Cycling Performance Information

CYCLING PERFORMANCE TIPS — Compiled from Various Sources

Fundamentals:

 Oxidation (releasing food energy)

 ATP (transferring food energy to the muscle cell)

 Aerobic/anaerobic metabolism (oxygen requirements for energy production)

 Energy content of the food we eat

 

Energy to power muscle contractions is released when oxygen combines with chemical compounds in the cell to produce Adenosine Triphosphate or ATP. This chemical reaction is called oxidation. The amount of energy produced is limited by the amount of oxygen available within the cell and the chemical compounds (carbohydrates, fats, and protein) available to be oxidized (the “fuel”).

The foods we eat provide the fuel for cell energy production. They contain three energy-containing compounds: carbohydrates, fats, and protein. Carbohydrates are the primary energy source for short, maximum performance events (sprints) and for the average cyclist. Fats can also serve as an energy source for the cell, but are more important in endurance events (usually performed at less than 50% VO2 max.) Proteins are generally used to maintain and repair body tissues, and are not normally used to power muscle activity. When there is adequate oxygen to support the energy needs of the cell, metabolism is said to be aerobic. When the demand for energy outstrips the ability of the cardiovascular system to provide oxygen for oxidation, a more inefficient form of metabolism, anaerobic metabolism, occurs.

OXIDATION & ATP

Food energy is released through a chemical reaction with oxygen in a process called oxidation. In the body food energy needs to be released more slowly and in a form that can be harnessed for basic cell functions and transformed into mechanical movement by the muscle cells.

This is accomplished by “refining” the three basic food materials (carbohydrate, fat, and protein), converting them into a single common chemical compound adenosine triphosphate (ATP). It is this ATP, synthesized as the cell metabolizes (or breaks down) these three basic foods that transfers the energy content of all foods to muscle action.

ATP is composed of a base (adenosine), a sugar (ribose) and three phosphate groups. The chemical bonds between the phosphate groups contain the energy which is stored in this molecule. And it is the breaking of these bonds (as ATP is converted into ADP or adenosine diphosphate) that provides the energy to power muscle contractions and other cellular functions.

PRODUCTION OF ATP – THREE PATHWAYS

There is a limited capacity to store ATP in the cell, and at maximum work levels this ATP stored in the muscle cells is depleted in several seconds. In order to sustain physical activity, the cells need to continually replenish or resynthesize their ATP. There are three pathways to accomplish this, and which one is used by the cell depends on the level and duration of the physical activity.

The first breaks down phosphocreatine - another high energy, phosphate bearing molecule found in all muscle cells – to directly resynthesize ATP. But it is also in limited supply and provides at most another 5 to 10 seconds of energy, limiting its usefulness to sprint type activities. At this point, the body must switch to either of two other biologic processes to regenerate ATP – one requiring oxygen (aerobic) and another that does not (anaerobic).

Aerobic metabolism, which is oxygen dependent, is the name for several different chemical processes in the cell, and can produce ATP from all three food elements – carbohydrates, fats, and protein. Aerobic metabolism supplies the ATP needed for endurance activities.

Glycolysis, also known as anaerobic metabolism, is limited to the breakdown of carbohydrates (glucose, glycogen). Anaerobic metabolism is limited by the buildup of lactic acid which begins within minutes and degrades athletic performance by impairing muscle cell contraction and producing actual physical discomfort or pain. Anaerobic glycolysis is the source of energy for short bursts of high level activity lasting several minutes at most (sprints).

THE BALANCE OF AEROBIC AND ANAEROBIC METABOLISM

As one begins to exercise, the anaerobic pathway provides ATP while the body increases breathing and heart rate to deliver adequate oxygen to the cell. As more oxygen becomes available, the aerobic pathways pick up the slack and anaerobic metabolism falls off. However, anaerobic pathways continue to

provide a small amount of ATP energy, and small amounts of lactic acid are still being produced. However this small amount of lactic acid is readily metabolized by liver and muscle cells, and does not accumulate to the degree that occurs at with anaerobic ATP activity (as in a sprint, for example).

