B Strong. B Fast. Just Fit.

Strength Training for Endurance: Part 1

Published March 27th, 2009 in BAMFing, Endurance, Strength Training

Just like the Hatfields versus the McCoys, the Montagues versus the Capulets, and Snow Miser versus Heat Miser, Endurance training and Strength training will always be fighting for supremacy from the opposite sides of the street. As Rudyard Kipling said, “never the twain shall meet.” However, to refresh everyone’s memory, they all worked better when they worked together! (Well, Romeo and Juliet didn’t really get the chance, but when they were together, it was pretty good.)

Obviously, given our topic, you know that I’m going to tell you that STRENGTH TRAINING IS GOOD FOR ENDURANCE, but before I do (damn, did I tell you already?!), you should have a basic understanding of the difference between the two.

If you go by the dictionary definitions, Endurance is ‘the ability to bear prolonged exertion’, and Strength is ‘the physical power to carry out demanding tasks’. Ability and power are essentially the same thing, just as exertion and demanding tasks could be considered equals. Thinking about it this way, they don’t seem so opposite. The key difference in these definitions is the word “prolonged.”

So what gives us the ability to “go long”, and what gives us the power for “demanding tasks”? What exactly moves us? Ok, here are a few hints. It’s one word, two syllables, and sounds like Brussels; you got it, muscles! Yes, there are other things involved, but without muscles, no one is going anywhere.

In basic terms, muscle fibers can be divided into two groups; Slow-twitch muscle fibers, and Fast-twitch muscle fibers. These can also be classified as Type I and Type II muscle fibers respectively, with Type II being further categorized into Type IIa and Type IIb fibers. Are you still with me? Good.

Slow-twitch fibers develop force and relax slowly and thus have a long twitch time. In contrast, Fast-twitch fibers develop force and relax quickly with a short twitch time. Guess which fibers are predominately used for endurance? Of course, the slow-twitch, or Type I fibers. They are fatigue resistant and have a high capacity for aerobic energy. Fast-twitch or Type II fibers fatigue quickly, develop force rapidly, and have a high capacity for anaerobic power. Type IIa fibers show a greater resistance to fatigue, more capillary density, and thus a higher capacity for aerobic metabolism than Type IIb fibers. Completely confused? No worries, all will become clear as we go.

The chart below gives you a short breakdown of each fiber type’s characteristics.

Characteristics of Muscle fiber types:

Type IType IIaType IIb
Contraction speedslowfastfast
Force productionlowmediumhigh
Power outputlowhighhigh
Capillary densityhighmediumlow
Mitochondria densityhighmediumlow

Now that you have a basic understanding of muscle fibers, let’s look at some other physiological adaptations to the different forms of training.

We already know that Endurance training primarily uses Type I, or Slow-twitch muscle fibers. The main focus of Endurance training is to increase maximal oxygen consumption in the effort to perform at sustained levels of exercise for long durations. In other words, keep going, and going, and going. Think Energizer Bunny. Some adaptations to endurance training include, increased respiratory capacity, lower blood lactate concentrations, increased mitochondrial and capillary densities, as well as catabolic muscle degradation and a reduction of power. What was that? Yes, due to the increase of the hormone cortisol, a catabolic environment is created within the muscle, breaking down muscle protein. Ouch!

Strength training primarily uses Type II, or Fast-twitch muscle fibers. The main focus of Strength (resistance) training is to increase maximal force production. Adaptations to strength training include, increased muscle size, a reduction of mitochondrial and capillary densities (hmmn), and an increase in muscle strength. The increase in the hormone testosterone creates an anabolic environment within the muscle enabling protein synthesis, and an increase in power production.

Check out the chart below for another brief breakdown.

Physiological Adaptations to Endurance Training and Strength Training:

Endurance TrainingStrength Training
Muscle strengthno changeincreases
Muscle enduranceincreases for low power outputincreases for high power output
Aerobic powerincreasesno change or increases slightly
Max force productionno change or decreasesincreases
Anaerobic powerno changeincreases
Sprint speedimproves slightlyimproves
Muscle fiber sizeincreases slightlyincreases
Capillary densityincreasesno change or decreases
Mitochondrial densityincreasesdecreases
% Body fatdecreasesdecreases
Fat Free Massno changeincreases

So, where does all this leave us? Endurance training increases our ability to utilize oxygen to “go long”, but decreases muscle size and force production. Strength training increases muscle size and force production, but doesn’t do much for aerobic energy. You mean to tell me that I went through all that information and all we are is back to the beginning? Yes and no.

If endurance and strength training accomplish completely opposite objectives, is strength training appropriate for the endurance athlete?

One of the biggest arguments against it is that strength training will create too much muscle, and thus bulk, for the endurance athlete to carry, and ultimately slow the athlete down. One great example of this argument comes from one of the kings of endurance sports, Lance Armstrong. Lance was a good cyclist before he went on his run of 7 Tour de France wins. He won a stage of the race, but he was never thought of as someone who would win the whole thing. The big reason; he was too bulky from his swimming and triathlon days, and carrying more weight up those hellish climbs in the Alps than the top contenders. When cancer completely ravaged his body, the difficult treatment process transformed him physically. He lost a large amount of body mass and was no longer too big in his upper body. It was one of the things people noticed during his first tour win. Of course the mental toughness gained from his ordeal was a major factor in his success, but it’s tough to fight the argument against strength training for endurance athletes given this example.

As you might have guessed, however, there are many shades of gray. Let me give you a couple of things to think about. First, let’s take another look at muscle fiber types.

In a study by Kraemer et al. they looked at the effects of specific training on muscle size. They found that when only strength training was done; there was an increase in both Type I and Type II muscle fiber size. When solely endurance training was done; there was no increase, but a decrease in size of Type I muscle fibers. When both were done concurrently; muscle size increased only in Type II fibers. The fascinating thing was that there was an almost complete change of Type IIb fibers into Type IIa fibers. If you recall from above IIa fibers are more aerobically inclined than IIb fibers. So, what am I saying here? Well, it seems that although strength training does not truly help maximum oxygen consumption, it does help create more endurance by increasing the size and number of Type IIa muscle fibers.

In another study by Kraemer et al. they found that women who performed both endurance and strength training had greater aerobic development than those that did endurance training alone. Incorporating strength training into an endurance program can improve the heart, lungs, and circulatory system during conditions of high pressure and force production as in the final sprint to the finish, or being first out of the transition area in triathlons. It helps augment the development of maximal aerobic capacity, and running economy.

Here’s another thought for you. If you remember back to our dictionary definitions, I mentioned that “exertion and demanding tasks could be considered equals.” Another way of describing these two terms is to call them “work.” I also said that “ability and power are essentially the same thing.” In physics, Power = work/time. In other words, power is the rate at which work is done. The faster something is done; the more power is exhibited to do it. The last part of this equation is “time.” Remember the key difference in our two definitions was the word “prolonged”, which is a description of time. Last I checked the goal of any endurance event is to finish first, or the fastest, or at least faster than your previous time. In order to do that you need to generate more power than the competition or than you did in your last race.

Since going faster requires more power, and strength training creates more power, it makes sense that strength training is good for endurance. Power can also be expressed as force x velocity, or strength x speed for our purposes here. Since strength training also increases our strength and speed, it follows that it’s a good idea for endurance athletes to do it.