what happens to your body when it “hits a wall” during physical activity?

When the body "hits a wall" during physical activity, it means it has suddenly run out of its primary energy source, glycogen, stored in muscles and liver. This depletion causes overwhelming fatigue, muscle weakness, dizziness, cognitive impairment, and a dramatic drop in performance. The body then shifts to using fat as a less efficient fuel, leading to increased effort, muscle cramps, and heavy limbs. Heart rate and breathing increase as the cardiovascular system tries to compensate for low energy availability. This condition is common in endurance sports like marathons and can be mitigated by maintaining glycogen through nutrition and pacing strategies.