Functional strength, speed, and power can be targeted using resistance bands. Make sure you tie them tight. Thursday, while rushing, I failed to double check my band and it came loose coming from up underneath my left (practicing left hooks) catching me in my eye(OOOWWWW! @#%*&!!)
From the pole, secure your (depending on what punches you are practicing) arm in the band "loop" and begin throwing whatever punch you are practicing keeping sure to fully rotate your upper and lower torso and pivoting on the appropriate foot (left foot for left hooks and right foot for right hooks) just as if you were hitting someone for real.
What I do is concentrate on the rotation of the upper /lower torso, WITHOUT EXTENDING THE ARM, in the proper direction of the punch pivoting on the corresponding foot.
Embrace the pain...train hard bro...TRAIN!