6th Grade · Science · Reading Passage · shared by Luke Morgan
Get a free 6th Grade Science reading passage on human body energy: explore glycogen, ATP, and fat as fuel for exercise.
Maya felt the starting gun's boom and sprinted forward, her legs pumping rhythmically as she began the cross-country race. She pushed her body across challenging hills and winding trails, her muscles immediately engaging in hard work to propel her. These muscles were transforming stored energy directly into the powerful movement needed for running. At the beginning of a long race, her body primarily uses a stored sugar called glycogen . This glycogen, found abundantly in her muscles and liver, acts like a readily available fuel, giving her the quick power for the initial burst of speed.
Inside Maya's active muscle cells , a complex process was taking place with every single step she took. The chemical energy locked within the glycogen molecules was being carefully released through a series of intricate reactions. This released energy creates a special molecule called ATP , which functions as the direct power currency for cellular activities. When ATP breaks down, it provides immediate energy, allowing tiny protein fibers within her muscle cells to slide past each other. This crucial sliding action causes the entire muscle to contract, creating the powerful mechanical force that moves her legs forward with each determined stride.
As Maya continued her race, pushing through mile after challenging mile, her body worked tirelessly to maintain her pace. However, around the halfway point, she started to feel a heavy and undeniable fatigue, often called "hitting the wall" by experienced runners. This happens because her body's easily accessible glycogen stores were becoming significantly depleted. Her muscle cells were now urgently searching for other energy sources to keep her moving forward. The brain then signals her body to switch to burning fats for fuel, a process which…