Why and What Ifs

Energy for Cycling: It's The Blend That's Important. For cycling, let's simplify the body into three parts: heart, legs, and lungs. Your heart, or fuel pump, sends blood to your legs, the pistons that do the mechanical work. Your lungs, a carburetor that exchanges carbon dioxide for oxygen that is used by your legs, help your heart. Correct training makes your heart, legs, and lungs stronger and therefore more efficient.

ATP and Mechanical Work. Your body uses one chemical molecule for energy: adenosine triphosphate or ATP. ATP starts as a relatively docile molecule called adenosine diphosphate or ADP. Your body makes and stores millions of ADP molecules each day in every cell in your body. Each ADP molecule is loaded with enormous potential energy waiting to explode (similar to your teenager sitting at home on a Friday night). The continuous transformation of ADP molecules into ATP molecules creates the energy you need to cycle as well as to perform all biological functions.

How Does ADP Change Into ATP? By "borrowing" electrons (negatively charged ions) from other chemicals such as carbon and hydrogen, found in the foods (protein, carbohydrates, and fats) you consume, and oxygen, found in the air you breath as well as the water and foods you eat. For short-term energy, these electrons come from your blood sugar or blood glucose. If your blood glucose drops too low or your demand for ATP is so great that your body can't synthesize it fast enough via the breakdown of body fat, your body makes more blood glucose by breaking apart glycogen (long chains of glucose stored in your skeletal muscles), which subsequently donates its electrons to make additional ATP molecules. Fat—stored as adipose tissue—in the presence of oxygen is the fuel of choice for long, sustained cycling efforts. When faced with severe physiological stress, such as an all-out sprint, your body uses a third fuel: creatine. Creatine is a specific amino acid, or protein building block, stored in limited quantities in skeletal muscles that can team up with a phosphate molecule to expedite the transformation of ADP to ATP.

Aerobic Metabolism. The energy pathway that yields ATP from the breakdown of fats and/or glucose in the presence of oxygen is called aerobic metabolism, designated ATP-aerobic. Waste products include carbon dioxide, water, and heat; all easily and quickly eliminated by breathing and sweating, which enables you to cycle for a long time without fatigue.

Anaerobic Metabolism. The energy pathway that uses creatine or glucose to make ATP molecules in the absence of oxygen is called anaerobic metabolism, designated ATP-anaerobic. ATP-anaerobic is further divided into two distinct pathways: (1) ATP via creatine phosphate, designated ATP-C and (2) ATP via glucose and its polymer glycogen, designated ATP-LA. The quantity of ATP contributed by each metabolic pathway during a single cycling event depends on how much work your heart, legs, and lungs must do over a specified time. ATP derived via the ATP-C pathway can sustain a short (5-to 10-second) all-out effort. Studies show that ATP-C-derived energy peaks 10 seconds after initiation of an all-out effort and abruptly halts within 30 seconds. ATP derived via the short-term glycolysis (ATP-LA) pathway sustains high-intensity, but not maximal, cycling for approximately 3 to 5 minutes. This pathway is invoked approximately 10 seconds after initiating an all-out effort, peaking between 30 seconds and 2 minutes. The short-term glycolysis pathway contributes approximately 50% of ATP needs after 2 minutes and up to 5 minutes of an all-out effort. Waste products include lactic acid (LA). Unlike water and carbon dioxide, LA is not easily eliminated from your body, and its accumulation causes fatigue and soreness. After 5 minutes of an all-out effort, your body derives an increasing quantity of the ATP needed to perform continued mechanical work from fat via the ATP-aerobic pathway. In submaximal cycling efforts, the contribution of the ATP-LA pathway depends on cycling intensity.

The Overload Principle. All three ATP-generating pathways can be trained and improved to meet your specific cycling goals. To complete the Death Valley ride, training should emphasize the ATP-aerobic pathway first and the ATP-LA pathway second. How? By applying specific overload to your heart, lungs, and legs. For a training effect (stronger and more efficient) to occur, stress (overload) must be applied to a muscle or energy system. For adaptation to continue, the load must be periodically increased or the muscle or energy system will plateau and so will the cyclist's performance. The overload must engage the appropriate muscles required by the activity as well as provide an exercise stress for the heart and lungs. The appropriate overload for each person can be achieved by manipulating combinations of training frequency, intensity, mode, and duration.

