Esther is $83$ years old, lives by herself and is quite independent.$$She relies on the bus and train for transportation, does her own shopping and house cleaning, and does not need assistance to do errands or to attend regular appointments $($ie$,$ at the doctor's office, hair dresser, etc.$).$Esther comes to you for resistance training instruction to maintain her independence.$$You work at a commercial exercise facility with an entire room of ~$15$ different weight machines that have fixed weight amounts $("$plates$")$ that can be adjusted using a pin to set the number of plates to be lifted.$$The facility is heavily used throughout the day.

Given this set up$,$ which of the following could be a barrier to using the weight machines for Esther's program?