In a 2015 study, Swedish researchers compared the effect of a slouched vs. normal body posture with regards to performing lifting tasks.

In particular, investigators wanted a better understanding of how a slouched posture affects neck and shoulder function and muscle activity in three large muscle groups—the upper trapezius (UT), lower trapezius (LT), and serratus anterior (SA)—during arm elevation to see if it affects range of motion, muscle activation patterns, maximal muscle activity, and total muscle work.

Study participants—non-injured, young adult males—perform maximum arm elevations in upright and slouched postures that researchers observed using a combined 3D movement and EMG (electromyography) assessment system. This measured the arm range of motion, velocity, and spine curvature simultaneously with EMG activity in the UT, LT, and SA muscles.

The research team found that participants in the slouched position experienced significantly less arm elevation and decreased movement velocity both upwards and downwards, in addition to increased peak muscle activity (that is, the muscles had to work harder) in all three muscles tested.

It appears that increased thoracic kyphosis (slouching) leads to a marked increase in physical requirements when performing simple arm movements. Over time, such changes in function could place added stress on the muscles, tissues, and joints of the neck and shoulder, leading to pain and injury. These findings add to a growing body of research regarding the detrimental long-term effects of poor posture as well as an understanding of how exactly faulty postures increase the risk of musculoskeletal disorders.

In their conclusion, the authors of the study write, “[Patients] suffering from neck-shoulder pain and disability should be investigated and treated for defective thoracic curvature issues.”