Thanks for the responses guys. One of the main reasons why I was thinking about this is that I did my first sportive last sunday (75 miles) and whilst my cardiovascular system seemed to handle it pretty comfortably, my legs suffered over the last 20 miles or so. Unfortunately due to time constraints, at present I only manage to get out on the bike for perhaps 30 - 40 miles on the weekend and once during the week. I also use a spin bike at home for three evenings per week.
My thinking was that if I were to use 10kg (5kg per leg) of ankle weights every day when I'm off the bike (for example at work), that all the walking around that I do would help in strengthening my leg muscles and as a result, make my legs more hardy for when I do the next sportive. I suppose I was likening wearing ankle weights to being able to exercise my legs whilst doing ordinary daily activities.
I think that I'll have to give the idea some more thought before making a final decision as the last thing I'd want to do would be to inadvertently injure myself somehow and as a result reduce my performance.
