You have to understand that our bodies undergo a wide series of internal changes in order to support the demands of a hockey game. First, due to your activity level, your heart rate and breathing rate will be extremely elevated in comparison to what it is during a rested state.
Second, you’re going to have a much higher rate of blood flow and blood content within the muscles that were worked. Third, you’re going to have a high concentration of by-products associated with fatigue within your muscle cells such as lactate and H+. Fourth, you’re going to still be psychologically aroused, which causes an array of neurotransmitter and hormonal shifts within your body.