Most climbers think finger strength is about weight, hold size, or grip type.
But the truth is simpler (and harsher):
Joint angles decide everything.
- whether a pulley survives or fails
- how force is distributed
- how tendons load
- how stable a grip feels
- how predictable a training session is
- why some holds feel sharp and others smooth
- why some climbers can train heavy without problems and others get injured with bodyweight
If you understand PIP and DIP angles, you understand 80% of finger mechanics.
This article makes it simple.
1. The PIP and DIP joints: the “hinges” controlling the whole force chain
Quick recap (no medical jargon needed):
-
PIP joint = the large middle knuckle
(most bending in crimping) -
DIP joint = the small fingertip joint
(controls fingertip curl)
These two joints determine the shape of the finger, and therefore the shape of the force line.
Translation:
- If the PIP collapses → A2 pulley takes a hit
- If the DIP unrolls → FDP tendon takes a spike
- If both stay stable → force distributes safely
Small changes = big mechanical consequences.
2. Why climbers injure themselves when angles drift
A finger is a mechanical lever.
If the angle changes even a few degrees:
- the force line redirects
- load shifts from tendon → pulley
- or from pulley → tendon
- or both get hit simultaneously
This is called angle drift, and it’s the main cause of:
- A2 injuries
- A3 irritation
- DIP joint soreness
- unpredictable fatigue
- tendon “pinch” sensations
- sharp pain during small edges
Angle drift is not a strength issue.
It’s a mechanical failure.
3. How each joint contributes to safe loading
The PIP joint (middle knuckle)
Controls:
- force redirection
- A2 pulley load
- fingertip stability
- overall grip shape
If the PIP collapses:
- A2 is overloaded instantly
- force becomes angular instead of smooth
- the load becomes chaotic
The DIP joint (fingertip joint)
Controls:
- fingertip contact
- friction
- tendon tension
- the final part of the force line
If the DIP unrolls:
- the FDP tendon gets hit
- force jumps to the fingertip
- grip feels unstable (“slippy” feeling)
Together, PIP + DIP create one mechanical system.
4. The “Angle Stability Zone” (the key to safe finger training)
For training and climbing, the ideal angles are:
- PIP partially bent (not collapsed, not straight)
- DIP slightly curled (not unrolled, not fully crimped)
This creates a smooth force line:
- force travels through tendon → bone evenly
- pulleys load predictably
- no angle spikes
- grip feels “secure” rather than “sharp”
This is the same angle pattern in:
- half crimp
- strong open hand
- controlled drag
It’s NOT present in:
- full crimp collapses
- tiny edges with collapsing PIP
- fatigued fingers
- “panic grips” mid-move
5. Why small edges cause big angle problems
On a larger hold, angles stay stable.
On a tiny edge:
- the PIP bends more
- the DIP straightens more
- the force line becomes more angular
- load concentrates at A2
- tendon tension increases sharply
This is why:
- the same weight feels more dangerous on a smaller edge
- training edge size must be chosen carefully
- joint stability → safety
- edge instability → overload
The edge changes the angle
→ the angle changes the force
→ the force decides the injury risk.
6. Fatigue destroys angle stability
Fatigue doesn’t just make you weaker.
It makes you mechanically unsafe.
Signs of fatigue-driven angle drift:
- DIP unrolling on rep 3
- PIP collapsing slightly
- fingertip losing “bite”
- grip feeling sharp instead of smooth
- wrist flexing to compensate
Strength work is safe
only if angles remain stable when tired.
When the angle fails, the structure fails.
7. Why training must prioritize angle control over load
Climbers often base training on:
- “how heavy can I hang?”
- “how small is the edge?”
- “how long can I go?”
But the body bases stress on:
- how stable are your angles?
Load progression is safe only when:
- PIP angle stays identical across reps
- DIP angle stays identical across reps
- fatigue doesn’t cause drift
- session-to-session angles match
This is why intensity increases are tiny
and volume must be repeatable.
You’re not training muscles —
you’re training joint stability under load.
Putting it all together
PIP and DIP angles determine:
- mechanical safety
- force distribution
- pulley stress
- tendon tension
- edge comfort
- training predictability
- injury risk
- long-term adaptation
Load is secondary.
Hold size is secondary.
Training protocols are secondary.
Angle stability is the primary control system of the finger.
If you control the angles, you control the forces.
If you control the forces, you control your outcomes.