Aerobic pathways are used preferentially by the muscle cells until VO2max. is reached. At this point, the cardiovascular system cannot provide adequate oxygen to the muscle cell to continue aaerobic ATP production, and either the phosphocreatine system, or anaerobic metabolism cover the extra energy needs. When the level of activity once again returns to aerobic levels (less than VO2max), oxygen is once again available to regenerate phosphocreatine and metabolize (clear) the excess lactic acid produced during the sprint type activity. With training, changes occur in the cardiovascular system and muscle cells that support higher levels and longer duration of physical activity before anaerobic pathways are needed, and also clear lactic acid more quickly leading to faster recovery from anaerobic sprints.

ENERGY CONTENT OF CARBOHYDRATES, FATS, AND PROTEIN

The energy contained in equal weights of carbohydrate, fat, and protein is not the same. Energy content is measured in Calories (note the capital C). Carbohydrates and protein both contain 4.1 Calories per gram (120 Calories per ounce) while the energy “density” of fat is more than double at 9 Calories per gram. The disadvantage of fat as a fuel for exercise is that it is metabolized through pathways that differ from carbohydrates and can only support an exercise level equivalent to 50% VO2 max. It is an ideal fuel for endurance events, but unacceptable for high level aerobic (or sprint) type activities.

Carbohydrate metabolism is much more efficient than fat metabolism assuming adequate oxygen is available (ie aerobic metabolism). But once VO2max has been reached, and anaerobic metabolism takes over, the efficiency of carbohydrate metabolism drops off dramatically. Carbohydrate will produce 19 times as many units of ATP per gram when metabolized in the presence of adequate cell oxygen supplies (aerobic) as opposed to its metabolism in an oxygen deficient (anaerobic) environment.

In the well fed and rested state, the human body contains approximately 1500 carbohydrate Calories (stored as glycogen) in the liver and muscle tissue, and over 100,000 Calories of energy stored as fat. The carbohydrate Calories are adequate energy for several hours of brisk cycling (80 to 100 % VO2max), and if one slows the pace to 50 – 60 % VO2max where fat Calories can be utilized, there are enough energy stores to support cycling at this reduced speed for days.

How can these facts help you in designing a program to maximize your performance?? If one does not supplement glucose stores in the body (snacking while riding), you will run out of carbohydrate stored in your muscle and liver cells after 2 hours of aerobic activity, and the bonk occurs. This term describes the fatigue resulting from muscle glycogen depletion. Without adequate carbohydrate to fuel continues high level muscle activity, it is impossible to maintain a high level of energy output and one has to slow to speeds of 50% VO2max where fat metabolism can provide the needed Calories. The bonk can be delayed by using oral glucose to supplement muscle glycogen stores. On a long ride, a rider that snacks will have more glucose available to fuel that final sprint.

Two other strategies are to 1) minimize extremely energy inefficient anaerobic sprints earlier in the ride (remember they are very inefficient in terms of ATP production) and 2) whenever possible, ride closer to 50% VO2max to take advantage of supplemental Calories available from fat metabolism. In addition to eating while riding, these two strategies will help to save a few more grams of muscle glycogen for that final sprint to the line.

CYCLING PERFORMANCE TIPS EXERCISE PHYSIOLOGY THE CARDIOVASCULAR SYSTEM & CONDITIONING

Delivering Oxygen to the Muscle cells

 cardiac output (transporting oxygen to the cells)

 VO2 (oxygen consumption with exercise)

 measures of cardiovascular fitness

 skeletal muscles

 changes in CV physiology with age

 

Regular exercise (walking, running, cycling, etc.) stimulates changes in the cardiovascular system, lungs, and muscle cells which improve work capacity – for both endurance and sprint activities. Added health benefits include a decrease in resting heart rate and a lowering of maximal blood pressure with submaximal exercise. These changes can be measured with an exercise program that elicits 60% of your

maximum heart rate for 30 minutes, 4 times a week. Understanding the physiology behind this training effect will help you in developing your own training program.

