Hypertrophy, Studies

August 13, 2014

Does Low-Load Resistance Training Fully Activate the Target Muscles?

There is compelling evidence that the onset of fatigue during resistance training results in an increase in motor unit activation, whereby the strength-oriented type II fibers are progressively recruited to sustain muscular contractions. Some have taken this to mean that any load, regardless of how light, will ultimately lead to full fiber recruitment provided that training is carried out to muscle failure (i.e. the point where you are unable to complete an additional rep with proper form).

Recently, my lab sought to test this hypothesis. Here is an overview of the study and its practical implications. The study, titled, Muscle activation during low- versus high-load resistance training in well-trained men, was just published ahead-of-print in the European Journal of Applied Physiology.

The Study
The purpose of the study was to compare muscle activation in the leg press at 30% and 75% 1RM when sets are carried out to muscular failure. Ten college-aged men were recruited for participation. Subjects were all experienced in resistance training, including regular performance of lower body exercise.

A within-subject design was employed where each participant performed both 30% and 75% 1RM conditions. Testing was carried out over two sessions. Subjects were initially tested to determine their 1RM in the leg press. They then returned to the lab at least 48-hours later for muscle activation testing of the quads (rectus femoris, vastus lateralis, and vastus medialis) and the hamstrings (biceps femoris) during heavy- vs. light-load training. The order of performance was counterbalanced whereby Subject 1 performed the high-load condition first, Subject 2 performed the low-load condition first, etc. In this way, we ensured that order of performance did not confound results. Fifteen minutes rest was provided between trials to ensure that previous fatigue was not a factor. We verbally encouraged subjects to perform each set to the point where they could physically no longer continue training with proper form.

Both mean and peak muscle activation was markedly and significantly greater during the heavy- compared to light-load condition (by 57% and 29%, respectively). Importantly, not a single subject displayed equal or greater activation during low-load training. These findings strongly suggest that training at 30% 1RM in a compound lower-body exercise is insufficient to recruit the entire motor unit pool for the target musculature.

Practical Implications
It has been well-established that training to muscle failure causes an increase in motor unit recruitment. This outcome was in fact confirmed in our study, as EMG amplitude increased in both the high- and low-load conditions over the course of each set. However, the magnitude of these increases were substantially lower during light- versus heavy-loading. The take home message here (in conjunction with a recent study on the topic using single-joint lower body exercise) indicates that a minimum threshold exists to achieve activation of the full spectrum of fibers and that 30% 1RM is below this threshold. Thus, it can be inferred that some of the highest threshold motor units — those associated with the type IIx fibers — were not recruited during the low-load condition.

From an applied standpoint, it might seem that these findings show training at very low-loads is useless. After all, why would you train with a load that does not generate complete fiber recruitment, right?

Not so fast.

Understand that there are two aspects to maximizing muscle development: recruiting a fiber and then keeping it stimulated for a sufficient period of time (i.e. time under load). While the loading strategy used in the light-weight condition here (i.e. 30% 1RM) did not bring about full muscle activation, it did maintain tension in the lower-threshold motor units for an extended time period. This could be particularly important in optimizing development of the type I fibers that are highly fatigue-resistant. This lends credence to the hypothesis that training throughout the full spectrum of rep ranges is the best strategy for maximal muscle hypertrophy. I have a longitudinal training study currently in review that seems to support this hypothesis. More on that in the near future.

An interesting secondary finding of the study was that the hamstrings displayed only minimal activation during the leg press — much less than that seen in the quads. This refutes the claims by some fitness pros that single-joint exercise is unnecessary provided you perform compound lower body exercises. Our results clearly indicate that movements such as the leg curl, stiff-leg deadlift, and good morning are important components of a well-rounded resistance training program to ensure proper symmetry between the quads and hamstrings.

A limitation of the study is that we only assessed a single set at each condition. Thus, it is not clear whether accumulated fatigue from performing multiple light-load sets would ultimately bring about complete recruitment. This requires further study. But even if this turns out to be the case — which is far from a certainty — it would mean that you’d need to perform a lot of additional volume just to achieve similar levels of activation; at the very least, an inefficient training strategy.

Final Thoughts
I am in the process of finishing a follow-up bench press study looking at 80% vs. 50% 1RM in an attempt to determine the approximate minimum threshold necessary for complete muscle activation. This will provide important info to those who are unable to lift heavier weights due to medical conditions or other issues. Realize, though, that muscle activation (and hypertrophy for that matter) do not necessarily translate into optimal strength gains. My recent study showed that even moderate load training (~10 RM) is inferior to very heavy lifting (~3 RM) if absolute strength is the goal. I discussed that study in-depth in this blog post

On a side note, I’ll be discussing the ramifications of this study and others currently in progress at my upcoming seminar in Montreal next month. Hope to see you there!


Cook SB, Murphy BG, Labarbera KE. Neuromuscular function after a bout of low-load blood flow-restricted exercise. Med Sci Sports Exerc. 2013 Jan;45(1):67-74.

