After wanting to know what they are for and the reason behind using them, I found this. I thought I would share this since I am new to PL and others on this board might be as well. All I did was cut and paste this. Enjoy the read
Powerlift Assistance Exercises:
Bands and Chains
by Gary F. Zeolla
The use of bands and chains are mentioned on the Powerlift Assistance Exercises pages. This page will describe their use. The use of bands and chains are especially recommended for those who compete using squat and deadlifts suits and a bench shirt. The bands and chains mimic the effects that the gear gives and provide extra work for the top part of each lift. However, those who compete raw (e.g., without such gear) will benefit from their use as well, but such lifters should be sure to balance off band and chain work with exercises that work the bottom part of each lift.
Bands are most popularly used on benches. For this exercise, for someone benching around what I do (215 at my last contest), you need a pair of "mini-bands." These basically look like fan belts, only a little longer. They are available from APT.
To setup the bands, loop each end of each band around the bar against the inside collars of the bar so that they will be inside of the weights. Then insert a 70-80 pound dumbbell through the bottom loops. The dumbbell should then stretch the band so that the dumbbell is resting on the floor. The bands will add about 70 pounds total of resistance at the top of the lift. So just the bands and an empty bar is the equivalent of about 115 pounds.
Once the bands are set-up, bench as usual. But what will happen is as the bar is pressed from the chest, the bands will stretch and add resistance. So the effect will be that of gradually adding resistance. This is the same effect a bench shirt gives. It helps the most at the bottom of the lift but gradually helps less as the bar is pressed, so, in essence, the weight gets heavier as the bar is pressed. So bands are an ideal training method for those who will be competing with a bench shirt.
One thing to note though, if you have short arms as I do, the mini-bands might be too long for you. The bands won't be stretched out enough at the top to give the full resistance. So what I do is wrap the bands around the bar once before setting them up. This effectively shortens the bands. It is with doing so that I get the above indicated 70 pounds of resistance at the top. Those with bigger benches than I might need to use two or three sets of bands to give sufficient resistance for the desired effect.
Along with in mini-band (1/2") size, band are also available in "light" (1-1/8"), "average" (1-3/4"), and "strong" (2-1/2") sizes. Each larger size gives increasing resistance. These bands are generally used on squats. The light size is for those squatting less than 450 pounds, the average size for those squatting 450-650, and the strong size for those squatting over 650.
When I first tried using light bands on squats, I had a couple of problems setting up them up. First, you're supposed to loop the bands over the bar and then "choke" them near the floor around the bottom of the power rack or dumbbells. "Choking" means to wrap the band around the support and then through itself. But the power rack I was using was not bolted down, so I couldn't use it. So I used dumbbells. But the problem was, with as short as I am (I'm 5'1"), the bands are too long. And choking them around the dumbbells didn't do much. So instead, I had to choke them around the bar, wrapping them around a couple of times.
Second, when I set them up at a gym, I was not able to walk the weight out in the power rack. It jerked me around too much. If I had a monolift to work out with, there would have been no problem. But with only a power rack, my only option was to start in the down position, with the bar resting on the safety bars. To do them this way, set the safety bars in the power rack, rest the bar on the safeties, squeeze underneath, then squat the weight up from off of the bars. For subsequent reps, just touch and go off of the bars, until the last rep, when the bar is rested back on the bars, and squeeze out. I have the safety bars set so that I am about an inch below parallel at the bottom.
However, once I set up my home gym, I found I was able to set it up so that I could walk it out. I think the key was setting things up so you only walk it out a very short distance. It still jerks around some, but not so much as to make it unmanageable.
But using bands on deadlifts is even trickier. There are two ways to set them up, both of which require the use of a power rack. The first requires a power rack in which the bases on each side are elevated enough that you can get the bands underneath and which is bolted to the floor. You choke the bands around each base, wrapping them around three times then pull the other end over the bar. Then deadlift as usual.
However, if your power rack (like mine) does not fit this description, then you will need to use dumbbells. What I do is to put the dumbbells inside of the bases on each side of the power rack. I then choke the bands around the bar, again wrapping them three times, then pull the other end around the dumbbells. But I found this still wasn't short enough, so I had to wrap them twice around the dumbbell bars. This was easy for me to do since I use changeable dumbbells. So put the bands on first then the weights. But if you're using pre-set dumbbells, then it might be difficult to get the bands wrapped around the dumbbells. But if you can get it set up, the bases will keep the dumbbells from being pulled out underneath the weights. For conventional stance deadlifters, then deadlift as usual. But for sumo stance deadlifters, you have to put your toes in-between the weights on the dumbbells.
