How hard am I working? Am I pushing myself and getting the maximum from my training efforts? These are common questions for any cyclist focused on a high quality workout.
There
are a number of metrics (or measures) of how hard you are working as
you cycle.
The
simplest of these is a rating of perceived exertion (RPE), a numerical self-assessment of your
perception of personal effort on a ride (or other activity) that requires no additional equipment. With a little practice, anyone can use this measure.
More
complex, but also more precise, are several laboratory-derived measurements
such as lactate threshold (LT) or oxygen uptake (VO2). But as they
require specialized equipment, they are not really available to the
average cyclist.
Between
these extremes we have the cycle computer, heart rate monitor, and
power (watt) meters.
What
follows is a summary of the most commonly used metrics in the
physiology and cycling literature.
Perceived
Exertion (perceived effort)
The
RPE is a simple self-scoring of how
hard you feel you are pushing yourself. The original RPE scale ranged
from 6 to 20 and assumed that adding a 0 to your level of
perceived effort would correspond with your heart rate (i.e. if
you were resting, a 6 on the scale your heart rate would be in the
neighborhood of 60). There is also a condensed 10-level version.
Although
RPE isn't accurate enough for detailed physiologic studies, research
has demonstrated an amazingly high correlation for an individual from
day to day. In other words if you felt you were exercising at 6 out of 10 (somewhat hard) on two different days, your heart rates would be quite similar.
Additional
links:
Energy versus Power
ENERGY is a quantity (or amount) of FORCE and is measured in joules, ergs, or calories.
When energy is applied (to move an object, a bicycle and rider for example) WORK is being done.
POWER is the RATE at which that work is done (energy is applied to the task) and is measured in watts. It takes more power to do the same work over a shorter period of time. Power in the bicycle world is expressed in Watts. 1 Watt = 0.86 Calories per hour. A biologic Calorie (capital C) is equal to 1000 physical chemistry calories (small c).
When energy is applied (to move an object, a bicycle and rider for example) WORK is being done.
POWER is the RATE at which that work is done (energy is applied to the task) and is measured in watts. It takes more power to do the same work over a shorter period of time. Power in the bicycle world is expressed in Watts. 1 Watt = 0.86 Calories per hour. A biologic Calorie (capital C) is equal to 1000 physical chemistry calories (small c).
An example: You use 100 Calories of energy on a 1 hour ride and then later in the day do another 100-Calories ride in only 30 minutes. You did the same amount of work on both rides, but the 30 minute ride was more difficult. You needed to be a more "powerful" rider to complete it in 30 instead of 60 minutes.
In terms of power:
In terms of power:
100
Calories over .5 hours = 200 Calories/hour. 200 Cal/hour divided by
0.86 = average power output of 232 Watts.
100
Calories over 1 hour = 100 Cal/hour. 100 Cal/hour divided by 0.86 = average power output of 116 Watts, a much easier ride (less power applied) even though the same work was done.
Your road speed reflects the amount of power being delivered to the pedals. But air resistance increases exponentially with speed so you can't just substitute road speed for watts being generated.
Another example may help in the explanation. To win a race, or
finish first on a ride (assuming an equal weight of
bikes and riders, aerodynamics, etc) you need to power your pedals at a HIGHER
AVERAGE WATTAGE than your competitors. If all riders and their bikes
are the same weight, you will all have expended the same total
energy in the event. But as the winner spent less time on the course, his/her average energy
expenditure per minute (or wattage) will have been the highest of all the riders.
Peak
power output is a measurement of the maximum power you can generate
over a short, several second interval (e.g a power lift in the gym or
a sprint on the bike). Peak power reflects quadricep muscle strength,
while average power output (over 30 minutes for example) reflects
BOTH muscle strength and your level of conditioning, to allow you to use those muscles for a longer period of time before they fatigue.
So
we really have 2 power measurements – peak power and average power:
-
Peak power: the maximum power, usually in watts, you can produce in a short (several second) burst.
-
Average power: a power level you can maintain over a much longer period of time.
When
you read about cycling performance, the number most commonly
referenced is the average power. It is
measured with a
power meter which records watts of power being delivered to the pedals
(and then via the chain to the rear wheel).
Metabolic Measures
Let's review some basic
cardiovascular physiology. Oxygen is required to maximize the
efficient metabolism of carbohydrates and fats in order to produce Adenosine Triphosphate (ATP), the compound that powers muscle cell
contraction.
The delivery of oxygen to muscle
cells is a multi-step process.
