Warm-up in reference to Strength Training refers to the actual warm-up sets of the selected exercises.
Guidelines for Strength Training warm-up considerations:
The number of warm-up seat is highly influenced be the load in the first working set. If the load is high (higher intensity) then more warm-up sets may be needed.
When loading with greater the 5RM then repetitions should be consistent with the repetitions programmed. Therefore the reps should be approximately equal to the reps prescribed for the working sets and the load progressively increased towards the load used on the first working set.
When loading with greater than 5RM then repetitions can be progressively reduced as the load is increased. This allows to begin loading with the working set load without causing neural fatigue.
The exercise itself will also be influential in determining the number of warm-up sets required. A barbell squat at 5RM would require more warm-up sets then a barbell curl. In general larger compound movements will require a greater number of warm-up sets than a more isolation exercise.
Number of warp-up sets as influenced by load and reps of the work set:
To avoid residual fatigue in neural training, attempt to reduce the volume of the warm-up sets to the lesser figure as indicated in the above chart.
Below are some examples of progressive warm-up sets for different intensities or RM.