Follow through and overlapping action: the principle in Blender

What is follow through and overlapping action?

Follow through and overlapping action is the animation principle that makes a body start and stop in stages instead of all at once: loose parts keep moving after the main mass has stopped, and the parts of a body move at different rates. It is what gives a character weight and inertia.

It is one of the twelve basic principles of animation that Disney animators Frank Thomas and Ollie Johnston set out in their 1981 book The Illusion of Life: Disney Animation. The Wikipedia article on the principle, citing page 59 of the book, quotes Walt Disney telling his animators: "Things don't come to a stop all at once guys; first there's one part and then another". The two ideas are so close that they share one heading, and a third term, drag, often joins them.

Follow through, overlapping action and drag

All three describe inertia, at different moments of a movement.

• Follow through happens after the stop. Loosely attached parts travel past the point where the body stopped, get pulled back toward the center of mass and swing with less and less amplitude until they settle: a dog's long ears after it stops running, a coat swinging past the legs, a ponytail. Thomas and Johnston add that the way an action finishes is often more important than the action itself.
• Overlapping action runs through the whole move: the parts of a body move at different rates, so an arm does not keep the same timing as the head. The torso is the core, and the arms, legs, head and hair follow it. Soft tissue, such as a large belly or the loose skin of a dog, moves more independently than bony parts.
• Drag happens at the start: when a character starts to move, some parts take a few frames to catch up, whether objects like clothing or a car antenna, or body parts like the arms and the hair.

The book also describes the "moving hold": the character comes to a complete halt while its fleshy parts keep following through, which conveys weight. Even a character standing still breathes or shifts slightly, as in an idle animation.

Worked example: stopping after a run

The feet plant and the hips stop first. The chest carries forward a little and comes back, the head trails the chest, the arms swing past the body and fall back, and the hair or the coat go furthest and settle last, each part on a different frame, from the core of the body to its loose ends. As a starting point, if the hips stop on frame 20, try the chest on 22, the head on 23 or 24 and the hair around 30, then judge in playback.

How to animate overlapping action in Blender, step by step

Animate the main mass first, then make each part further from the core lag behind the one before it. Menus and shortcuts below are checked against the Blender 5.2 manual and its default keymap.

1. Block the main mass. In Pose Mode, pose the hips and torso on the key poses and press I to insert keyframes, keying the loose parts along with them for now. The manual notes that Constant interpolation is normally used for this blocking stage: T (Key > Interpolation Mode) > Constant, in the Graph Editor or the Dope Sheet.
2. Switch back to Bézier, the default interpolation, once the timing works. Everything now starts and stops together, which is the stiffness the next steps remove.
3. Offset the trailing parts in the Dope Sheet. Click a key on the channel of the first bone that should lag and press L (Select Linked) to select every key on that channel, then G to move them a few frames later; dragging works too. To delay only the end of the move, ] selects every key on or after the playhead.
4. Work down the chain, root to tip. In forward kinematics, each child bone inherits the location and rotation of its parent. Rotate each bone (R) and give it a slightly later timing than its parent: the movement travels down a tail, a ponytail or an arm like a wave.

Overshoot and settle in the Graph Editor

Where the body stops, the curve of a loose part should go past its final value, come back short of it, then land, each swing smaller than the last.

• Key the overshoot. New keys get Auto Clamped handles, which the manual describes as clamped to prevent overshoots between keyframes, so Blender will not invent one: key the extreme past the rest pose, a smaller one back, then the rest.
• Shape the handles. V (Key > Handle Type) sets Aligned for a smooth key or Free for a sharp change of direction.
• Stretch the settle. In the Dope Sheet, S scales keys in time only, around the playhead: put the playhead on the stop frame and scale the settle keys to slow it down or speed it up.
• Draft with Elastic. On the key just before the rest pose, T > Dynamic Effects > Elastic makes the value overshoot, rebound and undershoot with decreasing intensity until it settles. Amplitude and Period, in Sidebar > F-Curve > Active Keyframe, set the first overshoot and the time between oscillations. It looks mechanical on a hero shot, so replace it with keys.

