Tighten towards the front of the bike and loosen towards the back.
Now do this: remove the computer and turn the bike upside-down. Work out which way you need to turn the pedal spindle. Now set the spanner on the flats of the spindle so that it more or less parallels the crank, i.e. the end of the spanner is effectively adjacent to the bottom bracket. With the spanner in this position a hefty shove will not cause the cranks to turn but you will be applying leverage through the equivalent of around 175mm of the spanner.
This method will shift any pedal, easy ones can be done with the bike upside-down but really tight ones might need you to set the bike upright, get astride the bike and actually stand on the end of the spanner, with your foot right next to the bottom bracket bolt. In this position the crank and spanner would be forwards and you would be pushing downwards, i.e clockwise on the left of the bike and anti on the right. Got it?
Don't waste time with penetrating fluid, it doesn't penetrate a stuck thread until the bond is broken and space appears between the threads.