What else should be considered? The type of runner. Resistant types or slow twitch runner tend to have less problems or struggle less at running at half marathon pace than speed types or Fast twitch runners, who tend to struggle a lot more with half marathon pace and tempo work.... Nevertheless, any runner has to eventually build up to this type of work out (3X3 miles) using an extension of reps at half marathon pace and other work outs near this intensity or pace... Training individuality is another issue. Coaches have to identify the individual qualities (strengths & weaknesses of his athletes) and develop a plan that will suit each individual....