A magnesium bath after sport: what's in one and how much to use

Saturday afternoon, after the game. Or Tuesday night after training. The bath goes on, something gets poured in, and twenty minutes later you get out. This article covers what that something is, how much of it to use, and what the label should tell you.

What goes in

A sports soak on the Australian market is usually one of three things.

Plain magnesium chloride. Flakes evaporated from brine, about 12 per cent magnesium by weight. Sold by the kilogram. This is the base of nearly every "sports magnesium" product, whatever the tin says.

Magnesium with a scent. Magnesium chloride plus an essential oil, most often peppermint or eucalyptus. The oil is there for the smell and the feel; it doesn't change what the salt does.

A formulated blend. Several minerals and compounds in a measured dose. ThermoPure® is one of these: magnesium chloride, Dead Sea salt, OptiMSM® (a distilled form of methylsulfonylmethane), menthol and Tasmanian kunzea oil, in a 250 g pouch that is one bath.

The difference between the three is what you are paying for. Plain flakes are the cheapest per gram. Blends cost more because they contain more.

How much

There is no regulator setting a bath dose. The figures below are what manufacturers print and what most people use.

More salt makes a stronger solution. At these amounts every one of them is under one per cent concentration in a full bath, and all of them dissolve completely.

Warm bath or cold plunge

Cold water immersion after sport has a long history in professional sport, and a warm bath has a longer one everywhere else. They are different experiences.

A cold plunge is 10 to 15 °C. It is unpleasant for the first minute. Most club players who do it use a wheelie bin, a stock trough or a chest freezer conversion, with ice or a chiller.

A warm bath is 37 to 40 °C, the temperature of a normal bath. It takes twenty minutes and needs nothing except a bath.

The minerals dissolve in either. In cold water they dissolve more slowly — stir. Menthol, if the soak contains it, makes cold water feel colder on the skin; in warm water it gives a cooling note over the warmth.

Reading the label

Bath soaks are cosmetics in Australia, not medicines. The label has to list ingredients but does not have to say how much of each.

Things worth looking for:

The first ingredient. Ingredients are listed by weight. If the first item is sodium chloride, you are buying table salt with a small amount of magnesium in it.

Magnesium chloride vs magnesium sulphate. Different compounds. Magnesium chloride has a little more magnesium per gram and dissolves faster. See the Epsom salt comparison for the full picture.

Fragrance vs essential oil. "Fragrance" or "parfum" means a synthetic scent blend. A named oil — Kunzea ambigua leaf oil, Mentha piperita oil — means the plant extract.

Weight per bath. A 1 kg tub at $30 that says "one cup per bath" is about four baths at $7.50 each. A 250 g pouch at $19.95 is one bath. Work it out per soak, not per tub.

Claims. A cosmetic bath soak that says it treats, cures or prevents anything is making a claim it is not allowed to make. Treat that as a sign about the seller, not the product.

A club-night routine

1. Get the water running at 38 °C as soon as you're home; a bath takes ten minutes to fill.
2. Pour the soak in under the running tap.
3. Fifteen to twenty minutes in.
4. Shower off if you want to. Drink water.
5. Wash the kit while you're at it, because it will still be in the bag on Thursday otherwise.

For teams: a 750 g three-pack or a 1.75 kg seven-pack of ThermoPure® is the same product as the single pouch, per soak. The larger packs cost less per soak.

Frequently asked questions