Joint actions: kinetic chains, open vs closed

Open chain vs closed chain

The distinction comes down to where the distal segment is.

Open-chain: the distal segment (foot or hand) is free to move. Leg extensions, lat pulldowns, dumbbell curls, leg curls. The hand or foot moves, the body stays still. Closed-chain: the distal segment is fixed against an immovable object (the floor, a wall, a fixed bar). Squats, deadlifts, push-ups, pull-ups, lunges. The body moves around the fixed point.

Why the distinction matters

Closed-chain movements:

Involve more muscles (the whole chain must stabilize)
Better for athletic transfer (most sports use closed-chain at the foot)
Better for stability and joint coordination
Less isolation, more compound recruitment

Open-chain movements:

Better for targeted hypertrophy
Useful in rehab when you need to isolate a weak muscle
Lower demand on neighboring joints
Common in machines

Kinetic chain concept

Movement doesn't happen at one joint in isolation. A squat travels up through ankles, knees, hips, spine, shoulders. A bench press involves wrists, elbows, shoulders, scap, thoracic spine. Each joint affects the next.

When something fails mid-chain, the rest of the chain compensates. Bad ankle mobility → knees cave in squats. Tight thoracic spine → shoulder pain on overhead pressing. Trainers who understand chains don't treat the spot that hurts — they look upstream and downstream.

Programming choice

For a knee rehab client, you might start with open-chain leg extensions (isolated quad work) before progressing to closed-chain squats once stability returns.

For an athlete, closed-chain dominates because that's how the sport works.

For a beginner, closed-chain teaches them to control their whole body — but assistance machines (open-chain) can build foundational strength before they're ready for closed-chain compounds.

TL;DR