Effects of Surface Inclinations and Carrying Aid Types on Postural Stability During Posterior Load Carriage in Rural Agricultural Tasks

Dear Editor,

We read with great interest the article by Khoirul Muslim et al.[1] The study addresses an important occupational health problem and provides valuable preliminary insights into how different carrying aids influence balance on steep slopes. We would like to raise several points regarding this study.

First, the absence of electromyography (EMG) recordings limits the physiological interpretation of the reported “discomfort” and “strain,” as reduced center-of-pressure sway does not necessarily indicate lower muscular demand but may instead reflect increased cocontraction associated with higher joint loading. Without EMG data from key muscle groups (e.g., erector spinae, quadriceps, and tibialis anterior), it remains unclear whether the observed stability represents efficient load management or merely a transient stiffening strategy during the brief 75-second trials. Furthermore, the short exposure duration may not adequately capture time-dependent viscoelastic responses of spinal ligaments and intervertebral disks that can develop during prolonged load carriage under conditions more representative of agricultural work.

Additionally, the use of a single load magnitude (30% of body mass) may obscure potential nonlinear effects on postural stability. The reportedly greater weight of the custom frame backpack compared with the fabric shawl also introduces possible confounding, as observed differences in postural control may be attributable to total mass rather than load distribution. Evaluating multiple carrying aids of comparable weight across varying load magnitudes would better isolate the true ergonomic effects. Furthermore, the use of least significant difference post hoc testing in a small sample with multiple outcome measures may increase the risk of type I error. The application of more conservative correction methods, along with fuller statistical reporting, would strengthen confidence in the study’s conclusions.

An important aspect that could further strengthen a study focused on posterior load carriage (PLC) is the inclusion of spinal kinematic measurements. Injury risk associated with PLC is often influenced by shear and compressive forces acting on the lumbar spine. The compensatory forward lean described by the authors suggests possible alterations in lumbosacral alignment; however, in the absence of thoracic and lumbar motion markers, it remains difficult to determine whether the apparent stability observed with the framed backpack may be accompanied by altered spinal loading or changes in trunk flexion patterns.[2]

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.