The short answer: Both work. Research shows that light weights (down to about 30% of your one-rep max) and heavy weights (70% or more) build similar muscle and strength, as long as you work till your reps slow down and feel challenging to complete. Heavy lifting only wins if your specific goal is a bigger one-rep max. If you’re training for longevity, choose a weight that feels challenging within 6 to 15 reps.
If you’re like me, you see a lot of fitness content on Instagram. And some of this content shows people pulsing 1 to 2 pound dumbbells for super high repetitions, while other posts show people max deadlifting for less than 5 reps.
So which is best?
In order to answer this question we have to define “best,” because this is going to vary depending on your goals.
At Loa, our goal is improving quality of life — meaning we train to increase strength and build muscle (hypertrophy) for the sake of feeling good and aging well.
So for Loa members, the “best” way to strength train is effectively and efficiently building muscle in the safest way possible.
When we look to the research, most studies point to needing at least 30% of our 1 Rep Max (1RM) and working to the point of muscle fatigue in order to increase strength and induce hypertrophy.
So let’s say you’re bicep curling a 5 pound dumbbell. Is this enough?
We want 5 pounds to be at least 30% of your 1RM, so this would make your 1RM about 16.6 pounds.
(16.6 lbs X 30% = 5 lbs )
So it totally depends. If you can curl 17 lbs more than once… then 5 lbs is most likely too light to create significant muscular adaptions.
And to be clear, this doesn’t make pulsing light weights bad! It just hasn’t been shown to be as effective when it comes to improving muscle strength and hypertrophy.
So does this mean we need to be using super heavy weights (above 70% of our 1RM) to create change?
Actually, no…
Many studies (like this Systematic Review and Meta-Analysis), show significant increases in BOTH muscle strength and hypertrophy in individuals who trained for high reps at 30% of their 1RM and those who trained for lower reps at 70% of their 1RM.
To quote the discussion of this study:
“The findings therefore indicate that both heavy and light loads can be equally effective in promoting muscle growth provided training is carried out with a high level of effort.”
The one difference that we DO see in those who lift closer to their 1RM (70% or higher) is that they have greater improvements in their 1 Rep Max…
which makes total sense due to the S.A.I.D. Principle (which stands for “Specific Adaptations to Imposed Demands”). Basically, if you want to get better at lifting super heavy, the best way to do that is lift super heavy.
But in my opinion, this isn’t the ultimate goal of longevity-focused fitness. I’m not training for an Olympic Weightlifting competition. I’m training to steadily increase my strength in a manner I can sustain.
This means as long as I’m lifting above 30% of my 1RM, I’m going to achieve that goal.
So do you need to be doing tons of math to calculate your 1RM for your workouts?
Actually, no again…
This is why we teach a mix of set lengths in Loa Movement classes, all taken to the point of muscle fatigue: 1-minute sets, 45-second sets, and 8-rep sets. Rotating through them gives you a variety of rep ranges, so your muscles get different challenges while every set stays in an effective range.
In a 1-minute set, if you average between 2 and 4 seconds for each rep, this means you’re performing anywhere between 15 and 30 reps. #math
2 seconds per rep X 30 reps = 60 seconds
4 seconds per rep X 15 reps = 60 seconds
(depending on the movement, certain reps may take longer than others).
A 45-second set lands at roughly 11 to 22 reps using the same math.
Based on this knowledge, we can use the Holten Diagram (below), showing that our 1-minute sets have us lifting anywhere between 60 and 75% of our 1RM, our 45-second sets around 70 to 80%, and our 8-rep sets around 80 to 85%.
Holten Diagram for calculating 1 Rep Max (image from physiotutors.com)
This puts us well above the 30% threshold, and takes less time to get to muscle fatigue, than say lifting right at that threshold.
So in conclusion,
If your goal is longevity (improving muscle strength and hypertrophy to minimize aging and feel your best), then choosing a weight that gets you close to muscle fatigue within a 1-minute set, a 45-second set, or 8 reps will accomplish this!
No math required!
Frequently Asked Questions About Light vs. Heavy Weights
Can you build muscle with light weights?
Yes, as long as the weight feels challenging in ~25 reps or less. Pulsing tiny dumbbells for 50+ reps is not optimal.
How do I know if my weights are heavy enough?
If you can keep going well past a minute (or 30+ reps) without hitting failure, it’s time to go heavier.
Do I need to calculate my one-rep max?
No. Taking each set close to fatigue within about one minute or less puts most people in an effective range, with no math required.
Are heavy weights better for strength?
Heavy loads build more maximal strength (your one-rep max specifically). For everyday strength and muscle, light, moderate, and heavy loads all work.
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Sources:
Burd, N. A., Mitchell, C. J., Churchward-Venne, T. A., & Phillips, S. M. (2012). Bigger weights may not beget bigger muscles: evidence from acute muscle protein synthetic responses after resistance exercise. Applied physiology, nutrition, and metabolism, 37(3), 551-554.
Schoenfeld, B. J., Grgic, J., Ogborn, D., & Krieger, J. W. (2017). Strength and hypertrophy adaptations between low-vs. high-load resistance training: a systematic review and meta-analysis. The Journal of Strength & Conditioning Research, 31(12), 3508-3523.
Weakley, J., Schoenfeld, B. J., Ljungberg, J., Halson, S. L., & Phillips, S. M. (2023). Physiological responses and adaptations to lower load resistance training: Implications for health and performance. Sports Medicine-Open, 9(1), 28.
