This is decent video to get most of you up to speed on muscle fiber types and how resistance training can cause muscular damage leading to growth (hypertrophy). I will admit that I was a bit disappointed because the video seemed very rushed and ended abruptly, missing a lot of key points. I was also quite surprised that they even made mention of muscular hyperplasia. Hypertrophy is the actual enlarging of muscle cells (increase in volume) whereas hyperplasia is the division of muscle cells - increase in overall quantity. Although it is certainly possible to increase the overall number of muscle cells, the evidence for this isn't entirely clear and most likely does not apply to the general population (those not on steroids).
While strength/power and endurance training could be considered a "skill," hypertrophy should be considered a stimulus. In other words, our training is creating a specific demand within our muscle cells to signal growth. This is one area that not only generates a lot of interest amongst fitness enthusiasts, but researchers as well. For years, many have thought that training within a 6-12 rep range was optimal for muscular hypertrophy or growth. Research, although not necessarily refuting that evidence, is trying to explain the greater picture in how or why muscles grow and how varying stimuli can promote muscular growth.
As it turns out, the number of repetitions you do does not entirely matter in how much muscular growth is promoted. In other words, rep range does not matter for hypertrophy.
In conclusion, this study showed that both bodybuilding- and powerlifting-type training promote similar increases in muscular size, but powerlifting-type training is superior for enhancing maximal strength.
Ideally, your training should meet your needs, goals, and desires. If you wish to train to improve strength and/or performance, then stick to lower repetition ranges with higher intensity. If you wish to train for more aerobic events, then lower intensities and higher repetitions should be targeted.
This study demonstrates that both intensity and exercise-induced metabolic stress can be manipulated to affect muscle anabolic signaling.
What about our previously-thought belief that rest periods determine the growth of muscles? Well, apparently not.
In conclusion, the literature does not support the hypothesis that training for muscle hypertrophy requires shorter rest intervals than training for strength development or that predetermined rest intervals are preferable to auto-regulated rest periods in this regard.
One more variable we can throw into the mix is research that has looked at oxygen restriction and how it affects hypertrophy signalling. One study used tourniquets to restrict blood flow to working muscles to discover whether or not this would alter training stimulus or signalling.
Blood flow restriction resulted in significantly greater gains in strength and hypertrophy when performed with resistance training than with walking. In addition, performing LI-BFR 2-3 days per week resulted in the greatest effect size (ES) compared to 4-5 days per week.
Hypertrophy training has been, and continues to be, a topic that many are interested in. More and more studies are now finding that overall volume - the amount of weight lifted despite repetitions in a set, and training close to, or to failure, are the most important factors that stimulate the signalling needed to elicit muscular growth.
Tyler Robbins B.Sc. CSCS
Director of Fitness
Head of CrossFit