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  Last updated: 11/12/2012


The energy needs for a ride are dependent on: The Calories to fuel the ride are supplied from the body's internal energy reserves in the liver, fatty tissue, and the muscle itself (fat, glycogen) supplemented by Calories eaten during (or just prior) to the ride.


First, let's review our terminology energy, force, power, Calories, and watts. Energy is the ability to perform work. The presence of energy is revealed only when change takes place. Potential energy is stored energy (the energy which will let you roll down the hill on your bike, starting from a dead stop, without ever pedaling). Kinetic energy is the energy of motion (the energy contained in you - and your bike - when already rolling down that hill and evident if you run into someone while in motion). The measurement units for energy (either potential or released) are calories or Calories.

Force is the ability of that energy to make a change - to change the state of rest or motion in matter. When force is actually applied, work (force applied over some distance) is done. The same amount of work is done if the task is accomplished in 5 seconds or 5 minutes. The rate at which the work is done is power - the more work per minute or second, the more powerful the force applied to do that work. And watts are the units used to measure power. The more force applied to accomplish the task in a shorter period of time, the more work done and the more power required to do it.

Energy output can be expressed in absolute terms (time interval independent) or in as energy released over a specified or defined time interval (time interval dependent). The most common time independent energy unit used in the cycling literature is the Calorie. In the physical sciences (physics, chemistry), a calorie (small "c") is the quantity of energy required to raise the temperature of 1 gram of water 1 degree centigrade. As this unit is too small to easily express the energy needs of biologic systems, the Calorie (large "C"), which is equivalent to 1000 calories (small c again) or 1 kcal, is often used. Unfortunately most nutritionists forget to capitalize the "C" when they are writing about "calories" (they really mean Calories), so don't get confused. If the energy released is measured over a set period of time, it is expressed in watts, and is a measure of the total power used over time.

Approximately 60% of the Caloric energy from the food we eat is lost as heat during the fabrication of ATP (adenosine triphosphate), the high energy, intermediary molecule actually used by the muscle cell to power muscle contraction. Additional energy, again reflected as heat production, is lost when ATP is metabolized in the actual mechanical work of muscle fiber contraction. The net result - only 25% of the Caloric energy in the food we eat is actually used to power the mechanical work of the muscle cells. The initial heat loss associated with the conversion of Calories in food into ATP occurs slowly over several hours and is easily compensated for by our body's temperature control mechanisms, but the heat produced with the metabolism of ATP to power muscle contraction is concentrated over a shorter period of time and is why our body temperature rises (and we sweat to compensate) when we are exercising.

Our bicycle, on the other hand, is very efficient in terms of energy loss. Over 95% of the muscle energy we use at the pedals is translated into forward motion and less than 5% is lost (again as heat) from the rolling resistance of the tires, bearing friction, etc. Some of the things we can do to increase the efficiency (decrease resistance losses) are:

The website Analytic Cycling has a nice calculator that lets you calculate your power output in Watts - you enter your own parameters. As energy used in Watts is directly proportional to Calories, this calculator will let you play with the numbers for weight, position on the bicycle (frontal surface area), road grade, and air resistance/wind which we will discuss below.


The combined weight of the cyclist and equipment impact the energy requirements of a ride. This relationship is directly proportional i.e. a doubling of the weight on the bike doubles the number of Calories expended. And 2 pounds on a cyclist is just as much a problem as 2 pounds of equipment on the bike frame itself. Austin did a nice analysis on the effect of weight on performance. Here's his conclusion: I thought it would be interesting to see how weight would influence these curves. If I lost 10 lbs (about 5%), I would be able to go about 5% faster on the steepest hills, 0.4% faster on the level, and about 2% slower on the downhills. Over a simulated 20-mile closed-circuit ride with a variety of grades, a 10-lb difference produced a 33 second difference. This may or may not seem significant in the context of a time trial. On the other hand, there are two hills on this simulated route where the heavier rider falls back 14 seconds. That is, about 200 feet back and well-dropped. A two-lb difference that you can buy at a bike shop for $500 amounts to only 7 seconds on this circuit, but again, this could mean cresting a hill 50 feet behind your better-sponsored buddies.