Schoenfeld BJ, Contreras B, Willardson JM, Fontana F, Tiryaki-Sonmez G. Muscle activation during low- versus high-load resistance training in well-trained men. Eur J Appl Physiol. 2014 Aug 12. [Epub ahead of print]

Schoenfeld BJ, Ratamess NA, Peterson MD, Contreras B, Tiryaki-Sonmez G, Alvar BA. Effects of different volume-equated resistance training loading strategies on muscular adaptations in well-trained men. J Strength Cond Res. 2014 Apr 7. [Epub ahead of print]


  1. If muscle fibers cannot resupply during a set (I have only experimented with biceps curls but for me it requires a smaller load than 30%rm to resupply my biceps fibers during a set) then one would expect muscle fibres to drop out during the 30%rm set as they exhaust their anaerobic energy stores and so have lower peak and mean muscle fiber activation during the set while still fully exhausting the fibers controlled by the largest motor units.
    I don’t have the slightest idea if this shows up on the emg of motor units.

    Comment by Seantheaussie — August 13, 2014 @ 9:44 pm

  2. Nice work. Why do studies comparing intensity use such wildly different and unrealistic percentages?

    Would 80%+ versus 50/60% RM not be a more real life comparison? Pitting 14 reps against 44 reps seems a little one sided. Failure due to pain is not quite the same as failure due to exhaustion.

    5 reps versus 20 reps would be an interesting comparison as would slower speeds …

    Anyhow, it’s great to see work like this being designed by someone whom actually lifts. Thank you.

    Comment by Ham — August 14, 2014 @ 10:11 am

  3. Also, it’d very interesting to see the EMG results of the MVIC tests before and after the procedure to compare against the dynamic numbers…do you have those data?

    Comment by Ham — August 14, 2014 @ 10:13 am

  4. DOh…just saw your last section about 80 vs 50%….pardon my rush!

    Comment by Ham — August 14, 2014 @ 10:50 am

  5. The reason I chose 30% 1RM was because there is some research showing that this level of intensity produces similar gains in hypertrophy to heavy-load training. Thus, if the activation is less in 30% 1RM, it would indicate differencs in fiber-type specific responses to generate equal whole muscle growth.

    As noted, I am currently carrying out a study comparing 50% to heavy load trainin. Should have finished data collection in a few weeks.


    Comment by Brad — August 14, 2014 @ 5:21 pm

  6. Hey Brad,

    How does speed of movement factor into this? If 30% of 1RM was moved explosively as possible within the set would the activation change? I’m assuming it would. Is speed/tempo a confounding variable not accounted for here?

    Comment by Andre — August 14, 2014 @ 6:38 pm

  7. […] 1RM to failure produced significantly lower muscle activation compared to 75% 1RM. I also wrote an accompanying blog post where I break things down into consumer-friendly language and discuss the study’s […]

    Pingback by » Random Thoughts and Happenings — August 17, 2014 @ 4:07 pm

  8. For too long a time now, lifting weights has only been thought of for male athletes, bodybuilders or meat-heads. Well, times and knowledge have changed-and it’s about time. These days, everyone can lift weights regularly and achieve a more capable, leaner and healthier body. There are many ways to perform a weight training program. Depending upon your specific goals, you can scale the type of weight training to your needs and wants.

    Comment by Jean Walter — September 12, 2014 @ 12:45 am

  9. I am not that familiar with EMG and how it works but from what I ve no it gives you the electrical stimulation in the muscles during contractions. Then lifting a load equal to 75 % of your 1 RM you have to recruit a lot more fibres simultaneously compared with 30 % of 1 RM. So for each rep it seems quite clear that the EMG will show higher values for the 75 % intensity compared with the 30 %. But isn’t this phenomenon due to the fact that at 30 % less alpha motor neurons are recruited at the same time I guess some of them could be completely off at the start and as others fatigue they will come in to play.

    So as I see it the activation for each muscle fibre fast twitched or slow twitched could be the same just that the process is of more simultaneously character at the higher intensity. Great post as always!

    Comment by Alfred — September 24, 2014 @ 12:12 pm

  10. […] Lihaskasvussa olennaista on lihasproteiinisynteesi. Proteiinisynteesin maksimoinnin puolesta löytyy tutkimuksia molempien kuormien suuntaan (Kumar ym. 2009; Burd ym. 2010). Tässäkin haasteena on se, että alhaisia kuormia suosineessa tutkimuksessa treenin kokonaistyö oli selvästi enemmän (sarjat x toistot x kuormat) Burd ym. 2010) ja se selittää miksi alhainen kuorma pärjäsi niin hyvin. Sen sijaan kun kokonaistyö mätsättiin samaksi, niin isommat kuormat > 60 % 1 RM olivat tehokkaampia lihasproteiinisynteesin kasvun kannalta (Kumar ym. 2009). Yhtenä syynä tähän voi olla isompi mekaaninen kuormitus tai mahdollisesti parempi kaikkien lihassolujen aktivointi työhön kuten lihasten EMG-tutkimukset ehdottaa. […]

    Pingback by Isoilla kuormilla kovimpaan kuntoon: Ethän pelkästään ”jumppaa”? – Forssell ja Hulmi | Lihastohtori — July 23, 2016 @ 1:14 am

RSS feed for comments on this post.

Sorry, the comment form is closed at this time.