Im not sure how ISU went from one of the least injured team for CPR's first 3 years to the most in his last 2. Its really strange. That being said, Sams injury does not have much to do with conditioning.
IMO it has a lot to do with # of reps. Young team equals needing more reps in practice. Veteran team less reps needed. It's probably over simplifying things but as a former coach I worked young guys harder to get those reps in. Just a theory.