Fuelling a long distance ride

Posted on 7 Jul 2016 13:04:34 Posted By Tim Lawson

Fuelling a long distance ride


Pace judgement and energy conservation in long distance events

 

Within the first week of the 2016 Tour de France we have already seen examples of riders who have used up their energy stores by going in early breaks then suffering later in the day.  We have also seen the cumulative effects of long glycogen depleting efforts over several days and observed the efforts teams go to in order to preserve their team leader’s energy stores for the critical points of this 3 week marathon.

Here we look at some of the issues surrounding the fuels used during exercise and how awareness of these concepts may be useful to us in long distance training and racing.

Fuel sources for endurance exercise

Compared to other food major groups fat is both an efficient and significant energy provider and most people carry a significant, if not prolific, energy store, as body fat or adipose tissue.

It is important to recognize that fats are much more than just an energy supply and consist of many different fatty acids, the composition of which in the diet can have profound effects on health and performance.  (another article perhaps but hence why Secret Training produce the omega shots)

It is also recognized that there is increased interest in low carbohydrate ketogenic diets, and other methods to increase ketone levels, that may challenge some of these concepts.  However, it is still useful to understand the importance and limitations of fat as a fuel for endurance performance.

Fat as energy

When you look at fat as a supplier and store of energy, without consideration of the difficulties of accessing that energy effectively, it would be easy to wonder why carbohydrate energy drinks are so effective, or indeed why you would have to bother eating or drinking on a ride at all.

Each gram of fat typically provides 9kcal, some fats such as medium chain triglycerides found in coconut oil contain 7kcal but this is still approximately twice that of carbohydrate at 3.75kcal.  At 15% body fat (slightly less than average) an 80kg cyclist would have an astonishing 108,000kcal of energy stored away as adipose tissue.  That is sufficient energy to fuel more than 10 consecutive queen stages of a major tour without eating anything at all.

Using fat for energy

Unfortunately, when it comes to accessing all that energy stored as fat it is not quite such a rosy picture, since the body has a limited ability to burn fat during exercise. 

At low intensities fat can provide most if not all of the limited energy required to fuel the muscles, but as the intensity increases the energy demands become more significant and the body relies more upon carbohydrate. Absolute fat usage will at first increase more or less linearly with intensity, but then rates of increase will fall as carbohydrate kicks in to top up the energy requirement.  Crucially there then comes an intensity where fat burning tops out (fatmax) and starts to decrease in absolute terms not just as a percentage of the total.

Many people are familiar with the concept of a maximal fat burning zone through the heart rate zone training charts often found in gyms and health clubs. These charts depict that at low intensities fat contributes most of the energy but as the intensity increases the fat contribution falls and the body has to rely more and more on carbohydrate for fuel.  These charts often confuse people into working out at a super low intensity where fat contributes the biggest percentage of the energy, rather than an intensity that burns the most mass of fat per hour. The distinction can be appreciated more easily when individual data is expressed in percentage and absolute terms as in graphs 1 and 2.

The fat burning zone is often misused to justify short easy workouts for weight loss.  If you only have a short amount of time, then a strategy of going as hard as possible in the time available will burn more calories during the workout and increase metabolic rate during recovery.  Interestingly several studies show increased weight loss with short high intensity interval training than longer less intense training sessions.

At exercise intensities above fatmax carbohydrate not only has to provide the energy for the increased work rate, but also to replace those provided from fat at lower intensities.  For short rides where carbohydrate supply is not limiting this is not a problem.  Unfortunately, the body has much less capacity to store energy as carbohydrate than as fat.  Typically, a maximum carbohydrate store would be around 500g composed of muscle glycogen, liver glycogen and some circulating glucose.   It is important to remember that carbohydrate provides much less energy per gram than fat.  For every gram of fat that is not used nearly 21/2 g of carbohydrate are required to make up the difference -on top of those required for the increased work rate. 

Charts showing percentage energy contribution and absolute contribution from an individual cyclist

 

Perhaps more importantly for long races these charts do not illustrate the absolute carbohydrate cost of exercise above the fat max intensity. 

It is for this reason that intensities above fatmax are exponentially costly in terms of carbohydrate usage.  In the example shown the rider could cycle for less than 2 hours at 300W before completely running out of carbohydrate.  In reality, since the brain runs on glucose it is likely to protect its energy supply by slowing you down long before all carbohydrate is used up.

Sprint type efforts are totally reliant on carbohydrate as a fuel since it is not possible to fat anaerobically.  So once you are feeling the lactate type burn in the legs you can be sure you have been well into costly carbohydrate burning.  A sportive rider for example, is thus advised to burn these matches sparingly at the beginning of a long ride if they wish to be complete the entire distance in the best possible time.

