Choose the appropriate weight matching your fitness level and training type. Grab the bar attached to the pulley using an underhand grip at shoulderwidth and sit on the machine seat with arms outstretched. Bend back slightly (a hint of leaning) but without lumbodorsal overarching. Keep holding the bar with your arms outstretched upwards in line with the pulley.
From the position of arms stretched upwards do the motion by flexing your elbows and pulling the cable towards your chest (contracting your back muscles). Exhale whilepulling the bar towards your body and inhale while returning to the starting position.
When bending back make sure that your torso does not engage in lumbodorsal bending. Lead your elbows slightly away from your body and do not bend your wrists. Keep your feet fixed on the floor.
Start with lighter weight to master the technique well.
Underhand cable pulldowns are similar to chin-ups but the exercise is done using a pulley.
The correct grip is underhand and less than shoulder-wide. Alternatively you can use a v-bar attachment and neutral grip.
The difference between overhand and underhand cable pulldown is not great. Both are targeting the same muscle groups, mainly lats and biceps.
The same is true about the pull-ups and chin-ups.
The main difference is that in underhand (or neutral) grip the arm is positioned more favorably for biceps muscle. Biceps and the surrounding muscles (brachialis, brachioradialis) are in “stronger” position and relatively less work is done by lats.
The torso should lean backwards in an angle of about 30 degrees. At the end of the contraction you should squeeze the shoulder blades together (scapular retraction).