by Arnie Baker, MD
The lungs are usually not the limiting factor in aerobic fitness. They are very efficient in transferring oxygen from small airways to the blood. Although not the limiting factor, the athlete’s perception of aerobic limitation is usually felt in the lungs.
Fitness means different things to different people. Some aspects of fitness are very specific to specific sports. Weight lifters think of fitness differently than curlers or chess players.
Lung power can be a limiting factor in the presence of disease (for example, asthma), at altitude, or at high levels of exertion in trained athletes. It is valuable to know about the elements of cycling fitness, because knowing what elements are important helps us decide how to train.
The muscles are important in the aerobic chain. Fit riders extract more oxygen from the blood as it courses through the muscles than less fit riders. Although some aspects of fitness do have genetic limits, most athletes are limited by their training rather than by their heredity.
Aerobic fitness can be measured by a VO2 max test. This test measures the volume (V) of oxygen (O2) the body can use, in liters of oxygen per minute. Power demand is ramped up in 10 to 50 watt increments, depending upon the protocol used. Oxygen use is measured from a formula whose terms include the total volume of air breathed and the amount of oxygen in inspired and expired air. This test is fair at predicting flatland time-trialing ability.
When it comes to the elements of bicycling fitness, the performance of most non-racer cycling enthusiasts—century riders, all-day riders, randonneurs, tourists—depends chiefly on the first three. Racer success may be limited by any of the major eight fitness elements though.
Types of Cycling Fitness
VO2 max is often scaled to the rider’s mass, or weight, in which case it measures the volume of oxygen used per minute per kilogram. Scaled to weight, the test is a good predictor of long, steady hill-climbing ability.
Many elements of cycling fitness belong to more than one type of fitness and so it is sometimes hard to tease out the fitness elements, or understand them clearly. (Consider, as an analogy, various systems on your bicycle: The cogs on your back wheel belong to the drive-train system as well as to the wheel system.)
VO2 can be estimated from the power achieved in ramped tests. Arnie’s formula is VO2 = 12 x watts/kilogram + 3.3.
Simple field measures cost nothing and are as good or better at predicting performance. For example, after testing hundreds of athletes, I have found that timing ascent up our local 1.3 mile Torrey Pines climb, with 440 feet of climbing, predicts VO2 as follows: 360 / time in minutes = VO2. A 6-minute climb equates to a VO2 max of 60 milliliters per kilogram per minute.
The ability to use oxygen for energy production. This is important for performance in any event longer than 30 seconds. The heart, lungs, blood vessels, and muscles are all involved in the aerobic chain.
Although considered a measure of aerobic function, not muscular function, a VO2 max test really does involve muscle mass too. Without adequate muscle mass, there is insufficient oxygen demand, and values will be low.
The amount of blood the heart can pump is a product of how much blood the heart pumps with each beat and how many times the heart beats per minute. Most of the change in aerobic fitness is due to the amount of blood the heart pumps with each beat.
More important as a predictor of performance is how much oxygen the body can use at submaximum levels, say at time-trial pace, or at other thresholds.
In a strict sport science sense, muscle strength refers to 1-rep maximum strength—the amount of weight that a muscle can lift, push, or pull one time. One-rep muscle strength is a function of fast- twitch muscle fibers. It is easy to measure 1-rep muscle strength in the gym, although the machines that isolate different muscle groups are not always cycling specific.
General aerobic fitness is trained at moderate exertion levels that correspond to roughly 65% to 85% of an individual’s maximum heart rate.
High-level aerobic fitness is trained at exertion levels that correspond to roughly 80% to 85% of an individual’s maximum heart rate. Athletes can train at such levels for up to about 120 minutes per week. Training time beyond this amount is limited by high-energy fuel—the ability to incorporate carbohydrate into muscle.
In cycling, muscle strength over a period of time, or power, is crucial. To contract repeatedly, muscles need energy. The energy may come from metabolic reactions with or without oxygen.