INERTIAL WEIGHT - a special case

With sprints (or other riding situations where there is an ongoing variation in your speed) inertial resistance (the resistance to setting an object into motion) comes into play. It takes more energy to accelerate a heavier rider/bike combination in a sprint than a lighter one. Extra weight in some bike components (rims for example) may require twice as much energy to accelerate as an equal weight in the frame. (Note: this means you should upgrade your tires, rims, crankset, and shoes before you spend your extra $$ to decrease your frame weight an equal amount). I have had regular riders tell me that they could tell the difference on a 50 mile ride when they were using new, lighter rims. This may be due to the constant variation of speed that occurs on long rides with a decrease in total energy needs as there is less inertial resistance with the lighter rims.

The bottom line - the heavier you are, the greater the total energy requirements for your ride. And except for the special case of inertia, all weight is equal. So don't forget that the extra water bottle, the larger heavier tool set, and even that extra pancake you ate in the morning all require additional energy on the ride. And saving a few ounces by eating one less pancake will have as much impact on your performance as that expensive titanium item you've been saving to buy.


Horizontal distance. We all know that it takes more energy the further we carry any object. The same is true in cycling. On level terrain, the number of Calories expended is directly proportional to the distance and doubling the distance (weight remaining the same) will double the number of Calories required.


Vertical distance, i.e. climbing a grade or hills requires additional energy as you overcoming gravity (essentially lifting the cycle/rider to a higher elevation). A common question is how speed on the flats compares to speed on an uphill slope. Using the Analytic Cycling website, I first calculated the power output for a 170 pound cyclist & 22 pound bike on the flats at 20 mph. It was 210 watts. Keeping energy output steady (at 210 watts), I then calculated the speed on a 1% (17.25 mph), 2% (14.6), 3% (12.3) and 5% (9.0) grade.

What about descents and hilly terrain? How does weight factor into these riding conditions? You may have noticed that a heavier rider descends a hill faster (energy expenditures being applied to the pedals being equal) than a lighter one. This seems to fly in the face of a fact you learned in physics class about all objects falling at the same speed independent of their weight. But when going biking down a hill, the slope factor needs to be taken into account. The final speed down a long hill is the balance between the propulsive forces - total rider/bike weight x the sine {that's a trigonometric function} of the angle of the hill - and the resistive forces - wind resistance is the big one. And the heavier rider comes out ahead. If one does the exact calculations with twin brothers weighing 175 pounds, descending a medium slope hill, riding similar bikes, and in exactly the same aerodynamic positions, with one carrying 25 pounds of lead shot, the heavier one would go 26.73 mph while the lighter one would be slightly slower at 25 mph.

And what about rolling terrain?? With climbing, the lighter rider has a definite advantage over the heavier one. And in rolling terrain with repeated ups and downs, the lighter rider comes out ahead.


Along with the Calories needed to

you also have to overcome air resistance. That's the resistance produced as we cycle (from the air molecules all around us).

Air resistance increases with your air speed (the velocity of our travel through that mass of air). Even with the best riding technique, a head wind will increase your energy expenditure per mile for any specific ground speed (the speed indicated on your bike computer). With the head wind, your air speed (and air resistance) is now GREATER than your computer indicates, the air resistance is higher than at a similar ground speed in calm conditions, and your energy needs are greater. Likewise a tailwind will decrease our air speed relative to your ground speed and make it easier to maintain any specific ground speed. And worst of all, this relationship is an "exponential" one which means that doubling our air speed MORE THAN doubles the Calories expended per mile traveled.(This graph visually demonstrates the fact.)

A headwind on an out and back course always results in a slower total ride time than for the same course ridden in calm conditions as the time gained on the return trip with a tail wind doesn't make up for the loss from grinding into the wind on the way out. For a 12 mph wind, total time will rise by about 7%.

Remember that the "speed" that determines your energy needs to overcome air resistance is your AIR speed, not the GROUND speed which is read from your computer. When you are calculating energy needs for a ride, it is the air speed that is used. A head wind should be added to your average ground speed to determine your air speed (and thus air resistance) while a tail wind should be subtracted from your ground speed. If you think about it, this makes sense - it is always easier to ride with a tail wind, ground speed staying the same.

At cycling speeds greater than 15 mph, the energy needed to overcome AIR RESISTANCE greatly exceed those of the rolling and mechanical resistance in your bike. For example, in going from 7.5 mph to 20 mph:

This is why drafting (which cuts down air resistance) provides such an advantage in high speed events. At 20 mph, drafting a single rider reduced energy requirements (measured by VO2 needs) by 18% and at 25 mph by 27%.