The cardiovascular (heart and blood vessels) and pulmonary (lungs) systems work together to deliver the oxygen necessary for efficient (aerobic) energy metabolism to the exercising muscle. Oxygen is extracted from air in the lungs and then transported in the blood to the cells where it is extracted and utilized. The byproduct of energy production, carbon dioxide, is then transported back to the lungs by the circulating blood and leaves the body in expired air.

CARDIAC OUTPUT

The major reason for an increase in exercise capacity with an aerobic training program is the rise in the maximal cardiac output (amount of blood pumped by the heart per minute). It plays a bigger role in increasing maximal exercise performance than does the increase in oxygen uptake and utilization by the skeletal muscle cells. Since our maximal heart rate does not change, and may even be lower, following exercise training, this increase in cardiac output is the result of a higher stroke volume (amount of blood pumped per heart beat). Cardiac output = stroke volume x heart rate.

The increase in stroke volume is a result of both a hypertrophy (enlargement) of the left ventricle muscle (athlete’s heart) as well as an enhancement of the heart’s contractile state, probably mediated by the autonomic nervous system.

THE LUNGS

The lungs job is to exchange (extract) oxygen from air drawn into the microscopic air sacs (alveoli) for carbon dioxide, a waste product of metabolism. Normally a half liter of air is drawn into the lungs with each breath (which for the average cyclist is about 3.4 to 4 liters per minute – respiratory rate x air exchanged per breath). A competitive cyclist can exchange an additional 2 liters (6 liters per minute) while the legend Miguel Indurain was reported to have a respiratory capacity of 8 liters per minute. Although our respiratory capacity is relatively fixed (as a result of inherited factors such as body habitus and the size of our thoracic cavity), you can, with practice, increase your lung capacity to some degree.

OXYGEN CONSUMPTION (VO2)

VO2 is the amount (expressed as a volume or V) of oxygen used by the muscles during a specified interval (usually 1 minute) for cell metabolism and energy production. Maximum oxygen consumption (VO2max) is the maximum volume of oxygen that can be used per minute, representing any individual’s upper limit of aerobic (or oxygen dependent) metabolism. It can be expressed as an absolute amout (again as a volume per minute) or as a % of each individual’s personal maximum (%VO2max).

VO2max. dpends on:

 lung capacity (getting oxygen from the air we breath into the blood which is passing through the lungs

 cardiac output (the amount of blood pumped through the lungs, and of course the muscles as well, per minute)

 and the ability of the muscle cells to extract oxygen from the blood passing through them (the arterio-venous or A-V O2 difference)

 

Each of these factors improves with aerobic training and results in an increase in VO2max.

The arterio-venous (A-V) O2 difference results from oxygen being delivered and extracted form the blood being delivered to an organ (usually muscle), the arterial concentration, and the blood leaving, the venous concentration. Oxygen extraction) and thus the A-V O2 difference, increases with exertion (almost doubling at maximal exercise versus at rest) as well as with training (increasing for any set level of exertion).

At levels of exertion greater than the VO2 max., the energy needs of the cells outstrip the ability of the cardiovascular system to deliver the oxygen required for aerobic metabolism, and oxygen independent or anaerobic energy production begins. Anaerobic metabolism is not only less efficient (less ATP is formed per gram of muscle glycogen metabolized) resulting in more rapid depletion of muscle glycogen stores, but also results in a build up of lactic acid and other metabolites which impair muscle cell performance (even when adequate glycogen stores remain). The build up of excess lactic acid will be ultimately be eliminated when exercise levels decrease to an aerobic level and adequate oxygen is again available to the muscle cell. The build up of lactic acid (and amount of oxygen which will ultimately be needed to

eliminate it) during anaerobic metabolism is responsible for oxygen debt (the period of time required to remove the excess lactic acid) and recovery phase that follows anaerobic exercise.

