Long story short, a meta-analysis of 10 placebo-controlled studies of glucosamine and chondroitin (together or separate) showed no benefit in osteoarthritis. (H/T Neurologica Blog.) I posted about glucosamine before, based on earlier data consistent with this result.
Granted, "it doesn't help arthritis" isn't the same as saying "it doesn't help runners' sore and stiff joints."
But if you had to make a bet, and take this new information into account, which way would it sway you? And how confident are you that these two supplements can help you?
The kicker is, you are making a bet with your hard-earned money, every time you buy glucosamine or chondroitin. The supplement business is a huge, multi-billion dollar a year industry, and they're not interested in letting you know when their products have been shown to be snake oil. So remember this study, and save your money for better gear. Eventually there probably will be a study directly on either joint function or pain in otherwise healthy athletes. Want to make a bet on what it'll show?