Ethan Ostrom et al. have recently published in the journal of Free Radical Biology and Medicine a new study demonstrating the muscular redox stress response to high intensity muscle stimulation vs low intensity muscle stimulation. The authors found that there were no differences in redox stress response activation when comparing high intensity stimulated muscle and low intensity stimulated muscle.  However, there was activation of the redox stress response in contralateral unstimulated muscle of the high intensity group, but not the low intensity group. These data suggest that high intensity muscle contraction releases some kind of signal that acts systemically via the blood stream to activate the stress response in other tissues – in this case the unstimulated muscle. Low intensity muscle contraction does not have the same effect on unstimulated muscle compared to high intensity contraction. Together, these data indicate high intensity contraction, but not low intensity contraction, causes a systemic redox stress signaling effect that could be driving some of the differences in exercise adaptation efficiency between high and low intensity exercise.