Principle of Backrest Office Chairs

The principle of backrest office chairs involves achieving natural support and dynamic adjustment of the human spine through structural design, material selection, and mechanical devices, with the core aim of dispersing pressure, maintaining a healthy sitting posture, and enhancing comfort.

I. Principle of Supporting the Human Body

The core function of a backrest chair is to provide mechanical support for the spine and pelvis. When seated, the weight of the upper body is transferred to the seat surface through the ischial tuberosities, while the backrest needs to share the pressure on the lumbar and thoracic spine to prevent excessive curvature or backward tilt of the spine. Key design considerations must balance three factors:

1. Seat height and tilt angle: These must match the length of the lower limbs to avoid leg suspension or compression of the blood vessels at the back of the thighs.
2. Backrest curvature and support point location: The lumbar region requires a convex support (lumbar support) that fits the physiological curvature of the spine.
3. Overall structural stability: Ensure load-bearing capacity through frame materials (such as metal or nylon) and connection processes (such as injection molding).

II. Principle of Backrest Support

1. Angle and surface design:
   • The optimal angle between the backrest and seat surface is 100°-110°, which maintains a natural lordotic curve of the lumbar spine and reduces intervertebral disc pressure by approximately 40%.
   • The backrest surface should protrude in the lumbar region (lumbar support) and be gentle in the thoracic region, forming an "S" shape that fits the spine.
2. Material impact:
   • Frames are commonly made of plastic or metal to provide structural support.
   • The filling layer uses foam or mesh: foam needs to balance hardness and resilience, as being too soft can lead to collapse and being too hard can cause pressure concentration; mesh disperses pressure through tension and offers better breathability.

III. Working Principles of Different Types of Backrest Chairs

1. Mesh backrest chairs:
   • The backrest is fixed with a high-elasticity mesh by a nylon frame, forming a dynamic support surface through tension that fits the back curve.
   • The seat cushion uses high-elastic foam to buffer pressure, and the chair legs are made of lightweight nylon.
2. Office chairs with wheels:
   • Elevation function: A pneumatic rod (filled with high-pressure nitrogen) adjusts the seat height through a valve.
   • Mobility function: A five-claw base (metal/plastic) disperses pressure, and omnidirectional wheels (PU material) with built-in bearings enable 360° rotation.
   • Reclining function: The backrest adjusts its angle through springs or hydraulic devices, with some models equipped with a locking function. The lumbar support design further reduces fatigue from prolonged sitting.

IV. Principle of Backrest Tilt

Based on the ergonomic "golden 110° sitting angle", the reclining mechanism achieves angle adjustment through mechanical structures:

1. Types of reclining mechanisms:
   • Back reclining: Only the backrest angle changes, suitable for short breaks.
   • Seat reclining: The seat surface and backrest tilt backward simultaneously to maintain even pressure distribution on the legs.
   • Synchronous reclining: The backrest and seat surface move in a fixed ratio, simulating the natural movement trajectory of the human body.
2. Damping/locking devices: Control the reclining resistance through hydraulics or springs to ensure the chair back remains stable at specific angles (such as 100°-110° for work or 130°-150° for rest).