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  Latest update: 8/18/2023

Exercise Physiology

Energy Requirements in Bicycling

The energy requirements in cycling are a function of: The Calories to fuel the ride are supplied by the body's internal energy reserves in the liver, fatty tissue, and the muscle itself supplemented by Calories eaten during (or just prior) to the ride.



Let's say you want to push a 500 pound block up an inclined ramp. This task, which means overcoming the resistance of the block to the ramp surface as well as gravity, requires a specific amount of total work (force x distance) which is the same whether the block is moved over 5 minutes or 5 hours. If you want to add a time element, that is you want to move the block over a shorter period of time, you add the idea of power into the discussion.

The energy needed to accomplish the task can be expressed in absolute terms (time independent - i.e. total work done) or as energy released over a specified time interval (i.e. power - expressed in watts - with more power required to move the block over a shorter perios of time).

The most commonly used time independent energy unit in the cycling literature is the Calorie (note the Capital "C") which is equivalent to 1000 calories (note the small "c") used in the physical science (physics, chemistry) literature. A calorie 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, a Calorie (large "C"), which is equivalent to 1000 calories (small c again) or 1 kcal, is used. Unfortunately most nutritionists forget to capitalize the "C" when they are writing about "calories" so don't get confused. Approximately 60% of the Caloric energy in the food we eat is lost as heat during the production of ATP (adenosine triphosphate), the high energy, intermediary molecule actually used to power muscle cell contraction. Additional energy, again reflected as heat production, is lost when ATP is used to produce the 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 shed by the body's temperature control mechanisms, but the heat produced with exercise when ATP is used to power muscle contraction is concentrated over a shorter period of time, raising our body temperature. We then sweat to increase the rate of heat loss and protect a stable body temperature.

Our bicycle, on the other hand, is very efficient when it comes to mechanical energy loss. Over 95% of the muscle energy at the pedals is translated into forward motion with less than 5% lost (again as heat) from the rolling resistance of the tires, bearing friction, etc. We can increase the efficiency (decrease resistance losses) by:

If you are interested in the amount of personal power needed to ride at a certain speed, you are interested in watts. The website Analytic Cycling has a great calculator which lets you calculate your power output in Watts when you enter your own parameters (weight, speed, road incline, etc.). This calculator lets you play with the numbers for weight, position on the bicycle (frontal surface area), road grade, and air resistance/wind.

This article describes what we can assume is close to the human maximum when it comes to power output - an analysis from the 2023 Tour D'France. At 7 watts per kg and assuming an average 70 kg rider (I have no idea how much Jonas Vingegaard actually weighs) it comes out to around 500 watts, held at various times for over 10 minutes.


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 (lighten) 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, air speed should be used. A head wind should be added to your ground speed to determine your air speed (and air resistance) while a tail wind would 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. 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


Comments below are based on the in depth analysis in this article.

At 20 mph, if you draft a single rider you can reduce your energy requirements (measured by VO2 needs) by 18%, and at 25 mph by 27%.

In order to benefit from drafting, you need 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 that rider 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 here 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 (~3 percent energy savings). The low pressure behind the lead rider is increased in a pace line, giving the leader a slight "nudge" from the pressure differential between the high pressure ahead of them and the low pressure behind. The same thing happens in NASCAR where a car will go 1-2 mph faster when being drafted.

And the bigger the group drafting together, the more the benefits. The article referenced above, using wind tunnel tests, demonstrated that in a 121 man peloton (such as in the Tour De France) a rider in the rear can get a 95% reduction in wind resistance!

I always wondered how Tour De France riders could maintain such high speeds day after day on for 100 miles. As you can see in this graph, if you increase your ground speed by 5 mph from 15 to 20 mph, the total energy you expend doubles from 100 to 200 watts. But if you are pack riding (with 121 other riders) a rider in the back can eliminate their air resistance (yellow). Then by extrapolating the purple (all other resistance) you can see that for a mere 100 watts of power a rider could manage to maintain between 30 and 35 mph.


The traditional teaching has been that drafting on a hill climb was of no significant value. You were moving at a speed where wind resistance was not a factor. That is drafting a teammate would have no effect on drag reduction for a grade greater than 7%.

However this study has now laid that teaching to rest. Using a study group of 12 strong, amateur cyclists, they found a 4% improvement in times on a 7.4% gradient. And it was presumed that there would have been an even greater benefit on lesser grades.

Further analysis indicated that 2/3 of the improvement was an aerodynamic advantage (less wind resistance even at this slower speed) and the other 1/3 was from a psychologic boost which included a decreased time in the final sprint to the line.

So it appears that drafting offers a competitive advantage in almost every riding situation.


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.


Have you ever wondered how Caloric needs compare between running, walking, and cycling? Maybe you are calculating replacement snacks for an upcoming weekend ride. Or want to justify that extra large portion of desert after a long run.

Estimates for walking include two variables - your weight and the distance walked. Put on a heavy backpack and you will use a few more Calories per mile than for an after lunch walk. Climb a hill, and you need to add in the Calories used to lift yourself and possible backpack against the pull of gravity. Intensity is not a factor. A power walk won't use any more Calories than a stroll covering the same distance.

Here is a quick link to a calorie calculator specific to walking. Results are expressed in Calories per hour for various walking speeds but you can easiy calculate Calories per mile (which for a 170 pound walker are ~ 100 calories per mile). The site suggests it takes a few more Calories per mile to run rather than walk - supposedly for the small amount of energy expended in the up and down movement of the body. But science isn't entirely supportive of that difference.

This study compared 3 groups - normal weight walkers, overweight walkers, and marathon runners. The energy expenditure was equal (per mile) for running versus walking for normal weight athletes. And correcting for obesity by normalizing to Calories per kg fat free mass, energy expenditure was equivalent across all three groups. Calories expended per mile for a normal weight walker (Using my weight of 170 pounds or 77 kg) is 99 Calories per mile (1.29 cal/mile/kg x 77 kg).

Biking calculations require a third variable, wind resistance, which climbs exponentially (not directly or linearly) as air speed increases. The most accurate numbers for cycling come from Dr. Edward Coyle of the University of Texas in Austin.

Wind, hills and drafting which can modify energy expenditure by up to one-third, were not accounted for.

So you can compare these 3 modes of travel in terms of efficiency (Calories needed to cover 1 mile) or intensity of the activity (Calories used per hour). The following used average speeds (based on a Google search).

For Efficiency of travel - Calories expended per mile covered:

For Intensity - Calories expended per hour by the average athlete:


This article gives us the answer.

In 20 minutes, the 9 riders riding at a conservative 20 mph would have covered a total of 9 x 20mph = 180 miles/hour x (20min/60min) = 60 miles for 20 minutes.

The Tesla? 1.2 miles for the same amount of energy.

And walking? Being bout 1/3 as efficient as Cycling = 20 miles covered for the same numbers of Calories used.

So we now have relative efficiency as a means of travel:

Using a bicycle is 60 times as efficient as driving as a means of travel.


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 5.5kgs 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 70KGs 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 100ks. There was no real wind to speak of. I did have some niggly feelings in my legs at about 95km 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 7km 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 formula 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.

All questions and suggestions are appreciated and will be answered.

Cycling Performance Tips
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