How to Perform Dumbbell Concentration Curls
The bicep brachii comprises roughly one-third of the upper arm and is comprised of the long and short heads. The brachialis, also referred to as the side arm or lower bicep, is commonly considered part of the bicep muscle group even though it's technically different.
The biceps are primarily built through pulling movements such as chin-ups and elbow flexion exercises such as curls. Most bicep movements are performed in vertical plane although the torso angle may also be slightly backward (e.g. incline dumbbell curls) or forward (e.g. concentration curl) depending on the exercise. Whether you're a top tier athlete or weekend warrior a beastly set of biceps will set your physique apart from the rest.
The concentration curl is an isolation pull exercise targeting the brachialis, also referred to as the lower bicep. The biceps brachii (short and long heads) and brachioradialis (upper-outer forearm) act as supporting muscle groups during this movement. 
Supporting muscle groups assist the target muscle group in completing the movement. The middle and upper trapezius, levator scapulae (rear neck), obliques (abdominals), erector spinae (muscle running along both sides of the vertebral column), and wrist flexors act as stabilizers during this exercise. 
Stabilizer muscles help maintain a posture or fixate a joint by contracting without significantly moving.  The concentration curl is one of the best exercises to build the bicep peak.
How to Perform the Concentration CurlThis walkthrough will focus on performing the concentration curl with a dumbbell but you can also apply the general form and tips if you choose to perform the exercise with a cable apparatus.
Walk to the dumbbell rack and select the appropriate working weight. This exercise only requires one dumbbell as you will be performing this movement using one arm at a time. If this is your first time performing the exercise then pick a conservative weight that you can safely lift for 8 to 12 repetitions.
The working weight will be lower than amount used for traditional dumbbell curls. When in doubt, start with a conservative weight and work your way up; this will leave more room for progression and ensure you develop properly form early on.
Once you've selected the working weight grasp the dumbbell, sit on one end or directly in the center of the flat bench pad, and place the dumbbell in between your legs. Your feet should be flat on the floor, shins should be perpendicular with the ground, and thighs should create a V-shape. Your knees should be wider than shoulder width; a stance that is too narrow will affect the movement's range of motion.
Decide which arm you're going to perform the movement with first and use that arm to pick up the dumbbell with a traditional (thumb wrapped around the fingers) or false grip (thumbs wrapped around the same side as the fingers). Place the lower part of this arm's tricep and elbow on the corresponding inner thigh.
If you're curling the dumbbell with your right hand first then the lower arm and elbow should be in contact with the right thigh. A slight forward lean in the torso to get in to position is acceptable but ensure your lower back is neutral and your shoulders are down and away from the ears. This is your starting position.
After setting your starting position take a deep breath, brace your abdominals, squeeze the dumbbell as hard as possible and begin pulling your hands towards your shoulder. During this arc motion your elbows and upper arms should remain in a fixed location. Do not allow the upper arms or elbows to drift out of place; doing so will take the stress off the biceps.
Continue curling the dumbbell until your forearm are in between parallel and perpendicular with the ground. The lower part of your tricep and elbow should remain in contact with your thigh throughout the entire movement.
The precise top position will vary with the individual, depending largely on your upper arm strength, form, and shoulder flexibility. While some trainees prefer to curl the dumbbell until the forearm is perpendicular with the ground, this may require your elbow to move off your thigh or shoulder to roll-in or raise.
Curl the weight towards your shoulder as much as possible, stopping just before your elbow and shoulder changes positions. This cue will maximize engagement of the lower biceps. Continue squeezing the dumbbells and flexing the biceps, holding at the top position for 1 to 5 seconds.
Once you've held the dumbbells at the top of the movement for the desired duration lower the dumbbells in a slow and controlled motion back to the starting position. The movement pattern for the lowering portion should be the exact reverse of the pulling portion. Complete for the desired number of repetitions and then switch arms.
Perform the same number of repetitions and sets for both arms. Some lifters choose to exhale while curling the dumbbell, at the top of each rep, or in between in each repetition. Choose a breathing pattern that feels the most natural and comfortable for you.
This exercise can be performed using straight sets, pre-exhaust sets, drop sets, rest-pause sets, supersets, trisets, giant sets, paused reps, partial reps, forced reps, or slow negatives. As with any exercise, the two most important components are high-quality form and progression.
Progression can take a variety of forms (e.g. more weight, sets, or reps, decreased rest period, improved rep quality, etc...) but strive to improve every training session.
Dumbbell Concentration Curls Form TipsAvoid Momentum - The concentration curl provides maximum benefits when it's perform in a controlled full range of motion. Check your ego at the door and don't immediately attempt 75lb dumbbells. Do not use momentum, raise your hips off the pad, or allow your lower arm to leave your thigh to bounce the dumbbell from the bottom position to the starting position.
This momentum dramatically increases the likelihood of injury and minimizes the stimulus of the target muscles.
Hold the Squeeze - Increase intensity by holding the top position of the concentration curl for 5 to 10 seconds. Really focus on squeezing the biceps and gripping the dumbbell as tightly as possible.
This will increase time under tension and the burn in the biceps. Increased time under tension is an excellent variable to adjust for progressive overload and enhanced muscle growth.
References1) Griffing, James, et al. "Dumbbell Concentration Curl." ExRx.net. N.p., 2015. Web.
2) Griffing, James, et al. "Kinesiology Glossary." ExRx.net. N.p., 2015. Web.