Fat facts: going for the burn

Sports Performance Bulletin looks at the science & practicalities of maximizing fat burning for endurance athletes who want to get or stay lean

Whenever you ride your bike, run, swim or perform any steady-state exercise, you burn fat. But what a lot of athletes want to know is whether there’s any way of maximizing the body’s fat burning ability? The good news is that there is, the key to success being the practical application of fat-burning science. If you’re new to this topic, this article on the science behind fat burning is strongly recommended reading. Understanding the principles behind fat burning will help you put together better fat-burning training protocols – an important consideration during the off season, when extra and unwanted body fat tends to make an appearance.

Why burn fat?

Let’s start by asking why endurance athletes might benefit from increasing fat burning during training. Firstly, unless you’re already very lean, losing some extra body fat can be a very effective way of increasing your performance. That’s because as far as exercise against gravity (cycling, running etc) is concerned, body fat is ‘dead weight’, which contributes nothing to propelling you from A to B. Shedding some excess fat therefore increases your all-important power-to-weight ratio, which means you’ll accelerate and ride/run up any inclines faster for the same effort. The potential gains of fat burning are also very large. For example, a cyclist might fork out a couple of grand for a fancy new bike that weighs 4lbs less than his/her existing steed. But when you can lose 10lbs for free by shedding some fat, that new bike idea suddenly looks much less attractive!

Secondly, while you’ll only lose fat if you burn more calories than you eat, the right type and intensity of exercise can help ensure than as much energy as possible for that exercise comes from fat burning – the so-called ‘Fatmax’. Fatmax is achieved by prolonged, moderate-intensity training in order to promote ‘aerobic’ energy production (because fat needs lots of oxygen to be converted to energy).

However, this shouldn’t be your only mode of training because we know that higher levels of fitness result in even bigger Fatmax values. In other words, in addition to longer, moderate intensity sessions, you still need to include some anaerobic, high-intensity workouts to build fitness because this higher fitness will allow you to work harder while still deriving lots of energy from fat calories, increasing your fat-burning capacity.

Another thing that needs to be understood is that the (gentle) exercise intensity at which you burn the biggest proportion of calories as fat is NOT the same as the (somewhat higher) exercise intensity that burns the biggest number of fat calories (see figure 1). It’s also important to realise that the kinds of foods you eat before you train and when you eat them can affect the amount of fat burned for energy.

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Figure 1: Exercise intensity and Fatmax

For the majority of endurance athletes with reasonable fitness, Fatmax will occur at around 70-75% of maximum heart rate or within ± 5 beats per minute of this figure. Very fit athletes may have a Fatmax nearer to 80% of maximum heart rate while beginner/recreational athletes will probably have their Fatmax somewhat lower – around 65% of max heart rate. If fat burning is your main goal, you should stick to these training guidelines. In addition, you should also perform some regular higher intensity training to boost your maximal capacity to burn fat.

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Fat burning theory into practice

Understanding the theory of fat burning is all well and good, but putting that theory into practice is another matter. Let’s look at some simple ways you can apply this theory in your own training, starting with training structure.

*Training intensity

Going back to the Fatmax concept (the intensity at which you burn most fat during exercise) studies have shown that in trained athletes, training at a fairly moderate intensity (around 70-75% of maximum heart rate (MHR = approx. 220 minus your age in years) is optimum for fat burning. In novice or less fit athletes however, Fatmax occurs at around 65% of maximum heart rate^(1,2). In reality, the exact intensity at which fat burning peaks is less important because within 5-10% of this intensity (or 10-15 beats per minute), your fat burning rate will be similarly high. If you increase your training intensity too much, your fat oxidation will drop rapidly because your muscles will now want to burn mainly carbohydrate for fuel instead. However, it’s easy to identify whether you’ve strayed above your optimum fat-burning zone because at this point, many people will perceive a significant step up in their rate of exertion. The use of a heart rate meter also helps remove any guesswork!

Strategy #1 – Experienced/fit athletes should train around 70-75% of MHR to burn fat. Novice/less fit athletes should stick to around 65%MHR

*Training session length and frequency

As for duration and frequency of your rides, when it comes to fat burning, the most important factor is your total energy expenditure over any given time period. So for example, six rides/runs per week of 45 minutes’ duration at 70% MHR would be equivalent to three sessions of 90 minutes at the same %MHR (four and a half hours in total). The goal is to increase your total weekly volume so that you burn more fat calories. However, there is good evidence to suggest that fewer but longer training sessions (fitness permitting) are better for fat burning than more short sessions. This is because we know that fat becomes an increasingly important fuel as the duration of exercise increases⁽³⁾. So for example, in the example above, three sessions of 90 minutes may be preferable to six sessions of 45 minutes because more of the energy in the 90 minute sessions will come from fat calories. Another benefit of structuring your training this way is that it allows longer periods of recovery in between each session.

