How to Build Back Muscle
To build back muscle, try doing bodyweight exercises like low planks, supermans, reverse snow angels, and pull-ups. If you have a gym membership or some free weights at home, do dumbbell and barbell exercises that target back muscles, like arm rows and bent-over rows. Also, consider incorporating weight machines into your workout, like pulley, cable, and lat-pulldown machines, which are great for building back muscle.
Do arm rows to build both sides of your back separately. Kneel on a padded gym bench. Place your left foot on the ground and your right knee on top of the bench. Place your left hand in front of you for support. Grab a dumbbell with your right hand and pull the dumbbell up to your armpit. When the dumbbell is fully lifted, it should be parallel to your chest. Do this in 1 smooth, slow motion, and hold the weight in place for about 3 seconds. Hold the weight in place for 3 seconds, and then slowly lower your arm and shoulder to lower the weight. Control your arm as you release your hold position. A controlled lowering gives you the greatest benefit for this exercise. Perform 10-12 reps in each set of arm rows. When you're first starting out, you may only be able to do 1 set of 10-12 reps. As you feel more comfortable performing rows, add on a second set. You may need to decrease the number of reps to 6-8 to be able to complete both sets. As your back becomes stronger, you can increase the number of sets you do. Aim to perform 3 sets of 10-12 reps each. Once you've done a full set of arm rows with 1 arm, switch sides to exercise the other half of your back. Try a barbell bent over row to bulk up your lower back. Stand in front of a barbell and keep your feet shoulder-width apart and bent over so your back is parallel to the floor. Grab onto the bar with a shoulder-width grip. Your hands should be about 2–3 feet (0.61–0.91 m) apart. Then, flex your back muscles and lift the bar up to your lower chest in 1 smooth motion. Hold the bar for 2-3 seconds, and then lower the bar back down slowly. Use your back muscles to control the bar's descent. Repeat for 3 sets of 10-12 reps. This will help your lats to bulk up quickly and will allow you to see fast results. If you need to work up to this goal, start with only 1 set of 12 reps. Throughout the bent over row, make sure that your knees and legs flexed slightly to support your lower back. Perform lat pulldowns to strengthen your upper back and shoulders. This exercise is great for bulking up your traps, and also your rhomboids and the middle trapezius. Raise your hands and grasp the pull down bar. Make sure that your back is straight and your chest is pushed out to maximize the benefit of the pulldown exercise. Make sure that you bring the bar in front of your head. If you try bringing it down behind your head, you may injure your shoulders. Draw the pulldown bar down to your chest. Flex your back muscles to engage them and try to pull with your back and not with your biceps. Ensure that you're using your back muscles by keeping your back straight and pushing out your chest and squeezing your shoulder blades back to retract them. Tighten your abs as you pull down the bar. Then, slowly raise your hands to return to the starting position. Don't let the weight fall suddenly, or you may damage your shoulders. Perform 1-2 sets of 6-8 reps until you're comfortable doing more. As your back builds up, increase the reps to 10-12. If the weight and amount of reps are correct, you should struggle to complete the last 1-2 reps in each set. Work your upper and lower back and shoulders with seated cable rows. Sit at a low pulley machine and rest your feet on the platform in front of you. Bend over to reach the pulley, with your hands about 3 feet (0.91 m) apart to engage the central muscles of your upper and lower back. Then, flex your arms and bring your elbows up to your chest. As you tighten your back muscles and flex your biceps to pull the pulley into your chest, also push outward with your legs. To finish, slowly extend your arms to return to your start position. When doing cable rows, set the machine at a weight that allows you to do about 12 reps for 3 sets. Doing 12 reps will allow you to build up back muscle without exhausting yourself or potentially straining your muscles. Build upper-back muscle with full-range motion lat pulldowns. Stand in between 2 pulley machines and attach the pulleys on both sides to the highest setting. Grab the right pulley with your left hand, and grab the left pulley with your right hand. Then, lower the handles down in front of your chest until they're crossed in front of your sternum. Finally, release the weight by returning the handles to the overhead position in a slow, controlled manner. Slowly bring your arms back in to your chest. Bring your arms to your chest slowly, without letting the weight jerk your shoulders. Start out with 3 sets of 10-12 reps. If you've set the weight right, the last 2 or 3 reps of each set should burn. If this is too challenging at first, lower the weight and try to complete 1 full set of 10-12 reps. Do pull-ups to strengthen your shoulders and upper back. Grab a pullup bar with your palms facing outward. Then, lift yourself up until your chin is above the bar. Lift yourself slowly to fully engage the muscles in your shoulder and back. Lower yourself down slowly to complete the pull-up. Use your shoulder and back muscles to lower yourself at the same speed you used to pull yourself up. If you jerk and twist your back as you pull yourself up, you'll risk straining a muscle. Start with as many pull-ups as you can manage, and try to add 1-2 more each workout. For example, start with 10. Next time you do pull-ups, aim for 12. Perform low planks to strengthen your lats and build your core. Lie on your front, with your elbows bent and your weight resting on your forearms. Then, push your hips up until your back is parallel to the floor. Retract your shoulder blades to engage more of your back muscles. Hold the position for 15 seconds. Try doing 2 sets of 15 reps. Once you're comfortable doing low planks, try adding high planks into your workout routine. The only difference is that, instead of resting on your elbows, you'll fully extend your arms and rest on your hands. Try the “superman” to strengthen your lower back and core. Lay flat on your stomach and straighten your arms out in front of you, palms down. Then, slowly and simultaneously raise your arms up until your hands are about 6 inches (15 cm) off the ground and raise your legs so your feet are also raised 6 inches (15 cm) off the floor. Squeeze your legs together and keep them straight. Hold the pose for 15-30 seconds, and perform 3 sets of 10 reps. You can increase or decrease the difficulty of the superman pose as needed. Try raising one arm at a time, then build toward raising one arm and the opposite leg at the same time. Move to raising both arms but not your legs, then both legs but not your arms to prepare you for the complete pose. This exercise works your back extensor muscles, which run down your spine and impact your posture. Strengthen your mid-back and shoulders with reverse snow angels. Lie flat on your stomach for this exercise. Push your shoulders back and raise your arms until they're about 4 inches (10 cm) off the ground. Hold your arms outstretched so they're parallel with your shoulders, and then slowly move them down until they're at your sides. Keep your elbows locked, and repeat the exercise 5 times while keeping your arms lifted off the floor. Try doing 3 sets of 5 reps. Reverse snow angels will engage your mid-back lats, rhomboids, posterior deltoids, trapezius, and teres major. 
Do arm rows to build both sides of your back separately. Perform 10-12 reps in each set of arm rows. Try a barbell bent over row to bulk up your lower back. Perform lat pulldowns to strengthen your upper back and shoulders. Draw the pulldown bar down to your chest. Work your upper and lower back and shoulders with seated cable rows. Build upper-back muscle with full-range motion lat pulldowns. Do pull-ups to strengthen your shoulders and upper back. Perform low planks to strengthen your lats and build your core. Try the “superman” to strengthen your lower back and core. Strengthen your mid-back and shoulders with reverse snow angels. 