If you prefer to have your legs covered, MTB trousers are comfortable on the bikes and offer a good on the bike fit for easy riding and efficient pedalling. The fit tends to be slim to stop unwanted flapping about, but their technical fabrics and cycling specific cut ensures unrestricted movement on the bike while leaving room for knee pads.
One of the main benefits of trousers over shorts is that they keep your legs warm dry and clean when riding wet trails, ensuring at the end of a ride, that all the mud goes with them instead of staying on your legs.
Stretch in the fabric is essential for allowing you free movement on the bike while maintaining an efficient slim fit. Stretch panels in key areas give you all the movement you need but higher end trousers offer more overall stretch for improved comfort on the bikes.