And what that means is more thermal energy is produced as a byproduct. Thermal energy is energy that cannot be used to do any useful work. And so what the cells actually do is they release that energy into the blood plasma of the nearby capillary. So let's take a look at the following diagram to see what exactly we mean. So, we have the exercising cells found within our tissue, and this is the nearby capillary that is carrying our blood plasma that contains the red blood cells and the hemoglobin within those red blood cells. Now, as these exercising cells are carrying out metabolic processes at a higher rate, they produce more thermal energy.