When we have set out on a piece of muscular work or head work, we might expect to find a steady, regular increase in the fatigue that resulted from it — so much work, so much fatigue. But that is not the case. The “fatigue curve” is not a straight line sloping evenly upward from one corner of the chart diagonally to the opposite. Instead, it goes sharply upward at the start; then for a long distance it runs along on an approximate level; and then it takes a sharp upward turn again...FROM THE BOOK