How do you accurately measure leg length?

[big booty]

I think my left leg is slightly longer than my right leg. How do you accurately measure leg length? Just with a tape measure from ground to hip bone? Or some other point? Can you then put some sort of packing under one cleat to compensate for the shorter leg?

[NeillS]

I've been doing it for a long time and even I sometimes get it wrong in the clinic, it's suprisingly hard. Tape measures are useless. The only 100% accurate way is with a standing leg length xray taken with knees locked into extension and arms stretched out over your head towards the ceiling, or with a CT scan. I prefer the single image as it's less radiation for the punter. Locking the knees and stretching the body removes most of your postural controls from the situation and usually gives an accurate measurement to within 2mm or so.

Adjusting for the LLD requires cleat shims and longer bolts. Anything over 6-8mm and I start pulling the cleat back a little on the shoe to negate the rocking torque from the shim stack.

[trailgumby]

CT scan. I have a 5mm difference: 8mm right femur and 3mm left tibia. Not really enough to justify shimming.

[big booty]

Thanks guys. Not sure I can justify a xray or CT scan. Thought there might have been an "easy" method. If there really is a difference I don't think its large so was hoping there was a quick and easy way of measuring the difference.

[NeillS]

most riders will eventually pull up with a niggle, a pain or a proper injury if doing enough distance, at enough intensity, with enough fitness (fit riders push harder on the pedals and create larger forces) with anything more than 4mm or so difference. There are exceptions to every rule though - I've seen riders with a 15mm difference who had no idea it was even there!

[Davobel]

Did you have someone set you up on your bike? They should be able to see if your pedaling stoke is even. I'm a chiro and I've been checking people clinically for years. There are lots of different factors that can account for a difference but is that difference anatomical or physiological? I've had patients with differences (physiological) of 35+mm and walk out less than 10mm. But there are so many variations with the +15,000 different people I've check in the past 25 years that to give you a simple answer is impossible.

[big booty]

Ive set the bike up myself (with some helpful Q&A emails with Steve Hogg). I think Ive gotten close as it feels pretty good. I noticed however that while my right knee was pointing straight ahead while pedalling my left knee was pointing slightly outwards. I put this down to perhaps one leg being longer than the other. But now Im not sure if this is the case. Ive been actively training the left leg to point straight ahead, so perhaps it was more to do with a bad habit I had formed rather than a physiological reason.