外侧广肌（Vastus lateralis)是大腿股四头肌的一部分，是为大腿最外侧的肌肉也是属于抗重力肌，占整个股四头肌群最大的部分。外侧广肌的主要功能是伸展膝关节以及协同关节动作。在运动时，外侧广肌扮演非常大的脚色，包覆整只大腿的股骨。年龄增长会造成外侧广肌的退化，导致膝盖关节无法正常伸直或弯曲,站姿呈现老态。

The Vastus lateralis (/ˈvæstəsˌlætəˈreɪlᵻs/ or /ˈvæstəsˌlætəˈrælᵻs/), also called the ''vastus externus'' is the largest and most powerful part of the quadriceps femoris, a muscle in the thigh. It arises from a series of flat, broad tendons attached to the femur, and attaches to the outer border of the patella. It ultimately joins with the other muscles that make up the quadriceps in the quadriceps tendon, which travels over the knee to connect to the tibia.