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As we age, the physical world starts to come across as a less-friendly place. As our body's limitations become more obvious and pronounced, hills appear to be steeper, and distances seem longer than they once did.

Well, recently published research suggests a simple way to lessen that will-sapping perception of difficulty, allowing us to access reserves of strength we didn't know we had. It simply involves thinking about someone who has wronged you—and forgiving them.

"The benefits of forgiveness may go beyond the constructive consequences that have been established in the psychological and health domains," writes a research team led by Xue Zheng of Erasmus University's Rotterdam School of Management. "Our research shows that forgivers perceive a less daunting world, and perform better on challenging physical tasks."

"A state of unforgiveness is like carrying a heavy burden—a burden that victims bring with them when they navigate the physical world," they add. "Forgiveness can lighten this burden."

In the journal Social Psychological and Personality Science, Zheng and her colleagues describe two studies. In the first, 46 undergraduates were recruited to participate in two ostensibly unrelated experiments.

A lack of forgiveness "can increase rumination, which may decrease the availability of cognitive resources such as glucose that can otherwise be used to cope with physical challenges such a jumping or climbing a hill."

Half of them began by writing about "a time when they were seriously offended by another person, and ultimately forgave them." The others wrote about a similar incident from their past, but one where they continued to hold negative feelings toward the other person.

Afterwards, each "walked individually to a predetermined point at the base of a nearby hill," and estimated its slant. Those who had recalled forgiving another perceived the hill to be less steep than those who had been thinking about a grudge they continued to hold.

The second study featured 160 undergraduates from two continents—72 from Erasmus University, and 88 from the National University of Singapore. One-third wrote about a time when they suffered harm but forgave the other party; one-third wrote about a similarly painful situation, but one where they had not forgiven the person who harmed them. A final third wrote about a "recent interpersonal interaction" that did not involve forgiveness.

Afterwards, participants took part in an "ostensible physical fitness task," in which they were asked to jump five times without bending their knees. The height of their jumps was recorded in centimeters.

After controlling for such factors as overall fitness and regular amount of physical activity, the researchers found those who had written about forgiveness jumped higher, on average, than those who had just recalled incidents marked by a lack of forgiveness.

There was no significant difference in jumping height between the forgiving participants and those who wrote about the benign interaction. To the researchers, this suggests those who had failed to forgive felt weighed down, leading them "to jump less high than they otherwise would."

Zheng and her colleagues could not pinpoint the mechanisms that drove these results, but they note several possibilities. "Victims who are unable to reconcile with their offenders often feel a sense of powerlessness," they note. Perhaps forgiveness leads to increased feelings of personal power, which manifest themselves in greater physical strength.

They also note that a lack of forgiveness "can increase rumination, which may decrease the availability of cognitive resources such as glucose that can otherwise be used to cope with physical challenges such a jumping or climbing a hill." In other words, sitting around and stewing about a slight takes energy that can be put to better uses.

So if your physical strength isn't what you'd like it to be, consider for a moment whether you're still angry at the jerk who cut you off on the freeway this morning. If so, you might want to release those negative emotions. Lifting a weight from your shoulders can really make a difference—even if it's merely metaphorical.