International Amateur Athletic Federation (IAAF) – the international governing body for track and field  

Insole – a removable inner layer of “Cushioning” above the midsole that often includes curved padding for arch support

Intensity – amount of energy and strength expended

Intervals – a workout schedule alternating running a set distance with a recovery jog 

International Olympic Committee (IOC) – the international committee governing the Olympics 

Junk Miles – slower paced miles run in order to pad a mileage total instead of increasing running ability

Kick – the faster-paced sprint toward the end of a run