Which of the following activities is most likely to result in the highest level of blood lactate accumulation?

The activity most likely to result in the highest level of blood lactate accumulation is indeed the 400-yard dash. This sprinting activity is performed at a high intensity for a short duration, leading to anaerobic energy production. During intense exercise, the body relies on anaerobic glycolysis, which breaks down glucose for energy without the use of oxygen. This process results in the production of lactate as a byproduct, causing a rapid increase in blood lactate levels.

In contrast, marathon running employs a steady, moderate pace that mainly utilizes aerobic metabolism. The energy system used during marathon running efficiently processes oxygen, which minimizes lactate production. Activities such as leisurely walking and swimming at a moderate pace also predominantly utilize aerobic pathways, resulting in minimal lactate buildup. Therefore, these activities do not place the same demand on the anaerobic system as the 400-yard dash does, leading to lower blood lactate levels compared to high-intensity sprints.