCr/alactic system. ‘This system is involved in very high but very brief intensity efforts,’ says Chris Easton, lecturer in clinical exercise physiology at the Institute for Clinical Exercise and Health Science, University of the West of Scotland. ‘That means any kind of effort lasting between one and 10 seconds, such as a standing start or track sprint to the line. Beyond those 10 seconds the body moves into the next pathway, which is anaerobic glycolysis.’ Essentially, this is the breakdown of glycogen stores (glucose) in the muscle to release energy. Like the PCr/alactic system, it doesn’t rely on oxygen and again it’s only viable for a short period of time, up to four minutes at the most. ‘This pathway would probably be relied upon mostly by track riders and climbers,’ says Easton, ‘whereas the pathway most associated with road cyclists is the aerobic one.’

This is the name given to the system that breaks down the macronutrients – the proteins, fats and carbohydrates that we eat – in the cells’ energy-producing mitochondria to produce more ATP. ‘As long as you continue to feed the body it can continue to break down fats and carbohydrates in the presence of oxygen all day long,’ says Disley.

Cycle specific

It would stand to reason then that if you’re a track cyclist or a sprinter you’d want to tailor your training to focus on the anaerobic side and make sure those energy pathways are functioning as efficiently as possible. Conversely if you’re a sportive rider you’d find the mode of training that best mirrors what you’re going to be doing during the event. 

‘Whatever your event, the aim of training is to increase force production from the muscle and improve recovery from such efforts,’ says Easton. ‘So specific training is almost intuitive when you look at how the systems supply their energy.’ To improve the PCr/alactic system, follow the basic principles of very high intensity interval training, maximal or supramaximal efforts. ‘This means going all out for very short periods of time,’ says Easton. ‘High-intensity work for 30 to 40 seconds followed by a recovery period of, depending on your goal, 15 to 180 seconds.’

Anaerobic training also works on the principles of high-intensity training but using longer periods of work and recovery, usually between one and four minutes again at a very high intensity probably close to 90% of maximum.

Aerobic training introduces the longer duration rides beloved of sportive and club riders – two or three hours of continuous effort at 60-80% maximum effort. 

Despite sounding pretty cut and dried, it is of course nothing of the sort. ‘The difficulty of translating all of this,’ says Easton, ‘is that you also get beneficial effects on your aerobic system by doing the high-intensity work as well. It’s not true to say you can only train one energy system at a time – you can prioritise one over the other but any type of training will have beneficial effects across the board.’

Take a deep breath

‘All cycling is biased towards aerobic performance, even on the track,’ says Disley. ‘Chris Hoy had huge aerobic capacity, as does Jason Kenny. At competition level a rider would be expected to do their flying 200m sprint, and 45 to 90 minutes later they’re back sprinting, which, if they win, means they’ll be repeating those efforts again. At the end of the day they’re knackered! If you’re someone like Jamie Staff who just rode flying 200s or the first lap of a team sprint you may get away without having to hit the road, but for everyone else aerobic training is very important.’ 

Disley offers up the Wingate Anaerobic Test (WANT) as an example: ‘It’s a classic all-out 30 second test that uses an ergometer to measure things such as a rider’s peak power output, anaerobic work capacity and anaerobic fatigue. When you look at the results though you’ll see there’s definitely some aerobic contribution – even a 10 second sprint will have an aerobic element. It’s difficult to completely isolate the anaerobic system during training – there’s always going to be a bit of crossover.’

While training for specific energy pathways appears to have benefits across all systems, it’s high-intensity interval training (HIIT) that gives the most bang for your buck.

‘The body responds best to varied stresses,’ says Disley, ‘and training in that way will give you better physiological adaptation. Riders who go out at 85% of their maximum HR week in, week out, will improve certain things but it’s not going to be as much as if they varied their range of power outputs and effort levels.’

Plus there’s a practical reason for swapping at least one of those long rides for a quick HIIT session. ‘Obviously the key point is you achieve results in far less time,’ says Easton. ‘It might take you four times as long to achieve the results you get with HIIT from endurance training.’

Disley agrees: ‘You get a lot of benefits from this short-term anaerobic stuff, including increased metabolic rate and improved insulin sensitivity.’ You want to be insulin sensitive as it helps your body break macronutrients down for fuel. ‘You see improved insulin sensitivity if you get people to do sprint efforts for a few weeks rather than just long aerobic sessions. The University of Birmingham carried out a study where subjects did four to six 30-second efforts for three days a week as opposed to 40 to 60 minutes of exercise five days a week and the improvements in insulin sensitivity were exactly the same.’ 

One to another 

Turbo training

Despite all this, there’s still a school of thought that states the best way to train for an endurance race is to hit that aerobic system full on and get the miles in. Disley admits that most cyclists don’t tend to use their anaerobic capacity that much so why put yourself through painful HIIT sessions if you’re going to be cycling 100 miles plus?

‘The point is to understand what the training is doing to our bodies,’ says Disley. ‘It doesn’t matter whether you’re a track sprinter or someone doing the Etape du Tour, you need to look at what the training session provides rather than what the training session actually is.’ For some, this may seem counter-intuitive but just because The Dragon Ride doesn’t require half a dozen 30-second sprints at 170% VO2 max doesn’t mean sportive riders won’t benefit from adding them to their training programme. Rather, look at what physical adaptations they provide and how they improve overall performance.

Interestingly, an Australian paper published in 2013 followed 174 cyclists and triathletes over the course of 30 years of training and found that, while their peak anaerobic power and anaerobic capacity decreased fairly dramatically over the years their aerobic power, in terms of statistical significance, didn’t change that much. According to Disley this is due to those anaerobic pathways becoming less efficient as we age, but the results also reinforce the idea that even though the traditional HIIT training no longer caused continued adaptations to the system it initially targets, it did in fact continue to benefit the aerobic ones. 

‘Adding a weekly interval session to your sportive training will give you myriad benefits,’ says Easton. ‘It’s also the sort of thing that can keep you ticking over during winter when you don’t want to be doing a four-hour session on icy and dangerous roads.’

With all this in mind it’s clear that even the longest club run or shortest sprint session will engage legs and lungs and everything in between. ‘Anything over 30 seconds will target all your energy systems all the way through,’ concludes Disley. ‘It’s not just off-the-mark power or sprint speed or longevity, it’s a big continuum of all three.’

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