Does arm span and reach predict climbing grade?

We analysed thousands of client records to test this question.

The answer: barely.

Finger strength and training matter far more.

"Ape index" - the difference between arm span and height, is widely discussed in climbing culture as a determinant of ability, on the assumption that a longer reach confers a meaningful advantage. Existing sport-science literature has generally found this assumption weakly supported at best. We’d also looked at this ourselves in the past, in the early days of Lattice...

What was our objective?

To test, using our own client base, whether ape index relates to climbing grade, examined separately for bouldering and sports climbing and also separately by gender.

The method

Height, arm span, gender, and self-reported best grade were drawn from a datapool of client records and cleaned to remove placeholder and implausible values. Ape index was calculated both as an absolute difference (arm span minus height) and as a ratio. The relationship to grade was tested with correlation analysis, separately for boulder and sport grade and separately for men and women, with results checked two independent ways before being treated as reliable.

The results

Across the client base as a whole, ape index showed only a weak relationship with grade. It’s certainly ‘real enough’ to be statistically detectable, but small enough that it accounts for only a small fraction of the difference between climbers of different grades. This presented in the findings consistently whether the specialisation was boulder or sport.

So, what conclusion can we draw?

In the climbing population, it’s unlikely that ape index is a significant, meaningful advantage or disadvantage. This is consistent with prior published research and with Lattice's broader coaching position…. Which, guess what… is that trainable qualities of strength, technique, work capacity explain far more of the gap between climbers than body proportions do!

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Ask at a forum, crag or climbing wall of climbers whether reach matters, and most will have an opinion — usually a strong one, and usually about whether they have a "good ape index" or not. It's one of the most persistent pieces of climbing folklore: the idea that a longer wingspan is a giving you a grade or two… AKA something you either won or lost at the genetic lottery.

The existing sport-science literature has looked at this question a few times, and the consistent theme is that reach is, at most, a minor factor. It remains nowhere near the outsized role it's often given in climbing mythology. We wanted to check how this looks in our own client base, using real height, arm span, and grade data rather than folklore and small bits and piece of research in existence.

Ape index rises gently across grade, but the relationship is weak.

Looking across the client base, a weak-but-real upward pattern was detectable. Higher-grade climbers had, on average, a somewhat larger ape index than lower-grade climbers. Knowing someone's ape index tells you almost nothing useful about what grade they climb. This came up, whether we looked at boulder grade or sport grade and whether ape index was measured as a raw difference or a ratio.

When we plotted the full distribution of ape index at every individual grade (not just grouped into bands) the spread of values within any single grade dwarfed the difference between grades. Climbers at every level, from intermediate through elite, span the full range from a notably negative ape index to a notably positive one. There is no grade at which a particular ape index becomes a prerequisite. Which is good news for most!

By gender, the picture is asymmetric but not necessarily the finding itself.

The weak pattern described above was clearly statistically detectable among men, where we have a large sample. Among women, the point estimate ran in the opposite direction, but the sample was small enough that the result comfortably could have gone either way by chance. Unfortunately, we don't yet have enough data to say whether the same pattern strictly presents for women.

We’d love more data!

So what are we thinking…?

None of this is a surprising result. Published research on climbing anthropometry has consistently found that body-proportion measures like ape index explain very little of the variation in climbing performance. One key study found that anthropometric measures accounted for a small fraction of a percent of the variance in climbing performance, while training-related variables accounted for the majority of it (Mermier et al., 2000). Other work has found that climbers as a group tend to have a slightly longer reach than non-climbers, but that this doesn't distinguish stronger from weaker climbers once you're looking within the climbing population itself (Watts et al., 2003). Possibly because everyone ‘serious enough’ to be in the sample is already in a fairly narrow range.

Our own data lines up with that picture almost exactly. There is a distinct pattern that reach isn't completely irrelevant in a statistical sense, but it's almost a rounding error next to what actually separates climbers of different grades. The more useful question for a climber wondering about their own progress isn't "what's my ape index," but "how strong are my fingers, how good is my technique, how good is my work capacity?" These are the things that in both the literature and our own testing, actually move the needle.

Some caveats…

This is correlational, not causal. Nothing here tells us whether ape index has any causal bearing on climbing outcomes, only whether the two are related in this sample. Grade is self-reported "best ever," not a verified or current measure of ability. This is a long-time issue in climbing research if we’re being totally frank!

The female sample is considerably smaller and the female-specific result should be treated as inconclusive rather than as a confirmed absence of effect. Finally, this describes engaged Lattice clients who have entered both a measurement and a grade, not necessarily the climbing population at large.

Tl;dr

Ape index is unlikely to be a meaningful advantage or disadvantage in climbing - we certainly pay little attention to it here in our coaching and training plans. A small, statistically detectable relationship does exist (driven mainly by a much larger male sample) but it explains only a small portion of what separates climbers at different grades. The rest is mostly down to the things you can actually train. Thank goodness!

What can you actually do to improve your climbing grade?

Testing — knowing which trainable physical attribute is holding you back is where all progress begins.

We have free climbing assessments that allow you to do this.

Training — consistent, structured, specific climbing training over a long enough period of time, focused on the trainable physical attribute(s).

We offer a range of climbing training plans for all abilities and disciplines.

Tracking — Retest and monitor your progress to see what's working, recognise when you've plateaued, and ensure you're effectively programming your training and progressively overloading.

You can retake our free assessments again and again to track your training progress over time.

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Sources: Mermier, C.M., Janot, J.M., Parker, D.L., & Swan, J.G. (2000). Anthropometric and physiological determinants of sport climbing performance. British Journal of Sports Medicine. Watts, P.B. et al. (2003), as summarised in secondary climbing-science coverage.

Data source: Lattice Training client records (height, arm span, gender, self-reported grade).