Testing Quadriceps Strength
Key point: Testing your quadriceps strength can vary based on what you have available to you as well as what phase you are in.
There are multiple valid testing methods for quadriceps strength. Whichever method you have access to, is easy to perform, and you can do consistently during your rehab, is the one you should perform.
Isokinetic Dynamometer
This testing is only available at speciality clinics. For ACLR rehab, it measures quadriceps force output by exposing the leg to a constant angular speed with variable resistance, and is best done with the Leg Extension. If you are working with a clinic that has access to this device, the clinicians will know how to operate the machine to produce repeatable, accurate results.
Isometric Handheld Dynamometer
This is a simpler test that most clinics can implement. Handheld dynamometers like the one shown are much cheaper to buy and are reliable if the setup to do the test is reproducible. In this test, the athlete simply flexes their leg at 90 degrees as hard as they can for a set amount of time, and the peak force measurement is recorded. Remember, this test is only as good as the setup used to conduct it! If the variables such as the length of the strap or the material of the strap (uncomfortable strap could lower force output due to pain) change, the test won’t be valid.
One Rep Max (1RM) Calculator
This is a much simpler method for testing and requires no devices. Only access to a gym. Those who have done strength training before might be familiar with 1RM testing. Two common exercises are used for this test:
Single Leg Leg Extension
This is the gold standard. It is highly recommended to use this exercise for the test when possible. There is no way to hide strength deficits using this test.
Single Leg Leg Press
If the Leg Extension is not feasible for any reason, this is your next best option. The most important aspect of testing with this exercise is to ensure the feet are low enough on the pad that the quadriceps are the main muscle used to perform the movement. If the feet are placed up too high, the glutes become much more involved in the movement. Not being mindful of this can lead to an overestimation of quadriceps strength, leading to premature milestone completion. Better to underestimate strength with too strict technique during rehab than to overestimate strength with inattentive technique.
In this phase, performing the exercise to 90 degrees range of motion is enough for the test. Going lower is good for muscle development, but the joint might get cranky, especially during a max effort test.
If selecting this exercise, make sure the weight is recorded properly! Depending on the machine used, it should be the weight of the sled that holds the weights AND the weight you add.
Execution
The instructions here apply for this particular phase. AVA will provide you with new instructions for 1RM testing as your knee’s capacity increases.
First, perform a general warmup. Medium-intensity cycling for 3-5 minutes should raise your body temperature and activate your leg musculature enough to prepare you for your test.
Once you have selected an exercise, perform a light warm up set with about 50% of your estimated 1 RM. This is something you’ll have to feel out your first time doing it.
Then, on the next set, use 60-80% of your estimated 1RM, and do as many reps as you can. If you perform more than 10 reps, up the weight by an amount you think you can hit 10 reps with. Rest for 3 minutes, and then try one more time.
Only repeat this test one or two times. 10 rep testing can be fatiguing and can interfere with the results. It’s okay if you don’t hit 10 reps with the final attempt. That number is still usable. However, any number above 10 reps is not, so aim to hit 9-10 instead of 11 or 12 reps.
Calculation
Plug your numbers into a 1RM calculator to find your “estimated” 1RM. Use this number and the LSI equation to calculate your LSI.