The quality of soil on which the horse works is very important. Which (multiple) of these statements are true?

Question

Hard soil tires out the joints.

Mixed soil is harmful to horses as it tires out both the tendons and the joints.

Deep soil tires out the tendons.

The frog has a shock-absorbing role; it must be released to work well.

Sticky soil which forms packets under the horse's hooves enable it to absorb shocks better.

Answer 1

They are all true.

Answer 2

They all can be true, depending on the weather conditions & the toxins that eventually can get into the dirt from various elements.  The most important one would be the water that is applied to the track & mixes with the dirt, thus affecting the soil.  Rainfall can bring toxins from the air.  The water truck can bring toxins from the groundwater or other sources.  Then there's the dirt that is trucked in from unknown sources & toxins from every horse & rider that sets foot in that dirt on the track.  Also, each horse is different.