Choose an appropriate weight matching your fitness and coordination level. To begin, first set the bar on a rack, just below shoulder level, place the back of your shoulders across it. Straighten up your torso. Place your pelvis into a neutral position.
Step away from the rack and step forward with one leg; squat down while maintaining the line of your starting position. The heel of your rear leg slowly rises off the floor. Do not allow your knee to go forward beyond your toes as you come down, as this will put undue stress on the knee joint.
Come back to the starting position in the same way. Breathe in as you go down and breathe out as you go up. Alternate legs, striding forward.
Maintain correct stance and keep your torso muscles tight.
The step forward is performed within the starting position line without rotating inwards and outwards.
Make sure you are not rotating your toes while stepping forward (both feet should be oriented frontwards).
Do not allow your knee to go forward beyond your toes, keep a correct angle in your knee joint.
It is best to perform the exercise in front of the mirror and watch yourself sideways to make sure your technique is correct.
Choose an appropriate weight matching your fitness and coordination level; i.e. start with lighter weight to master the technique well.
Barbell lunges are the most popular and most basic one-leg exercise. One-leg exercises are particularly useful for persons with lower back problems as they put more load on the individual leg without increasing the pressure on the back and shoulders.
It is very important not to lower the head so as not to get dizzy. This is an exercise that requires good sense of balance and the main danger is in losing the balance and falling down.
Notice that the eccentric (lowering) part of this exercise is much more demanding than the eccentric movement in most two-sided exercises (e.g. squats). Therefore the lunges increase a type of strength called eccentric strength.
You can either repeat several repetitions with one leg and then move on to the other leg or you can alternate each leg.