I have been given a cheese-master quality york home gym which I have been using the past while for my strength training in the off season. The leg extension portion of the machine is low quality and uses weights placed on a pole which is welded onto the bottom of the main tube as opposed to a cable and weight stack. To compound the shoddy gym, I of course have sand weights which are quite a bit wider at the hole than metal weights. Due to the length of the pole on the leg extension portion, and the wide weights, I am only able to get 50 pounds of weight on the machine. This however is not enough. I was wondering if anyone knew if it would be safe to put both legs around the pads like normal, but lift with one leg and leave the other on the floor. Are there any joint and or muscle issues with this? Thanks for your time.

I think doing single leg extensions are fine as long as you use proper form and exercise both legs to avoid inbalances.However heavy extensions are not a particularly safe exercise on the joints in any form particularly in the lockout position where maximum stress is on the knee(so I would avoid the lockout full extension position if you do go heavy).There are better freeweight exercises to go heavy on for strength saving extensions for warming up or detailing.Have you considered just buying the less bulky metal weights to allow more weight on the notch?

Yes, I have considered metal, but I would rather put the money into the bike (i'm a student, I'm sure you know how that goes. Now that I'm thinking about it, I haven't really done much research, how much do they cost???) Sorry for my lack of lingo knowledge, but what is the lockout position? (one leg on the floor???) Thanks again.

I think you can get them new for 30cents/lb if you shop around but can often get real steals from garage sales etc.When you extend the lower leg all the way up so that it is parrallel to the upper leg that is lockout and at that point significant weight is taken off the muscles onto the knee.So if going fairly heavy for strength consider stopping just before parrallel.

Lifting with one leg for single leg extensions is safe, if you remember that you should only do them with light weight and always proper form. If you go too heavy, you can do some serious damage to your knee(s). I do single leg extensions at the end of my leg workout just as a "finishing" exercies and when I do them, I never use more than 50lbs and I always concentrate on flexing my muscles at the end of the lift. I have weak knees and this exercise has worked wonders for me.

I agree with Dipper here ie with a light weight a full flex even holding the burn will strengthen the knee and surrounding muscles while this same technique with a heavier weight will do serious damage.

I do leg presses with one leg. Alternating the leg with each rep. Simulates riding and teaches you to create more power with a single leg's exertion rather than relying on two.

Single leg extensions on a flimsy machine will put added shear stress on your knee capsule, over and above what leg extensions already put on your knees (which is considerable).

Have you tried things like single leg bodyweight free squats, split lunge walks etc?