Office Chair Posture and Arm Placement

The correct sitting posture on an office chair for arm placement can be summarized as the third right angle in the 'three right angles' principle, with the core being to achieve natural arm relaxation through 90° flexion of the elbow joint. The specific placement method needs to be distinguished based on whether the chair has armrests, and attention should be paid to avoiding muscle strain or nerve compression due to improper posture.

Chairs with Armrests:
The forearm should be flexed at approximately a 90° angle and placed steadily on the armrests. At this time, it is necessary to ensure that the height of the armrests matches the height of the desktop, allowing the forearm to extend horizontally. Avoid having the armrests too high, which can cause the shoulders to hunch up (triggering trapezius muscle tension), or too low, which can cause the elbows to hang in the air (increasing the load on the forearm muscles). If the armrests are adjustable, it is recommended to adjust them to be level with the desktop or slightly lower by 1-2 cm to accommodate users of different body types.

Chairs without Armrests:
The arms need to be placed directly on the desktop, maintaining a 90° flexion of the elbow joint. At this time, it is necessary to ensure that the height of the desktop is consistent with the position of the elbows when they are hanging naturally. Avoid having the desktop too high, which can force the shoulders to abduct (easily causing shoulder and neck pain), or too low, which can cause the body to lean forward (increasing the pressure on the lumbar spine). If the height of the desktop is fixed, it can be matched by adjusting the height of the seat: after sitting down, place both feet flat on the ground with the thighs parallel to the ground, and at this time, the elbows naturally bend to touch the desktop, which is the appropriate height.

Key Details:

1. Angle Control: The flexion of the elbow joint should be strictly maintained at 90°±5°. Excessive flexion can cause continuous contraction of the forearm muscles, while insufficient flexion may compress the ulnar nerve (triggering 'mouse hand').
2. Shoulder State: Regardless of whether there are armrests or not, the shoulders should hang naturally. Avoid rounded or hunched shoulder postures. Regular shoulder-circling exercises can be performed to relieve muscle stiffness.
3. Dynamic Adjustment: Maintaining the same posture for a long time can easily lead to fatigue. It is recommended to slightly adjust the position of the arms every 30-45 minutes (such as briefly raising the arms or changing the support points on the armrests) to promote blood circulation.

Warning about Incorrect Postures:
If the arms are in a state of 'elbow adduction (clamping the arms)' or 'excessive abduction (spreading the wings)' for a long time, it can respectively increase the load on the triceps brachii and deltoid muscles, and even induce tennis elbow or frozen shoulder. In addition, avoid operating with the arms completely hanging in the air above the keyboard. This posture can cause excessive tension in the forearm extensor muscles and accelerate the occurrence of carpal tunnel syndrome.