Now we know how many times during a gig we rhythm guitarists have to tense and release our fretting hand it makes sense to do this with as little effort as possible, so we can still be fresh at the end of the evening and not drag the tempos down. Sometimes, especially on high profile gigs, I find that my left hand is beginning to form a death grip around the guitar neck and the bounce is disappearing from my rhythm. I have now developed a warm-up exercise that gives me great feedback about how much (or little) pressure I do need to exert on the fretboard to play the notes.
I start off by fingering a chord around the fifth or sixth fret (such a Bb maj6/9) but I don’t press down hard enough to make contact with the fretboard. I then start playing a regular four to the bar rhythm pattern with my right hand to produce a rhythmic sound without any pitch. I then slowly increase the presure in my fretting fingers until notes begin to sound on the first and third beat of each bar. I don’t mind if this is rather irregular at first because I am trying to find the minimal amount of pressure that will sound each note in the chord so I will oscillate around the sounding/non-sounding threshold initially. Once I have the first and third beats sounding then I add the shorter louder second and fourth beats. This gives my fingers the feedback they need to know what is the minimal amount of pressure required to produce the sound of the chord.
Of course this pressure varies at different points along the fretboard so you might want to try it at lower and higher frets. I also stop during practice to do this exercise again to make sure that tensions in my left hand haven’t crept up without my notice. Obviously one can’t do that on a gig but my alternative strategy for that environment is to focus on listening to the upstrokes and make sure that they don’t have any musical pitch – indicating that I have released the tension enough at that point.