Heavy or Light Weights To Help Your Clients Gain Muscle?

By Gregg Slater.


Think back to your personal training course and you’ll probably remember being told that heavy weights (1-6 reps) were for strength, moderate loads (8-15) for hypertrophy and anything above that endurance.

Fortunately, an ever-growing body of research has disproven this formally held rep dogma and in doing so, has opened up a whole world of programming possibilities.  


Heavy Loads = Best For Strength & Hypertrophy?

It may surprise you to know that as far back as 2012 the notion that relatively heavy loads were required in order to produce optimal gains in strength and hypertrophy was being challenged. Don’t worry, I’m not going to bore you with the nitty-gritty details of the science and the studies but if you’ll allow me a few lines to provide some details.

In 2012 Mitchell ran a study comparing 30% 1RM to 80% 1RM sets to failure on leg extensions over 10 weeks.

The outcomes? Almost identical increase in quadriceps size.

That’s right, sets of 30-40 repetitions in the low load training got the same hypertrophic response as high loads of 10-11 reps!

This study is far from alone and the results have been replicated a number of times over the following 8 years (Schoenfeld 2014, 2016, 2018). Lasevicius (2018) even showed that sets with as little as 20% of 1RM, or 70 reps to failure, could produce hypertrophy! Now it should be noted that 20% didn’t do as well as 30%+ and I can’t imagine many of us are thinking of utilising sets with such light loads, but it’s nice to know.


So, What Does This Mean?

Well, it appears that sets of anywhere between 6-30 repetitions produce similar hypertrophic responses when taken close to concentric failure (0-3 RIR).

From a coach’s perspective, this is magic.

Busy gym and can’t get the dumbbells I need? In a mobile setting with a band and bodyweight? Got a client that is intolerant to heavy squatting?  No problem, all I need to do is find a way to challenge someone (0-3 reps in reserve) in the 6-30 rep range and we’re in the right ballpark.


High vs Low Loads – Similar But Not The Same

Now as a sidebar, if we’re talking strength, it’s very much skill-specific and, whilst low load (light) training can produce improvements in 1RM in some populations, high load training often produces better results due to the specificity of training.

However, let’s get back to this claim that in producing similar hypertrophic responses, sets of 6’s to failure are basically the same as sets of 30 reps failure.  


Are Sets of 6 to Failure The Same as Sets of 30 to Failure?

Let’s question this claim, firstly with a thought experiment.

You’re working with a client whose 1RM is 100Kg.

You place 80Kg or 80% of their 1RM on the bar and ask them to go to failure.

They manage a tough but proficient 8 reps, in doing so we have effectively generated enough fatigue to bring the 1RM below 80Kg.

You then take 40Kg off the bar, leaving 40Kg remaining.

They are then tasked with going to failure again, in doing so they manage another 15 repetitions! We have now generated enough fatigue to bring their 1RM from 100Kg all the way down to below 40Kg in the moment of failure.

In the initial set of 80kg, they had already reached failure once, as such we could consider it a “hard set”.

Yet when the load was reduced to 40% 1RM they had to perform another 15 reps, after they had initially failed, in order to make that load meaningfully challenging.

As you can see, that low load set requires far more fatigue to be generated and thus requires far more work. This has consequences! 


Low Load Training Can be Brutal

Firstly, it elongates recovery time between sessions.

A recent study by Farrow (2020) showed that a single set of low load training with 40% 1RM took over 48 hours to recover from, compared to just 24 hours for the high load (80% 1RM) group.

This was just a single set, we might imagine a much greater effect with multiple sets, over multiple exercises. This is often a drawback of some of the research, it doesn’t always look like real life. 

Secondly, it’s more painful!

In a study involving 22 resistance-trained males, Ribiero (2019) found low load sets of 25-30 reps induced higher degrees of effort and discomfort than higher load sets of 8-12 reps.

Not many people are choosing sets of 25-30 when 8-12’s can get the job done in less time and with less discomfort.

Thirdly, it may change the stress of each exercise.

Not only will load impact the inertial effects of the exercise, and thus the relative challenge, but it will also impact the duration. This can be a big factor in exercises like bent-over rows where the ability to maintain a neutral spine for 40, 50 even 60 seconds during a low load set may now become the limiting factor compared to a high load set of 20-30 seconds. The need for greater external support and guidance may increase with low load training. 


So What’s The Takehome? 

High load and low load sets, whilst potentially producing similar outcomes, are not the same. Knowing that the tool of using external load is a versatile one that we can manipulate based on current circumstances is a profound step forward in our coaching practice, allowing us to adapt to a number of challenging situations. However, if we are to become masters of our craft, we must understand that each change to our programming brings with it a subtle change in the stress imposed on the body. As always, it’s about selecting the right tool, at the right time, for the right job. 


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