Yes, Sportslegs are mostly lactic acid. For years, it was known that your muscles produce lactic acid during heavy exertion, and for that reason it was blamed for making your legs sore after a heavy workout. A few years back, it was learned that your muscles use it for fuel. So all it does is provide more fuel for your legs. It'll delay the point at which you run out of gas, and taking it after the ride may help you recover better -- IF you depleted yourself.