Q: I was wondering if there is a minimum amount of resistance you have to lift to stimulate growth? When I was performing incline bicep curls going slowly on the eccentric and holding at the top at the end of my workout and in order to get higher reps (10-12ish) with the objective of stimulating hypertrophy I would have to drop the weight very low in the 3rd and 4th sets (10 lbs.). Is this still enough resistance to cause the muscles to adapt or will this only cause a good pump?
A: The standard textbook when training for hypertrophy is to use loads of about 70-85% 1RM (about 6-12 reps). There is not a universally applicable scientific minimal level. It varies a lot depending on the individual’s genetics and experience level. For example, someone just starting off can make progress with a lot lower % of 1RM than one who has trained for years. Those who are mesomorphs (i.e. a body type genetically gifted for building lean muscle) can do a lot of different things and gain muscle size that may not work for those with less-than-ideal muscle building genes. Also those with a higher percentage of fast twitch fibers will get less out of light weight training.
For the genetically average individual with a solid base of experience, I would say that 5-8 reps is a good way to go for a lot of hypertrophy training. In addition to this range, sets with heavier weights and lower reps as well as sets with lighter weight and higher reps may also be beneficial. The pump seems to help, although there is still a lot to learn. Also, it is hard tell when there are some many other factors (e.g. the previously done heavy work, genetics, steroids, etc).
Many programs over the years have used some light-weight pumping sets after heavier training or on a different day. This may give the best of both worlds. Arnold though famous for the pump (if you have seen the movie Pumping Iron, you know what I'm talking about) also moved some serious iron! This also makes sence scientifically as the stress of heavy weights (and thus low reps) is great for increasing testosterone while fatigue and lactate build-up from the the higher rep sets with shorter rest intervals is great for increasing hormone levels of growth hormone and IFG-1 (insulin-like growth factor 1).
If you are examining research studies on this issue, be sure to look at the research design and see who the subjects are. Often they are untrained university students and this can make even a good research study non-applicable for someone with a solid base of experience.
If you study bodybuilding, you will see different bodybuilders getting great results from different methods. Some have traditionally been more of “pumpers” while others have been more known for lifting some heavy iron. Both work. However, those that lift heavy seem to have a harder, more dense look (less puffy) and have usable strength. Personally, I’m biased to the heavy weight approach because I have never had light weights work for me and I want a body that can perform well.
In making these training decisions, it is also important to consider training time and recovery ability. You only have so much of both and you want to use it as effectively as possible. Prioritize the big exercises for that moderate rep range with progressively heavier weights. If you can do this and still have time and energy for some pump work, then try it.
The bottom line is to be evidence-based. If you want to try it, measure your arms, try the light weight sets at the end for a while and then re-measure. Note: re-measure several days after you finish – not the next day so you can get a better idea what is actual hypertrophy and what is just short-term swelling.