Reactions without oxygen (or anaerobic energy production) are characteristic of many fast-twitch muscle fibers, called glycolytic fibers. Reactions with oxygen are characteristic of slow-twitch muscle fibers. A subtype of fast-twitch muscle fibers may also use oxygen. Those fibers, which characteristically use oxygen to produce energy, are called oxidative fibers.
All the aerobic capacity in the world will not get you anywhere if you do not have the right muscles to use that energy.
Although in pure track sprinting fast-twitch strength is crucial, in most cycling events slow-twitch strength is more important—but slow-twitch strength is very difficult to measure, in part because when slow-twitch fibers reach their limit, fast-twitch ones take over.
What muscles do is contract, or shorten, when stimulated to do so by the nerves that supply them. They contract because of filaments of actin and myosin that form chemical/mechanical cross- bridges and move relative to one another.
One lab test that comes closer to measuring what is important for most road cyclists (for most of us) is muscle fatigability. One way it is measured is by seeing how many repetitions can be performed at 70% of 1-rep maximum, or at a percentage of body weight.
The importance of sport-specific muscle strength is well known. For example, elite runners who try bicycle riding are often not very fast; same with bicyclists who try running. Sport-specific slow- twitch muscle strength is trained during specific sport training. Although weight-room work may help, more sport-specific exercises such as hill running for runners and isolated leg training or big-gear riding for cyclists is often better.
Tests show that elite aerobic endurance athletes are generally not world-class when it comes to strength testing in the lab. Again, these measurements of primarily fast-twitch muscle strength are not relevant to the type of strength that aerobic-endurance athletes need—slow-twitch muscle strength.
Broadly speaking, there are two types of muscle fibers: Fast- twitch and slow-twitch.
Cycling muscles are trained by cycling—by just riding along. You are specifically strength training your cycling muscles when you feel them working.
Short, high-power efforts are associated with fast-twitch fibers. For a given power output, the slower the cadence the higher the percentage of fast-twitch fibers recruited.
Big-gear riding and climbing provide aerobic-muscle-specific work. Sprint work provides anaerobic muscle-specific work.
For the most cycling muscle-specific work, I separate out the muscle element of cycling fitness with isolated leg testing and training. In my experience, the power that one can generate with one leg riding at 60 rpm for three minutes is an excellent measure of cycling muscle fitness.
This aspect of fitness comprises many factors. Here are some well-known elements in metabolic fitness:
Read more about muscle-strength fitness training under Isolated Leg Training on page 28.
Mitochondrial energy production. Mitochondria are the energy factories of the cells. They produce energy through biochemical reactions involving oxygen (for example, the Kreb’s citric acid cycle). The number and function of mitochondria can be improved with training.
Energy can also be produced without oxygen (anaerobically). Chemical reactions that involve stored adenosine triphosphate (ATP) and creatine phosphate (CP) are important in producing energy anaerobically.
This is the ability to last. Endurance is required to get to the finish of an event.
When work is accomplished without oxygen, lactic acid is produced. Lactic acid clearance involves the ability of the body to buffer (or temporarily neutralize) lactic acid as well as the ability of the body to metabolize (or burn) lactic acid. This involves many chemical substances and reactions in the muscles and in the blood (myoglobin, bicarbonate, and hemoglobin, to name only a few). As with the fitness elements listed above, training helps.
Endurance can mean different things. Most sport science discussions about endurance concern events lasting one to three hours. Ultra riders may think of endurance as what Tour de France or Race Across America (RAAM) riders possess. However, track coaches think of pursuiters, as opposed to sprinters, as endurance riders. On the track, the ability to last 4 minutes is endurance.
Although many equate endurance with aerobic fitness, and although there is some overlap, they are not the same. It is possible to be able to perform a 40K time trial in 50 minutes, showing elite level aerobic ability and a VO2 max over 80 mL / kg / min., yet fall apart in races over 100 miles.
