Importance of Resistance Training Intensity and Key Intramuscular Changes

by Chad Kerksick PhD September 24, 2012 5 min read

Resistance training is your pathway to getting stronger, getting bigger and to some extent getting leaner.  Sure, you can get super lean performing crazy amounts of prolonged, endurance exercise, but this does very little to keep what muscle you have.  And try putting on muscle performing long bouts of endurance exercise.  Well, you can forget about it.  For the majority of you having size is just as important as being lean.  As a result, you better perform resistance training and if you’re not, get started!   A number of key variables must be considered with your resistance training program (Spiering, Kraemer et al. 2008), but paying close attention to the intensity at which you are training and manipulating it in ways to jump start desired changes to your muscles is critical.

Intensity in resistance training is determined in two primary ways: percentage of your one-repetition maximum (%1RM) or repetition maximum (RM).  The first is simply taking a straight percentage of whatever your one-repetition maximum (1RM).  Your 1RM is the highest amount of weight you can complete with excellent technique as well as good control over the weight.  If this number is 200 pounds for a given exercise and you want to train at an intensity of 70% 1RM, you will be using 140 pounds for that exercise (200 x 0.70 = 140).  From here, intensity prescriptions using %1RM can vary from 60 – 100% RM depending on the exercise goal.  If you want to gain more muscle, the prescription typically involves performing multiple sets (3 – 4 sets) in repetition ranges of 8 – 12 repetitions at 65 – 80% 1RM.  Overall, scientists will commonly refer to this as higher volume training because you end up performing a much higher total number of repetitions at resistance levels that are far from insignificant.

If the goal is strength, the prescription changes slightly.  In short, the numbers of sets may go up (4 – 8 sets, or more), the repetition numbers will decrease (2 – 8 repetitions) and the %1RM will go up to areas around (80 – 95% 1RM).  Here the focus zeroes in on quality repetitions rather than instigating metabolic and neuromuscular fatigue.  Many scientists feel that the widespread changes which occur during fatiguing bouts of resistance exercise is the primary perquisite for growth or hypertrophy.


The other means of monitoring resistance training intensity is with repetition maximums (RM).  Essentially, it’s the same concept but with less numbers and a more instinctive approach.  Training according to RM means that you end up selecting a weight that will lead to muscular failure within a certain number of repetitions.  Hence, it the maximum number of repetitionsthat can be performed at any given level of resistance.  Again, if hypertrophy is the goal, a common RM is 10 – 15 reps and if maximal strength is the goal, a RM of 2 – 8 reps is often the goal.

Years of research and examining the changes in strength and muscle mass tell us that the numbers provided in this article are excellent starting points to instigate these changes.  As with anything related to the human body, these guidelines are best viewed as ranges or simply a place to start.  A myriad of factors dictate exactly how one person changes and for this reason, it’s commonly suggested for slight changes to occur for a number of different variables.

A recent study by William Kraemer (University of Connecticut) and research colleagues in Scandinavia completed a very detailed examination where they had eight untrained men around 28 years of age complete two different resistance training workouts using the leg press exercise (Hulmi, Walker et al. 2012).  One workout was a “hypertrophy” workout and consisted of 5 sets of 10 repetitions at a moderate intensity of 60 – 80%; equivalent to a 10RM load.  The other “strength” workout consisted of 15 sets of 1 repetition at 100% 1RM.  All of the subjects completed both workouts approximately one week apart and had muscle samples removed from their thighs before and 30 min after they completed each workout.  The researchers also removed muscle samples at the same times from a group of similar men who didn’t perform any resistance exercise (aka, the control group).  Inside the muscle samples, the researchers examined the activation changes and content of a number of proteins known to be related to muscle growth.   For starters, both styles of workouts activated key proteins related to muscle growth to levels that were anywhere from 2 – 16 times greater when compared to the control group (NOTE: As expected, no changes at any time point were seen in the control group).  But it should be mentioned that greater higher activation levels were seen when the hypertrophy workout was completed.  Furthermore, some additional proteins appeared to only be activated after the “hypertrophy/growth” workout.

These findings are awesome and important because they show scientists just exactly how certain prescriptions of resistance exercise are working inside the muscle.  As our understanding grows, so too will the prescription of exercise to be more and more effective.  Does this mean that the “strength” prescription was worthless or second-rate?  Absolutely not!  It simply means (somewhat as expected) that when prescriptions of resistance exercise are changed to initiate more of a growth response that the activation of key muscle growth proteins is in fact greater and provides valuable information to explain how muscle growth occurs.

While no nutrition was provided, a fascinating and interesting follow-up investigation should employ the provision of a healthy dose of leucine, the essential amino acids or a high quality whey protein isolate to determine to what extent these anabolic nutrients can further stimulate and turn on these key proteins.  In summary, when training for muscle growth, the weights must be heavy (65 – 80% of the maximum weight you can handle), you must complete a relatively high number of repetitions (3 – 5 sets of 10 – 15 repetitions) and it wouldn’t hurt to keep your rest to a minimum (60 – 90 seconds).



Hulmi, J. J., S. Walker, et al. (2012). “Molecular signaling in muscle is affected by the specificity of resistance exercise protocol.” Scand J Med Sci Sports 22(2): 240-248.

Spiering, B. A., W. J. Kraemer, et al. (2008). “Resistance exercise biology: manipulation of resistance exercise programme variables determines the responses of cellular and molecular signalling pathways.” Sports Med 38(7): 527-540.



























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Chad Kerksick PhD
Chad Kerksick PhD