Which of the following is a sign of dehydration during exercise?

Dark yellow urine is a sign of dehydration during exercise because the color of urine is a direct indicator of hydration status. When the body is adequately hydrated, urine typically appears light yellow or clear, as it contains a higher water content. As fluid loss occurs—especially during intense physical activity—urine becomes more concentrated due to the reduced volume of water in the body, leading to a darker hue. This change reflects the body conserving water due to decreased hydration, signaling that the individual may need to replenish fluids. Monitoring urine color is a practical method to assess hydration levels, especially during exercise when fluid loss through sweat can be significant.