I'm certainly not a fitness guru but I have had to deal with burning or pain in my muscles (and in my case in my joints, not arthritis). I have found it has been helpful to reduce acidity by doing things to alkalize my body daily on a more consistant basis. From what I know of your diet VV, what with the organic veggies and other paleolithic features, you are probably pretty balanced in the acid / alkaline area. However, you never know; you are physically active in a whole range of ways and your acid / alkaline balance may be suffering. I do know from reading I've done that athletes often have to buffer excess acidity in much the same way. If you can stomach it, you may want to try drinking the following concoction before and after your workout to see if it helps. Having a highend juicer (I use a Champion Juicer) helps with the limes if you leave the peel on. I drink this blend 3 -4 times daily to offset the acdity of medication throughout the day. You are not likely to need it as much as I do (you are in excellent condition by all appearances). I've come to like this drink but I'm sure many people will find it gross and bitter. Anyway here's the recipe:
In a glass mix the following:
-juice from 1 freshly squeezed lime (organic, of course, for VV! I juice it whole with the skin on but that's not mandatory)
-a shot glass of organic applecider vinegar
-1/4 teaspoon of sodium bicarbonate or potassium bicarbonite (I use pb because sb raises my blood pressure, pb can be hard to find, though)
-the contents of 1 probiotic capsule (yes, break the capsule open so the stuff is free)
-Some aloe juice (it use the new non-gluely variety)
-Fill the remainder of the glass with water (forgot to put this in the first time - w/o water it would be too strong, may want to dilute even more the first few times)
The first two ingredients are mandatory, using all together is best. Getting the probiotic powder to mix in can be a challenge. All these ingredients turn to alkaline ash when processed in the body. I start the day by doing a whole batch (3 or 4 servings) and carrying it with me in a sports bottle. After a week or so I actually found it to be refreshing, especially cold. Some people will find sodium bicarb or potassium bicarb hard to drink at first, so you may want to use a smaller quanitity and build up. Some people won't be able to handle either at all, and will have to leave it out. If you try it, you'll have to use it for at least a week to see if it works. In my case it reduced muscle pain and burning to almost nil and also stopped the nausea caused by excess acidity due to meds.
You may also want to look at your running routine and those that support it. Is it time to get new runners? Are you stretching all attending muscle groups in a balanced way? When I was your age I had to change some aspects of my running routine (e.g. more recovery time, variations of the lunge along with squats, etc.) and lifting regime to offset some body changes. I know you're really up on stuff like this but I thought I'd mention it anyway.
Also your body may be telling you that it's suffering more oxidation and free radical damage (hard to say why- more pollution, whatever), so you may want to look at taking a greater range of antioxidants, vitamins and minerals. When it comes to antioxidants you get what you pay for and you'll want to take at least the big 5 together: vitamin C, alphalipoic acid (R+ form ONLY), (NAC) N-aceytel cycteine (sp?), full spectrum vitamin E, and CoQ10. AOR makes very high quality versions of each of these. Body Energy Club on Davie just of Granville carries AOR often. You would also likely benefit from doing IV vitamin C and getting glutathione (sp?) treatments (via nebulizer). There naturopaths that have these skills. Pricey it's true , but if I had a body like yours and wanted to preserve it's natural strength and beauty, I'd consider all this at some point. Again I'd recommend Michael Colgan's books on proper exercise combinations (he's rehabed many professional athletes) and especially for antioxidants, vits and mins.
For your consideration VV.
Being the bright lady you are, I'm sure you'll figure out what works for you. (We'd all hate to think of the consequences of VV out of the game!)
CODe333