运动并不是量越大越好，运动过量则可使免疫功能受到损害，影响健康。剧烈运动时，体内会产生相当多的肾上腺素和皮质醇激素。当这些激素增加到一定数量时，可使免疫系统中的脾脏产生白细胞的能力大为减弱；使淋巴细胞Ａ细胞、Ｂ细胞及自然杀伤细胞（ＮＫ细胞）活性大为降低。 Exercise is not the greater the better, exercise too much immune function can be compromised, affecting health. Strenuous exercise, the body will have a considerable amount of epinephrine and cortisol. When these hormones are increased to a certain amount, the ability of the spleen in the immune system to produce white blood cells is greatly diminished; the activity of lymphocyte A cells, B cells and natural killer cells (NK cells) is greatly reduced.