Run-up and Step up

Run-up noun - A substantial increase over a relatively short period of time.

Step up and run-up are semantically related. In some cases you can use "Step up" instead a verb phrase "Run-up".

Step up verb - To make markedly greater in measure or degree.

Run-up and step up are semantically related. Sometimes you can replace phrase "Run-up" with "Step up", this terms are similar.