Is There a Training Effect?

Some studies show that people become more efficient after training at one speed, not the other. It's possible that there's a training effect that has nothing to do with you being more efficient. Tempo runs should be like your the pace you can run an hour at, or like a ten k pace or something. Do you know why they mean tempo runs? Why don't they call em leg screaming, chest burning, hell runs? Cause that's a bitter tats,. An actual better description for em is "hell runs"