The Specificity Principle. The adaptation must be specific to the type of stress or load imposed. That is, sprint workouts will make the ATP-C pathway in your legs more efficient. In a similar fashion, distance sessions will improve the ATP-aerobic pathway, and steep climbs will enhance the ATP-LA pathway. Although different cycling workouts will improve the efficiencies of all three ATP-generating pathways, these adaptations will occur only in the muscles doing the actual mechanical work; for the cyclist, these improvements will be seen in the legs (as well as heart and lungs).

ATP-Aerobic Energy: Endurance Training. The purpose of distance training is to improve the ability of your leg muscles to oxidize fats. To be successful, you must (1) cycle for a long time, ensuring that a large volume of blood is pumped through your heart, and (2) cycle at relatively high leg speeds (95 to 110 RPM) using low resistance. Your performance and aerobic power will be improved because oxygen transport and utilization in the trained muscles will improve. Aerobic improvements may also result from greater regional blood flow in trained muscles because of increased microcirculation or more effective distribution of cardiac output or both. Many factors contribute to individual variations in training response, collectively known as the Individual Differences Principle. Initial fitness and activity levels influence training response; the less trained you are, the more improvement you will see. Training improvements generally occur rapidly and continue in a steady fashion, provided intensity is regularly adjusted. It is common for your resting heart rate to be lowered by 10 to 20 beats per minute as a result of aerobic conditioning.

ATP-LA Energy: Glycolytic Training. The rationale for interval training has a sound basis in physiology. Beyond 10 seconds, the contribution of ATP via the ATP-C pathway decreases, and the contribution via the ATP-LA pathway increases. Exhaustion occurs as the level of LA rises to a point where it can do longer be eliminated efficiently. Training to develop the ATP-LA pathway is physiologically and psychologically taxing and requires considerable motivation. To ensure that maximum levels of LA are produced during each training session, the cycling effort should be repeated several times, interspersed with relief recovery periods. Each successive exercise interval causes a "lactate stacking" that results in higher levels of LA being generated in your muscle cells and in your blood than would occur with just one bout of all-out effort to the point of voluntary exhaustion. Training the ATP-LA pathway results in increases in resting levels of anaerobic substrates such as ATP, creatine phosphate, and glycogen; (2) increases in the quantity and activity of key enzymes, particularly in fast-twitch muscle fibers that control the anaerobic phase of glucose breakdown; and (3) increases in the capacity to generate high levels of blood lactate during all-out exercise probably because of increased levels of glycogen and glycolytic enzymes as well as an improved motivation and pain tolerance for fatiguing exercise.

How To Train the ATP-LA Pathway. Hill interval workouts—and working intensely in big gears—at heart rates greater than your lactate threshold (approximately 90% of your maximum heart rate) are examples of ATP-LA training. The intensity of the exercise is related to the particular energy systems you wish to train. The higher the intensity, the shorter the interval. For lactate threshold training (which begins at heart rates between 84 and 90% of your maximum) on a flat terrain, it is common to start with two or three 8-minute intervals and add 30 seconds to the exercise interval each week. For lactate threshold training on steep hills, the exercise interval ranges from 2 to 5 minutes. At a heart rate between 90 and 93% of your maximum, the exercise interval is between 4 and 8 minutes. As the duration of each interval increases, the number of repetitions decreases. That is, lactate threshold training usually involves two to three relatively long repetitions. Aerobic power and hill repetitions usually entail four to ten shorter repetitions. Relief or rest intervals can be passive (rest relief) or active (exercise relief). For ATP-LA training, the recommended relief interval is three times longer than the work interval (a 1:3 ratio).

