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Tuesday, July 08, 2008

le Tour de France 2008: Feed them well

Why eating is important

The 2008 edition of le grande boucle, as it is affectionately known, is now fully underway, and so far each stage has been quite exciting. The tour started without the traditional prologue, and instead was a full on stage. It's slightly uphill finish effectively neutralized the sprinters, and so it was not surprising to see all the main GC contenders at the front. In fact Alejandro Valverde won the stage and took yellow, although we spoke about how much of a challenge it would be to go "wire to wire" in yellow.

Sunday's Stage 2 had its fair share of bumps with four categorized climbs and also a slightly uphill finish. It seemed that again the sprinters would be neutralized, and it was Fabian Cancellara that attacked with one km to go. He could not hold it, though, and even Valverde had a go, but also faded. In the end a big man took victory---Thor Hushovd from Norway powered across the line for his fifth stage win in le Tour. Valverde remained in yellow, however.

During the first two stages there were crashes as the riders passed through the feedzones. These are designated areas where support crew hold out bags full of food and drink. The riders slow down a bit and grab them as they whiz by. Fortunately Stage 3 saw no crashes in the feed zones, but let's looks at why it is so important to eat on the bike.

Energy balance

We can all agree that the energy demands placed on tour riders are pretty astronomical, but it makes more sense to break it down into a specific context. Therefore let's take your "average" 75 kg cyclist and his daily energy demands. His resting metabolic rate, or RMR, is the amount of energy he requires to sit there do nothing all day long. In other words, it is the energy required by his body to maintain all of its life-sustaining functions. For him it is around 1500 calories.

But our cyclist is not just sitting there all day. . .in fact, he is covering upwards of 180 km per stage, often with significant uphill sections which require more energy. Cycling is a pretty efficient activity, however, and it costs our cyclist in the range of 0.3-0.4 calories per km cycled per kg of body mass---or about 25-30 calories per km. The bottom line here is that a 180 km stage will cost our athlete around 4000 calories, depending on the amount of drafting.

It's a lot of cheeseburgers!

Any way you calculate it, our cyclist's total energy expenditure for one day of the tour is very high. His RMR (1500 cal) plus his exercising energy expenditure (4000 cal) adds up to a whopping 5500 calories, which is probably the equivalent of 15+ cheeseburgers! So just to remain in energy balance our rider must consume 5000+ calories a day. Believe us when we say it: that is a lot of food. Add to this the fact that he is on the bike for four or more hours during the day, plus the "anorexic effect" of exercise, plus 8-10 hours of sleep. Suddenly he has only a relatively small window of time to consume large amounts or calories.

If we assume he is otherwise occupied for up to 16 hours a day with riding, sleeping, and other activities, he has only about 7-8 h to ingest 5500 calories, which works out to about 700+ calories an hour during the time he is available to eat and drink. So remaining in energy balance is actually a huge challenge for our tour rider.

Fortunately the race organizers allow the cyclists to grab the feed bags and eat while riding. This is crucial for two reasons. First, it provides more opportunity to choke down a portion of the 5500 calories he needs in a day. Second, the ingestion of carbohydrates during exercise prevents the dreaded "bonk," or hypoglycemia. Many of you probably have bonked before, and therefore you know that when it happens you are finished---no more racing for the day as you limp home and consume gross quantities of food along the way to fill the hole in your tummy!

How much to eat then?

Klaas Westerterp and his colleagues in Maastricht (Netherlands) actually measured the energy intake and estimated the energy expenditure in five cyclists in the 1988 Tour de France. Their average intake was almost 6000 calories per day, while their average expenditure was nearly 6100 calories per day---indicating that these cyclists did a remarkable job of (nearly) maintaining energy balance. They accomplished this by ingesting 49% of their energy while riding, which amounted to whopping 94 g of CHO per hour during each stage! Furthermore, a full 30% of their carbohydrate intake was in fluid form, which makes it substantially easier to meet energy requirements during the 7-8 h when they are not racing or otherwise occupied.

