Speed sessions.

[Deleted User]

Hi all,

 i'm fairly new to running and i'm following a beginners marathon program to build a decent base to work from.
I've keep reading aboutthe importance of things like speed sessions and hill work and have a question.

How early should a runner start doing such sessions & how do i integrate these sessions into my weekly routine.

For example - if my weekly plan says ......4 - 5 - 4 - 6.....when do i do the speed session.
Do i do it as part of one of the short runs? And if i do, do i make up the miles with my warm up/warm down ?

 Also - what is 'fartlek' training ?

 Many thanks

 Neil