45° Leg Press Machine v. Barbell Back Squat
Most regular weight trainees find they can leg press more than twice the weight they can back squat. But why? And is there a way of calculating roughly 'equivalent' weights for each lift? The 'why' involves too many factors to discuss here, but by taking just three things into account, we can come fairly close to the actual numbers for folk who regularly train both these lifts.
More specifically, suppose you have a good idea of what weight you can manage on the 45° leg press machine for no more than four or five good, deep reps. The aim is to use that weight to calculate what barbell weight you could be expected to back squat for a similar number of strong, deep reps ... or vice versa.
Here's my shot at building a formula. Starting with the leg press weight:
Multiply the total weight on the press (plates plus sled) by sin45° (which is about 0.707). This applies to all individuals because, assuming the sled has negligible friction on the rails, that's the fraction of the weight you need to push the sled with, in line with the slope, to get it moving.
Now multiply by about 85%. This is an estimated average of what strength you lose by not having your back supported against the pad. The number will vary between individuals. For example, it may be smaller if your 'core' is weak relative to your legs and glutes, or if you're simply not suited to deep squats.
Finally, subtract about 80% of your body weight because, as well as the barbell, you have to lift roughly that percentage of your body weight when you squat. Again this is an average and will vary slightly between individuals, based on their body geometry and weight distribution.
Putting these together as a formula:
Wsquat = (Wpress × 0.707 × 0.85) - (0.8 × Wbody)
When rearranged to estimate the press weight from the squat weight, the formula is:
Wpress = (Wsquat + (0.8 × Wbody)) ÷ (0.707 × 0.85)
It's fairly simplistic, but the comparison shouldn't be too far away from what you might experience.
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Example 1 180 lb person with 660 lb on the 45° leg press machine Equivalent back squat weight: ≈ (660 × 0.707 × 0.85) - (0.8 × 180) ≈ (660 × 0.601) - 144 ≈ 396.7 - 144 ≈ 253 lb Example 2: 220 lb person with 400 lb barbell back squat Equivalent leg press weight: ≈ (400 + (0.8 × 220)) ÷ (0.707 × 0.85) ≈ (400 + 176) ÷ 0.601 ≈ 576 ÷ 0.601 ≈ 958 lb Choose example weights in kg lb |
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Calculator Find approximately equivalent back squat and leg press weights (kg or lb) based on the above formula. First, enter a body weight, then either a press or a squat weight ... |
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