Hi there ur symptoms are clearly linked to you having active 'Myofacial Trigger Points' along ur lateral lower limb muscles, namely the Peroneal longus & brevis & potentially to other adjacent muscle groups such as the extensor Digitorum longus...?
Either way the accumilative effects of Trigger Points within contractile tissue (i.e muscles) essentially alters the contractile biomechanics of that muscle group thus eventually effecting the sensory-motor system mechanism which gives rise to referred (or cascading) pain along that tissue and can even refer / cause further tissue sensitisation and assimilate neurological symptoms like pins and needles and numbness etc. Basically those trigger points (commonly felt as knots in the muscle) need deactivating by pressing onto the most tender point(s), usually found in the belly of the muscle...! Press and hold for as long as it takes (usually 10secs or so +/-) until that sensitised pain begins to subside....! Continue to find those points and deactivate them - remember this pain does not equate to harm so dont fret about the pain ok...! Apply a hot pack / bottle over the muscle x1/day for
5-10mins then simply rub some Biofreeze gel (from Boots) firmly / deeply into the muscle(s) to help desensitise the tissue further prior to stretching that tight muscle (but not into extreem pain - just a sufficient stretch needed) and hold 10 secs & repeat 5x
2-3x/day ok lass... Within a couple of days you will start to feel a release / normalisation of the tissue as an increase of soft tissue circulation will begin to nourish the muscle thus restoring function and endurance to the stress loads. Do as i say and you will see the benefit. Now the question begs - what is the predisposing factor to you forming these trigger points along ur lateral lower limb muscles..? The most common cause is usually having poor foot and ankle mechanics....i.e low medial foot arch causing pronation of your hind and forefoot....! This effectively induces the lateral lower limb muscles to work over time when u carry out ur activities such as horse riding as ur foot / ankle muscles / joints are constantly engaged in the stirups..! You will probably need arch supports (from Boots u can purchase these from) to help bring your ankles closer to neutral alignment thus enabling even activation to the lower limb muscles. Always ensure u keep a good knee-toe alignment...i.e centre of knee should be over the 2nd toe (next to the big toe which u should be able to see when u look down the knee to the foot...!)... Let me know how you get on lass ok ...x Merry xmas