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Why Strength Training is Important for Endurance Athletes

And how it leads to better performance.

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Triathlon is an endurance sport, plain and simple. So why should you consider strength training a necessary part of a triathlon training program? The short answer is that strength training makes muscles stronger, and stronger muscles can perform longer at higher intensities before they fatigue. To fully understand what is happening during strength training and endurance training you must break down and examine the subtle differences and similarities between the two. This takes the long route because when you understand how the body works, it’s much easier to plan training programs that work to your advantage.

RELATED: Strength Training for Triathletes

Making the Case for Strength Training

If you ask any triathlete what endurance training is, the most common answer has something to do with swimming, biking, or running. Technically, endurance training is any type of exercise that is rhythmical, maintains an increased heart rate and oxygen consumption, and uses large muscle groups to propel the body. It is also referred to as aerobic training because the body relies on a continuous, increased supply of oxygen during the energy-making processes at the cellular level. This supply of oxygen comes from increased respiration, usually the result of taking deeper breaths and breathing more frequently. In addition to increased respiration, the heart must pump more blood to the muscles to deliver the oxygen. So there is an increase in heart rate and respiration that is maintained throughout exercise: That’s endurance training.

Ask the same triathlete what strength training is, and the answer usually involves some sort of weight lifting. In the most literal sense, strength training can be any type of training that increases the endurance, size, power, or strength of the specific muscles being used, regardless of what type of exercise is being done or whether someone is actually “pumping iron.” Strength training is done in short bouts, with rest periods interspersed throughout the workout; is not rhythmical; and involves many different muscle groups, some large and some small. Strength training is considered anaerobic, or without oxygen. Even though you are breathing and your body is delivering oxygen to the muscles, the processes that provide energy for strength training do not rely on oxygen as the aerobic processes do.

Strength training can be any type of training that increases the endurance, size, power, or strength of the specific muscles being used, regardless of what type of exercise is being done.

Another difference between strength and endurance training is that strength training does not improve the cardiovascular system to any great extent. Each exercise requires a short burst of effort that doesn’t require large increases in blood flow from the heart. During endurance training, as the heart rate rises, the heart is doing more work, so the heart muscle must be able to keep up the pace. To do this, the cardiac muscle tissue gets stronger, and the heart becomes more efficient at pumping blood. During strength training, significant, sustained increases in heart rate don’t occur, and increases in oxygen delivery to the muscles are not needed, so the heart doesn’t have to become stronger or more efficient.

The energy systems involved in endurance and strength training also differ in what they use as fuel. Along with delivering oxygen to muscles, the blood carries glucose (blood sugar) to the working muscles, where it is used as energy, stored as glycogen, or stored as fat. During endurance training, a large and steady supply of energy is required over a long period of time, so glucose is broken down to provide that energy and to allow the processes that burn fat stores to continue. You do not store enough glycogen in your muscles to sustain exercise for very long, so more glucose must be delivered by the blood to keep you moving. During strength training, the body must supply energy quickly but not in large amounts, so you use stored adenosine triphosphate and phosphocreatine (ATP-PC), along with the stored glycogen in your muscles. These energy systems provide a quick burst of energy, which is fine because a set of a strength training exercise doesn’t take very long, and then you get to rest. Very little glucose or fat stores are used during strength training.

Anatomically, there is a great difference between strength and endurance training, but there are also some areas where the two overlap. Think about how often you lift weights during a triathlon. Other than lifting a cup of water to your mouth, taking your bike off the rack, and maybe picking yourself up off the ground, you don’t lift that much—or do you? When you stop thinking of weight as a piece of iron attached to a barbell or machine, you realize that your body is a weight that you must lift and move all the time—and your muscles do the work. When you run, your legs have to push and hold up your entire body weight. When you swim, your arms help pull your body forward against the resistance of the water; and when you ride, your arms support your upper body as your legs push against the forces of the bike and pedals to propel you forward. In fact, we are continually lifting weight during endurance training and racing. It may not seem like much weight, but over the course of an endurance training session your muscles become fatigued from all that lifting, and your heart gets tired from all that pumping.

Strength training creates a more powerful engine than if you were to rely on endurance training alone.

If strength training makes our muscles stronger, then it makes sense that swimming, cycling, and running make our muscles stronger, because we are working with the weight of our bodies. The weight is just a mass of muscle and bones rather than iron plates. You have probably experienced your muscles becoming stronger as a result of your swimming, cycling, or running program. If so, then congratulations—you have been doing a form of strength training all along.

