I weight train 2 days on, one day off. The off is for recovery. After doing legs at noon, I sometimes spin on the bike or light run later that day at about 5 p.m. Partly because I want to maintain other sports but also I think it helps remove lactic acid buildup and I'll be less sore the next days.

Comments from others with experience? Can I do a run later the same day after doing a legs session or do a paddle later the same day after a shoulder or back session?

Turns out that lactic acid isn't really the enemy -- it actually provides energy to the muscles. But that's besides the point.

The key is that you need to have recovery days. So if you double up on legs one day (by both lifting and running), try taking it very easy on legs the next day, and just do upper body weight lifting. It also depends on your age and fitness level, but everything I've read stresses the importance of recovery/rest days.

Yoga is fantastic for lightening the lactic acid buildup...A good class will make you sweat unlike anything else...it's great for your digestion and metabolism and for recovery. Plus you sleep incredibly well after a good class.

In the swimming world it is conventional wisdom that "active recovery" between sets is more effective than just resting. Moving the muscles promotes blood flow in the muscles and flushing out accumulated waste byproducts.