Exercise does mobilize mercury, but it's one of the best ways to get rid of it so long as you're sweating. Exercise raises endorphins, stimulates digestion (helping you get rid of waste), and clean the lymphatic system. In fact, it's the best way to clean the lymphatic system because, unlike your heart, the lymphatic system has no pump. It only has one-way valves so circulation, and therefore cleansing, only takes place with physical movement.

I don't believe that exercising moves mercury into the brain per sa, unless you have a damaged blood-brain barrier, which mercury will cause over time. If that is the case, then any mercury mobilization could redistribute mercury into the brain to some degree. Unfortunately, mercury mobilization is necessary for detox, but there are protective measures you can take, namely, what I call "The Big Three". These are the three most important supplements for mercury toxicity and can be taken while fillings are still in (C, E, Algin). See below...

Algin

Citrus Bioflavonoids (Vitamin C)

Vitamin E with Selenium

The problem with exercise and mercury toxic persons is that exercise increases free radicals. Well, oxidative damage is already a problem with mercury toxicity, which is what Citrus Bioflavonoids (Vitamin C) are good for. So, if you're mercury toxic and exercising, you may want to increase your antioxidants.

I take these Citrus Bioflavonoids daily, but if I exercise, I'll add in High Potency Grapine. The rule is to take 1 mg for each pound of body weight.

There are posts on this thread that also talk about feeling flu-like symptoms after exercising. This is exactly what used to happen to me when my fillings were still in. The key to eliminating this symptom is to stimulate the immune system. I've found an herbal combination that works really well for this called Nature's Immune Stimulator

Of course, the other reason you can have issues with exercising causing low energy is simply the multitude of actions of increased mercury in the system. One of the effects I suffered was depressed thyroid function. One of my favorite supplements in the world helps this problem: Thyroid Support

I also find that it's important to start out slow when beginning an exercise program, there can be an initial "inrush" of mercury from stores in the lymphatic system that, once drained, will allow you to feel better after a few days or a week.

Rebounding is probably the best way to circulate the lymphatic system. You can get a small rebounder for under $50. This is like a mini-trampoline.

Finally, the supplement that got me through the last couple years of mercury toxicity was a growth-hormone stimulating supplement. There is virtually no end to the health benefits of growth hormone but I personally would not take it for long periods of time (such as more than a year or two) because in people with tumors, it can speed tumor growth, so this is a just precaution. It truly is amazing however, and if someone is looking for a strong but temporary solution for the ailments associated with mercury, this may be what you've been looking for. Here is NSP's version: IGF-1

To experience some mercury symptoms with exercise is inevitable, but with some help from natural supplements, I made it through. In fact, I'm in the alternative health field today only because of the incredible truths I learned when doing research on herbs and alternative supplements while trying to solve my mercury-induced health issues.

All the best.