You may be tempted to stop here, deciding that endurance training provides all the strength training you care to (or need to) do. After all, if your body weight is the only thing you are lifting during a triathlon, why would you need a training program that uses free weights or machines? But if what you have been doing were good enough to bring you the performances you want, you probably wouldn’t be reading this.

The problem with solely relying on your body weight to increase strength during endurance training is that your weight cannot provide adequate stimulus to bring about significant adaptation—your body is already used to it. To produce improvement in any type of training program, there has to be an overload, and the only way to provide it is to first make your body carry that weight in longer training sessions. But longer training sessions will not improve your performance and speed for shorter distances, so you have to add external weight in a manner the body is not accustomed to; that’s how you create the correct stimulus.

Here’s an analogy that may better explain this concept. Say you have a really cool muscle car, but it came with a tiny four-cylinder engine, so it doesn’t go very fast or have much power. You take it to the repair shop, where the basic engine is replaced with a big, strong V8 engine. Now you can speed along as fast as you like and have plenty of power to pass slower cars. Your body is just like the muscle car. If you keep the same body but change the engine that moves it, so that it’s stronger and has more power, then your athletic performances will improve and you will be passing slower competitors.

To produce improvement in any type of training program, there has to be an overload.

Obviously the mechanics of a conventional strength training program using some form of free weights or machines are quite different from those of conventional endurance training used by triathletes (swimming, cycling, and running). However, the type of strength training you do should directly benefit your swimming, cycling, and running. This is called sport-specific strength training. It mimics the movements of the sport, uses the same muscles used in the sport, and is applied in such a way that the intensity promotes the sport. Strength training for triathletes isn’t a matter of just going to the gym and using whatever machine you find there; it has to be done in a deliberate and efficient way for you to achieve the desired physiological outcomes.

A physiological outcome is the way the body changes—in this case, how your muscles adapt. Four possible physiological outcomes can be achieved through a strength training program:

  • Muscular endurance: the ability of a muscle to withstand repeated use over a period of time.
  • Muscular hypertrophy: an increase in muscle mass, or size.
  • Muscular power: the ability to move the body quickly through the use of very fast muscular contractions.
  • Muscular strength: the amount of weight that the muscles can move in a single effort.

It’s very important to remember that strength training doesn’t necessarily mean you will bulk up. Far too often I hear the excuse, “I don’t want to lift weights because it will make my muscles too big.” That’s just a simplistic generalization of what happens during strength training. Increased size is only one possible outcome, and you don’t have to train for hypertrophy if you don’t need to. Each of these outcomes has a place in a triathlete’s training program. The key is to achieve just the right amount of each outcome at just the right time.

How Strength Training for Triathletes Is Different

Strength training routines can be wildly different depending on the sport they are intended to complement and on an individual athlete’s needs. What constitutes a successful sport-specific strength training program for one triathlete may not work as well for another triathlete. It all depends on your level of training, the length of the triathlon you are training for, and your individual needs. But one thing is universally true: Strength training for triathletes should be very different from programs used by bodybuilders, powerlifters, and the general public. Everyone has the same muscles and bones, but everyone uses them in completely different ways. Different training goals, or outcomes, are reached by using different combinations of exercises, sets, repetitions, rest periods, exercise order, weight, and progression plans.

For example, a bodybuilder is interested in one thing: size. In their case, the bigger the muscle, the better. Having large, bulging muscles is not what a triathlete wants, because body mass negatively affects endurance efficiency, and larger muscles add a lot of mass but not necessarily a lot of strength. The bigger your muscles are, or the more mass they have, the more strength it takes to move that mass, especially over a long distance. Mass also creates increased frontal resistance in the water and frontal air resistance on land.

However, the triathlete can benefit from larger muscles if that increased size is kept in check and is used properly. If you want to increase the performance of a muscle, sometimes you have to start by increasing its size. After all, you can’t make a muscle stronger if you don’t have enough muscle to begin with. Once the muscle size is where it needs to be, you can change the emphasis of your strength training to move toward your desired outcome. A muscle that is the right size can be made stronger and more powerful or be given more endurance. So don’t immediately rule out using a strength training program that focuses on hypertrophy, because it may be exactly what you need. For example, most of us have a dominant side that includes an arm or leg that is larger and stronger than the other side.

The triathlete can benefit from larger muscles if that increased size is kept in check and is used properly.

