Implications of Training Both Strength and Endurance

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Guest writer John Grace does it again with another solid article for The Strength Agenda. Check out his latest article explaining how training  for optimum strength and endurance is a lot harder than you think and how your body responds to the effects of this training.

With CrossFit-style training becoming an extremely popular mode of fitness, USAW is reaping the benefits in the form of a huge revitalization in the sport of weightlifting. CrossFitters have a reputation for being generalists- they are good at many different tasks, but not elite at any one of them. There is some debate on whether CrossFit athletes that double as nationally competitive weightlifters would be better if they specialized; meaning they concentrate on weightlifting only.

The goal is not to side with one end or the other, but to bring some science into the discussion. There is in fact a phenomenon known as the “interference effect”. The interference effect says that if you train strength and endurance simultaneously, endurance training hinders your ability to gain lower body strength, speed, and power. Research (1,2,3) indicates that this concept is true.

To explain this concept further, let’s look at the energy systems and how they can affect our training. The energy systems should not be thought of as three separate entities and they most commonly are; rather, they should be thought of as an energy system continuum.  The aerobic energy system on one end, anaerobic lactate in the middle and the anaerobic alactic energy system on the opposite end. The reason I say it should be viewed as a continuum is because each energy system bleeds slightly into the one beside it as you move right and left down the continuum.



The anaerobic lactate energy system is mainly used during CrossFit-style workouts, i.e. the training that leaves your muscles in agonizing, burning state.  Short bouts of high intensity work, like weightlifting, can be characterized as alactic anaerobic, while aerobic activities can be classified as long bouts of low intensity work, like long distance running.

In short, a weightlifter, who would fall on the far right side of the continuum, would make a poor marathon runner; conversely a marathoner, falling on the far left, would make an even worse weightlifter. CrossFitters, on the other hand, fall somewhere in the middle and would probably be decent at both as the anaerobic lactate system bleeds into both aerobic and anaerobic alactic qualities.

Everyone is born with a certain amount of Type I and Type II fibers; the former being your long duration, low intensity activities and the latter more useful for short, high intensity activities. Type I fibers are great at the events on the left side of the continuum, while Type II fibers great at events on the right side. Luckily for those of us that want to be speed-power animals and not genetically gifted with an abundance of Type II muscle fibers, you can alter (to an extent) muscle fiber type percentages depending on how you train. For instance, if an athlete was born with predominantly Type I fibers, but primarily trained their Type II fibers over the course of their life, they would most likely become Type II dominant.

If CrossFit participants moved solely to weightlifting, while I don’t see them flipping the weightlifting world upside-down, they could potentially put up some bigger totals based on what we know about the interference effect. Anaerobic lactate athletes are great at what they do, but are setting some limitations on what they can achieve on both ends of the continuum.


1. Hennessy, Liam C.; Watson, Anthony W.S. The Interference Effects of Training for Strength and Endurance Simultaneously.Journal of Strength & Conditioning Research. 8.1. (1994)

2. Hickson, Robert C. Interference of Strength Development by Simultaneously Training for Strength and Endurance. Eur J Appl Physiol. 45. 255-263 (1980)

 3. Jones TW, Howatson G, Russell M, French DN. Performance and Neuromuscular Adaptations Following Differing Ratios of Concurrent Strength and Endurance Training. Journal of Strength & Conditioning Research. 2013 Mar 21. Epub ahead of print.

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