**Core Concept**
The kinetic energy of the body refers to the energy of motion, which varies throughout the walking cycle due to changes in speed, stride length, and body position. In gait analysis, kinetic energy is critical in understanding the biomechanics of walking and identifying potential issues.

**Why the Correct Answer is Right**
During the walking cycle, kinetic energy is least during the single support phase (also known as the single limb support phase). This phase occurs when one foot is in contact with the ground and the other foot is in the air. The body's weight is temporarily concentrated on a single limb, resulting in a brief decrease in kinetic energy. The single support phase is typically the shortest phase of the walking cycle, lasting around 10-15% of the total cycle duration.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the double support phase is characterized by both feet being in contact with the ground, resulting in increased kinetic energy due to the combined weight-bearing capacity of both limbs.

**Option B:** Incorrect because the mid-stance phase is a part of the single support phase and does not represent the phase with the least kinetic energy.

**Option C:** Incorrect because the late swing phase is a part of the double support phase and does not represent the phase with the least kinetic energy.

**Clinical Pearl / High-Yield Fact**
When analyzing gait patterns, it's essential to consider the kinetic energy of the body in different phases of the walking cycle. Identifying abnormal kinetic energy patterns can help diagnose and treat conditions such as gait disorders, joint injuries, or neurological impairments.

**Correct Answer:** D.