What is "halfway"?

This is day one of Week 10 out of 18. Today chronologically marks "halfway" in my training for Barcelona 2014. I suspect, however, that the halfway mark in a training programme is like the halfway mark of a marathon. Ahead of me lie, amongst other distances, a 17, an 18, and two 20 mile runs, whereas behind me lies an inverse taper up to 15 miles. I would guess that halfway in a marathon in terms of effort lies around the 19 or 20 mile mark. After all, if you've already expended 50% of your energy in reaching 13.1 miles, you're not going to have a happy race. Those final 6.2 miles can be nasty.

This is my week ahead:

Monday: circuits
Tuesday: 3 miles + yoga
Wednesday: rest
Thursday: 5 miles
Friday: 17 miles
Saturday & Sunday: rest

Happy running!