speaking from personal experience: i added sprints to the bill starr 5x5 and tried to do it as carefully as possible… but it lead to overtraining. The bill star 5x5 just has too much heavy lifting to add psrints to it IMO… you should maybe look into westside for skinny bastards or a conjugate split which allows for more flexibility. Eitherway… you generally want to be sprinitng on your weights days, and in between weights do low intensity work (ie tempos, cardio) or rest.
We know you’re 15, but what are your training goals? For our college age athlete, we don’t even have them run ANY sprints until mid June. They’ve just completed spring ball, and the upcoming season is brutally long. This is going to be a big weightlifting phase right now, with emphasis on increasing strength & size (like many 15 year olds might need…) Your B. Starr workout should be fine for an average 15 year old…the westside modifications would be fine as well at this point.
Then, as we turn to power / speed-strength mid summer, we’ll start running.
5x5 is fine. Just adjust the weights to allow for sprint work as well. If you go heavy Mon and Fri, with Wed. focused on form and “easy speed” in the reps you should be fine. Just make sure your weights on 5x5 aren’t too high, ESP. if you have to lift first.