Why Do You Feel Tired Even When "Just Sitting" on a Train? — How a 15-Degree Torso Angle and Ergonomic Backrests Support Passengers

When commuting or traveling, have

you ever felt inexplicably tired even

after getting a seat on the train? In

fact, even while seated, the human

body constantly works to maintain

balance and posture, and this fatigue

is deeply connected to the backrest

angle.

The angle of a seat backrest is known

as the "torso angle," and body weight

distribution changes dramatically at the

15-degree mark. When the torso

angle is under 15 degrees, almost all

body weight is concentrated on the

seat cushion. Consequently, core

muscles such as the abdominals and

back muscles must constantly tense

and relax to stabilize the upper body

against train movement. Conversely,

inclining the seat to 15 degrees or

more effectively distributes upper body

weight onto the backrest. This reduces

pressure on the seat cushion and

allows core muscles to relax.

Yurikamome was among the first transit

systems to introduce this 15-degree

torso angle for longitudinal seat

arrangements. On Yurikamome, in

addition to setting the torso angle to

15 degrees, the seats were designed

with a contoured bucket shape and

backrests extended up to shoulder

height. Supporting both shoulders

prevents lateral swaying during transit

and provides enhanced stability.

This design philosophy—combining a

15-degree torso angle with shoulder

-height backrests—has spread to many

AGT systems, including Yurikamome,

the New Shuttle 2020 series, the

Nippori-Toneri Liner 330 series, the

Astram Line 7000 series, and the Leo

Liner L00 series. Behind these

vehicles lies the dedicated effort of

designers responding to the hidden

need of easing passengers'

unconscious fatigue through

ergonomics.

I hope you look forward to the next

AGT Blog!