To improve grip on Bar or rope, kids at Technics Gymnastics dab their hands with a sticky cloth.
Gorilla Gold Non-toxic Grip Enhancer For use on hands, gloves and grips for many sports. Clean alternative to pine tar. Effective on wood or aluminum bats. Ideal for wet grass or sweaty hands when fielding. Non-toxic. Approved by MLB, PGA, LPGA, NCAA Softball, ISCl, ASA and USTA. Resealable bag. One cloth. Cloth lasts 3-6 weeks.
The first time I’ve seen that product in a gym.
Gymnastics Coaching.com 