The current theory of muscular contraction differs from the earlier explanations of the function of the contractile tissues notably with respect to the precise rôle of oxygen. It is now believed that the chemical changes leading to muscular activity take place in the absence of oxygen, while the recovery processes are dependent on the presence of this gas. The production of lactic acid thus becomes an essential feature of muscular contraction. In harmony with this, it has been demonstrated that during and following severe muscular exercise lactic acid appears in abnormal quantities in the blood. The urine, however, does not always similarly show the presence of this muscle catabolite.
In explanation of this phenomenon, Hewlett, Barnett and Lewis1 of the Stanford University School of Medicine in San Francisco appear to have demonstrated that there is a renal threshold value for lactic acid somewhat as there is for circulating glucose.
OXYGEN AND MUSCLE WORK. JAMA. 1927;88(13):1005. doi:10.1001/jama.1927.02680390033013
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