The simplest explanation is that physical activity increases blood circulation and lung ventilation, which (as long as one is not exercising in a polluted envir

The simplest explanation is that physical activity increases blood circulation and lung ventilation, which (as long as one is not exercising in a polluted environment) helps the liver and kidneys process and excrete various toxins at a greater rate. It also reduces body fat, which can store fat-soluble toxins. There's also a high likelihood that people who get regular exercise are also eating healthier food that hasn't been highly processed and loaded up with pesticide residue, biocides that slow fungal and bacterial growth, animal growth hormones, etc. The fundamental equation is something like: (body load of toxins) = (ingestion rate) - (excretion rate)