Older adult after knee injury - leg strength imbalance

[Ondrej.Petrzilka]

Today at gym, my 72-year old friend asked me for an advice: How to "fix" his right leg strength? (more below)

He's an older guy, rather thin, physically active, visits gym twice a week, enthusiast skier (Alaska freerides )
The need for fixing his leg/knee comes from his love of skiing.

His lifts:
bodyweight chin ups for 3 reps (chin over bar)
50 kg bench press for 5 reps
30 kg overhead press for 6 reps
bodyweight BOSU ball squats for 20 reps
70 kg leg press for 16 reps

When he tried doing single-leg leg-press, this was the result:
60 kg left leg press for 10 reps
10 kg right leg press for 10 reps !!

Similar imbalance is apparent on leg curls and leg extensions (tried that to see whether it manifests on curls as well, not part of his training routine).

He had right knee injury in past (years) and other issues few month ago which involved liquid removal and some injections. He used Knee orthosis for some time in past (still has it at home).
He also had left ankle injury which resulted in limited ankle mobility. On stairs, right leg gives him some issues, otherwise walks fine. Both of his legs appear to carry similar amounts of muscle.

He can leg press without pain. He's doing BOSU squats to "be able to ski next winter", his toes are way below his heels, his center of mass is more on left.
Not sure if he's able to squat normally due to his ankle mobility.

How would you approach this?

[neilc1]

start with an empty bar (?)

[Will Morris]

Today at gym, my 72-year old friend asked me for an advice: How to "fix" his right leg strength? (more below)

He's an older guy, rather thin, physically active, visits gym twice a week, enthusiast skier (Alaska freerides )
The need for fixing his leg/knee comes from his love of skiing.

His lifts:
bodyweight chin ups for 3 reps (chin over bar)
50 kg bench press for 5 reps
30 kg overhead press for 6 reps
bodyweight BOSU ball squats for 20 reps
70 kg leg press for 16 reps

When he tried doing single-leg leg-press, this was the result:
60 kg left leg press for 10 reps
10 kg right leg press for 10 reps !!

Similar imbalance is apparent on leg curls and leg extensions (tried that to see whether it manifests on curls as well, not part of his training routine).

He had right knee injury in past (years) and other issues few month ago which involved liquid removal and some injections. He used Knee orthosis for some time in past (still has it at home).
He also had left ankle injury which resulted in limited ankle mobility. On stairs, right leg gives him some issues, otherwise walks fine. Both of his legs appear to carry similar amounts of muscle.

He can leg press without pain. He's doing BOSU squats to "be able to ski next winter", his toes are way below his heels, his center of mass is more on left.
Not sure if he's able to squat normally due to his ankle mobility.

How would you approach this?

Unilateral exercises will rarely bring about the changes you desire. In almost all cases, loading the movement in a symmetric, bilateral approach will bring about better improvements. You take advantage of the cross-over effect and the body's desire to be symmetric.