Don't know really but I've been asking around a lot and thinking a lot, cause this is a problem I've got to get round.
Some say liver has to clear biproducts from muscles (as well as restock). Evidence in favour of this is that if you have ever had hepatitis, you will have had the ultimate experience of heavy limbs. Couldn't bear to brush my hair, comb even was far too heavy. Also as I appear to have never quite recovered from the experience (to judge from my inability to hold my own at the pub) I am very interested in what an enormous difference the walking bits in run/walk make. It's easy to believe that 60 seconds in which the clearing of biproducts exceeds production of same is the what is happening. Can keep going if I can keep clear enough.
But why should muscles clogged up with biproducts make limbs feel heavy? Guess because a proportion of the muscle fibres aren't working, so the fewer that are have to do proportionately more work. Also tallies with my experience with the lurgy: when hand muscles are hit, the cast iron frying pan seems to weigh hugely more.
Take notes: do you have a bad run after a hard night's drinking? Perhaps not in any case if your liver is up to the job.
