Which of the following is an example of a compound exercise?

A compound exercise is characterized by the involvement of multiple muscle groups and joints working together to perform a single movement. Squats are a prime example of a compound exercise because they engage several major muscle groups, including the quadriceps, hamstrings, glutes, lower back, and core. This multi-muscle engagement not only enhances strength but also promotes stability and functional movement patterns, making it an effective exercise for overall fitness.

In contrast, the other options focus on isolation movements. Bicep curls primarily target the biceps without significantly engaging other muscle groups. Plank holds are static and primarily target the core muscles rather than involving multiple muscle groups in a dynamic manner. Similarly, leg lifts primarily isolate the hip flexors and lower abdominal muscles, lacking the multi-joint engagement that defines compound exercises. This distinction helps in planning balanced workouts that include both compound and isolation movements for comprehensive strength and conditioning.