Joint Action & Muscles Worked for Various Exercises

When you work out, your muscles move your joints through particular ranges of motion. Anatomists use technical terms to describe joint actions. For instance, flexion and extension refer to bending and straightening your joints in a forward and backward plane. Abduction and adduction refer to side-to-side motion away from the body and toward the body. Knowing how your joints move and which muscles are responsible will help you understand the effects of your workouts.

Lowering into a squat requires your knees and hips to flex and your ankles to dorsiflex. As you stand up, your knees and hips extend and your ankles plantar flex. The primary muscles you're working are your quadriceps, which extend the knee. Squats also target the gluteus maximus and hamstrings, which extend the hip, as well as the gastrocnemius and soleus, which plantarflex the ankles. A deadlift employs similar joint actions to a squat, but with less hip and knee flexion. In a deadlift, the muscular emphasis is on the hip extensors, especially the gluteus maximus and the hamstrings. In both squats and deadlifts, the erector spinae muscles of your back work isometrically to stabilize your spine.

During a bench press your shoulder joints adduct and your elbows extend to press the bar upward. You primarily use the pectoralis major muscles of your chest, the anterior deltoid muscles of your shoulder, and the triceps muscles on the back of your arms. Shoulder presses require shoulder flexion and elbow extension to lift the weight overhead. The anterior deltoids and triceps are the principle muscles involved. In addition, your trapezius and serratus anterior muscles upwardly rotate your shoulder blades during a shoulder press to allow your arms to reach overhead.

To perform a pullup, your shoulder joints must adduct and extend while your elbows flex. The latissimus dorsi pull your arms down, while the biceps brachii and brachialis muscles are responsible for bending your elbows. In rowing exercises, such as seated cable rows or bent-over rows, your shoulder joints extend as your elbows flex. Your latissimus dorsi muscles pull your arms back, and your biceps brachii and brachialis muscles flex your elbows. In addition, the rhomboids of your upper back work to adduct your shoulder blades.

During a situp, your spine and hip joints flex. The rectus abdominis, or "six-pack" muscle of your abdomen, flexes the spine, while the iliopsoas and rectus femoris muscles flex the hip joints. If you add a twist to a situp, you also emphasize your abdominal oblique muscles. In a back hyperextension, your spine and hips extend. The erector spinae muscles extend the spine, and the gluteus maximus and hamstrings extend the hips.