The American College of Sports Medicine advises adults to do resistance training for each major muscle group two or three days per week. But if you're a novice exerciser or new to weight training, identifying major muscle groups and which exercises work them may be a conundrum. Looking at your body in segments and categorizing muscles by the movements they perform can help you decipher the mystery of weight training and set you on your way to a better body.
Working the Trunk
Your trunk muscles support your spine and vital organs, so keeping those muscles strong is essential for optimal health. At the top of your posterior trunk, your trapezius lifts your shoulders toward your ears. At mid-back, your latissimus dorsi and rhomboids retract your shoulder blades and squeeze them together, and your erector spinae muscles support your mid and lower back. Do shrugs for your traps, pull-downs and rows for your lats and rhomboids and back extensions for your erector spinae. At the front of your trunk, your pectoralis major and other lesser muscles bring your shoulders toward the front of your body; do pushups and bench presses. Your rectus abdominis flexes your trunk forward, your internal and external obliques rotate and stabilize your trunk, and the deep muscles of your core stabilize your pelvis and low back. Do crunches, cross-over crunches, trunk rotations and front and side planks.
Building the Upper Body
Your upper body extremities include muscles that move your shoulder, elbow and wrist joints. Your deltoid and triceps muscles work together with the muscles of your chest to produce pushing movements. Your biceps work together with your back muscles to produce pulling movements. These muscles work together with the muscles of your chest and back in exercises such as rows and pushups, but you can isolate them by doing overhead dumbbell presses and lateral raises for your deltoids, and elbow extensions for your triceps. Work your biceps with dumbbell curls, and your wrist extensors and flexors with pronated and supinated wrist curls.
At Your Hip
Your gluteus maximus and hamstrings work together to extend your hip, as when rising from a sitting position. Your hip flexor muscles lift your knee toward your chest. Your abductor muscles lift your leg to the side and your adductors bring it back toward your midline. All of these muscles work together with your core to hold your pelvis in place and maintain correct spinal alignment. Do squats and bench step-ups for your hip extensors and flexors. Do side-lying or cable leg lifts for your inner and outer thighs.
Knee and Ankle Action
Your quadriceps and hamstrings cross over both your hip and your knee joints. Your quadriceps extend your knee and work with your hip extensors to rise from sitting. Your hamstrings bend your knee and help extend your hip. Your calf muscles make you rise up on your toes, and your anterior tibialis lifts your toes toward your shin. Do squats and lunges for your quads and hamstrings, then isolate them by doing knee extensions and leg curls. Work your calves by doing toe raises, then rock back on your heels and lift your toes off the floor to work your tibs. Be sure to include stretches for all your joints and major muscle groups.