Given this information now, it should now make total sense when you watch the riders rolling through the French countryside, shoving energy bars and other products down their gullets. Hungry or not, they must get the calories into their bodies. Failure to do so will almost certainly result in fatigue and an early exit from the race, because when cycling four or more hours each day it does not take long to accrue a serious energy deficit. When your body does not get enough energy, cycling four hours or more a day becomes an unnecessary activity, and our bodies have an uncanny way of keeping us healthy---suddenly getting on the bike and pedaling requires substantial effort, more so than a few days ago, and eventually you will not be able to keep up with the bunch.

Stay tuned to le Tour---plenty of action ahead

Looking ahead to Tuesday's stage, we see the first individual time trial. It is a pancake flat 29 km ride and will do two things. First, it will create a pecking order for those who will contend for the GC. Second, it will limit any one rider's gains or losses as the distance is so short, and therefore the race should remain close and within reach for the contenders. It also will set the stage for Stage 6 on Thursday, which is the tour's first mountain top finish, and is sure to produce some fireworks!


Seb said...

In french, it's LE tour, but LA grande boucle. Ah, this nice grammar :)

Anonymous said...

About glycogen consumption: I have a lab tested consumption of 4 grams of CHO per minute at Marathon pace speed when running. I haven't had a lab test in cycling, but I plan to get one soon. Are there any studies comparing consumption during running vs cycling?

My limited personal experience with cycling is that bonking appears suddenly in cycling whereas in running you start to feel the effects of hypoglycemia gradually. Maybe this has to do with the fact that in cycling you are seated (at least most of the time) while in running you are carrying your whole weight all of the time?


Ross Tucker and Jonathan Dugas said...

Hi Seb,

Thanks for visiting The Science of Sport and for helping us out with our French grammar.

My Spanish is pretty good, but my French is pretty non-existent!

Kind Regards,

Ross Tucker and Jonathan Dugas said...

Hi George,

Thanks for your question about your rates of CHO oxidation.

Although cycling and running are different modes of activity, the one variable that will best predict how many grams of CHO you use per minute is your metabolic rate. This is simply how hard you are exercising.

So whether or not you are running or riding, if you are exercising at the same metabolic rate then your rate of CHO oxidation will be similar between the two sports. But why?

The amount of substrate you burn each minute is driven by how much energy you need per minute. In turn, the amount of energy you need is determined by how much muscle you activate. . .and so at similar metabolic rates you are activating similar volumes of muscle and therefore have similar energy demands, and therefore similar rates of CHO oxidation.

Regarding your second question about bonking, I have bonked on the run and also on the bike, and I must say that my experience is one of gradual fatigue. That is, it becomes increasingly harder to keep the pace. Then suddenly it is as if someone has pulled the plug, and the symptoms of hypoglycemia kick in---light-headedness, extreme fatigue, nausea, and extreme hunger.

In fact in both sports you must carry your weight, and so whether or not you are seated does not change this scenario. However, we will all have individual perceptions when it comes to bonking, and there is not necessarily a universal experience!

Thanks for the comment!

Kind Regards,

Anonymous said...

Jonathan wrote:
"In turn, the amount of energy you need is determined by how much muscle you activate"

Thinking again about my incident I recall that I suddenly felt that I ran out of steam when I encountered an uphill section with my bike. Before that uphill the road was level and I felt well. So your explanation ties in perfectly, I believe:

During the flat section muscle activation was low, but when climbing an uphill significantly more muscle had to be used which resulted in the dreaded bonk.

Since that incident I have changed my diet while riding by ingesting not only gels and isotonic drinks but also solid food such as energy bars, bananas and raisins. A few days ago I completed a quite demanding course with many uphill sections and I felt strong all the way, so diet does play a great role!


Anonymous said...

A very interesting followup to this article is from a 2006 post on boston.com. Here they talk with the chef for the Phonak cycling team and details the contents of the feed bags mentioned above. Neat stuff!


vikram said...

How quickly can the body digest the food consumed ? Liquid foods and solid foods. Also, my personal experience of consuming liquid CHO is that after a while it begins to taste horrible, causing GI distress.

