According to researchers at Erasmus University carrying a grudge can weigh you down—literally. The researchers asked study participants to write about a time when they'd experienced a conflict. Some were instructed to reflect on a time when they didn't forgive the offender, others were told to think about the time they did forgive the person, and a third group wrote about a comparatively dull social interaction. They were then given a small physical challenge: jumping five times, as high as they could, without bending their knees.

They then asked their human guinea pigs to jump as high as they could, five times, without bending their knees. Those who had been thinking about a time when they'd forgiven jumped highest, about 11.8 inches on average; those who had written about their grudges, on the other hand, jumped 8.5 inches. There were no significant difference in the jumps of those in the non-forgiveness and neutral conditions. In another, similar experiment, people who'd been set up to think about a time they held a grudge estimated that a hill was steeper than people who were thinking about a time they forgave someone.

The results suggest that the "weight" of carrying a grudge may be more than just a metaphor. The lead researcher for the study wrote, "A state of unforgiveness is like carrying a heavy burden—a burden that victims bring with them when they navigate the physical world. Forgiveness can 'lighten' this burden."