MEASURES OF CARDIOVASCULAR FITNESS

VO2 max. or maximum oxygen uptake, is considered the gold standard of cardiovascular, pulmonary, and muscule cell fitness. It is usually standardized per body weight and expressed in milliliters of oxygen per kilogram of body weight per minute, and is the maximum amount of oxygen your body (basically your muscles) can utilize. The VO2 max for an elite cyclist can range from 70 to more than 80 ml/kg/minute. It is generally measured on a treadmill or bicycle ergometer at a sports medicine clinic with the appropriate equipment. Exertion at or beyond 100% VO2max can be sustained for a few minutes at most. With training, you will increase your VO2max. as well as the ability to ride for longer periods at any % of your VO2max.

The following all indicate that an individual’s VO2max has been reached:

 VO2 plateau – no further increase in oxygen use per minute even with an increase in work performed

 heart rate within 10 beats of the age predicted maximum heart rate -this is the basis for using your maximum heart rate as a surrogate for your VO2 max when designing your personal training program)

 plasma (blood) lactate levels > 7 mmol/liter

 

For those of you interested in the mathematical expression of VO2max, it is the product of the arterio-venous oxygen difference (the oxygen content of blood leaving the heart minus that returning to the heart and thus the amount being extracted by the working skeletal muscles) and the maximal cardiac output (the maximal heart rate times the volume of blood pumped per beat). This is called the Fick equation.

 Ranges of VO2max by age/sex

 Calculating %VO2max based on your % of your MHR (Maximum Heart Rate).

 

Anaerobic Threshold (AT; also known as lactate threshold)is the level of physical performance at which the muscles produce more lactic acid than can be removed (by the liver and muscle enzyme systems). It is expressed as a percentage of VO2 max – or as indicated above as a % of its surrogate or maximum heart rate. At levels of exertion appraoching VO2max, there is a rapid increase in blood lactate levels. Cr. Concimi, a physiologist, suggested that it can be identified as the pulse rate deflection point with increasing exrcise (see the Concini test below).

Your AT limits your rate of maximal exertion (remember it can be exceeded for only a few minutes as you build up oxygen debt) and thus can be assumed to be reflected as the maximum physical effort you can maintain continuously for 30 to 60 minutes. The more you exceed your LT or AT, the more quickly lactic acid will accumulate and thus limit further increases in your performance. As most cyclists don’t have access to lab facilities, you can estimate your AT with a 30 minute (about 10 mile) time trial. The average heart rate you can maintain is a good approximation of your AT.

An individual’s AT will improve with training, and cyclists with a higher AT can work at a higher level of energy expenditure for longer periods, defeating opponents of equal (or even greater) physical strength but with lower ATs. This concept explains why interval training, which is generally anaerobic, will improve performance.

Concini Test Another method of measuring your AT (and LT) is the Concini test. As a cyclist’s efforts increase, their heart rate generally increases in a direct relationship to the energy expended (a linear relationship). But at some point the heart rate begins to level off even as the speed (and energy expenditure) continues to increase. This is the anaerobic threshold, that point at which oxygen cannot reach the muscles fast enough, lactate accumulates, and performance suffers. After an appropriate warm up, using a single gear and a relatively high speed, the rider gradually increases his or her speed by 1 km per hour every 300 meters or so. Heart rate is graphed versus speed, and the break point on the graph is the AT.

Lactate Threshhold Recent work has focused on the blood lactate threshold (LT) as a reflection of an individual’s level of training. The lactate threshold is that % of VO2 max. at which the cardiovascular system can no longer provide adequate oxygen for all the exercising muscle cells and lactic acid starts to

accumulate in those muscle cells (and subsequently in the blood as well). At high levels of activity (but below 100% VO@max), there are always a few muscle cells (not entire muscles, but a small number of cells within those muscles) that are relatively deficient in oxygen and thus producing lactic acid. But this lactic acid is quickly metabolized by other cells that are still operating on an aerobic level. At some point, however, the balance between production of lactic acid and its removal shifts towards accumulation. This point is the LT. It is usually slightly below 100% VO2 max., and will improve with training (move closer to 100% VO2max). Those with an increased LT not only experience less physical deterioration in muscle cell performance for any level of %VO2max, but also use less glycogen for ATP production at any level of performance. Thus an improvement in LT allows the individual to perform at maximal levels for a longer period of time before running out of adequate energy (glycogen) stores.

