For urban planners, park designers, and anyone who enjoys lingering on a park bench, the angle of chair armrests is a crucial yet often overlooked element of comfort. Extensive ergonomic research indicates that the optimal angle for park chair armrests to significantly reduce user fatigue is a 15 to 20-degree downward tilt (from horizontal).

This specific angle is not arbitrary. It serves multiple physiological functions. A slightly downward-sloping armrest promotes superior shoulder relaxation by allowing the upper arms to rest naturally without hunching or straining. This position decreases tension in the deltoid and trapezius muscles, which are common sites for stiffness during prolonged sitting. Furthermore, this angle gently encourages the forearms to pronate (rotate inward) slightly, a neutral and relaxed position for the wrists and hands, whether they are resting on one's lap or holding a book.

This design also enhances stability. The angle provides a subtle gravitational guide for the arms, preventing them from sliding off and minimizing micro-adjustments that contribute to mental and physical fatigue. It creates a supportive structure that aligns with the body's natural seated posture rather than forcing an unnatural one.

While flat armrests are common, they often cause the elbows to splay outwards, creating muscle tension. Sharply angled or vertical armrests, conversely, can feel restrictive and uncomfortable. The 15-20 degree sweet spot offers the perfect compromise: enough slope to guide the arms into an optimal position for blood flow and muscle relief, yet gentle enough to remain comfortable for extended periods. Therefore, specifying this precise angle is a simple, effective way to transform public seating from merely functional to genuinely restorative.