The most common and affordable system is the chain drive system. A simple 135-lbs has left many-a strong squatter sore beyond belief. Another method go is by using your two legged bodyweight movements. take your normal squats and analysis . http://kpro.shanghaiopen.org.cn:8005/derrickperrier/topone-chain2002/wiki/Tight-Hips-And-The-Domino-Have-An-Effect-On-Training