Even the most experienced runners can throw their pace and distance goals out the window when running on the beach. Beach sand, even when packed firmly, is not the same as the packed earth that forest trails may offer or the hard, even asphalt of roads. On the beach, there is always a little give in the surface of sand, which may mean less impact stress to bones, tendons and muscles, but the biomechanics are decidedly different as your feet sink in and your body’s kinetic chain reels to find balance across the varying terrain
Expect to tire quicker than normal when running on the beach, so build in rest accordingly. For example, try integrating a minute or two of walking for every 10 to 15 minutes of running.
Also, expect to be sore the next day, especially in the muscles throughout your feet and calves. Soreness may occur more prominently on one side of your body, depending on how uneven the surface is and how much you overcompensate given the additional challenge.
You can modify your form by shortening your stride, but if the sand is too boggy, simply focus on keeping a forward momentum, and walk whenever necessary to recover from the extra effort it takes to run on the beach.