-
First, we need to move oxygen from the air we breathe into the blood stream. In a normal individual, this step, which depends on lung capacity and the diffusion of oxygen across the alveolar wall into the blood, is NOT rate limiting.
-
The oxygen binds to hemoglobin in the red blood cells and is then transported to the muscle cells. The amount of oxygen delivered to the muscle cells depends partly on the oxygen concentration in the blood (Training, EPO, and blood doping all increase the blood hemoglobin levels and in turn the amount of oxygen that will bind to a cc or milliliter of blood).
-
The volume of blood passing by individual cells also determines how much oxygen is delivered. The volume increases with an increasing heart rate and stroke volume (the volume of blood pumped per beat). The stroke volume, and thus oxygen delivery, increases with training.
-
Finally, oxygen is extracted from the blood by the muscle cells. A training program will increase the efficiency of oxygen extraction by increasing the density of small blood vessels or capillaries around individual muscle fibers.
Additional
links:
Heart
rate
The
body adjusts the heart rate to meet our oxygen needs. As the
intensity of exercise increases, the body responds by increasing the
heart rate. Thus it is an easy way to quantify exercise intensity.
Maximum
Heart Rate (MHR)
Everyone has an individualized maximum heart rate or MHR. As muscle oxygen delivery = heart rate x stroke volume, our heart rate indicates the relative amount of oxygen being delivered per minute, and the MHR the upper limits of oxygen utilization. As it is much more easily measured than maximum oxygen consumption (VO2max) (read below), which requires a physiology lab and expensive equipment, the MHR is often used as a surrogate.
%
Maximum Heart Rate (%MHR)
This
number is a reflection of the intensity of aerobic effort. A higher
%MHR indicates a greater aerobic effort.
VO2
(oxygen consumption)
VO2
is a direct measure (heart rate was an indirect measure) of the
amount of oxygen being extracted from the air you breathe to produce
ATP to power muscle (and other cellular) activity. It is expressed as
a volume (V) per specified time interval (usually 1 minute).
VO2max
VO2max
is the maximum volume of oxygen that an individual can extract from the air by breathing and represents the upper limit of aerobic (or oxygen
dependent) metabolism.
As
levels of exertion outstrip the cardiovascular system's ability to
deliver the necessary oxygen (exceeding the individual's VO2max), anaerobic (or oxygen independent) energy production takes over. Anaerobic
metabolism is not only less efficient (less ATP is formed per gram of
muscle glycogen metabolized) with a more rapid depletion of muscle
glycogen stores, but leads to a progressive build up of lactic acid
and other metabolites that ultimately impair muscle cell performance.
%VO2max
This
is a measure of how close an individual is to their personal aerobic
maximum expressed as a % of their personal VO2max.
Lactate
Threshold (LT; also known as functional
threshold power or FTP, anaerobic threshold or AT, maximal lactate
steady state or MLSS), and onset of blood lactate or OBLA)
In an exercising muscle, the blood flow to individual muscle cells is quite variable. The cells that receive less oxygen will produce more lactic acid (from anaerobic metabolism) than those that are well perfused with oxygen-rich blood. In addition, muscle cells with an adequate oxygen supply also actively remove lactate from the blood. The blood lactate level reflects the final balance between production and clearance.
If exercise intensity is plotted against blood lactate levels (see graph), there is a point at which the blood lactate concentration begins a rapid rise. We call this exercise intensity the lactate threshold. Although generally expressed as a %VO2max or %MHR, it can also be stated as an absolute power output (in watts).
Lactic acid has a direct negative effect on both muscle cell contraction and cellular energy production.
When there is excess oxygen being delivered to a muscle cell, both fat and carbohydrates are used to supply energy for muscle contraction. As the oxygen supply becomes more limited, fat metabolism falls off. And when oxygen demand finally outstrips supply, the cell becomes anaerobic and can only metabolize glycogen. Because anaerobic carbohydrate metabolism is less efficient (than aerobic metabolism), producing less ATP per molecule of glycogen metabolized, there is less total energy available before you bonk – run out of gas.
An individual's lactate threshold varies with their level of conditioning. A training program increases the number of capillaries per muscle cell as well as increasing the rate at which lactate is removed from the blood. The net effect is an increase in the LT as a %V02max.
When there is excess oxygen being delivered to a muscle cell, both fat and carbohydrates are used to supply energy for muscle contraction. As the oxygen supply becomes more limited, fat metabolism falls off. And when oxygen demand finally outstrips supply, the cell becomes anaerobic and can only metabolize glycogen. Because anaerobic carbohydrate metabolism is less efficient (than aerobic metabolism), producing less ATP per molecule of glycogen metabolized, there is less total energy available before you bonk – run out of gas.
