For our very first guest post we have a post from our long time supporter and friend Tim Lawson. Tim has supported Legro’s training camps for many years now. First as director and founder of SiS and now as founder Secret Training. Here he shares some insights and the science on feeding and pacing your big ride. Perfect if you planning to do any of Legro’s big rides, especially Legro’s Big One

Introduction

Have you ever ridden a sportive or been out on a long training ride and, despite feeling good for the first few hours, suddenly come to a point where you can barely turn the pedals, let alone tackle a testing climb? If so, it’s likely you’ve made a mistake with your pacing or nutrition and, as these two aspects of performance are intrinsically linked, more than likely both. Crucial to the fuelling of endurance activities is how we utilise fat as a fuel, how pacing impacts its use and its relationship with carbohydrates.

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 recognise 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.

It is also acknowledged 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.

The Potential of 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.

The reality of 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.  See Figure 1). Crucially there then comes an intensity where fat burning tops out (Fat Max) 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 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 weigh loss with short high intensity interval training than longer less intense training sessions.

Figure 1:

Substrate Utilization and Exercise Intensity for reasonably trained cyclist

The danger of exceeding Fat Max

Perhaps most importantly for long events is the absolute carbohydrate cost of exercise above the ‘Fat Max’ intensity.

At exercise intensities above Fat Max 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 2^1/₂ g of carbohydrate are required to make up the difference -on top of those required for the increased work rate. It is for this reason that intensities above Fat Max are exponentially costly in terms of carbohydrate usage.

Sprint type efforts are totally reliant on carbohydrate as a fuel since it is not possible to burn 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.  There’s no denying the truth in the old adage that ‘fat burns in the fuel of carbohydrate’. 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.

It can be seen from the substrate utilization graph that intensities above fatmax are very costly in terms of carbohydrate usage.  The extent of the carbohydrate cost of working at these intensities is often lost in the typical “fat burning zone” charts that simply display the relative fuel contribution.  At intensities above fatmax, actual fat usage is less than at lower intensities, so carbohydrate has to carry the burden of not just the increased work rate, but also make up the calorie contribution supplied by fat at the lower work rates.  Since carbohydrate has less than half the amount of calories per gram than fat, more than 2g of carbohydrate is lost for every gram of fat that would have been used at lower work rates, this is obviously very costly in terms of carbohydrate usage.

It is also evident from the fat utilization graph that all significant work intensities require at least some carbohydrate contribution, so when carbohydrate supply is limited work rates are significantly reduced.  This is particularly important in an event such as the etape since it is quite possible that the work rate required to keep moving could be higher than that attainable in a carbohydrate depleted state.  The steeper parts of the Col d’Izoard occur in the last 6km of the 30Km climb where altitudes greater than 2000M will also have an adverse effect on exercise capacity.  The following example demonstrates how inappropriate pacing could result in carbohydrate depletion before its summit.

The subtlety of Fat Max

Increasing Fat Max, 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 Fat Max intensity and the carbohydrate cost implications of riding at intensities above it, in addition to optimising 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 Fat Max 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 Fat Max 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 modelling the fat and carbohydrate usage figures for a cyclist 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.  However, if 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.

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 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. Learn accurate pacing using either a heart rate monitor or power meter and then practice it in training. Be ultra-disciplined about sticking to zones and following a regimented fuelling regimen.

Try to do some long rides without a café stop, or extend the riding time before a café and 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 tends to be optimised at 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.

Remember, 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.

 

About the author

Tim Lawson is the Founder of Secret-Training and previously the founding director of SiS (Science in Sport). With a lifetimes interest in sport and nutrition he has a Masters Degree in Sport and Exercise Physiology, is an Honours graduate in Sports Science and a member of the British Association of Sport and Exercise Scientists.

 

REFERENCES;

1, Data from Bradley J.  University Central Lancashire.

2, Jeukendrup A.E. and Wallis G.A., Measurement of Substrate Oxidation During Exercise by Means of Gas Exchange Measurements, Int J Sports Med 2005; 26 (Suppl 1): S28-S37