What Your Finger Length Could Reveal About Your Cardio Fitness

Look at your hand right now. Is your ring finger longer than your pointer finger? If so, you may be athletically gifted, according to new research.

The meta-analysis, which was recently published in the American Journal of Human Biology, suggests that people whose ring fingers are longer than their pointer (index) fingers—a phenomenon called a lower 2D:4D digit ratio—can better tolerate harder, longer workouts.

The researchers believe the report is the most comprehensive analysis to date linking digit ratio to exercise tolerance and endurance performance.

“Those with lower digit ratios are more likely to succeed in endurance sporting events like long-distance running, walking, cycling, or rowing, or team sports that provide a strong aerobic challenge,” study author Grant Tomkinson, PhD, a professor in human movement and exercise and sports science at the University of South Australia, told Health. “Digit ratio may be a useful, low-cost screening tool for certain aspects of cardio fitness, such as exercise tolerance and endurance performance.”

The researchers reviewed 22 studies that evaluated 5,293 individuals across 12 countries. They specifically investigated how people’s 2D and 4D lengths related to various measures of cardiorespiratory fitness, including how well their bodies utilized oxygen during intense exercise and how vigorously they could exercise until they became fatigued.

People with a lower 2D:4D ratio, meaning their index fingers were shorter than their ring fingers, had better exercise tolerance and endurance performance. No relationship was found between the 2D:4D ratio and other aspects of athleticism, such as aerobic capacity and efficiency.

Other studies have linked finger-digit ratios to various traits, including heightened physical aggression and increased competitiveness.

The lower 2D:4D ratio has also been associated—albeit weakly—to multiple measures of athletic performance, including greater handgrip strength, faster sprinting speed, and higher explosive strength, said Michael Fredericson, MD, a sports medicine physiatrist with Stanford Medicine.

“Some studies suggest that the effect is more pronounced in males and in sports that require endurance or explosive power,” he told Health.

A few studies have found that people with lower 2D:4D experience more intense spikes in testosterone during intense exercise, which may help them tolerate discomfort. And elite athletes generally tend to have lower 2D:4D ratios than non-athletes. However, “this is not a universal finding across all sports, and the effect size is generally small,” Fredericson pointed out.

Past research suggests your finger size is related to how much testosterone you were exposed to in the womb—and that those exposed to more testosterone may have lower 2D:4D ratios.

Prenatal testosterone, some scientists believe, may enhance how well the body utilizes oxygen during exercise.

“Prenatal testosterone exposure has long-term effects on the growth and development of several bodily organs—like heart, lungs, muscles, bones—that may help cardio fitness levels,” Tomkinson said. Together, these effects could also impact how the endocrine system responds to challenging situations, like a running a race, he added.

Older research suggests that prenatal testosterone could influence how motivated a person is when they workout—and the more motivated they are, the stronger they can perform.

But some scientists are skeptical of the influence prenatal testosterone has on finger length. That includes James Smoliga, PhD, a professor in the Department of Rehabilitation Sciences at Tufts University School of Medicine. 

According to Smoliga, digit ratio changes over time, with adult digit ratio often differing from the ratio measured after birth. “So, it makes no sense that we can use adult digit ratio to gain insight into what was happening in utero,” he told Health. 

In addition, Smoliga pointed out, identical twins can have different digit ratios, despite being exposed to the same conditions in utero. 

Finally, “there’s really no clear way to confirm the hypothesis that digit ratio—even after birth—really does reflect prenatal testosterone,” he said. Measuring fetal testosterone exposure would require continuous monitoring of levels in the amniotic fluid, which isn’t feasible.

The study researchers say that identifying people with a lower 2D:4D ratio could help sports scientists identify talent and help athletes understand their athletic potential. But Tomkinson noted that scoping out finger length shouldn’t replace direct fitness assessments.

More research is needed to better understand how finger length could help athletes and coaches map out people’s potential, he said.

Other scientists, like Smoliga, question the role finger length may play in sports. “The utility of digit ratio is really questionable,” he said. He believes it’s unlikely finger size could predict one’s endurance performance.

Fredericson feels similarly. Much of the research conducted on digit ratio has been observational, which can’t establish causation, he noted. “Further research is needed to clarify the underlying mechanisms and to determine any practical implications for talent identification or athletic training,” Fredericson said.

As for what definitely can help your aerobic performance? Training. Aerobic and resistance training can drastically improve your cardiorespiratory fitness, research shows. “One’s training is a lot more likely to influence performance than digit ratio,” Smoliga said.