Most right-handed people will have larger muscles in their right shoulder compared to their left. People who drive a lot have larger calf muscles in their right leg because of all the “reps” they do pushing the accelerator pedal. Sometimes we need to focus on hypertrophy to even out the body. Additionally, if you have ever suffered a serious injury that required rehabilitation, there is a good chance that one limb is larger than the other. This happens when rehab is focused on the injured limb and neglects the unaffected limb—allowing only one limb to get stronger or larger. On the other hand, long-term rehab, in which both limbs are used, allows the unaffected limb to get stronger or larger while the injured limb progresses more slowly. In each case you have a unilateral deficiency in both size and strength that could be fixed with focused strength training with hypertrophy as the goal.

Athletes who compete in powerlifting and weightlifting are not usually as big as bodybuilders; however, they are very strong for their size. In these sports, success depends on how much you can lift, not on how big you look. Powerlifters who compete in contests for bench press, squat, and deadlift, as well as weightlifters competing in the Olympic lifts—the snatch and the clean and jerk—are usually very strong for their size. (Some of the strongest lifters pound for pound are actually women.) But remember, these heavyweight sports have almost no endurance component, because a competitive lift consists of 1 rep that will last anywhere from 2 to 20 seconds. A triathlete needs compact, strong muscles but requires much more endurance from them.

General fitness programs are likewise not useful for triathletes, mainly because of their wide range or variety and their lack of sport-specific exercises. Training for general fitness is more about working all the different parts of the body in a manner designed to work as many muscles at one time as possible, often using machines that are designed to make the exercise comfortable rather than to mimic a sport’s movement. So although most of the exercise programs you find in popular magazines will improve your fitness, they won’t do much to improve your triathlon performances. The key is to choose exercises that mimic the sport of triathlon and put them together in a way that works for you.

When you have more muscle to rely on, it takes longer to wear it out.

How Strength Training Leads to Better Performance

You will more than likely boost your race results if you incorporate strength training into your triathlon training, because stronger muscles deliver increased power, speed, lean mass, and muscular endurance. Your race focus, experience level, and current body composition will inform how these benefits contribute to your performance gains.

Muscular Power

The first benefit of strength training is muscular power, or the ability to produce force quickly. In a triathlon this is useful during a short sprint to pass a competitor, uphill cycling, and transitioning into and out of the water. A powerful muscle is able to call upon its anaerobic energy stores to support quick movement. Strength training increases muscular power in two ways:

  1. The more muscle you have, the less effort it takes to produce a given amount of power (remember the muscle car analogy), and
  2. strength training teaches your muscles to reproduce energy quickly so they can better recover from short bouts of high-intensity movement.

Energy production and recovery happen deep down in the muscle fibers, where glycogen, enzymes that increase the speed of muscular contraction, and creatine and phosphocreatine (energy substrates) are all increased because of strength training.


Second, you can increase your speed through strength training, regardless of what race distance you compete in. This is the result of the selective recruitment of fast-twitch muscle fibers during strength training. During endurance training you mainly use your slow-twitch fibers, which are designed for low power output and long durations. During strength training you have to call upon the fast-twitch muscle fibers for their high power and force output. The downside to fast-twitch fibers is that they fatigue quickly—usually in less than five minutes. When you put out a sudden burst of speed in training or racing, you know that you cannot sustain it for very long before slowing back down to your regular pace. Strength training builds up the ability of the fast-twitch muscle fibers to activate and provide that burst of speed. You will still have to slow back down, but you can obtain a higher-intensity burst of speed (meaning faster) and recover from it faster, which means you can do it again when you need to.

Lean Mass

The third performance benefit of strength training comes from an indirect effect: a reduction in body fat because of an increase in lean mass. Decreasing one’s body fat is typically equated with losing fat, but the equation has two sides—you can also increase lean tissue. Endurance training burns a lot of fat, but it doesn’t build much lean tissue. Strength training is all about increasing lean tissue. Again, we are not talking about bulking up your muscles, but about making the muscles you have more dense. Increasing muscle density decreases your fat-to-lean ratio, which ultimately improves performance. Fat doesn’t assist in movement—it’s just along for the ride, which increases the demand on the muscle to move it along. More lean tissue means more muscle to produce movement, which is exactly what you want, because muscle essentially carries itself.

Muscular Endurance

Finally, increasing muscular strength increases muscular endurance. When you have more muscle to rely on, it takes longer to wear it out. If you find that you sometimes reach muscular fatigue before you reach cardiovascular fatigue, then you should increase your muscular strength so that you have more in reserve. Endurance training decreases cardiovascular fatigue; strength training increases muscular endurance, which in turn decreases muscular fatigue.

Adapted from Strength Training for Triathletes by Patrick Hagerman, with permission of VeloPress.