Accommodating resistance (Why it works)
Accommodating resistance involves the usage of an added piece of equipment (bands or chains) to increase the resistance of the load throughout the range of motion.
Accommodating resistance is often praised for its ability to fit (somewhat fit) exercises to strength curve of a movement (1). For example, if you had a maximal squat of 400lbs, it would simply mean that at your weakest point of your movement you could lift 400lbs (A one rep max is a representation of the maximal strength of your weakest position). So, theoretically the points at which are not considered your sticking point might actually not be having to produce maximal amounts of force and therefore you might be leaving some strength on the table. This is kind of true, you can probably un-rack twice as much weight as you can actually squat, so technically at the top position of a one rep max you are not working at 100%. However, this brings up two questions…
1) If you do use accommodating resistance, you are going to have to reduce the total bar weight (obviously cannot have your 1rm on the bar plus accommodating resistance), which in turn will jeopardize the amount of tension that is actually occurring at other regions in the movement, especially regions before the sticking point. No matter how you twist it, whether it is at the top of the movement or the bottom, you are going to be leaving some level of strength (maximal tension) on the table unless you have some sort of isokinetic device.
2) Is an accommodating overload at the top even applicable/useful to add for max strength work? Maybe, for a powerlifter (especially those that are geared), but for the common athlete, maybe not (not a whole bunch of research pointing one way or the other).
So, maybe Max Strength isn’t best used with accommodating resistance **Unless used with highly trained individuals who need such variability to improve technique and variety** (I am a huge fan of Westside Barbell and think what they do for their sport and the world of strength and conditioning is greatly understated ), but I do think it is best suited for power development, especially speed-strength and strength-speed.
Why to use it?
During a normal barbell movement (non-ballistic), the athlete accelerates the bar from the bottom position to the top. At the top position, the bar is no longer moving, which means the athlete had to decelerate the bar at some point. Depending on the percentage of 1 rep max, the bar may decelerate for different periods of time. For example, a heavier weight will have a longer acceleration phase than a lighter load. This is where accommodating resistance can play a large role.
Accommodating resistance can actually increase the amount of time the bar acceleration occurs for. For example, when using a light load (~50%) for power development, without accommodating resistance the deceleration phase is nearly half of the movement. However, the usage of accommodating resistance will increase the amount of time the athlete will accelerate the bar via increasing the mass/band tension being lifted throughout the entire range of motion. Why is this important? Increasing the amount of time the athlete can accelerate the bar means you will have a greater range of motion working to produce a positive acceleration and more total muscular activation. It also means that a greater acceleration phase will allow for greater average velocities to be achieved and therefore greater average power outputs for a given percentage of 1rm
Accommodating resistance is a good way to teach an athlete what it feels like to aggressively accelerate a bar. Often young, relatively low trained athletes do not know what it means to exert a force into the bar. One of the safest ways to teach this without having them perform a one-rep max is through the usage of chains, not bands. The chains allow for much more stability than bands (when set up properly), and teach the athlete to drive the bar upward without having to load the deep positions (typically weakest point) of the squat.
Working around injuries
Accommodating resistance can also be used to work around injuries. From elbow pain to knee pain, accommodating resistance will allow the load at vulnerable ranges of motion to be minimized. An example of this can be seen with skull crushers and tricep extensions. With free weights, the elbow is put in a very uncomfortable, limiting, and vulnerable position. Accommodating resistance allows the proper loading through all ranges of motion, without having to jeopardize your weak positions.
Strength curve (1) Zatsiorsky, V., and Kraemer, J. (2006). Science and Practice of Strength Training. Champaign, Illinois: Human Kinetics