The aerobic threshold is the level of physical effort at which a person's cells are just beginning to carry
out fermentation to meet some of their energy
needs. Marathon runners try to stay at or below
the aerobic threshold so that they can go longer
distances without experiencing difficulty. While
running up and down the hills of San Francisco,
the runner was focused on trying to maintain the
pace he had when he was running on flat land.
What impact did this focus have on his ability to
maintain his aerobic threshold?

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