ATP-C Energy: High-Energy Phosphate or Sprint Training. Maximum overload of this phosphate pool in specific muscles can be achieved with all-out bursts of effort for 5 to 15 seconds. To train the ATP-C energy pathway, perform repetitive bouts of intense, short-duration exercise. The training activities selected must engage the muscles in the movement patterns for which you want improved anaerobic power. For example, proper sprinting workouts should invoke the exact muscle fibers you wish to train to promote adequate neuromuscular adaptations in these fibers. To improve your ATP-C pathway, cycle for 10 to 30 seconds, using a leg speed of 140 to 160 and a heart rate between 91 to 100% of your maximum. Rest completely (passively) for 20 to 60 seconds (a 1:2 ratio); perform 4 to 10 repetitions.

WHAT IFS?—How Intensely Should You Cycle?
To observe a cardiovascular improvement, the minimal stimulus must be at least 50 to 55% of your max VO₂ or 70% of your maximum heart rate. An alternative method to establish a training threshold is the Karnoven method, defined as 60% of the difference between resting and maximum heart rates. Studies show that cycling at this threshold for 20 to 30 minutes at least three times a week has resulted, in individuals classified as average for max VO₂, in an improvement of 5 to 25% (in max VO₂) following a 12-week program of aerobic training. Cycling for longer times can sometimes offset lower-intensity training. Although cycling at an intensity less than 70% of your maximum heart will not elicit a cardiovascular response, it will help "burn" additional calories, maintain leg flexibility, and tone musculature.

What's More Important— Frequency, Duration, or Intensity?
In decreasing order of importance: intensity, duration, and frequency. Intensity is the most critical factor related to successful conditioning. Simply stated, fewer, shorter, wind-sucking rides will preserve (and improve) your max VO₂ to a greater degree than more-frequent, easier rides. For example, cycling at 73 to 84% of your maximum heart rate once a week is more beneficial than cycling at 66 to 72% of your maximum heart rate twice a week. Intensity can be expressed in several ways: (1) as calories expended per unit time; (2) as a particular level or power output; (3) as a level of exercise below, at, or above the lactate threshold; (4) as a percentage of max VO₂; (5) as a particular heart rate or some percentage of maximum heart rate, and (6) as multiples of the resting metabolic rates (METs) required to perform the exercise. If you ride only three times a week or find cycling at heart rates greater than 90% too discouraging, concentrate on training your aerobic pathway two days a week. Each week, include at least one long ride—greater than 50+ miles over varied terrain and several steep climbs. Cycle at a heart rate between 73 to 84% of your maximum. Spend the third day cycling near your lactate threshold, a heart rate between 84 to 90% of your maximum, doing two to three long intervals with exercise relief between each exercise interval. If that doesn't suit you, try cycling over a long distance once a week and, on the other two days, cycle as part of a group or power cycling class. Riding with other cyclists is an excellent way to ensure that you'll hit all three energy pathways during one workout. When possible, supplement your hard cycling days with easy cycling days. Frequency—Studies indicate that at least three days a week (for six consecutive weeks) is necessary to bring about adaptive changes in the aerobic system. Several studies indicate that the improvements from training four or five times a week are either no greater or only slightly greater when compared with exercising only three times each week. Duration—Continuous and more intense intermittent overload are effective in improving aerobic capacity. Simply stated—intensity being constant—longer, less-frequent efforts are more beneficial than shorter, more-frequent efforts.

What Leg Speed Should You Use For Difficult Climbs? Difference sources—all reputable—tell a different story. A former world-class triathlete and cyclist with a doctorate in kinesiology recommends a leg speed of 45 to 65 RPM. However, several professional cyclists and trainers, as well as a few medical practitioners, suggest that a leg speed less than 60 RPM when climbing (or when using high resistance) can damage knee tendons and ligaments. The USCF recommends a leg speed of 80 to 90 RPM for climbing. Proper seated-climbing techniques develop strength in your gluteals and hamstrings. Standing during a climb is not recommended except to relieve back strain. However, if you routinely alternate standing and sitting positions during a steep climb, shift your weight between your quadriceps, hamstrings, and gluteals. Proper cycling techniques will ensure that your knees (and their associated tendons and ligaments) are never used for any other purpose than stabilization. Prudent advice is to always use a leg speed—which means that you may have to constantly adjust your gearing—that allows you to cycle properly regardless of the terrain.