Injuries while running... Running faster increases possibility of injury, so when you are going to run faster, subthreshold isn't that much less than threshold. Run shorter time at threshold, instead of longer at subthreshold reduces risk. Cycling at subthreshold allows you to go further without increasing your chance of injury (assuming good bike fit).

I'm not a Dr. or coach, just information based on what I've read and been instructed.

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Not a coach. Not a FOP Tri/swimmer/biker/runner. Barely a MOP AGer.
But I'm learning and making progress.