Why is sand good?
Basically, if you don’t already run economically or you are prone to high levels of running injuries, sand running does not teach you to run well and hold good form (even when tired)… it actually forces it. Over 15 years of experimenting on hundreds of athletes tell me that if your strike rate is low (under 90 steps per minute), if you over stride, if you are a heel striker or if you oscillate… you will sink into the sand, finding it very difficult to run well. Another benefit of the low impact - on the whole, the age groupers I coach will run 3 times per week, but I can double their running frequency using sand without negative outcomes and still maintain freshness for the bike and swim sessions.
The science
The force/load generated during ground contact time (GCT) is obviously where most running injuries occur. Don’t get me wrong, I want to train and make the stretch-shortening cycle in the muscles, ligaments, and tendons strong, but the sand is working for the antagonist muscles groups on strike. You are training the body to lighten the strike/to pull the foot off the ground quickly before it sinks too far and you lose friction. Moreover, you are teaching/forcing the body to hold good form from the hips through the shoulders and head, because if any part of the body is not connected thus working with/through the kinetic chain, again you will sink into the sand and lose the feeling of running well.
Outcome
Those who have never used sand before will always comment, post running back on the hard surface how they feel like they are ‘floating’. I like to mix the sessions up and have a rep or two on the hard path beside the beach for contrast.
If you have ever had the privilege of running with a good elite running or observed them running, you will see that they float across the ground (even triathletes after a 40k hard bike). The air-time they achieve is incredible (time neither foot is in contact with the ground). But next time, also observe how quiet they are… you won’t hear hard thudding on the ground of the poor runner and as I like to say to the guys I coach… “Silence is deadly”.
JB