This post looks at barbell circuits also known as barbell complexes. These complexes are designed to improve speed, conditioning, strength endurance and can have some aerobic benefits. The idea is to perform a circuit of barbell exercises back to back without any rest and ideally without putting the bar down. Since you are performing a group of exercises together the amount of weight you use will be much less then if doing the exercises individually. As mentioned barbell complexes are designed more for strength endurance rather than pure strength or muscle hypotrophy (increased muscle size). Complexes are also designed to be completed as fast as possible while maintaining good technique, this will help to improve your speed and will help to keep your heart rate elevated causing you to burn a significant amount of calories. I have posted 2 examples of barbell complexes that you can try. Complete 15-20 reps of each exercise and once you have completed them all rest for 1-2 minutes before repeating. Aim to complete 3-4 complexes. Increase the amount of weight you use once you can do 20 reps of each exercise and complete 3 complexes comfortably. 

Complex 1:

Press up

Deadlift

Bent over row

Push press

Lunges

Good mornings

1. : 

Complex 2:

Clean and press

Squat

Reverse lunges

Stiff legged deadlift

Upright row

Bent over row (underhand grip)

1. :