In recent years, however, some health specialists have begun to apply the terms "well" and "wellness" only to those who are actively striving to maintain and improve their health. (06.12 Passage 2)

　　主干：some health specialists have begun to apply...

　　主句部分，不定式to apply...用作begun的宾语。apply...to...表示“把......应用于......”，句中表示“把well和wellness这样的词只用来指那些人”。who引导的定语从句修饰those。

　　译文：然而，近些年来，一些健康专家开始把“健康”和“健康状况良好”这样的字眼只使用到那些积极努力去保持并改善自身健康状况的人身上。