Some indication of metabolic function can be gained through lab studies including chemical analyses and muscle biopsies. For example, lactic acid levels in muscle or blood lactate levels can be measured with standard workloads or at threshold. Mitochondrial density can be determined in muscle biopsies. These tests are not as good as those discussed above in predicting human performance.
Endurance for events up to a few hours in duration can be predicted by the tests for aerobic fitness described above.
Endurance in the sense of stage racing or ultra-distance events is not measured in the lab. It requires field evaluation.
For example, the best measure of your endurance for the Tour of the California Alps (a 129-mile ride with 16,000 feet of climbing) is simply how well you adapt to long hilly training rides.
The ability to produce work without oxygen is vital in many forms of bicycle racing. This is a combined metabolic (anaerobic) and muscle-strength (glycolytic) fitness.
Anaerobic fitness is necessary whenever attacks occur, when the pace gets super high, when the period for maximum effort is short.
In fact, this is what mass start group racing is usually all about— riders do not usually get left behind until fitter riders push the pace and force them to exceed their aerobic and anaerobic limits.
The amount of work that can be performed over short periods (less than 30 seconds) can be measured in the lab or in the field. Peak power in the lab can be measured by computerized cycling ergometers in standardized Wingate tests. In the field, one can measure, for example, 200-meter sprint times.
Leg speed is a neuromuscular fitness. It is a skill. It is not strength; it is not related to aerobic or anaerobic function. The ability to respond to changes in tempo, especially in criteriums, requires the ability to move those legs quickly. Successful sprinters have excellent leg speed.
This type of fitness is not particularly important for century rides or all-day touring. Although some anaerobic training may improve your aerobic fitness, you should rarely, if ever, be anaerobic during any part of such events.
Can you hold 140 or more rpm for several minutes on a stationary trainer with low resistance? Can you spin over 200 rpm for short bursts? If so, you have good to excellent leg speed.
Neuromuscular fitness is important not only for leg speed, but for cycling economy.
For most cyclists, power is the most important lab predictor of cycling performance. After all, it is power that gets you down the road. It is a more important predictor than VO2 max.
Imagine your right leg rotating though a clock circle. Most of your right leg power comes from pushing down or forward, between about one and five o’clock. You want to stop your nerve cells from activating your right leg push down/forward muscles before you get to the six o’clock position and return your leg back up to twelve o’clock.
For track sprinters, maximum power in 3- to 30-second tests provides an excellent predictor of track sprinting fitness. The shorter the test, the more pure muscle strength is measured. When the test approaches 30 seconds, combined muscle fitness (glycolytic) and anaerobic metabolic fitness is measured. Again, anaerobic fitness has little importance for century riding or most-of-a-day events.
Although much has been written about a smooth pedal stroke and pulling up after pushing down, studies show that even professional cyclists do not do this. What is important, and what economical cyclists do, is to not push down on the returning (right) leg while the other (left) leg is in its power phase pushing down or forward. Or, at least, not pushing down too hard.
For most other riders, power at time-trial threshold is key to performance. Alternatively, maximum power on a ramped test lasting about 15 minutes. This is really a test of combined muscle- fitness (oxidative) and aerobic fitness. (There is a close correlation between power and oxygen uptake. Where they diverge, power is more important.)
Isolated leg exercises at low power (in easy gears) at about 80 rpm are an excellent for improving neuromuscular fitness.
Although important in some specific bicycling disciplines, leg speed is of little importance to bicycle touring or most all-day riding—except that at moderate to high power levels cadences closer to 90 rpm are less fatiguing than those closer to 60 rpm.
This type of fitness is poorly understood, but important. It includes some of the following areas: Pain perception and the neurohormonal response and tolerance of training volume and intensity. How brain cells talk with one another, and how the body’s hormones respond and adapt to stress.
By understanding cycling fitness, you can understand how to train to improve your performance.