|
|
CYCLING PERFORMANCE TIPS |
|
|
|
CYCLING PERFORMANCE TIPS |
|
ENERGY - POWER, CALORIES & WATTS
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.
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.
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
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
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 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.
AIR RESISTANCE, WIND, AND DRAFTING
Along with the Calories needed to
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:
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!
POST EXERCISE CALORIES EXPENDED AFTER THE DIRECT WORK OF CYCLING
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.
HOW DOES THE WORK OF RIDING A TRAINER COMPARE TO ROAD RIDING?
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:
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 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.
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.
AND THEN THERE ARE THOSE POST RIDE CALORIES
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.
you also have to overcome air resistance. That's the resistance
produced as we cycle (from the air molecules all around us).
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%.
SHOCKS/SUSPENSION
QUESTIONS/COMMENTS
THE BOTTOM LINE - HOW MANY CALORIES DO YOU "BURN"
WHILE CYCLING?
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.)
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:
QUESTIONS
Home
|
Table of Contents
|
Local Services/Information