In order to benefit from drafting, you've got to be in the drafting bubble behind the cyclist immediately in front of you. And in a crosswind the bubble will NOT be directly behind the rider in front but will be some angle away from them. The effectiveness of this bubble decreases with the distance, being the greatest if you draft closely and falling off until there is minimal benefit at 5 or 6 feet. The important fact is that you will get some benefit 3, or even 4 feet, back - and it’s a lot safer than being directly on the rear wheel of the rider in front of you.

The rider being drafted also gains a slight advantage. This is explained by the fact that the low pressure behind the lead rider is increased in a pace line, giving the leader a slight "nudge" due to the pressure differential between the high pressure ahead and the low pressure behind. This is why a NASCAR racing car will go 1-2 mph faster when being drafted.

Since wind resistance plays such a great role in the overall resistance we get when riding, it makes excellent sense to draft. Better if closer, but that comes with practice and skill as well as trust in the front-rider's smoothness and consistency.

Your frontal surface area affects your air resistance. Wind tunnel results show that eliminating the drag created by projecting 4.5 inches of a pencil into the airstream will provide a 158 foot finish line advantage to a cyclist in a 25 mile time trial. That baggy jersey or upright position may be costing you minutes.

Let's review the factors in air resistance again:

Air resistance =.5*(rho/g)*Area*Cd*V^2


Shocks, both front and rear, will affect your riding over uneven terrain on a mountain bike. Front shocks decrease vibration transmitted to the shoulders and allow more concentration on the course (no energy issues here). The older rear suspended bikes without a rigid rear triangle could absorb some pedal/rear wheel energy, but this is less of an issue with the newer rear suspensions. One study did compare rigid frame (RIG), front shock (FS), and fully suspended (FSR) mountain bikes using the same riders and course. The front suspended bikes finished 80 seconds ahead of the RIG and FSR bikes over a 31 minute course!


For years, there has been a debate about a post-exercise boost in metabolism which will "burn" more Calories beyond those expended while on the bike. This article is a well done review of the subject and provides a reference with solid evidence that there is a post exercise increase in Calories expended per hour compared with a non exerciser. But, and there always seems to be a caveat, it occurs ONLY with vigorous exercise in the range of 70 - 80% of your VO2max.


Here is an interesting question re the ability to "train" to increase power - with a f/u. It is anecdotal, without proof, but is worth considering.

Q. I have added a ballast of 5.5kg's to my hydration pack(so my buds don't see) to see if I can train with it and then shed it on race day. I also always ride with my Sigma light and battery firmly secured in my water bottle cage(another kg at least) telling my mates its just too much trouble to take it off and put it back on again. I also have my race wheels that are 600g lighter than my training wheels.

I have read a lot of hill training tips and routines but the underlying goal is to increase your power to weight ratio. So I figured that if I weigh 70KG's and upped that to 77 for training, then shed it on race days, I would be scoring an increase in my P 2 W ratio which would help me get to the top of the hills in touch with the real climbers. What I have found is, that I don't notice the extra weight once I have the pack on and I'm riding. I just find that when we dice for the crest of the hills my legs are on fire and I may come second, but I am not even thinking about the extra weight. Slowly I have managed to get back to where I was in the ranks of my chain gang with carrying the extra weight. I don't have any power measuring equipment only HR and my HR on the climbs is +-8 BPM higher than before, depending on how steep the climb. I do manage to stay with my mates though. Do you think my plan has merit?

A. If one believes that training (cardio and strength) is the body responding to stress, then adding extra weight for training and shedding for the race should work. I'll be interested to hear about your results. It is the same concept as doing intervals to increase your cruising speeds. Don't forget to let me know.

F/U Hi Dick, I had a great race today rode 2Hrs 29min 15secs for 100k's. There was no real wind to speak of. I did have some niggly feelings in my legs at about 95k's but no full blown cramps. If I can repeat this performance in November(19th), when I go up to ride the 94.7 in JHB, I'll be really chafed. It is at an altitude 1500m higher than Cape Town and has a "sort of" climb in the middle of about 7k's 3.2% gradient. The rest of it is rolling hills. My goal there is a sub 2H30.


Is there a training advantage to a trainer over riding on the road? That is common gym club folklore. Is it true? Here are my thoughts:

Q. Is 1 hour on a trainer equal to 2 hours of riding on the road?

A. The answer is no if by “equal” you mean you are doing an equal amount of work (or burning an equal number of Calories per hour).

