Strength for me, as a runner size is not important, working the core and having the strength to run with bags etc is vital. This year I am training my legs big time, something I've never done before but my trail runs are getting harder as the years go on lol

Oh and Speed
That's just me though

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There's no such thing as bad weather, only inappropriate clothing. Sir Ranulph Fiennes

If you're going through hell, Keep going. Winston Churchill