Force, time, and stress distribution determine injury risk in climbing. High force, long duration, or unstable mechanics each increase load on pulleys and tendons—and when two or more combine, injury risk spikes sharply. Structured progression works because it controls these variables.

Hold size changes tendon path, joint angles, and pulley stress. Larger edges keep forces smooth and stable, 10 mm edges increase sensitivity, and 6 mm edges create sharp angles that multiply load and instability. You don’t get strong from small edges—you get strong toward them.

Crimp, open hand, and drag grips change tendon path, joint angles, pulley stress, and load distribution. Open hand is smooth and safe, half crimp balances strength and stability, and full crimp creates the highest mechanical stress due to sharp tendon angles.

Bowstringing happens when the flexor tendon lifts away from the bone, increasing pulley tension and destabilizing the finger. It’s the core mechanical failure behind most pulley injuries and is triggered by PIP collapse, DIP unrolling, small edges, dynamic catches, and fatigue-driven angle drift.

Ligaments, joint capsules, and other passive structures stabilize the finger and limit motion under load. They become overloaded when technique collapses, angles drift, or sessions are chaotic. Stable joint angles, slow progression, and predictable training protect passive tissues and reduce irritation.

The forearm flexor system powers climbing finger strength. FDP creates deep pulling force, FDS stabilizes the PIP joint, and key wrist flexors ensure efficient tension transfer. Forearm mechanics explain grip strength, fatigue, and load safety better than finger isolation alone.

FDP and FDS are the two flexor tendons that power your fingers in climbing. FDP is the main engine that pulls through the fingertip, while FDS stabilizes the PIP joint and supports crimping. Different grips shift load between them, and understanding their roles explains why certain positions feel strong, weak, sharp, or risky.

The A3 and A4 pulleys are small but essential stabilizers in the finger. A3 controls tendon alignment at the PIP joint, and A4 stabilizes the fingertip joint. They rarely rupture but strongly influence force distribution, grip stability, and how “smooth” or “sharp” a hold feels. Protecting them requires stable joint angles, avoiding tiny edges under fatigue, and progressing load slowly.