As the man walks, each foot strike creates a noticeable vibration that travels up through the lower leg immediately after ground contact. Because the concrete surface is rigid and does not deform to absorb impact, the force is transmitted back into the body, producing a brief oscillation of the soft tissues and muscles of the lower leg. This visible vibration reflects the body's response to the impact forces generated with each step on an unyielding surface. You may want to listen to the podcast: Think Up, Lean Fodrward
