Downpicking, sometimes referred to as Downstroke picking, is the technique used by musicians that perform on plucked string instruments in which the plectrum, or pick, is moved in a downward motion, relative to the position of the instrument, against one or more of the strings to make them vibrate. If downstrokes are played without the addition of upstrokes (as in alternate picking), the tip of the pick never comes in contact with the strings during the time the hand is moving back up to repeat the downstroke.
Guitarists of hard rock genres will often use downpicking to create a "heavier" sound than what can be achieved with alternate picking, which generally produces more cleanly melded strumming sounds. Downpicking also effectively doubles the effort one would need to alternate pick at the same tempo, however this is hardly noticeable at medium to slow tempos. Downpicking can also be used in a technique called sweep picking, or 'raking'.
Extremely fast eighth-note downstroke picking was used in the mid 70's and beyond by famous punk guitarist Johnny Ramone, who used the technique to play full live shows at fast tempos (usually around 180 to 200 bpm). This required extreme levels of stamina, but produced a very high-energy, aggressive sound. This extremely demanding, then-uncommon and somewhat innovative style contributed to Johnny Ramone's reputation as a legendary guitar player, and it influenced many now-famous rock guitarists. Downstroke picking has become a common technique in metal and thrash rhythm playing, notably exemplified by Metallica's James Hetfield (who has been regarded as God of Downpicking), Misfits' Doyle Wolfgang von Frankenstein, Megadeth's Dave Mustaine, Slayer's Kerry King, and Anthrax's Scott Ian among others. The guitar work of Metallica's "Master of Puppets" is almost entirely played using downstroked eighth-notes at a tempo of 212 BPM (about 7 downstrokes per second).
Up-tempo downstroke picking requires a strong wrist to keep all the muscle movements as tension-free as possible. For long or extended passages, endurance becomes the focus, as fast downpicking can quickly cause a burn in the wrist, sometimes extending up into the arm and causing the muscles to seize up. If the guitarist has a difficult time keeping the strokes smooth, the quality of the music can suffer, often sounding sloppy and/or strained. While downpicking in general is sometimes considered a good beginner's technique for learning at slow tempos, it requires a great deal of skill to perfect and utilize downpicking in much faster applications where alternate picking is quite often used as a "short-cut".
It is normal to feel the picking arm "burning" while practicing this technique. Experts in downpicking suggest for the beginners to stop when the ache comes, rest 2 minutes then repeat the process 3 times per day in order to build up stamina.