The short answer
Keep your main lifts for four to eight weeks at a time, or for as long as they keep moving. Change accessory exercises whenever you like, even every session. Change the whole structure, such as your split or the number of days, only when your week changes or the current one has stopped working.
Main lifts: keep them long enough to compare
Squats, presses, rows and deadlifts are where you measure progress. Changing them every week means you never build up comparable numbers. Keep each one for a block of several weeks, and change it when it stops moving, not because a date has passed.
Accessories: vary them freely
Curls, raises, rows on different machines and other smaller exercises can change often. Swapping a cable fly for a dumbbell fly keeps training interesting without losing much, because the main lifts still carry the progress.
Signs it is time to change
- A main lift has been flat for three or four sessions while you are sleeping and attending as normal.
- An exercise keeps causing discomfort. Swap it, and get it checked if it continues.
- You regularly skip a session or put off starting one.
- Your available days or time have changed.
Signs it is too early
- You have had one bad session.
- You are bored after two weeks, but the numbers are still going up. Change the accessories, not the main lifts.
- You came back from a break and the first sessions feel heavy. Give it a week or two.
An example
You have done the same four-day upper and lower routine for ten weeks. Squat and bench are still improving; overhead press has been flat for a month. Keep the squat and bench. Swap the overhead press for a seated dumbbell press in a higher rep range, change two accessories you are tired of, and review in four weeks. For how to make the change itself, see refreshing a gym routine without starting over.
How Kit helps
Kit keeps to the routine you chose while varying the exercises from one session to the next, so accessories stay fresh without you planning it. Its exercise charts show when a lift has gone flat, and you can swap any exercise you do not want.
