Your heavy legs have finally crested that last awful peak and now the worst is over. Or is it? Sure, it's literally "all downhill from here" but there are still more than 9 miles to the finish line. Much of what makes the Equinox Marathon so difficult is its demanding transitions in muscles and cadence (not to mention climate). Once a comfortable rhythm is developed, an entirely new terrain appears. For the downhill section of the course, runners must shift from the short, toe-based stride typical of climbing hills to much longer, stretched steps that land on the heels. With each foot fall, the body is also jarred by a high-intensity impact due to the extra "help" forward from gravity. Now, only air resistance and the ever-present downward pull of gravity, along with a healthy respect for the disaster potential of uncontrollable momentum, hold the runner back.

As before, an idealized force diagram can help explain how our tireless runner can use physics to get the most out of her downhill effort on race day.    Although the forces are slightly different, she should maintain the same form running downhill as she followed on the uphill. Because most runners use downhill segments to "catch up" some of the time lost on the uphill slog, it is still most efficient for her to shift her center of gravity above her front foot and to pump her bent arms. These same techniques will produce the same applied force, however, now the runner is not fighting Fgravity(x): Consequently, Fapplied will have a larger effective magnitude and result in more speed and acceleration. At a certain point, either to avoid injury or over-exertion, a reduction in applied force will need to moderate the increase in pace. Physics shows that the runner can activate her "brakes" without changing the launching force from her legs by shifting her center of gravity back into the hill, reducing arm pumping, and/or increasing the angle of elbow bend to > 90 degrees.