One of the most confounding things about recovering from ACL surgery is how difficult some very simple actions become.
Take, for instance, jumping and bending the knee.
I anticipated that it would be hard for me to bend my leg in the first few weeks after surgery. (It's shocking how much enthusiasm the physical therapists, who in my clinic all seemed like the girl next door, put into bending my leg to its extremely painful limit!)
However, I didn't anticipate that, a few months later, it would be difficult to support my body weight while bending my knee. Even just a little bit.
One of the first ways you notice this is how difficult it is to descend a stairway in normal, "reciprocal" fashion (right leg goes down a step, then left leg). This is something you feel long after you've begun walking again without a brace.
One of the exercises my physical therapists gave me later in my five months with them was to stand on a step or platform, weight on the recovering leg, and simply bend the knee enough that your other heel touches the ground. It's almost embarrassing how difficult it is to accomplish. As the exercise progresses, the therapist raises the platform higher.
Now, I don't know if this diffculty is unique to having gotten a patellar-tendon graft, rather than an allograft or hamstring graft. But I have a feeling it affects all types of ACL surgeries to some degree.
The most frightening thing my therapists asked me to do is to jump a couple of inches off a platform and land on my recovering leg. (This is clearly an advanced level of PT.) My therapists said it's very common for people to feel afraid about this. For one thing, before surgery, if you jumped and landed on your knee, you would collapse painfully because your knee was unstable. For another, you've just been through the most painful period in your life, centered on this knee--so you're very protective of it. Here again, part of the issue is you need to bend your knee to absorb the shock when you land, and that's hard to do.
I got my surgery in late March, and today I'm walking stairs reciprocally without limping or needing to hold onto a rail. But truth be told--this speaks to Michele's point about it taking up to a year to get your strength back--I still feel a little weaker in my left knee walking down stairs.