Resting heart rate, your heart rate on awakening in the morning, is a simple but effective indicator of your level of training. It will fall as you train, but then begin to rise again with overtraining.

Cardiac Stress Testing for asymptomatic coronary artery disease.

THE SKELETAL MUSCLES

There are two types of fibers: type I, or slow twitch, and type II or fast twitch. The slow twitch fibers are more energy efficient and use both fats and carbohydrates as an energy source. They are the major muscle fiber in use at 70-80% VO2 max. Fast twitch fibers on the other hand are less efficient, use mainly glycogen as fuel, and are called into action for sprints as the athlete approaches 100% of maximum performance. Although the ratio of slow to fast twitch fibers is generally controlled by genetic (inherited) factors, this ratio does change (often over years) with an ongoing training program.

Along with these visible changes in the muscle cells, there are microscopic and metabolic changes at the muscle cell level with training. These include an increase in the size and number of the muscle cell mitochondria, an increase in the activity of various metabolic enzymes in the muscle cells, and an increase in the number of capillaries in the muscle that supply blood to the individual muscle cells. The net result is an increase in the amount of oxygen extracted from the blood in a single pass through the muscle (the arterial – venous oxygen difference).

SUBMAXIMAL EXERCISE

Endurance training (usually defined as training at less than 60 – 70% VO2max) improves the overall efficiency of the cardiovascular system as reflected in a smaller increase in heart rate for any given exercise intensity, and is also thought to promote a shift towards the use of fat as an energy source (more efficient with 9 Cal per gram versus 4 Cal per gram with carbohydrates). This is supported by the observation of a smaller increase in the plasma free fatty acid levels (indicating enhanced fat oxidation) at these activity levels.

CHANGES IN EXERCISE PHYSIOLOGY WITH AGE

Aging results in a progressive decline in the functional capacity of various body systems, and is reflected in a 9 to 10% decrease in maximal aerobic exercise capacity in sedentary individuals. It is well documented, however, that endurance training can attenuate this age related decline to about 5% per decade, and can also improve exercise performance in older men and women.And if you are more than 40, it may be time to consider cardiac stress testing for asymptomatic coronary artery disease.

CYCLING PERFORMANCE TIPS

EXERCISE PHYSIOLOGY

SKELETAL MUSCLE

Skeletal muscles makes up over 1/2 of the body weight in a lean individual. All muscles (quadriceps, biceps, etc.) are composed of thousands of muscle cells. And these individual muscle cells contain two proteins – actin and myosin – which chemically interact and shorten the cell (and along with it the muscle itself) when the muscle cells are stimulated by a nerve impulse. The interaction of the actin-myosin complex, which results in the shortening or contraction of the muscle cell, requires the energy in the form of ATP.

TWO TYPES OF MUSCLE FIBERS

The muscle cells contain two distinct types of muscle cells or fibers.

Type I (slow twitch, SO fibers) – These muscle cells shorten at a relatively slow speed and generate energy from both fats and carbohydrates via aerobic metabolism . They are the major muscle fiber in use at 70-80% VO2max. Type I cell characteristics include:

 

 high concentration of mitochondria for aerobic metabolism

 increased intracellular myoglobin (which gives the muscle its characteristic red color) to store and transport O2

 low concentration of glycolytic enzymes used for anaerobic metabolism

 relatively fatigue resistant

 

Type II (fast twitch, FG fibers) – These muscle cells are less efficient than the slow twitch cells and are almost entirely dependent on glycogen as fuel. They are called into action for sprints when the athlete approaches 100% of their maximum performance (and are working in the anaerobic range above 100% VO2max). Type II cell characteristics include:

 low concentration of mitochondria

 high concentration of ATP and glycolytic (ATPase) enzymes

 a rate of shortening 3 to 5 times that of a type I muscle cell

 

The relative proportion of type I and type II fibers within a muscle varies from person to person and is determined by genetics (ie inheritance from your parents). However, with limits, this ratio can be modified with exercise and training. Successful endurance athletes have a preponderance of slow twitch muscle fibers (up to 90% of the fibers in the calf in cross country skiiers) while sprinters have more fast twitch fibers. Short term studies in bicyclists (5 months) failed to show a change in the ratio of cell types (percentage of slow vs fast twitch fibers) in leg muscles, but a longer multi-year study has suggested that this ratio can change with time, continuing to change for at least 5 years with regular training.