Another way to use light, medium, or heavy bands is in a "reverse band" fashion. For this, you choke the bands around the top of a power rack or around safety bars set near the top. You then place the bar through the loops at the bottom and place sufficient weight on the bar to pull it down into place. The bands then give the effect of a suit or bench shirt in "pulling" the bar up from the bottom position, but less so as the bar is raised.
This setup can be used for all three powerlifts. Different placement of the safety bars at the top of the power rack and/ or wrapping the bands around more than one time around the top of the rack when choking them can be used to adjust the height of the bottom of the bands where the bar is placed. The ideal is to have the band tension setup so that the bands add about what your gear adds.
Chains are great way to train and are definitely worth the cost. The idea behind using chains is similar to bands. As you lift the bar, the chains will come off of the floor gradually adding weight to the bar. This will mimic the effect of a bench shirt or squat or deadlift suit. Ideally, the change in weight from the bottom to the top of the lift should be such that it feels like the effect of your suit or shirt.
Chains are available in 5/8" and 1/2" sizes. I got the 5/8" size. The full set consists of two each of a main heavy chain, a lighter leader chain, and a metal "triangle" that connects the two. The total weight is a little over 50 pounds. So just the chains and an empty bar is the equivalent of about 95 pounds at the top of the lift. And I found the change in weight from bottom to top to be sufficient for benches. However, for squats and deadlifts, I needed to add another pair of heavy chains to get the right effect. These can be ordered separately. With the two pairs of heavy chains, the total setup weighs about 90 pounds, or about 135 pounds with an empty bar. My contest bests are 410 - 215 - 410. So this should give you some idea of how many heavy chains you'll need for each lift.
To setup the chains, the leader chain goes around the bar and then through the triangle, connecting back onto itself. The main chain(s) then hang doubled over the triangle, so that the middle of the chain is over the triangle and each half is hanging down. Loop the leader chains over the bar and hook the clasps onto the leader chains so that length of the main chain is such that at the top position as much chain as possible is off of the floor but is still touching the floor. In the bottom position as much of the main chain as possible should be lying on the floor. For a video of chains "deloading" in this fashion, click here.
As a little tip, the main chains tend to slip off of the "triangle" in the middle of the set-up. So I purchased a couple of pairs of "C-clamps" from a hardware store and use these to hold the chains in place. Also from a hardware store, I purchased a couple of clasp-type hooks (the kind used on cable machines in most gyms) to use on the leader chains. These hold better than the hooks that came with the chains.
For squats and benches the leader chains should be placed inside of the weights, against the inside collars of the bar. But for deadlifts, I put the triangles directly on the bar, placed at the ends of the bar to prevent setting the weights down on the chains. They can be kept in place by using two sets of clip-type collars, one on each side of the triangles. I still use the leader chain, hanging it from the triangle with the heavy chains just for the little extra weight.
Advantages of Bands and Chains
There are several advantages to using bands and chains over other forms of assistance exercises and even over doing the actual powerlifts with gear.
First, the point of using chains and bands is that the "feel" of the lift is very similar to doing the actual powerlift with gear. There is more tension at the top of the lift than at the bottom. Yet, they are all full range of motion exercises and thus the carryover to the actual powerlifts is greater than when doing partial movements (like board benches).
Second, chains and bands provide variety into the workout. I mention in various places on this site the importance of periodically changing your assistance exercises. This is so that your body does not adapt to a particular exercise. But by training the actual powerlifts every workout, your body will adapt to them, and that could lead to stagnation. Now one approach to try to keep this adaptation from happening is to cycle from higher to lower reps. But for various reasons, higher reps are not the best training approach for a powerlifter. But to alternate the actual powerlifts with chain and band work is a way of changing the exercise and thus to prevent stagnation.
Third, putting on a tight suit or shirt and wrapping your knees between for every set is difficult and time-consuming. So workouts with gear tend to be rather long. But setting up the chains and bands is relatively easier and quicker, so the workouts are shorter. Workouts with gear also seem to be more demanding on the body than working with chains and bands. So using the chains and bands instead of gear on the powerlifts for some of the workouts gives a break from the difficulties of using gear but still provides a similar training effect.
Fourth, when doing chain and band work, it is best not to wear any supportive gear, not even a belt. This way, the joints and low back get strengthened. However, since the tension is sub maximal when the joints are at their least advantageous position (such as the bottom position of a squat), the risk of injury is far less than it would be doing the actual powerlifts raw.