There are many ways to assess knee function after anterior cruciate ligament (ACL)repair. Range of motion, function, and strength are the main tests. The single-legged hop test is an accurate test of power. It's a good test to compare one side to the other.
The test is done by having the patient hop as far as possible just on one leg. The patient's arms are fee to use for balance while taking off and landing on that foot.
Number of feet hopped is measured and compared to the other side.
At six months post-op you should have no problems completing this test. You should be concerned if you're leg is giving out from underneath you during regular walking or other activities. If you've followed a standard rehab program you should have stressed the knee like this during your exercise program.
Talk to your therapist about your concerns. Perhaps you aren't ready for this test and
need some more time to progress your exercise program. You can certainly practice hopping under the therapist's supervision. Most clinics have a pair of parallel bars you can use to hold on to during practice sessions until you feel the confidence you need to complete