The amount of work you are doing on a bike (or a trainer) is expressed in watts (measured at the rear hub). A watt being defined as the amount of work per unit of time (1 watt = 0.01433 calories/minute). So if you are putting in an equivalent effort (work) on a trainer as you are on a bike on the road, the amount of work you are doing per minute (In watts measured at the rear hub) should be equivalent as well.

How do we usually measure effort (if we cannot measure watts directly)?

The work being done by the muscles is fueled by energy produced by muscle cell metabolism. This energy production requires oxygen - which is provided to the muscles by the heart, lungs, and circulatory system. For a set amount of work per minute, a specific amount of blood (and oxygen) has to be delivered to the muscle cells per minute. The amount of blood circulated is directly proportional to the heart rate. Thus if you are working harder, the heart rate will be proportionally higher to maintain that higher level of work.

Ergo, if your heart rate is equal on a trainer and on a bike, I think it is fair to say you are doing equal work in watts. And if you are maintaining an equal heart rate on a trainer for an hour or on a bike for an hour, the number of Calories you are expending per hour is equal as well.

Work done = watts = Calories expended per set period of time. Do equal work and you will expend equal Calories. How you do it - bike or trainer - does not make a difference.


To calculate the Caloric requirements of cycling, you need to total the Calories needed to maintain your basic life processes (your basal metabolic rate or BMR) which are needed even if you were not exercising and the Calories used for the physical activity itself. A third component called the "thermic effect of food" refers to the energy expended in digesting, absorbing, and transporting food energy to the cells in the body. Thus your total Caloric needs can be expressed as:

CALORIC NEED = CAL(bmr) + CAL(physical efforts) + CAL(thermic effect)

As a rule, the average American, pursuing the average recreational activities and chores of daily living (mowing the lawn, etc.), uses:

  1. 23% of their Calories for physical activity
  2. 10% of their daily Calories for the thermic effect
  3. 67% of their Calories for the BMR

This is a straight 10% of all the Calories you actually eat, so you can easily calculate it. (You add up CAL(bmr) and CAL(physical effort) that need to be replaced and add another 10% to cover the energy needs of digestion and absorption.)


It was mentioned that a cold environment does NOT increase the BMR but requires the expenditure of additional Calories to produce heat energy and thus maintain a constant body temperature. Generally this is from muscle activity and an example is shivering to generate extra heat energy when your core temperature is falling.

While riding there will be some "waste" energy (from the inefficiency of converting eaten of stored Calories into power at the pedal) that will be used to keep you warm, but then again, the wind chill effect from riding will accentuate heat loss and tend to negate this benefit to some degree.

How many additional Calories are needed in the cold? At rest, roughly 16 Calories per day for every degree F below 98.6. Although one can argue about exact BMR and find different formulae to calculate basal Caloric requirements, the following gives an estimate of the approximate extra energy needs (again, per day): Additional Calories/day for a cold environment = (98.6 - ambient temperature in degrees F) x 16 which would then be added to the BMR calculation and Calories used for exercise.

But there is another factor to consider - the increased air density factor (cold air is more dense than warm air and thus provides more resistance) as well s a slightly increased frontal surface area (again more air resistance) from wearing extra clothes. How much - here is the calculation (done for Seattle comparing our normal spring temperature (60F) with a cold winter day (40F).

We will use the Analytic Cycling website to do the final calculation.

We changed 2 variables in this calculation - frontal surface area (assuming more bulk from a coat/hat/leggings) and air density (increased air resistance at a cooler temperature). The majority of the increase in energy needs was from the increased frontal surface area. Here are the specifics:

When you add together the effect of the cold on maintaining your core temperature as well as the actual physical work of riding through air that is more dense when cold with additional clothing, you can see that it is not just the tight leggings that are slowing you down, it is more work.


Finally, even though you are not expending them on the ride, I think it is fair to include them in the Caloric needs for a ride done at an intensity of >70%VO2max.


Question:I have a heart rate monitor that calculates Calorie burn based on my activity level and I was wondering if I should feed just that number or add that number to my daily requirements. - WTD

Answer: I wouldn't calculate your Caloric needs from a HR monitor. For example, does a 200 pound muscular guy with a HR of 180 burn as many Calories as an out of shape 200 pounder at the same heart rate?? Watts expended relate to work done. Heart rate doesn't. If your basal is 1700 and you really burn 1000 with exercise, you need to eat 2700 between the 3 meals and supplements during that 24 hours.

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