No, not the thing that fire fighters carry on their trucks (or appliances as they are actually called). Not even the agility ones that you see people using to do SAQ (Speed, Agility and Quickness) drills with. Ladders are a great way to organise a Small Group Training (SGT) class or your own training session.
A ladder is simply starting at 1 rep of a movement (or movements) and then doing 2, 3, 4 etc usually up to 10 (it can be done in reverse, 10 - 1), but the desired number is up to you and how much time you have (not to mention the complexity of the movements you choose). You can do every movement you choose in a ladder format or one or a few. It doesn't matter. What matters is they usually keep your and your clients minds focused on the session they're doing and they are a great way to increase the total volume of reps. Before we move forward I would like to mention that this format should still match the desires, needs and abilities of your client and their ability that day (how much stress, how much sleep, nutrition, hydration etc...). If they are ready for it a ladder is great way to challenge clients whilst letting them self select their intensity. If you would like more information on SGT training and how to do it well visit PT Academy and look at the Bridging Course, there is lots of great information on training not only 1 on 1 clients but how to apply it to group sessions as well..
Any number of different fitness tools can be incorporated into this format and you can format the movements to suit a variety of client styles. You can use traditional, hybrid and progressive movements in the session to help all client styles feel safe and enjoy the session.
Going from 1 to 10 is a great option as it achieves; 1. Practicing the movements without being fatigued (reps 1 - 4). 2. giving people a sense of mastery for the movements (reps 5 - 7) 3. A feeling of fatigue by doing the movement which some clients really like (reps 8 - 10). 4. A sense of accomplishment by finishing the session or if they have done it before by getting further in the count than last time.
I'm sure you could come up with lots of different variations of movement for the ladder format but one of my favourites at the moment is:
TRX Atomic Push-ups
ViPR Lateral Bounds (oh yer, because its one leg at a time, you have to double the reps :D)