About muscle activation, does cycling or running (assuming both are at the same HR) activate more muscle ? Based on feel, I would guess running.


Julie said...

"Add to this the fact that he is on the bike for four or more hours during the day, plus the "anorexic effect" of exercise, plus 8-10 hours of sleep."

What is meant by the "anorexic effect"?

Ross Tucker and Jonathan Dugas said...

Hi Julie

Sure, "anorexia" literally means "without hunger", and so when we refer to anorexic effect of exercise, it means the appetite suppression effects of exercise, particularly if you exercise at high intensities. I'm sure you've experienced that before at some time. After exercise, of course, you'll be very hungry, but for these Tour riders, five or six hours a day go by when the can't eat as normal, and it's more than just the fact that they're on bikes that causes this!

So the point Jonathan was making there is that DURING exercise, the capacity to eat is very low, which has implications for the replacement of the energy used.

The word "anorexia" has kind of found its way into the common vocab as the eating disorder, and the full name for the eating disorder is "anorexia nervosa", to imply the psychological component of the disorder.

Hope that clears it up a little!

Derek said...

"our bodies have an uncanny way of keeping us healthy---suddenly getting on the bike and pedaling requires substantial effort, more so than a few days ago"

Why is that? Is our brain really physically limiting the exercise that we can do?


Ross Tucker and Jonathan Dugas said...

Hi Vikram

Thanks for the questions. I'm going to cede to Jonathan on the first one, since he knows much more about the absorption rates than I do. What I will say is that most of the commercially available carb-gels and drinks are made specifically to maximize absorption in the intestines.

It's not so much about digestion in these products, because they're usually the basic units already (glucoses, fructoses, maltodextrins etc.) and so they're used taken up very quickly. The key factor there is the concentration - "optimal" is about 6% to 9%, which means for every say 7g of glucose, you need about 100ml of water. That's why some people get into trouble with energy gels - they often contain about 20 g of glucose per sachet, and then people will only drink about 100ml (concentration 20%).

This high concentration of glucose actually "pulls" water into the intestine, causing stomach problems like diarrhoea, so you have to be careful not to go too sweet. Coke does the same thing for many people - it's about 10%.

To answer your next question, on muscle activation, which I do know a bit more about, it depends.

First, there is the definition of muscle activation, and this depends on the intensity you exercise at. There's no absolute limit to muscle activation and so in theory, if you sprint as hard as possible on the bike and as hard as possible running, you'd activate a "theoretical" maximum.

Everything else would then need to be compared to that - so, running at 50% of your peak, or cycling at 50% of sprint power, you'd use roughly 50% of the available muscle. If the "maximum" was the same, then everything else would be too, if that makes sense?

Where you are correct is that running tends to use a greater overall muscle mass than cycling because it utilizes the arms and the legs. Cycling is predominantly leg-based, with only isometric activity in the arms. This is a reason why running produces a higher VO2max than cycling - more muscle, more oxygen. But one would not really say that "muscle activation" is higher, rather than a greater total muscle mass is used - it's semantics...!


Ross Tucker and Jonathan Dugas said...

Hi Derek

In a nutshell, yes. In a more complex form, well, that's a little more intricate.

Part of the body's response to a persistent energy deficit is to initiate a sequence of hormonal responses which include the release of cortisol, the stress hormone. This involves something called the HPA-axis - the Hypothalamic-Pituitary-Adrenal axis.

There are also all kinds of signalling molecules called cytokines that increase in the circulation, and the body develops a systemic inflammation in response to prolonged stress. Suppressed immune function is part of this response, which is why riders will often get sick when their energy intake is too low for their output.

The cumulative effect of all these things is of course mediated and "sensed" by the brain, and that "run-down" feeling is a characteristic part of the response.

When we eventually get back to our Fatigue series (my apologies, it's my fault!) we'll speak again about this self-perception of fatigue, which is crucial to moderate your behaviour. Think about it for a moment - if your body was undergoing all these changes (like the immune system, the inflammation, the cortisol) and your brain didn't "make you aware" of it, then the entire process would be wasted! So your brain ultimately generates this lethargic feeling, but raising your effort perception and making it seem harder. In response, you back off, and the body recovers.

