This is a great technique I picked up from Jim 'Smitty' Smith.
You can apply this to most exercises and you do not have to limit it to just 5 x 5, it can be any rep & time scheme you would like.
The idea is you perform 5 reps of an exercise and on the 5th reps you hold the rep in an isometric for 5 seconds.
That is 1 round.
Depending on the weight / exercise etc, you can do these for anywhere from 1 - 5 rounds.
Just be prepared for some soreness the next day
• Stand tall with feet hip width apart and abdominals braced. Hold a barbell in front of body with palms facing body.
• With a slight bend in knees, push hips straight back whilst flexing forward from waist and keeping back straight.
• Continue until chest is between parallel and a 45 degree angle to the floor. Arms should be hanging straight down with the barbell. Keep shoulders pulled back and down.
• Moving just arms, breathe in and pull barbell to stomach, around navel level.
• Breathe out and lower bar until arms are straight. Do not let barbell touch floor between reps.
• Complete for 5 reps and on the 5 rep, hold the barbell in the top position for 5 seconds. This is 1 round. Complete for the given number of rounds.
This is my, mostly, Personal Trainer musings and information which I hope you'll find helpful!