The weight doesn’t need to be heavy. But it actually does (but it really doesn’t).

How the tides have turned.  Just 10 years ago, gym-goers feared lifting heavy weights.  The assumption was that lifting heavy weights would lead to a bulky appearance and increase the risk of both acute and chronic injury.  Better to stick to light weights and do 15-25 reps. 

That was so 2005.  

In 2025, seemingly every podcaster, pundit, and author recommends just the opposite: Lifting heavy weights is THE key.  Lift a weight that allows you to fatigue by around 6 reps seems to be the widespread recommendation (especially for post-menopausal women).  

What’s the truth?

The scientific research is unequivocally clear:  The weight does NOT have to be heavy.  If your goal is muscle strength, muscle size, muscle endurance, improved bone mineral density, heart health, cognitive function, or preparing to wrestle bears, light, moderate, or heavy weights work equivalently well.  The only thing that matters is working at a high enough level of effort so that we achieve muscle failure (or come very close).  5 reps with a heavy weight, 15 reps with a moderate weight, or 35 reps with a light weight will all produce the same benefit.  

“You need to lift heavy weights” is a myth. But in reality, most people should probably…. Lift heavier weights.

Why?  

Because when you use a weight that is light, you are not likely to get anywhere near muscle failure.  The average gym goer self-selects a weight that is far too light to actually ever reach failure.  Of course, that weight will work; but they have to keep going, 1 rep at a time, and eventually get to 47 reps.  Most people don’t do that.  Additionally, it turns out that using a lighter weight and doing more reps is more uncomfortable (more muscle burn) when compared to lifting moderate or heavy weights.  The burn of lighter weights precludes us from getting to muscle failure.

So as a practical recommendation, we might want to consider lifting a heavier weight.  

Caveat:

The one exception to this is the case of training for a powerlifting competition in which one performs a 1-rep max in a bench press, squat, or deadlift.  In order to refine the neuromuscular skill of lifting a heavy weight, we need to actually practice lifting a heavier weight in our workouts (just like shooting free throws makes you a better free throw shooter).  If your goal is to get incredibly strong, (wrestling bears, playing NFL football, etc.) you don’t need to lift heavy weights.  If your goal is to do a 1-rep max, then you should practice lifting heavy weights.