What is also apparent from studying individual substrate usage and exercise intensity data is that significant carbohydrate is required to maintain the higher fat burning intensities.  The extent of the truth in the old adage that ‘fat burns in the fuel of carbohydrate’ is illustrated in the individual data graph.  In the given example it can be seen that a maximum fat burn of 40g per hour required twice the rate of carbohydrate usage.  If carbohydrate cannot be supplied at a fast enough rate then intensity has to be reduced.  In many cases once carbohydrate availability becomes limited it is not possible to produce sufficient power to continue to ride, especially when the road starts to climb.

Increasing fatmax, or the ability to use fat as a fuel is an important goal of training for success in long distance events.  Success on the day is dependent upon appreciation of the fatmax intensity and the carbohydrate cost implications of riding at intensities above it, in addition to optimizing carbohydrate delivery.  Over a long distance event subtle changes in pacing strategy can have a significant effect on performance.  Knowledge of these concepts can help a competitor control their effort especially in the early stages of an event.

The problem with fatmax is that it is possible to work above it for extended periods of time.  Working above lactate threshold has much more obvious warning signs, you may notice an increased breathing rate, increased perspiration and of course that burning sensation in the legs.  If you persist depending upon how much above threshold you are working you will have to slow down and perhaps even stop to ‘get your breath back’.  However, a short stop or ideally just reducing speed will quickly, in about 15 minutes clear the lactic acid from the muscles and you have received rapid feedback that you can’t ride that fast if you hope to complete the long distance sportive. 

The effects of riding above fatmax and or inadequate feeding may not be evident for several hours of riding, suckering many a rider into riding at a level far above their ability only to ‘blow up’ spectacularly at a later stage of the race or sportive.

WE can illustrate the importance of pace judgment by modeling the fat and carbohydrate usage figures from our cyclist in the previous exaple at different work intensities.  If we assume in each case that our rider starts with a full carbohydrate load of 500g and that he consumes a respectable 70g of carbohydrate each hour of exercise.  It can be seen that if our rider works at around 210W he is able to spread his carbohydrate supplies over more than 7 hours of continuous exercise.  If however, our rider become over ambitious and rides at 260W he will be able to ride for just less than 3 hours before calamity strikes.  Importantly he may have felt quite comfortable charging along with a group of elite riders for several hours.

(Note - the "fat max" rate for the line below should say 260W not 230W)

This model is particularly instructive for riders who frequently ride for 2 hours or so before a café stop and then ride 2 hours back but wish to take on a ride, which they hope to complete in 5 hours.  It would be easy for them to think that they regularly ride for 4 hours, so 5 should not be so much more harder than their regular ‘club run’.   They thus become accustomed to riding at a pace they can maintain for 2 hours before taking a break to replenish carbohydrate and then continue for a further 2 hours.  Come sportive day they then ride just a little faster than training, and hope to do this for 5 hours without a café stop to replenish carbohydrate.  The end result is often like the 260W example in our model, resulting in a massive forced reduction in exercise capacity often followed by being over taken my their more prudent club mate who they normally get the better of on a weekly basis!

Examples of this are seen on a regular basis at the Grand Tours with riders in long breaks using carbohydrate at a much more rapid rate than those taking shelter in the bunch.  On the last climb of the day the escapees have little carbohydrate to use on the last climb and have no choice but to pace their effort conservatively.  Those who have saved the most glycogen, either by having a bigger fat burning capacity or sheltering in the bunch are able to finish much faster often gaining 10 minutes or more in the last 6 km of an uphill finish. 

Improve ‘fat max’ – or make the most of what you have?

Certainly in the short term the biggest gains are to be made from pace judgment. 

Try to do some long rides without a café stop, or extent the riding time before a café stop nearer home in order to refine pace judgment over longer time periods.

Practice carbohydrate feeding on the bike, this is a skill that you do not want to learn for the first time ‘in competition’.

The body has a limited ability to process carbohydrate during exercise.  Performance is optimized a dosages of 80-90g per hour. 

To process this much carbohydrate per hour may rely on using technical products – don’t expect to be able to take on this much carbohydrate with ham and cheese banquettes.

If you forget to eat for the first few hours, or for any other significant time period, your body will not suddenly be able to process more than 90g per hour!

Little but often will limit the rate of carbohydrate depletion, once carbohydrate levels become critical you will need to stop or slow down. 

Once carbohydrate depleted fat burning is also compromised and it may not be possible to produce sufficient power to keep moving, especially if there is a significant gradient.

Since power increases as a cube of the speed there is a lot of time to be gained from having a carbohydrate reserve available for the last climb of the day where speeds are likely to be much slower.

Conclusion

Whatever your goal, make sure you plan your strategy well to make sure you can complete your event successfully and not be "running on empty" by stocking up on your Stealth nutriton products in plently of time.

You can head straight over to our on-line shop now by clicking here.

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