Checking arcs: Motion Paths instead of onion skin

Natural movement follows arcs, and a part that leaves its arc for no apparent reason looks erratic. In Pose Mode, select the bones, open Properties > Armature > Motion Paths (or Pose > Motion Paths) and click Calculate Path. Each frame is a dot, red before the current frame and green after, and the path updates as you edit keys. Set Bake Location to Tails to follow the tip of each bone. Blender's onion skinning belongs to Grease Pencil, so on a 3D character Motion Paths are the built-in way to compare frames.

Letting physics handle the loose parts

Capes, skirts and soft flesh can be simulated instead of keyed: the simulation reacts to your animation, so drag and follow through come out of it. Keep keyframes for what the acting depends on, such as the arms and the head.

Cloth for capes and skirts

The manual's example is a tunic held at the waist by a belt. With the armature in its bind pose, parent the clothing to it, put the pinned vertices (the belt area, the collar of a cape) in a vertex group with a weight of 1, add Cloth in the Physics tab with the Cloth modifier below the Armature modifier, pick the group as Pin Group in Physics > Cloth > Shape, and add Collision physics to the body. For a cloak held by a clasp, sewing springs pull two corners together and let it slide about the neck and shoulders.

Soft Body for jiggle

The manual says Soft Body was designed primarily for adding secondary motion to animation, like jiggle for body parts of a moving character. With Goal enabled, it uses the existing animation as the target of each vertex; a vertex group sets the goal weight per vertex, and Goal Damping sets how fast the wobble dies out.

Jiggle bones

For hair or tails rigged with bones, extensions.blender.org lists Jiggle Physics by naelstrof (Blender 4.2 and newer), a fork of the Wiggle 2 add-on. Its panel is in the Animation tab of the Sidebar (N): turn on the scene's jiggle with the eye icon, then tick Jiggle Bone on a bone in Pose Mode. It switches itself off during rendering, because Blender can render frames out of order, so it has to be baked first. The manual recommends the same for every simulation, so the result stays identical every time; for cloth, set Start and End in Physics > Cloth Cache and click Bake.

Secondary action is a separate principle

Secondary action is an extra action added to the main one, like a walking character who swings their arms, whistles or changes expression. The twelve principles list it apart from follow through and overlap, and its rule is that it must support the main action and never pull attention away from it. When the Blender manual calls Soft Body jiggle "secondary motion", it means what the twelve principles call follow through.

Rendering: motion blur and the overlap

By default Blender renders each frame as a perfectly still image, while a real camera blurs fast-moving objects in the direction of motion. On a whip of hair or a tail, the tip covers the most distance per frame: without blur it jumps between sharp positions, with blur it draws a streak along its path, and the trailing motion reads as one move.

• Where: Render Properties > Motion Blur, ticked in the panel header, in Cycles and EEVEE. Shutter is in frames: at 1.0 the blur covers one frame.
• Cycles: in Object Properties > Motion Blur, Deformation blurs deformed meshes such as animated characters, hair included. Its Steps improve accuracy and use more memory.
• EEVEE: more Steps give cleaner blur, but each step re-evaluates the whole scene and can add a lot to the render time.

The manual adds that unbaked physics can give incorrect or inconsistent blur. To measure the cost, render one frame of the fastest part of the shot with the final settings and multiply by the frame count; the render time calculator does that sum. In stylized work, smear frames show the same speed graphically.

Common mistakes

• Everything stops on the same frame. The character looks switched off. Select a key on the stop frame in the Dope Sheet and press K (Columns on Selected Keys): if every channel has a key selected there, the overlap is missing.
• Offsets too regular. Every bone exactly two frames after its parent gives a mechanical wave. Vary the delay with the weight and looseness of each part, and vary the size of each swing too.
• Overlap without a cause. A part trails because the body moved or stopped. Hair that keeps swinging after a tiny gesture, or a tail waving on a still body, looks random.
• Endless wobble. The settle has to die out within a few swings, each smaller than the last. Exaggerated follow through reads as comic, which suits a cartoon; realistic animation needs exact timing. In a Soft Body, raise Goal Damping.
• Breaking volume. Overlap is timing and rotation. Rotate the bones of a chain and keep their length; moving or scaling trailing bones to fake drag stretches the mesh like rubber. A part that should stretch on purpose is squash and stretch, with its own volume rule.