GHD trainer used to be the iconic equipment of the gym. Few people in the gym now use it for back stretching. The decline of GHD is related to the noise it receives. These noises are all kinds of warnings issued by the mass media, claiming that traditional sit-ups have a devastating effect on the back. Some people think that the main driving force of GHD sit-ups comes from hip extensors rather than abdominal muscles, which leads to the fact that this sit-up is as bad for abdominal muscle exercise as other similar actions, and letting hip extensors pull the body has a devastating impact on the lumbar spine.