Most carrying products ask you to take their word for it. We would rather show you the data and let you decide — including the parts that are less flattering.
In February 2023, The Body Shelf went through a combined objective and subjective ergonomic evaluation. The objective half used surface electromyography. The subjective half used a questionnaire. This article walks through how the evaluation was run, what it measured, every number it produced, and — just as importantly — what it does not prove.
If you only read one section, read What This Study Does Not Show.
What surface EMG actually measures
Surface electromyography — sEMG — places electrodes on the skin over a muscle and records the electrical signal the muscle produces when it contracts. More electrical activity generally means the muscle is working harder.
That is a precise thing to measure, and it is worth being precise about what it is not. sEMG is not a measurement of:
- Load, in pounds, on the spine
- Strain, in any engineering sense
- Pain, comfort, or perceived effort
- Injury risk or injury rates
- Total metabolic cost of the task
It measures electrical activity in a specific muscle during a specific movement. When that activity falls, it is reasonable to say the muscle in question did less electrical work during that task. It is not reasonable to translate that directly into "50% less strain," and we no longer describe it that way.
How the evaluation was run
Subjects
Eleven people participated: eight male, three female. Mean age was 43, with a range from 17 to 58.
Loads
Two sand-filled boxes, each measuring 12.5 inches by 12.5 inches by 16 inches. One was loaded to 25 lb, the other to 50 lb. Sand was used because it gives a consistent, repeatable weight in a rigid box with a stable centre of mass.
Male subjects handled both boxes. Female subjects handled the 25 lb box only. That asymmetry matters, and we return to it below.
Tasks
Each subject performed five task types, once with The Body Shelf and once carrying unaided:
- Flat carry
- Lift and twist
- Lift and pivot
- Stair climb without a handrail
- Stair climb with a handrail
The lift-and-twist and lift-and-pivot tasks were included deliberately. OSHA notes that bending, twisting and turning are the motions most commonly cited in back injuries, so they are the conditions worth testing rather than avoiding.
Measurement
Surface EMG electrodes recorded activity in back and lower-back musculature, left and right sides separately. The evaluation reported results per side and, for some female-subject tasks, an aggregate across measured sites.
The objective results, in full
These are reductions in measured back-muscle electrical activity when using The Body Shelf, compared with carrying the same load unaided.
Male subjects, 25 lb load
- Flat carry — 51%
- Lift and twist — 56%
- Lift and pivot — 60%
- Stairs, no handrail — 43%
- Stairs, with handrail — 56%
Male subjects, 50 lb load
- Flat carry — 36%
- Lift and twist — 35%
- Lift and pivot — 53%
- Stairs, no handrail — 22%
- Stairs, with handrail — 2.8%
Female subjects, 25 lb load
- Flat carry — 12.5% at the back sites, 19% aggregated across measured sites
- Lift and twist — 21% at the right lower back; the left side showed no reduction
- Stairs, no handrail — 36% at the left back
- Stairs, with handrail — 6.5% at the left back
The evaluation summarised the male results as approximately 50% at 25 lb and 39% at 50 lb. It did not publish the calculation behind those two summary figures, which is one reason we prefer to quote the task-level range — 36% to 60% for male subjects across 25 and 50 lb loads — rather than a single headline number.
What the pattern in the data suggests
Three things stand out, and two of them are caveats.
Reductions were larger at 25 lb than at 50 lb. Across every male task, the lighter load produced the bigger reduction. A plausible reading is that at 50 lb more of the handling work falls outside what a passive shelf can take on, but the study did not test enough load points to establish that.
The handrail changed everything on stairs. At 50 lb, stairs with a handrail produced the smallest reduction in the entire dataset — 2.8%. At 25 lb, the same condition produced 56%. A one-handed carry while gripping a rail is a fundamentally different movement from a two-handed supported carry, and the data says so clearly.
Results differed markedly by sex. Female subjects saw consistently smaller reductions, and on one task showed a reduction on only one side of the lower back. The evaluation suggested handrail height relative to subject stature may have produced asymmetric loading on the stair tasks. That is a hypothesis, not a finding.
The subjective results
Subjects rated their experience on a 1–5 scale, with and without the harness:
- Overall comfort — 4.5 with, 3.3 without
- Low back comfort — 4.75 with, 2.96 without
- Perceived productivity — 4.6 with, 3.1 without
Self-reported comfort is a legitimate outcome — it is a real part of whether someone will actually use a piece of equipment on a long shift. It is also inherently subjective and, in an unblinded test where participants know which condition they are in, subject to expectation effects. Both things are true.
What this study does not show
This is the section most product pages leave out. Here is the honest accounting.
- The sample is small. Eleven subjects. Three of them female. Conclusions from a sample this size are directional, not definitive.
- No statistical significance was reported. Without significance testing, we cannot rule out that some portion of these differences reflects normal variation between trials.
- It was not peer-reviewed, and the document does not name its authors, laboratory, or institution. We are working on commissioning an independent, properly attributed follow-up evaluation.
- It measured muscle activity, not injury. No injury rates were tracked. Nothing in this evaluation demonstrates that The Body Shelf prevents injuries, and we do not claim that it does.
- Female subject results were smaller and inconsistent. Reporting only the male summary figures would misrepresent the dataset.
- Only two load points were tested. The suggestion that roughly 20–50 lb is an optimal range is an inference from 25 lb and 50 lb, not a measured curve.
- Fit and technique affected results. Subjects who were more familiar with the device showed larger reductions. A poorly fitted harness is a different product than a well-fitted one.
Why we publish it anyway
Because a 36% reduction in measured back-muscle activity on a flat 50 lb carry is a real result, and because the 2.8% stair figure tells you something genuinely useful: if you are going up stairs with a heavy load and one hand on the rail, this product is doing less for you than it does on flat ground. You should know that before you buy, not after.
The Body Shelf is a passive carrying support. It transfers load off the arms, shoulders and neck and onto the core, hips and legs. It is tested to 50 lb and should not be loaded beyond that. It does not replace safe lifting technique, and it does not replace controls your employer is required to provide.
If you want to see how that load transfer works in practice, read how ergonomic carrying harnesses work, or go through our step-by-step fitting guide — fit is the single biggest variable in whether you get results like the ones above.
Read the full methodology and download the evaluation, or see The Body Shelf.
Figures on this page are from a February 2023 internal ergonomic evaluation of 11 subjects (8 male, 3 female). It measured muscle activity, not injury rates. It was not peer-reviewed and did not report statistical significance. Female subjects averaged smaller reductions. Individual results vary with fit, technique, load and task. The Body Shelf does not replace safe lifting technique or employer-required controls.