Semi‐implantable needle oxygen electrodes were used for forearm subcutaneous monitoring in human subjects undertaking high intensity cycling and fist clenching exercise. pO2 variations in the range between 40 and 100 mm Hg oxygen were seen. Superimposed on these were paradoxical rises in subcutaneous pO2, of up to 100 mm Hg which paralleled the scale of the exercise. This was indicative of increased blood flow through skin. Triton X‐100 incorporated into the sensor polyurethane membranes helped to give faster responses and reduced the possibility of biofouling and drift. The sterilizable system, free from internal electrolyte film appears promising for future clinical monitoring.