There are two considerations to this question. How easily do you get bored with a routine? Your muscles will adapting to the status quo of an exercise routine.

Muscles will adapt to the specific load placed on them. This also means to the lack of load like sitting on a couch.
A good trainer will change your routine every few weeks to challenge your muscles in a different way. That change can be a new weight level, a different exercise for the same muscle, include multi joint exercises to incorporate more muscles and a new exercise equipment such as an exercise tube instead of a free weight.

Our trainers provide a different exercise routine for each session. This insures that you are not getting bored with the same routine nor do your muscles stop adapting to new stimuli.