When to Lift With Lighter Weights

Heavy weights, low reps, long rest breaks.  That’s how you get stronger, right?  In order to get stronger, you have to keep lifting heavier and heavier weights – at least that’s what all the strength coaches say.

For the most part, I completely agree. You are not going to get anywhere unless, over time, you increase the poundage on the bar for the same about of reps.  Unless you are hopped up on drugs or have some weird mechanical advantage with your tendons, in order to get bigger muscles, you need to get stronger.  But.. sometimes is it OK to use lighter weights and more reps?  Current research says “yes!”

The main problem with using lighter weights is that people just use them at the wrong times or in the wrong way. For example, you should never do pyramids by doing light weights to failure or near failure and progressively moving to heavy weights.  To start off this article that gives reasons for using lighter weights, let’s take a quick look at an experiment:

Stuart Phillip’s and his team at McMaster University performed an experiment that showed some interesting results with “Low Load, High Volume Resistance Exercise”. For convenience, I’ll reprint their methods here:

Methodology/Principal Findings

Fifteen men (21±1 years; BMI = 24.1±0.8 kg/m2) performed 4 sets of unilateral leg extension exercise at different exercise loads and/or volumes: 90% of repetition maximum (1RM) until volitional failure (90FAIL), 30% 1RM work-matched to 90%FAIL (30WM), or 30% 1RM performed until volitional failure (30FAIL). Infusion of [ring13C6] phenylalanine with biopsies was used to measure rates of mixed (MIX), myofibrillar (MYO), and sarcoplasmic (SARC) protein synthesis at rest, and 4 h and 24 h after exercise. Exercise at 30WM induced a significant increase above rest in MIX (121%) and MYO (87%) protein synthesis at 4 h post-exercise and but at 24 h in the MIX only. The increase in the rate of protein synthesis in MIX and MYO at 4 h post-exercise with 90FAIL and 30FAIL was greater than 30WM, with no difference between these conditions; however, MYO remained elevated (199%) above rest at 24 h only in 30FAIL. There was a significant increase in AktSer473 at 24h in all conditions (P = 0.023) and mTORSer2448 phosphorylation at 4 h post-exercise (P = 0.025). Phosporylation of Erk1/2Tyr202/204, p70S6KThr389, and 4E-BP1Thr37/46 increased significantly (P<0.05) only in the 30FAIL condition at 4 h post-exercise, whereas, 4E-BP1Thr37/46 phosphorylation was greater 24 h after exercise than at rest in both 90FAIL (237%) and 30FAIL (312%) conditions. Pax7 mRNA expression increased at 24 h post-exercise (P = 0.02) regardless of condition. The mRNA expression of MyoD and myogenin were consistently elevated in the 30FAIL condition.

Now, just in case you didn’t bother to read that, they basically had 3 groups of people. One group that did leg extensions at 90% their 1-rep-max till failure, one group that matched the work done in the 90FAIL group, but did so by doing 30% their 1-rep-max, and one group that did 30% their 1-rep-max till failure.

Now, as your would hopefully predict, the 30 work-matched group came out the worst.  That’s no surprise. Likewise, the fact that the 90FAIL group had a very high protein synthesis 4 hours post workout shouldn’t be too much of a surprise.  However, the surprise comes with the 30FAIL group. This group matched the protein synthesis 4 hours post workout and was the only group that continued to have elevated myofibrillar protein synthesis 24 hours after exercise!

(As a side note, myofibrillar protein synthesis is when protein is actually added to to the muscle fibers, making them larger. This is the main thing that we want when building muscle.  Sarcoplasmic protein synthesis is an increase in things like glycogen storages in the muscles, capillary density, etc.  That type isn’t really as important, and shouldn’t be the goal of the workout.)

Thus, only the 30FAIL group was still building muscle 24 hours post workout.  This might seem to slap heavy lifting right in the face, but actually, it doesn’t.  You see, this doesn’t change that the body is an adapting machine and that lifting is as much neurological as it is physical.  If you don’t use heavy weights when you lift, you will eventually hit a “plateau”.  Heavy lifting trains your nervous system in a way that lighter lifting does not, and this is very important.  However, this research definitely suggests adding lighter lifts into your workout, but when?

To get the best out of both worlds (increased nervous system output [strength] and maximum protein synthesis), one could start the lifting session with heavy weights, reps around 4-6, and then as the session goes on, make the weighs lighter.  This is because using lighter weights in the beginning will use up the energy in your glycogen storages, which would hamper your later heavy lifts.  However, doing heavy lifts first uses almost only ATP, and the glycogen storages stay mostly full for the lighter lifts later on.

Basically, lighter lifts first will reduce the weight you can use for the heavy lifts later on, but heavy lifts first won’t hurt the lighter lifts later too much.

Also, just to be complete, there is more to building muscle than just protein synthesis.  The current theory is that as one gets stronger, protein synthesis starts to become less important and other things like the activation of satellite cells, which seems to be a response to inflammation (read: heavy lifting). But that is for a future article!

One last thing:  The 30FAIL group came out the best, but the 30WM (work-matched) group came out the worst. Why? Simple. The 30FAIL group needed to recruit their type IIb muscle fibers (which are the main fibers that actually grow) while the 30WM group did not, because the work was too easy and didn’t last long enough.  Type II muscle fibers are the stronger fibers that grow (type I hardly grows at all). However, the body prefers to use type I fibers before using type II, unless the weight is really heavy or a lighter weight is taken to a point where type I can no longer handle the load – i.e. failure. Thus, the type II fibers only got activated in the 30FAIL and 90FAIL groups.

As another side note: if you are using lighter weights, not every rep you preform actually contributes to muscle growth.  Since the body uses type I fibers first, the beginning of every set you start will not really contribute to muscle growth, only the last few reps will.  This can be partially avoiding by, once again, placing your lighter lifts at the end of your workout session and by using Blade’s Myo-reps, which I will describe in a future article (update: here it is!).

Well, that’s it for now! Make sure you leave your comments and questions below!