The tendon catches up slowly. This tells you when to push and when to wait.
Start a session, log each route as you go. Cleaner data, less to remember.
The signals behind your verdict — what each one means and where you stand.
Every number Belay Monkey computes, where it comes from, and an honest line between what the research establishes and what's a calibrated estimate. Built so you can defend the tool to anyone who asks.
Belay Monkey exists to manage one problem: muscle strength outpacing tendon adaptation. A prospective longitudinal study tracked adolescent athletes across a season and found those with tendon strain ≥9% had a 2.3-fold higher risk of developing tendinopathy, with tendon force rising before symptoms appeared — attributed to "inadequate adaptation of tendon stiffness to increases in muscle strength."1 That's exactly the mechanism Belay Monkey catches.
Each climb becomes one number. The structure encodes a research finding; the constants are tuned.
A systematic review of 34 studies found higher climbing intensity and bouldering raised overuse-injury risk, while volume was a weak, inconsistent predictor.2 So intensity can swing the score ~8× while volume swings it under 2×.
| % of your limit | intensity factor |
|---|---|
| ≤60% (easy) | 1.0 |
| 80% (hard) | 3.5 |
| 100% (limit) | 8.0 |
| beyond limit | 10.0 |
estimate The curve's shape follows from tendon mechanics; the values (3.5, 8.0…) are calibrated estimates real data would refine.
Load scoring (effort × duration) comes from session-RPE, validated across sports and for climbing, which captures general and local forearm exertion separately.3 A caveat shaping Belay Monkey: RPE works well for advanced climbers but tends to overestimate intensity for intermediates,4 so forearm pump is its own channel and grade alone isn't trusted.
3D motion-capture measured full crimp at 28–37° wrist extension — the most of any grip — lengthening the finger flexors and raising load across the A2/A4 pulleys; open-hand stays mid-range with lower strain.5 Crimp is independently linked to overuse risk.2
| grip | multiplier | basis |
|---|---|---|
| open / drag | ×1.00 | mid-range |
| half crimp | ×1.15 | 14–17° ext. |
| full crimp | ×1.30 | 28–37° ext. |
A logarithm so volume nudges but never dominates: 10 tries ≈ 1.0, 40 ≈ 1.7.
The headline gauge: is this week unusually hard versus what you're used to?
The acute-to-chronic comparison and its U/J-shaped injury curve come from established load research; a 2025 meta-analysis of 22 cohort studies rated the evidence good quality.6 Sweet spot 0.8–1.3.
| ACWR | zone |
|---|---|
| <0.8 | undertraining |
| 0.8–1.3 | sweet spot |
| 1.3–1.5 | caution |
| >1.5 | danger spike |
ACWR is contested — critics show it doesn't consistently predict injury and that one ratio oversimplifies multifactorial risk.7 Belay Monkey treats it as a spike flag, not a predictor, and always subordinates it to the 24-hour tissue signal. Claim that much and it holds up.
From the same framework. High monotony (>2.0) means dangerously samey training — the repetitive-load pattern most tied to tendon overuse, which ACWR alone misses.
The rule protecting the whole system: the 24-hour tissue signal overrides every computed number. Tendinopathy comes on and recovers slowly, so a rising next-day signal beats any load estimate. Heavy-slow resistance builds the tendon; isometrics calm pain but aren't curative; structural strength work — not stretching or warm-ups — is what's shown to prevent shoulder and elbow injury.2
The same review found BMI, warm-ups/cool-downs, stretching, taping and hydration not associated with overuse risk.2 Wrist wearables (Garmin) are excluded for load too — climbing's mechanism is local tendon tension, which heart rate barely sees.
Citation details are drawn from the published records; verify the DOI before formal use.
Or log routes without the timer — just start a session and use “Log route” each time.
Every session you've logged, and how your body felt the morning after. Tap a check-in dot to record or update the 24-hour signal for that day.