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When measuring leg strength or trying to build muscle in your lower body, two machines you may look to are the leg press and the leg curl. While there’s no exact ratio for the ideal amount of weight you should be able to lift on each, knowing the relative strength of the muscle involved — the quads and the hamstrings — may be beneficial in identifying weaknesses around your knee joints and planning your routine.


Pressing Ahead

The leg press is what’s known as a compound movement, meaning that there’s more than one joint involved. In fact, there are three joints involved — your knees, hips and ankles — as leg presses hit numerous muscle groups, including quads, glutes, calves and hamstrings. This can be a bonus and a drawback. If you’re looking to spread the load across different joints and muscles in your legs, the leg press is a good choice. If you want to isolate prime movers of the knee joint — the quadriceps — then the leg press is not your best option.

Curl Considerations

Unlike leg presses, curls focus almost solely on one muscle group and one joint — the hamstrings and the knee. Your hips remain firmly planted against the bench and your calves stay locked in position, which means your hamstrings have to do all the work. The greater degree of strain on the knee joint here can be hazardous for injury, claims Dr. Michael Yessis of SportLab. Your hamstrings must be strong to stabilize your knees, otherwise you risk injury. If your hamstrings are weak or you try to lift too heavy, all the strain is placed onto the tendons and ligaments around your knees, which may lead to injury.

Where the Ratio Falls Down

While you can get a basic idea of the strength ratio between your quads and hamstrings from finding your maximum weight on leg presses and leg curls, it isn’t the optimal way to do so. As leg presses are a compound move and curls an isolation one, it’s an unfair comparison, due to the fact that more muscles are working when you’re pressing than when you’re curling. If you’re stuck with just these two though, consider your foot position during the leg press. If you want to test quad strength on the leg press to compare it with hamstring strength on the leg curl, a narrow stance leg press will use your quads more, but also place more strain on your knee ligaments, according to trainer and kinesiologist Rick Kaselj.

A Better Option

A much more valid determinate of hamstring strength versus quadriceps strength across the knee joint is to compare the leg curl with the leg extension. Athletics coach Brian Mackenzie advises finding out your one-repetition maximum on both, then dividing your leg curl weight by your leg extension weight. Ideally your leg curl should be at least 80 percent of your leg extension, otherwise your knee flexors — the hamstrings — are proportionately weak to the knee extensors — your quads.