Strategy #2 – Gradually increase your total weekly mileage and if you can manage it, structure your training towards fewer, longer training sessions

*Training timing

For many of you reading this, lifestyle factors such as your work and family commitments will dictate what time of day you train! However, if you have any flexibility at all (eg at weekends), you can use this to help increase your fat burning while you train. The reason for that is because there’s plenty of evidence suggesting that the longer the period between your last meal and your next training session, the greater the proportion of energy during that session will be derived from fat⁽⁴⁾. The most obvious way to take advantage of this effect is to train first thing in the morning before breakfast and indeed, research has shown that the total fat oxidized during exercise (and for two hours after exercise) is greatest when morning exercise is performed in the fasted state - ie before breakfast⁽⁵⁾. It’s important to stress however that this approach becomes less appropriate for longer duration sessions (over one hour) where ‘training on empty’ could result in excessive fatigue as a result of low blood sugar and stored muscle carbohydrate (glycogen). If you want to train for longer, take some carbohydrate drinks/bars/gels with you and start feeding on the move once you reach the 60-minute mark - a strategy that is popular among some pro athletes!

Strategy #3 – Train for up to an hour before breakfast on an empty stomach

*Other training modes

As a general rule of thumb, the best way to improve cycling performance is to cycle and do lots of it! The same is true for runners, who need to run lots. When fat burning is your number one priority however, it might be useful to add in some other modes of endurance training. This is particularly true for cyclists, where for any given exercise intensity (heart rate), a cyclist will burn more fat while running (or walking) than if he/she were cycling⁽⁶⁾. The reason is that compared to cycling, the work done during running is spread over more muscle fibers because more muscles in total are involved in the running action. For the same workload therefore, these fibers don’t have to contract so intensely so can derive a bigger proportion of their energy from fat (at high muscular intensities, carbohydrate burning becomes much more dominant while fat use drops off). Another mode of training that all athletes should consider is resistance training, which builds/maintains muscle mass, increases your calorie burn at rest, which then helps to promote fat burning (see box 2).

Strategy #4 – Cyclists: try adding some long walks or runs into your weekly training schedule. All athletes: resistance train at least once per week

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Resistance training for fat burning

Adding in some resistance training to your weekly training plan is a great idea for athletes seeking fat loss. This is because resistance training increases muscle mass, which is a very desirable thing for two reasons; firstly, it’ll make you a stronger, more powerful rider and help protect you against injury. Secondly, because muscle mass is metabolically far more active than fat tissue, increasing your muscle mass with the addition of some resistance training means that the rate at which you burn up energy (even while resting) can be boosted significantly. This in turn makes it easier for you to achieve a negative energy balance, which is what you need to burn fat when you’re not riding.

Try adding one (or at the most two) session of resistance training into your weekly endurance program. You don’t need to spend hours at the gym; very significant benefits can be had with a quick 40-minute blast. A resistance session comprising of 10-12 exercises designed to work all the major muscle groups (one to two sets of 10-15 repetitions per exercise with enough weight set so that the repetitions can only just be completed) will produce great results in athletes who are not experienced resistance trainers!

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*On the move nutrition

Mention ‘fat burning nutrition’ to most athletes and they’ll assume you mean fancy pills and supplements. However, your most powerful nutritional weapon for fat burning is more about what you shouldn’t use. While carbohydrate drinks and gels have their place in maximising race performance, if it’s fat burning you’re after, these products should not be used before or in the early stages of your training session. That’s because carbohydrate taken before training can suppress your muscles’ ability to burn fat for energy by up to 35%⁽⁷⁾! The reason is that carbohydrate raises levels of the hormone insulin, which subsequently suppresses fat burning. By not taking a pre-exercise carbohydrate drink/gel/snack, you can ensure levels of insulin remain low (this is also the reason why pre-breakfast riding is effective for fat burning).

If you do find yourself in need of some pre-training energy, the best option is to eat some low GI carbohydrate – ie carbohydrate that releases its energy very gently – about 2 hours before you train. Good examples of these ‘low-GI’ carbs include oats, pasta, lentils, beans, peas, most fresh vegetables and fresh fruits such as apples, pears, cherries, peaches and plums. Why low GI foods? Well, the more gentle the release of energy, the smaller the rise in insulin that results, which increases the potential for fat burning. Indeed, studies have shown that compared to a high-GI carbohydrate meal, a low-GI carbohydrate meal increased the amount of fat burning by 118% in a subsequent training session⁽⁸⁾. One caveat however: while some carbohydrate restriction is good for fat burning in the initial stages of a training session, be very careful not to overdo it. During very long rides/runs rides and after all training session, you absolutely must consume plenty of carbohydrate in order to stop your muscles becoming depleted in glycogen (muscle carbohydrate), which will leave you feeling like a physical wreck!

Strategy #5 – Don’t consume carbohydrate drinks/bars/gels or snacks immediately before or during the early stages of a run or ride, and stick to low-GI carbs in the 3 hours before a training session

Summary

Although the science of burning more fat during exercise might appear quite complicated, the good news is that by applying a few simple training and nutrition strategies, you can significantly enhance your muscles’ ability to burn fat for energy. Manipulating the length, frequency and timing of your sessions can all boost fat burning, as can adding in a sprinkling of other exercise modes. Throw into the mix a little nutritional know how and you really will be going for the burn!

References

1. Int J Sports Med 24: 603-608, 2003.
2. Int J Sports Med 26 Suppl 1: S28-37, 2005.
3. Obesity (Silver Spring). 2007 Sep;15(9):2256-62
4. Int J Obes (Lond). 2005 Aug;29(8):966-74
5. Appl Physiol Nutr Metab. 2006 Oct;31(5):502-11
6. Metabolism 52: 747-752, 2003
7. J Sports Sci 21: 1017-1024, 2003
8. Med Sci Sports Exerc, 31(3): 393-9, 1999