Having established an active walk on the lunge its time to progress
to the trot.
Maintain your triangle with your horse with the lunge whip held out and encourage your horse forward with a positive vocal TERRRRROTT and if necessary flip the whip to back up your vocal command.
The upward transition into trot should be immediate and rhythmic; however this may take some practice.
If your horse does not respond at first, do not panic and start chasing the horse as this will only result in a hurried pace and loosing the circle, keep positive, flex the lunge line to get the horses' attention and repeat the command.
Trot for two or three circles then ask for walk - walk on - then trot again, these transitions will keep your horse interested and improve the horses respect for you.
As in walk, these exercises's on the lunge allows you to study your horses' self carriage, balance and rhythm of movement.
The head and neck should be carried in a relaxed way which will strengthen and tone the top line muscles along the mane line and the back; the tail should be carried straight and slightly away from their body, not stuck outwards or held at an angle as this is a sign of pain or a problem along the spine.
The gentle curve of the circle also helps tighten the abdominal muscles which is why it is very important to do the same amount of work on each rein.
The hind quarters produce the propulsion so actively working on a lunge without the rider unbalancing the natural gait will improve the engagement and help to strengthen and tone these huge muscle densities.
Note: A horse trots at approximately 6mph therefore in 10 minutes of lungeing they will have covered a mile.