But even without a change in the ratio of cell types, there is no question that both slow and fast twitch fibers can markedly improve their metabolic capacity with training. (see also Principles of Training)

MEASUREMENT OF ENERGY OUTPUT (POWER)

Energy output (or work) is expressed as power (the amount of work done during a specified unit of time). Power output can be measured as steady state power output (maintaining a steady speed for minutes to hours) or maximal power output – which require maximal activation of the ATP-CP energy system. The latter reflects the maximal muscle power of the athlete and is limited by the amount of ATP and CP available in the cell – about 6 seconds.

Curt Austin has put together a nice calculator to estimate power output (in Watts – you enter your own parameters) on his website. Malcolm Firth also published some comparative numbers in an online coaching forum. (As the amount of ATP-CP available to the muscle cell is limited, Malcolm’s maximum power output over several minutes would be lower than that achievable in a brief sprint lasting 5 to 5 seconds):

“In February 1998 I did a small research project in which a group of 24 cyclists were asked to do two tests on a CompuTrainer (an electomegnetically braked turbo trainer made by RacerMate of Seattle, USA). The first of these was a step increased load test to voluntary exhaustion in which the load began at 100 watts and was increased at approx 20 watts per minute. After a break of at least three hours the cyclists then rode a simulated ten miles time trial on the CompuTrainer with the instruction to complete the distance as quickly as possible. Some of the data is summarised below:

 Average Age: 33.17yr (standard deviation 12.97, range 16yr-61yr)

 Average Max Power for 1 min: 367.46 watts (st dev 62.74w, range 263w-487w)

 Average Max Heart Rate: 187.29bpm (st dev 12.16bpm, range 163bpm-211bpm)

 Average 10 mile Time: 25min 52sec (st dev 1min 50sec, range 29min 09sec – 23min 02sec)

 Average 10 mile Power Output: 286.46 watts (st dev 49.88w, range 215w – 375w)

 Average 10 mile Heart Rate: 177.08bpm (st dev 11.78bpm, range 145bpm-199bpm)

 

The average 10 mile heart rate worked out at 94.5% of the mean max heart rate.(st dev 2.81%, range 88.41%-97.41%). If you go to my web site at http://www.msfirth.freeserve.co.uk you will find an article giving details on how to use the average ten miles heart rate to estimate heart rates for other training and racing intensities.”

CYCLING PERFORMANCE TIPS

EXERCISE PHYSIOLOGY – ENERGY REQUIREMENTS OF BICYCLING

The energy requirements for a ride are dependent on:

 

 the weight of the cyclist and equipment

 the distance

 the terrain (flat versus hilly)

 the speed of the ride

 headwinds or tailwinds

 

And the Calories to fuel the ride are supplied (via the intestinal tract)from food eaten just before or on the ride, or from the body’s internal energy reserves (fat, glycogen) in the liver, fatty tissue, or in the muscle itself.

ENERGY – POWER, CALORIES & WATTS

Before we go any further, let’s review the terms energy, force, power, Calories, and watts which are often used interchangeably. 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 nutitionists 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 reflection of power.

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 contol 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:

 keep bearings and chain well lubricated

 use light oil in bearings and bottom bracket for time trials

 use light greases – paraffin gives more resistance than grease

 use tires with a small “footprint”

 keep tires maximally inflated to decrease rolling resistance

 use thinner, more flexible tires (less energy taken up in sidewall deformation)

 

Curt Austin has put together a nice calculator to estimate power output (in Watts – you enter your own parameters) on his website. As energy used in Watts is directly proportional to Calories, this calulator will

let you play with the numbers for weight, postion on the bicycle, road grade, and air resistance/wind which we will discuss below.

WEIGHT

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.

