been a gym rat for 15+ years, so i've seen a # of trends come and go. around 5 years back it was ab/bosu balls. so everybody was lifting while balancing on a ball. personal trainers still use that in some of their lifts, but most everybody else gave that up. then kettleballs became the new trend. a couple of the gyms that i've worked out at ended up buying a set, but they mostly just collected dust. and i think the only thing that brought them back into the spotlight was the last Rocky movie.
the new trend i'm seeing involves free weights and surgical tubing. so they are affixing the surgical tubing around a bench or machine, and then holding both handles or hooking the handles over the free weight bar. then they are lifting with resistance from both the free weight and surgical tubing. the tubing will change the intensity of the list based on how far the tubing is stretched. i.e. the tubing would add some additional resistance to the easier part of some lifts. but getting stronger on the easier part of the lift isnt the point. anyway, messing around with the tubing seems like more trouble than its worth. add more weight and train the sticking point