In the new episode of 'GYM JONG KOOK,' NCT 127 members Taeyong, Jaehyun, and Jungwoo appeared as special guests to get some tips from Kim Jong Kook.

In the video that was released on February 2, Taeyong confessed that he has a bad back that causes so much pain that he dealt with paralysis in his legs. 

On this day, the NCT 127 members revealed that Kim Jong Kook's YouTube show was the first show they appeared on to promote their new repackaged album 'Ay-Yo.' Kim Jong Kook asked, "Did you guys volunteer to appear on this show?" 

Taeyong replied, "I actually volunteered," and continued, "I have a really bad back. It's so bad that I have paralysis in my legs."

Kim Jong Kook shared, "I was part of a dance group since I was young, so I also was often hurt (in pain) and overcame it. I completely empathize with you, as I have had many similar experiences."

Throughout the rest of the video, Kim Jong Kook gave detailed advice on working out and watched the members' forms while exercising.