Serious mountain bikers usually choose mountain bikes with a lockout front suspension fork. But then again serious cyclists in general are more into cycling than they are into gear. What I mean is you don't have to own the perfect bike to be a good cyclist.
The lockout is a switch/lever on one of the tubes in your MTB fork that once turned makes your fork rigid. Some forks have what is called remote lockout - the lever is placed on the handlebar and thus you don't need to reach down at the fork to operate it. A cable connects the handlebar lever with the actual lockout switch on the top of the fork tube.
What Are the Benefits of Lockout MTB Fork
Having a rigid fork (suspension locked) is useful when riding uphill on even terrain. In this situation you usually get up from the saddle and push on the pedals using your own weight. If you have a regular suspension fork most of your effort dissipates in the fork itself. Instead of transforming your work on the pedals in covered distance you waste energy by allowing the fork to glide back and forth with each push you make.A rigid fork allows you to transform your pedaling into traveled distance. When riding out of the saddle you won't bounce (as with the suspension on) and you will gain distance more efficiently.
If you ride in the city and cycle in a soft manner (on the saddle) you may want to leave your suspension on as to decrease the breaking distance. Basically the same thing happens here - the kinetic energy is being absorbed by the fork enabling you to stop faster and keep permanent contact between your bike's wheels and the road.
