Your horse's fitness is one of the most important aspects of driving ...

...and following through a fitness plan with your horse can be a real challenge.
It requires selfdiscipline from you and a lot of hard work for both, you and your horse.

What does fitness actually mean?

A horse does not show any signs of distress during work and is able to do the tasks you ask for.
Its healthstatus is not affected by doing a certain distance at a certain speed.
After work it should soon breathe normally again and look happy and not distressed.
If it is heaving and sweating thoroughly even after 15 - 20 minutes, it needs to be exercised with a carefully adjusted exercise plan.

What factors should be monitored and measured?

One of my duties as a vet is to supervise horses during endurance competitions.

There are three physiological factors, which can easily be monitored:

Pulse rate

Respiration rate

Body temperature

The pulse rate reflects the heartbeat rate and is measured by placing two or three fingers (not the thumb!) of one hand underneath the lower jawbone, where the artery crosses over the bone.
Count the number of beats per minute.
The normal resting pulse rate is 30 - 40 b.p.m. (beats per minute).

In well trained horses during trotting phases it can go up to 150 - 180 b.p.m. and decrease after a 10 -15 minutes rest to around 40 - 50 b.p.m.

The respiration rate is measured by counting breathing intervals (= one in- and one outbreathing movement) per minute.
It needs a bit of practice to monitor movements and time at once.
The normal breathing rate at rest is around 10 - 20 breaths per minute.

The body temperature, is usually measured rectally with a thermometer. (Caveat: Be aware of being kicked!)
Normal temperature in a horse is around 37*C.

The shorter the time it takes for the horse's pulse and respiration rate to fall from the high rates achieved when working hard to the rates applying at rest, the better trained is the horse.

Weight Control

The horse's basic food is grass, but it won't become really "sporty" on a sole grass diet.

Weight control and an individually adjusted diet are crucial.
An overweight horse will struggle to pull a vehicle with you or even a few passengers and carry its heavy body on top of that.
Healthproblems will come up soon!
You need to follow an exercise regime to get your horse slowly and steadily fit.

See here for an example of a Fitness Plan for Your Horse