Final answer:
Downhill running involves eccentric activation of the quadriceps and hamstrings, controlling descent and stabilizing joints. In physics, calculating speed and time for a skier involves gravitational acceleration and kinematic equations. A running start may offer little advantage but is still useful due to air resistance and initial acceleration needs.
Step-by-step explanation:
Downhill running involves eccentric contraction of the muscles, which occurs when a muscle elongates under tension. This is typically observed in the quadriceps and hamstrings as they control the descent of the body. Eccentric activation provides braking force to control the speed and stabilize the joints, and it's more prominent during downhill activities compared to flat or uphill running.
In a downhill ski race, it's mentioned that the initial kinetic energy is small compared to the gravitational potential energy even on small hills. For the skier traveling 70.0 m down a 30° slope, we would calculate their final speed and time taken by using laws of physics that include gravitational acceleration, kinematic equations, and energy conservation principles. Getting a running start in competitive events, even if it offers little advantage due to the gravitational potential energy, could still be beneficial due to factors like air resistance and the importance of acceleration at the start of the race.