Squat Exercises and Leg Extension

The squat exercise and the leg extension exercise involve the quadriceps muscles, but that is where the similarities end. The squat is a compound, multijoint exercise that works several muscle groups in the lower body. The leg extension is a single-joint exercise that targets the quadriceps. You can lift significantly more weight during a squat than a leg extension.
Squat vs. Leg Extension
You can lift more weight during a squat compared with a leg extension because the squat involves more muscles. The only muscles working during a leg extension are the quadriceps, which are the muscles on the front of the thigh. The squat works the quadriceps, hamstrings and gluteus muscles. Although you can push more weight during a squat, it is difficult to directly compare it to a leg extension because you have to consider your body weight. During a leg extension, you only lift the resistance in the machine. However, during a squat, you lift your body weight plus whatever extra resistance you hold.
Ratio
The amount you can press on a squat compared to a leg extension depends on several factors, including bone length, muscle strength, flexibility, range of motion and equipment used. Strength is specific to each movement. According to the National Strength and Conditioning Association, lifters who trained on the squat exercise increased their squat weight but did not increase their leg extension weight. This means that the ratio of squat to leg extension strength will fluctuate over time based on the design of your program.
Your Ratio
You can determine your approximate squat to leg extension ratio. Calculate your one repetition maximum, or 1RM, for each exercise. You can approximate this number by attempting a 1RM lift. If you attempt a 1RM lift, start with a weight with which you can complete three or four repetitions. Add 5 percent to the weight and see how many repetitions you can do. If you do more than one repetition, add more weight, wait three to four minutes and try again. Continue until you can only do one repetition. To calculate your ratio, divide your squat 1RM by your leg extension 1RM. If your squat 1RM is 110 lbs. and your leg extension 1RM is 80 lbs., you can squat 1.375 times the amount you can lift on a leg extension.
Considerations
Regardless of the method you use to determine your 1RM, the result is only an estimate, not an exact number. If you do the lift test, the results may change on a different day depending on your energy level, sleep patterns and stress levels. If you do the squat 1RM test, use a spotter or power rack. Always warm up prior to performing any heavy lifts.