It's a tough balance.

In my workouts, my trainer and I agree that I SHOULD focus MORE on muscle-TONE rather than muscle-BULK.  When exercising, more repetitions enhances muscle-TONE.   Conversely, heavier weight causes greater muscle-BULK.   I'm trying for greater TONE.  But, I'm ALSO trying to improve my ENDURANCE, because I've noticed that FATIGUE tends to set in rather quickly during my Physical Therapy.  So, with "more reps", I'm actually trying for TWO GOALS.  Long story short, my trainer INSISTS that he's noticed some improvement on my ENDURANCE AND overall STRENGTH.   YAY!