So, to sum up, it's all regulated, but there's a lot of physiology happening at the same time - an "orchestra" of instruments and systems coming together, but the conductor must know the tune, or else it's just noise!


Mark said...

I just found your site through a link in a cycling forum. Keep up the good work!

Regarding calorie consumption while cycling. I have found that I need about 400 calories/hour for any ride lasting over 2 hours or so (I weigh 75kg). I use a mix of Hammer Nutrition's Perpetuem, along with some gel(with plenty of water), and Clif Bars. As long as I keep up the calorie intake I feel fine.

Re bonking: I have bonked twice on the bike and both times it was more of a slow progress to a point and then it felt like my energy fell off of a cliff, not fun.

vikram said...

Thanks Ross, You make a point about balancing fluid intake with CHO, in order to get maximal absorption. How does this interact with balancing fluid intake with outside temperature ?

In hot weather, the bodies fluid demand is higher. So assuming fluid with the optimal concentration of CHO is consumed, would that imply that an individual can consume more calories in hot weather ?


Anonymous said...

Ross, Johanathan

I am still hoping that you guys tap into the dreaded topic of weight loss for athletes.

Colenso said...

G’day Ross and Jonathan. Thank you both for yet another excellent, thought provoking article. Since the topic is energy use when cycling competitively in long stages, this caused my antennae to twitch in response. I’d like to offer the following observations:

1. In the older c.g.s (centimetre-gram-second) system, one calorie is the energy needed to raise the temperature of one gram of water through one degree Celsius. This amount is not constant but varies slightly according to the temperature of the water. The 15 degree calorie is defined as the amount of energy needed to raise the temperature of 1 gram of water from 14.5 to 15.5 degrees Celsius. This calorie is equivalent to 4.1855 joules. The International Table Calorie is defined as 4.1868 joules. To complicate matters further, nutritionists have long adopted the misleading convention of referring to one thousand calories as one Calorie (with the letter ‘c’ capitalised). While older c.g.s units such as the calorie (and the non c.g.s unit of Calorie) may still have a limited place in contemporary scientific discourse, I suggest it’s important to state all energy values using the SI unit of the joule. This is partly because of the confusion between calories and Calories, but mainly because we can immediately see the connection between energy needs and work done as follows:

2. For our cyclist in the Tour who has a body mass of about 75kg, assuming the mass of his bike and gear is about 10kg, the total mass the cyclist has to propel is about 85kg. Hence, the weight of our cyclist plus bike is about 850 newtons, acting downwards through the (moveable) centre of gravity of man plus machine.

Therefore, if the man and his machine were completely efficient, then for every vertical metre he climbed, the cyclist would have to expend 850 newton metres of work: 850 joules (about 200 calories).

3. However, only up to about 20% of the energy of combustion (as measured in a bomb calorimeter) of any food the cyclist consumes is converted by his body into useful work. Ignore for now the significant energy losses from drag (lower at the lower speeds of climbing), rolling resistance, flexing of the frame, forks and rims, and from losses in the transmission. Then, for every vertical metre he climbs, over and above his RMR the cyclist must consume at least 5 x 850 joules or 4250 joules. This is about 1000 calories (one kcal or Calorie) for every vertical metre climbed.

4. If our cyclist plus his cycle needs at least 4.25 kJ (1 kcal) for every vertical metre he climbs, then he needs 425 kJ (100 kcal) for every 100 metres climbed, and 4.25 MJ (1000 kcal) for every 1000 metres climbed overall.

5. Because the rate of energy expended during rapid climbing in a mountainous stage can be so high, we can conclude that the cyclist’s ability to minimise the work he must do when climbing by being as light as possible may be crucial to his success.

As you have explained so well, his success, however, also depends on him being able to access quickly his stored energy: blood sugar, glycogen and body fat; and, when that initial stored energy is depleted, on his ability to consume, digest, absorb and then use enough energy in ingested food before and during the climbs to sustain his high rate of energy outputs.