Kettlebell swing. A compound exercise, great for cardio circuits and strengthening the posterior chain. Target muscle: Gluteus Maximus. Synergistic muscles: Hamstrings, Adductor Magnus, Soleus, Quadriceps (Rectus Femoris, Vastus Lateralis, Vastus Medialis, Vastus Intermedius), Erector Spinae, Middle and Lower Trapezius, Anterior Deltoid, Lateral Deltoid, Clavicular (Upper) Pectoralis Major, and Serratus Anterior.