Double workouts - what do you do?

I'm looking at upping my weekly mileage a bit starting next month and want to do a 2x day on Wednesdays since I normally take Thursdays as a rest day. Later this spring, I might look at adding a second 2x day per week. For those of you who do some two-a-day workouts, how do you structure them? More distance in the morning, then a follow up in the evening (so say 3500 am, 2000 pm)? Or do you split them doing speed work in the morning? Looking for any ideas on how to break them up and still make them useful, not junk miles. Thanks in advance - Kari I was talking to a friend that was at the Olympics in 2012 about training, and what he said might be of interest. They tend to work a particular theme for a couple of weeks at a time - say speed or aerobic endurance. Although you do small amounts of other things in that block (to keep 'ticking along') the idea is to overload one system at a time, and let it recover, versus doing a bit of everything and getting generally fatigued. Using that rationale, it might make sense to stay with one theme, or at least make sure that if you do something different in the other session, that it isn't overly taxing - say some short, focused, sprint work mixed with technique, alongside a big aerobic set, rather than a big aerobic set then some lactic tolerance... As to "what do I do"? I don't generally!

I'm looking at upping my weekly mileage a bit starting next month and want to do a 2x day on Wednesdays since I normally take Thursdays as a rest day. Later this spring, I might look at adding a second 2x day per week. For those of you who do some two-a-day workouts, how do you structure them? More distance in the morning, then a follow up in the evening (so say 3500 am, 2000 pm)? Or do you split them doing speed work in the morning? Looking for any ideas on how to break them up and still make them useful, not junk miles. Thanks in advance - Kari I was talking to a friend that was at the Olympics in 2012 about training, and what he said might be of interest. They tend to work a particular theme for a couple of weeks at a time - say speed or aerobic endurance. Although you do small amounts of other things in that block (to keep 'ticking along') the idea is to overload one system at a time, and let it recover, versus doing a bit of everything and getting generally fatigued. Using that rationale, it might make sense to stay with one theme, or at least make sure that if you do something different in the other session, that it isn't overly taxing - say some short, focused, sprint work mixed with technique, alongside a big aerobic set, rather than a big aerobic set then some lactic tolerance... As to "what do I do"? I don't generally!