RSI or 'Reactive Strength Index' is a simple division of the calculated Jump height by the previous contact time for that jump.
In simple terms if two athlete have the same jump, lets say 80cm, yet athlete one has a contact time of 250mS, and athlete two is 300ms, it stands to reason that Athlete one has the more powerful jump (given equal body weight)
Thsi measure has no units, hence we call it an index.
- Athlete one 0.8/.25= 3.2
- Athlete two 0.8/.30= 2.67
The higher the index, the better the jump.