HORIZONTAL DISTANCE

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 (hills)

Vertical distance, i.e. climbing a grade or hills requires additional energy 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 Austin’s calculator, I first calculated the power output for a 170 poound cyclist & 22 poound 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.

INERTIAL WEIGHT

Finally, weight is a factor in sprints where inertia (the resistance to setting an object into motion – why it is harder to get up to speed on a bike than to maintain that speed) comes into play. It definitely takes more energy to accelerate a heavier rider/bike combination in a sprint. And extra weight in some bike components (rims for example) may require twice as much energy to accelerate as an equal weight in the frame. This is a result of the fact that with rotational speed you are accelerating these components much more quickly. (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).

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 tthe 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.

AIR RESISTANCE, WIND, AND DRAFTING

Along with the Calories needed to

 

 counter the effects of gravity

 over come the friction and rolling resistance in the bicycle

 

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:

 mechanical resistance increases by 225%

 rolling resistance by 363%

 air resistance by 1800%.

 

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

 rho=air density

 g=gravity

 area= frontal area of the rider and bike (scrunch down, less area, faster ride)

 

 

 Cd=coefficient of friction (smoother rider and helmet, and less protrusions from the bike, the lower the Cd. This also refers to the shape of the frame, wheels, etc. A tube, spoke, fork shaped like a wing has a lower Cd than round spokes, tubes,or forks.)

 V=air speed – which is squared (ie going from V=7mph to 21mph is a 3x increase in speed which is then squared and the force required is now 9x)

 

SHOCKS/SUSPENSION

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!

THE BOTTOM LINE – HOW MANY CALORIES DO YOU “BURN” WHILE CYCLING?

To calculate the Caloric requirements of cycling, you need to include the Calories needed to maintain your basic life processes – the BMR – and these 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

 

THERMIC EFFECT

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.)

ENERGY REQUIREMENTS IN A COLD ENVIRONMENT

It was mentioned that a cold environment does NOT increase the BMR but requires the expenditure of additional Calories to maintain a constant body temperature. While riding there will be some “waste” energy (from the inefficiency of converting eaten of stored Calories into power at the pedal) but the wind chill effect from riding will accentuate any heat loss. How many additional Calories are needed ? At rest, roughly 16 Calories per day for every degree F below 98.6. Although one can argue about exact BMRs and find different formulae to calculate basal Caloric requirements, the only formula I am aware of that corrects for the ambient temperature is:

Cal requirements/day = 4660-(15.9 x tempurature in degrees F)

Again, this was for an individual exposed for long periods to the ambient tempurature, not just a several hour ride. Unfortunately the level of activity was not defined and for cycling, wind chill may decrease the effective tempurature even further. Does exercising in the cold markedly increase Caloric needs? Probably not by a big factor for most of us, but it again demonstrates the multitude of variables we need to consider as we try to estimate the Caloric needs of exercise and cycling.

CYCLING PERFORMANCE TIPS

Formula for the Energy Requirements of Cycling

From Bicycling Science by Frank Whitt and David Wilson, p.157

W = Cv [K1 + {K2(Cv+Cw)(Cv+Cw)} + {10.32Em(s/100 + 1.01a/g)}]

Where:

 W = power in watts

o 1 W = 1 joule/sec

o 69.78W = 1000 calories/min = 1 kilocal/min = 1 Calorie/min

o 1 Calorie = 4186 joules

 

 

 Cv = speed of cyclist in meters/sec

o 1 mph = .447 meters/sec

o 1 mph = 1.609 kilometeres/hr

 K1 and K2 are constants (see table below)

 Cw = headwind in meters/sec

 Em = mass of cyclist and bicycle in kg

o 1 pound = .4536 kg

 s = slope or grade in %

 a = acceleration of the bicycle in meters/(sec)(sec)

 g = gravitational accel = 9.806 m/sec-sec at sea level

 

CONSTANTS K1 &K2:   ASSUMPTIONS BICYCLE WT RIDER + GEAR K1 K2

MTN BIKE 15 kg 80 kg 7.845 0.3872

ROAD BIKE 10 kg 75 kg 3.509 0.2581