Whether it's a personal challenge, for charity, or on your bucket list, marathons are one of the most sought-after goals for amateur and recreational runners worldwide.
Now, a world-first study from the University of South Australia and the University of North Dakota suggests that a person's marathon potential may be identified through a simple check of their hands.
In a meta-analysis of 22 studies (representing 5293 participants and 12 countries) researchers found that a lower digit ratio - when a person's ring finger is longer than their index finger - is a biomarker of cardiorespiratory fitness, specifically exercise tolerance and endurance performance.
The findings indicate that someone with longer ring fingers than index fingers may perform better in endurance sports like marathons or long-distance cycling.
While previous studies have explored digit ratio and sports performance, this is the most comprehensive synthesis of evidence for digit ratio and cardiorespiratory fitness, and the first meta-analysis to link it specifically to exercise tolerance and endurance performance.
Exercise tolerance is the level of physical activity an individual can endure before experiencing excessive fatigue. Endurance performance is the ability to sustain physical activity for long periods, often at a moderate to high intensity.
UniSA researcher and PhD candidate Bethany Gower says that digit ratios could present a useful, low-cost screening tool for spotting potential in high-performance endurance athletes.
"Measuring and comparing finger lengths might seem like a novelty, but research shows that this is a proven and biologically sound method for identifying muscle strength - and now, endurance performance," Gower says.
"Our research found that digit ratio is significantly linked to exercise tolerance, which reflects the highest intensity of exercise you can tolerate for a long time before it becomes too challenging to continue.
"What this means is that people with lower digit ratios - a ring finger longer than their index finger - are more likely to tolerate increasing exercise intensity and perform better in longer-duration activities, such as marathons or distance cycling.
"It's a significant finding that could help coaches and sports scientists identify talent, or help recreational athletes better understand their endurance potential."
With elite athletes soon to compete in the Tour de France (5 July - 20 July) or the TCS Sydney Marathon (31 August), it's a curiosity that could be put to the test.
Prof Grant Tomkinson says that digit ratios are determined during early foetal development.
"Greater exposure to testosterone in the womb has been linked with the development of lower digit ratios, which could influence a person's ability to exercise intensely," Prof Tomkinson says.
"It also has short-term benefits in later life by helping 'charge' the endocrine system to respond to challenging situations, like intense exercise, by suddenly spiking testosterone levels.
"This could manifest as people having stronger body systems or organs that physically improve their ability to tolerate intense aerobic exercise, or as a stronger psychosocial, competitive response to being challenged when exercising."
For everyday athletes curious about their fitness potential, Gower says there's a simple way to get a clue - just look at your fingers.
"Digit ratio is easy to measure - just compare the length of your index and ring fingers of your hand. If your ring finger is longer, you've got a lower ratio.
"You never know - your fingers might just reveal you're built for endurance."
The University of South Australia and the University of Adelaide are joining forces to become Australia's new major university - Adelaide University. Building on the strengths, legacies and resources of two leading universities, Adelaide University will deliver globally relevant research at scale, innovative, industry-informed teaching and an outstanding student experience. Adelaide University will open its doors in January 2026. Find out more on the Adelaide University website.