An individual's lactate threshold varies with their level of conditioning. A training program increases the number of capillaries per muscle cell as well as increasing the rate at which lactate is removed from the blood. The net effect is an increase in the LT as a %V02max.
The lactate threshold is in the range of 50 to 60% MHR in untrained individuals and with training will increase to 80 to 85% MHR. This means that for a similar level of exercise intensity (same %V02max or %MHR), the trained individual produces fewer inhibitory products of anaerobic metabolism, and internal energy supplies can support this power output (watts) for a longer time. Some competitors in an event might be able to generate a higher peak power output in a sprint, but the ultimate winner will be the rider who is able to maintain a higher average wattage for the entire event.
Metrics
to monitor your performance improvement.
I
break performance metrics into 3 groups..
The
first group monitors our real-time level of exertion just as a tachometer or speedometer in a car reflects how hard the engine is working. Percent maximum
heart rate (%MHR), percent maximum oxygen uptake (%VO2max), and power
output objectively identify how hard we are working. They help us track the intensity of our intervals or keep us from going
out too fast on a long ride .
The
second group tracks hard-wired physiologic upper limits which even
with training don't improve significantly. Maximum heart rate is
an excellent example. No matter how hard you train, this upper limit
is unchanging. Likewise VO2max tends to be a static number. With
training we can learn to push through the discomfort - tolerating higher levels of lactic acid for example - performing better at
these “maximums” (and in competition), but
the absolute numbers don't really change.
The
third group of metrics is used to measure your progress over a season
or as part of a regular reassessment in a training program.
Before
we look at my favorites in this third group, I want to emphasize the
importance of eliminating, as much as possible, any variables which
might impact results. If you are going to be assessing your
improvement (or lack thereof) you want the most reproducible and
accurate results possible.
Using
an indoor trainer (with the same bike and tires) is a simple way to
minimize external (weather) and equipment variables from day to day. Reproducibility is especially important for the power and lactate threshold
measurements described below.
Additional
testing considerations:
-
Test at the same time of day and with the same timing in relation to your last meal.
-
Maintain the same resistance (or gearing) on your trainer from session to session.
-
Keep the room temperature constant. (A fan is often a helpful addition.)
-
Keep notes, including the timing of the test in your training cycle and a self assessment of your fatigue level before and after the test interval.
-
Finally, you might want to go the extra step and do the testing after a day off the bike.
1.
Personal bests
Most
of us have favorite routes and track our PRs or personal best times. It is an easy measure of improvement as the season progresses, but because it is influenced by various
uncontrollable variables, especially weather and traffic, it is imprecise.
2.
Peak Power (maximal
anaerobic
or sprint effort)
This
is the measure of your maximum power output. Its advantage is that it avoids the negative impacts of both fatigue and the build up of acidic byproducts in the
muscles from an all out maximal anaerobic effort.
To perform this test go all out for six seconds with gearing set at a level allowing you maximize your RPMs without the need to change gears. From a dead stop,
standing, give it your all. Measure peak watts achieved (or top
speed on a cycling computer).
3.
Average Power (maximal
aerobic
power)
In
this test, you identify the maximum average power you can sustain for
three
minutes. The intent is to approach, but not exceed, an anaerobic effort with its build up of anaerobic metabolites. If
you start too fast (sprint speed), and go at an anaerobic pace, the build up of these acidic metabolites will negatively impact your three minute performance.
Using
a resistance that lets your maintain your cadence for the full 3 minutes (no need to downshift to an easier gear near the
end) and calculate an average power (or speed) over the full 3 minutes
(monitoring splits can help in the calculation).
4.
Lactate
Threshold
(maintainable power; 20 – 60 minutes)
This
test identifies the wattage (or speed) that can be sustained for
time-trial and similar intensity events of up to 1 hour duration. It is, I feel, the best
measure of overall cycling fitness. With a duration longer than
the average power metric, it naturally keeps you at an intensity where
there is an equilibrium between lactate production and lactate
removal. Go too fast, and the higher levels of lactate will slow you down until things come back into
balance.
The first step is to identify a resistance that allows you to maintain a relatively steady pace for a 20 minutes ride. Your watts or speed may vary a bit, generally slower at the
start, but at the end of the 20 minute interval you should feel you
have given your all.
Your
LT is approximately 0.95
x your average power (or speed) for the full 20 minutes. Why subtract 5%? Because you are using a 20 minute test to reflect an intensity you could maintain for a full hour's ride. The shorter interval tends to be about 5% faster than a full 60 minute effort.