Taking less than a minute, below is an eye opening technique that is a great addition to your toolbox.
The focus here is to test trigger points along the length of your horses back, neck, and hindquarters.
Pain is perhaps the number one reason for a wide range of physical, psychological and behavioral conditions that horses regularly exhibit. It still continues to stun me how many people ride horses that are in an extreme amount of pain, yet the owners seem unaware of the danger they are putting themselves in, and the damage they are doing to their horse.
Any area that responds to this test with an 'ouch' response is a trigger point for your horses pain.
Pain is perhaps the number one reason for a wide range of physical, psychological and behavioral conditions that horses regularly exhibit. It still continues to stun me how many people ride horses that are in an extreme amount of pain, yet the owners seem unaware of the danger they are putting themselves in, and the damage they are doing to their horse.
Any area that responds to this test with an 'ouch' response is a trigger point for your horses pain.

1) To begin start by placing your index or middle finger where the wither begins. Apply a firm but not excessive pressure to this area. Check for a response, if you get an ouch, you know you have neck pain.

2) Slide your finger along the muscles towards the midline of the wither. If you get a pain response here, your horse is struggling from shoulder or leg pain.

3) Continue down the wither to the lower wither, this is the third and final palpation point for this region. A pain response here indicates lower trapezius pain for your horse. This is especially common with poorly fitted saddles.

4) Now continue to slide down into the back, at this point where the wither joins the spine is your fourth palpation point.

5) Its now time to check the lats. Continue your way down until you reach this area - approximately mid back. If your horse has a pain response here you know the primary pulling muscle is in pain.

6) Now make your way across to this area, you are now checking the loin. If your horse has a pain response here, the longissimus (the muscle running the length of the back) is in distress.

7) Check over the S I Joint, and pelvis region.
Any reaction in the highlighted region indicates there is distress in the front of the pelvis. Many horses will display a pain response through here, and some may kick out - pay attention.
If you find a reaction here your horses abductors / ribs / public bone are being effected by unnecessary pain and additional workload.
Any reaction beyond this point of the sacrum is letting you know there is pelvis pain - this is where you find your primary driving muscles.
If in doubt you can palpate along the dotted line to confirm whether this is the case.
Any reaction in the highlighted region indicates there is distress in the front of the pelvis. Many horses will display a pain response through here, and some may kick out - pay attention.
If you find a reaction here your horses abductors / ribs / public bone are being effected by unnecessary pain and additional workload.
Any reaction beyond this point of the sacrum is letting you know there is pelvis pain - this is where you find your primary driving muscles.
If in doubt you can palpate along the dotted line to confirm whether this is the case.

8) Move your finger and test the area towards the middle of the sacrum. Should you find you have a reaction here, the muscles towards the rear of the pelvic girdle are under strain.
Now, continue to move your hand down unto you reach the top of the hamstrings (indicated in yellow). This is often slightly raised making it easier to identify, with horses in a lot of pain this raising will be very visible.
If you think you might have had a reaction here but are not sure you can test this. Taking one hand position it on the inside of the leg just under the tail, and roll over the muscle pulling towards you. Move your hand down, and test again. Often this muscle will be raised when in pain. If the hamstring is in pain you will see a visible reaction to these palpation points.
Now, continue to move your hand down unto you reach the top of the hamstrings (indicated in yellow). This is often slightly raised making it easier to identify, with horses in a lot of pain this raising will be very visible.
If you think you might have had a reaction here but are not sure you can test this. Taking one hand position it on the inside of the leg just under the tail, and roll over the muscle pulling towards you. Move your hand down, and test again. Often this muscle will be raised when in pain. If the hamstring is in pain you will see a visible reaction to these palpation points.

9) With this done its time to check the girthline either with the point of your thumb or flat palmed hand, apply a firm pressure starting at the "elbow" and slide under the chest.
Then (if you feel comfortable with this), applying reasonably firm pressure slide your hand along the yellow area.
Any pain indicators in these regions and your horse may currently be suffering from ulcers.
Then (if you feel comfortable with this), applying reasonably firm pressure slide your hand along the yellow area.
Any pain indicators in these regions and your horse may currently be suffering from ulcers.

10) Finally, there are three distinct groupings of muscle along the neck - these bands are attached to the point of the chest. Cup your fingers and working from the midline of the neck outwards, test these bands - you'll be aware that something is not right if your horse pulls away, becomes agitated, or tosses their head when you do this. You don't need to apply a lot of pressure here, just enough to get a grip on each group of muscles.
Its as straightforward as that. But taking the time to do this once a week will provide information that allows you to decide whether you need to cut back on the workload, learn some stretches to help these areas, or get a capable body worker to get the problem addressed at its source.