by Chad Kerksick PhD August 22, 2010 5 min read
Much of the basis of strength and conditioning and resistance training principles have centered upon using 70% to 80% of your one-repetition maximum for 10 to 12 reps with low rest to maximally stimulate hypertrophy (Fry 2004; ACSM 2009). This what is taught in every exercise science curriculum across the country, by strength coaches across the country and used as a basis for every professional fitness certification worth the paper it is printed. Interestingly, a group of data has started to evolve to suggest that intensity may not be the only critical factor to consider. Most recently, a group of researchers from McMaster University published some of their work just last week, which suggested that training to muscular failure may be the most important consideration irrespective of the intensity that is being used (Burd, West et al. 2010).
In this study, fifteen young (21 ± years), healthy (body mass index = 24.1 ± 0.8 kg/m2) men performed four sets of unilateral leg extension at different exercise loads and/or volumes of exercise. Three separate lifting conditions were presented. All groups first had their baseline maximal strength levels determined and then one group performed as many repetitions as they could with 90% of their maximal weight. The next group performed as many repetitions as they could with 30% of their maximal weight and the third and final group completed the same amount of work (amount of weight used x repetitions completed) as the first group, but only with 30% of their maximal weight.
To their credit, this research group completed a very technical array of research measures to determine the extent to which each exercise group stimulated increases in muscle protein synthesis or hypertrophy. What do you think happened? I know almost every one is conditioned to think “go heavy or go home”, but the group which completed the maximal number of repetitions with only 30% of their maximal weight showed the greatest benefit. As I said before, the researchers measured several different markers of muscle hypertrophy and surprisingly a number of them showed as good or greater responses than when those individuals completed repetitions to muscular failure and used 90% of their maximal strength. So it’s not like they got lucky or something and only found one marker to support this conclusion. How does one go about making sense of this? I know researchers out there and many coaches and athletes who simply will refuse to believe these findings. I mean years of slinging steel around or coaching athletes or training individual’s counts for something doesn’t it?
To make sense of this data, an important perspective needs to be developed when fully trying to understand this article. First off which the authors pointed out nicely is that their study is only in response to one exercise bout of each condition. The real test would be for someone to complete this type of research over the course of several months of training in this manner and measuring changes in strength and body composition to see which groups respond the most favorably. While these results do suggest favorable results after one session of training, things can change over the course of several weeks and daily disturbances in the person’s training program, nutritional habits, etc. can wreak havoc on these adaptations so a full blown study in this fashion would be helpful. Also, this study isn’t really saying that high intensity exercise doesn’t work. Many of the markers this research group used to measure muscle hypertrophy were increased several orders of magnitude as well when training to failure with 90% of their maximum. The increases just weren’t to the same extent when people trained to muscular failure with only 30% of their maximum.
Lastly, another key thing to remember as well is that the study’s outcome doesn’t tell us anything about strength changes, as the single bout of exercise didn’t allow for such as assessment. As many studies have shown us, there is a definite firm relationship between size (or hypertrophy) and strength (Fry 2004). To this end, most studies and review papers nicely illustrate the need to lift higher intensities to maximally recruit all muscle fibers and the higher the weight used, the greater recruitment of muscle fibers that occurs (Henneman 1957).
In this respect, what a study like this tells us is the importance of training to failure. As I mentioned before, it’s not so much about seeing the differences in intensities used and stopping there. Both groups trained to muscular failure and when you only use 30% of your maximum vs. 90%, what types of things are going to be different? For starters, the number of repetitions you can complete will be drastically different and this is exactly what was shown. When training to failure with 90% an average of 5 repetitions were completed while an average of 24 repetitions were completed with 30%. Similarly, the time spent lifting (called ‘time under tension’) was also quite different between groups as the 90% to failure group was under tension for an average of 16.3 seconds while the 30% to failure group was under tension for an average of 43.3 seconds, almost three times greater. These greater numbers of completed repetitions and time under tension also result in the 30% to failure producing 30% more work during the exercise bout when compared to the other two groups (Burd, West et al. 2010).
For those in the bodybuilding world, the results of this study may not be surprising, as many bodybuilders have been training this way for quite some time. In the end, embracing these results and using them as an alternative way of training may be an awesome thing. Practically, keeping this study in mind for a traveling businessperson who either may not have the time or the hotel gym doesn’t have heavy enough weights. Also, this could potentially be a great way for women and older adults to train as it allows you to use less weight, but still see the desired changes. The key aspect of this study, however, is reaching true muscular failure and the evidence of a relationship, which may exist between using lower intensities to allow for completion of an increased number of repetitions, and spending much more time under tension. For sure, this type of training won’t be for the faint of heart and training this way using large muscle group, multi-joint movements like the bench press, shoulder press, leg press, squat, etc. will maximally stimulate muscle which in the end could result in greater improvements in muscle hypertrophy.