Endurance athletes have commonly followed the approach of endurance based resistance training.  This involves performing high repetitions and sets in resistance training.  However, in recent years this view has changed.  Heavy load resistance training (HLRT) has become more of the norm.  HLRT involves using low repetition numbers with a moderate set numbers.  Loads are usually more than 80% of your one repetition maximum.

I decided to look at this logically and attempt to explain it in more simple terms.  Let’s start by looking at the muscle fiber types and their characteristics to help explain why HLRT is beneficial to endurance athletes.

Characteristics of Muscle Fiber Types:

Type I Slow Twitch (ST) – slow contraction time, small motor neuron, high resistance to fatigue, low force production, high mitochondrial density, high capillary density, high oxidative density.  Used in aerobic activities.

Type II A Fat Twitch (FT-A) – fast contraction time, large motor neuron, intermediate resistance to fatigue, high force production, high mitochondrial density, intermediate capillary density, high oxidative density.  Used in long term anaerobic.

Type II B Fat Twitch (FT-B) – very fast contraction time, very large motor neuron, low resistance to fatigue, very high force production, low mitochondrial density, low capillary density, low oxidative density.  Used in short term anaerobic.

Muscle fiber composition in the body is genetically determined.  However, numerous studies have proven that both the structure and metabolic capacity of individual muscle fibers can adapt to different types of training.

When we look at muscle recruitment in exercise, slow twitch muscles are recruited first.  This is regardless of the intensity.  As intensity level increases, recruitment of fibers is slow twitch first, then fast twitch A and lastly fast twitch B.  When we apply different types of training methods we are effectively trying to recruit certain muscle fibers types or to get certain muscle fiber types to take on characteristics of other muscle fibers types. 

For example, we could train FT-B fibers to take on some of the endurance characteristics of FT-A fibers.  This is how HLRT comes into play.  HLRT results in the body being able to recruit FT-B fibers as if they are FT-A fibers.  We are trying to make the muscle fiber stronger, more resistant to fatigue, and have greater mitochondrial and oxidative density.  Totally logical.

Of course, there are other benefits to HLRT.  HLRT, like plyometric training, increases leg stiffness which improves performance economy.  HLRT also stimulates neuromuscular efficiency and builds more power. 

Summary

A muscle which is stronger is going to be more resilient and fatigue resistant, and have better overall performance economy.  In endurance sports, performance economy is key.  If an athlete can use less effort at faster speeds, they undoubtedly become a faster athlete.  Totally makes sense to me.

The type of exercises that I recommend for endurance based athletes includes dead lifts, squats (different variations), steps ups, and lunges.  Like a properly mapped out endurance plan, a strength program needs to follow a periodization structure to reap the biggest benefits.