Resistance Training Part 4

Regardless of whether you are training with weights to develop the most muscle you can, sculpt just enough to look “toned” or simply achieve the many health-related benefits that this type of exercise offers, it’s essential to choose the right amount of weight to lift. Last month, I explained how this decision should not be based upon the specific look you are trying to achieve because that will be dictated by your genetic blueprint and how far you progress the stimulus once training-induced changes take place. Instead, you should choose a weight that will be most effective for getting the job done. And the job is to overload your muscles with a stimulus in excess of that to which they are accustomed.

Okay, your muscles won’t respond unless they are challenged beyond status quo. That should come as no surprise. But there are many physical challenges we encounter that are far in excess of what we normally do that won’t provide the specific stimulus we are seeking when lifting weights. For example, if you typically run five miles on a treadmill with no incline a couple of times a week, it’s safe to say that going out and running a half marathon over a hilly course would be above and beyond your muscles’ comfort level. But this would not be an appropriate way to strengthen/build muscle because it is an endurance-type activity that does not require activation of fibers that will be amenable to getting stronger and bigger. If this was not the case, marathon runners would have leg muscles as big as champion bodybuilders.

Elwood Henneman passed away in 1996, but he left a legacy that is still alive to this very day. Henneman was a neurophysiologist who published five important papers in 1965. This research provided a detailed account of how muscles fibers are called into action when we challenge them and his contributions were so monumental that the principle summarizing the findings still bears his name. In fact, despite numerous challenges during the ensuing years, Henneman’s Size Principle stands as one of the most widely recognized tenets of exercise physiology. And a good grasp of this principle is necessary when deciding how much weight to lift.

Henneman’s size principle suggests that there are muscle fibers with very different contractile properties that are recruited in a hierarchical manner depending primarily on the challenge at hand. For example, let’s say you’re standing on line at the food store, which shouldn’t be particularly challenging . . . at least not physically. However, even though you don’t realize it, there are myriad muscles that are active to allow you to simply stay upright without succumbing to the pull of gravity. And within these muscles, there are specific fibers that are very good at developing tension at low levels for extended periods without raising a fuss. Consequently, the job gets done with nary a second thought.

Slow-twitch oxidative (a.k.a. type I) fibers have a high capacity for endurance and are, therefore, activated quite easily any time we need even the most modest amount of tension to be developed. At the other end of the spectrum, fast-twitch glycolytic fibers are powerful, but limited in there capacity to contribute for extended periods. Consequently, these heavy hitters only get called into play when the going gets tough and if the challenge requires sustained involvement (for example, running a marathon), they can contribute for a very short period of time (a sprint to the finish line, for instance), but that’s about it. Fibers that have a mix of these properties are situated intermediate to these extremes and gradations exist such that as you traverse one end of the spectrum to the other, endurance capacity goes down as the ability to generate powerful muscle contractions increases.

The take-home message is that all muscle fibers are not created equal. And it’s a good thing for us that they aren’t! Consider this analogy: You own a high-performance race car that can run the quarter mile in 12 seconds flat. Do you drive it to work every day? I think not! Chances are you’d travel in some economy car that would keep you out of the poor house. And it’s also safe to assume that you wouldn’t inadvertently bring your gas saver to the track one week when looking to lay down some rubber. The bottom line is that if you want to span a wide range of performance capacities, you had better have system components that operate in a very diverse manner. And that is how human muscle has evolved.

Henneman’s Size Principle indicates that fibers at the upper end of the spectrum are only activated once those that reside lower have been called into play. And these “higher-order” fibers are the ones we want to target in the weight room. So, in order to get the resistance training job done properly, we have to force a drive through a significant portion of this recruitment hierarchy. The article I have referred to previously by Long Island’s own Dr. Ralph Carpinelli explains how there is a bit of misunderstanding in the field of strength and conditioning as to how to get this done.

This article was originally published in New Living Magazine, which can be accessed on-line at





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