mountain biker       
noun [ C ] uk/ˈmaʊn.tɪn ˌbaɪ.kər/ us/ˈmaʊn.tən ˌbaɪ.kɚ/
 登山车手,山地自行车手
someone who rides a mountain bike (= a bicycle for riding over hills and rough ground) either in races or for enjoyment
  The trails are open to mountain bikers and hikers. 这些小径对山地自行车手和徒步旅行者开放。 
 A mountain biker on the hills had phoned, saying he was lost.  一名登山车手从山里打来电话来说他迷路了。 
 - More examples
 - For many mountain bikers, nothing beats the rush of a 24-hour race.
 - Mountain bikers need quick near/far focus to see down the trail then right back to the rocks in front of their wheels.
 - The Cascade Mountains has a year-round community of climbers, kayakers, and mountain bikers.