OK, OK... my experience is that you can feel it readily, if in a hampered state (stress or post high exertion etc) then the feeling is very easy.
Bath hot as
you can comfortably take, 1/2kg or better 1kg, soak as long as you are comfortable, longer is better IMO (though much contested), then finish with a cool shower, gradually going colder as much as is comfortable, until the skin is cool to the touch.
Also, for high athletic recovery/significant need to regain ATP and stimulate oxygen into the body,
you may add 1.5l 12% Food Grade H2O2. Expensive, but very nice (your body cover in bubbles, the H2O2 is a weak bond that gives a super oxygen rich bath effectively).
Magnesium is an important micronutrient essential for various biological processes and its deficiency has been linked to several inflammatory disorders in humans. Topical magnesium delivery is one of the oldest forms of therapy for skin diseases, for example Dead Sea therapy and Epsom salt...
pubmed.ncbi.nlm.nih.gov
...we found that magnesium penetrates through human stratum corneum and it depends on concentration and time of exposure. We also found that hair follicles make a significant contribution to magnesium penetration.
Continuation of bathing for 7 days in all except 2 individuals gave a rise to a mean of 140.98 ± 17.00ppm/ml. Prolonged soaking in Epsom salts therefore increases blood magnesium concentrations. Measurement of magnesium levels in urine showed a rise from the control level, mean 94.81 ± 44.26 ppm/ml to 198.93 ± 97.52 ppm/ml after the first bath. Those individuals where the blood magnesium levels were not increased had correspondingly large increases in urinary magnesium showing that the magnesium ions had crossed the skin barrier and had been excreted via the kidney, presumably because the blood levels were already optimal. Generally, urinary magnesium levels 24h after the first bath fell from the initial values found after day 1 (mean 118. 43 ± 51.95) suggesting some retention of magnesium in tissues after bathing as blood levels were still high. Measurement of magnesium levels in urine 24h after the 7th bath gave values almost back to control levels.
This was based on 12minute baths. The optimal level comment for those whose levels did not increase is incorrect, IMO, it is my suspicion that those people were likely soo backed that all the Mg²⁺ ions were spin up in the Kidneys to help clear the backlog (but that's going off course to your needs).
Loads like this below, on Magnesium supplements more generally:
Magnesium is a cofactor of different enzymatic reactions involved in anabolic and catabolic processes that affect muscular performance during exercise. In addition, it has been suggested that magnesium could participate in maintaining muscle integrity during demanding effort. The main purpose of...
pubmed.ncbi.nlm.nih.gov
We conclude that magnesium supplementation seems to exert a protective effect on muscle damage.
Good crude schedule is Calcium early part of day, meeting together with Magnesium just before a Sporting event, then Magnesium post event (this suits the autonomic nervous system ideally, unless the event is late night or early day).
Think I remember you're a active sporty guy... hence I've made a little effort for you!
Hope these words are better, if not I have more!