Four (4) methods were used to measure the difference in Unassisted vs. Assisted (Ergogripper™) handling:
Figure A below shows a balanced seesaw. The flexion moment (rotation force) at the pivot point (green triangle) developed by the weight at left (LW) is neutralized by the force (F) at right. Both the weight (LW) and force (F) are equal because the Moment Arm Length (MAL - distance between the weight and force in relation to the pivot point) are the same.
Figure B shows the pivot point shifted to the right. In order to maintain the balance (cancel the flexion moment at the pivot point) the force at right "F" now needs to be three times of that in figure A because the Moment Arm Lengths (MAL) for the weight and the force are different.
The human spine, as shown in figure C, works similar to the seesaw in figure B (different Moment Arm Lengths). The important difference is that now the spine muscles need to lift the human torso weight (TW) in addition to the load weight (LW). The calculations in figure C show how much force the erector spinae muscles must exert to bring up the spine of an average male lifting a 30lb (13.6kg) box.
The Ergogripper™ effectively reduces both the torso and load Moment Arm Lengths to significantly decrease the amount of force (F) that need to be developed by the erector spinae muscles during lifting. A real life comparison is shown in figures D and E.
As shown in figure E, the Ergogripper™ eliminates reaching underneath the load resulting in a 35% reduction of spinal compression, from 649lb (294kg) to 420lb (191kg), while lifting a 35lb (15.9kg) load. No other manual material handling tool in the market can do this.
The resulting Moment Arm Length data for both scenarios is summarized in the table below along with the calculations of flexion moments and compression force in L5-S1.
|Torso Moment Arm Length
|Total Load Weight
|Load Moment Arm Length
|Erector Spinae MAL
The muscles mainly responsible for bringing the torso up from a bent position are the ERECTOR ESPINAE muscles. During an Engineering Master Thesis experiment at the Polytechnic University of Puerto Rico surface mount electrodes were used to measure and record the muscular activity of the main four (4) erector spinae muscles during the execution of a simple material handling task. The four monitored muscles where the left and right Longissimus Dorsi and the left and right Iliocostalis Lumborum. The electrodes were placed as shown in the figure at right.
The simple material handling task consisted of moving a 30lb (13.6kg) cardboard box from the floor to a table. Three handling trials for each of the participants were monitored using both arms (unassisted symmetric handling) and using the Ergogripper™ (assisted asymmetric handling). A total of 5 females and 5 males where used in the study and the muscular activity was measured along the four phases of the handling task : grasp (grip), rise (lift), carry (walk), and releasing (place).
A Biometrics™ Data Log EMG Signal Analysis Software was used to graph the data recorded during each phase of the handling task. Channels 1 through 4 each logged the data for one specific muscle as shown in the figure at left. Data logging started at a push of a button and a digital signature was introduced in the signal at the end of each of the handling phases (Grasp, Lift, Walk, and Place). Data was normalized and imported into a statistical analysis software Mintab™ for analysis of means and variances. Results showed statistically significant difference in the means and variances of muscular activity from both lifting techniques; the unassisted, double handed symmetric lifting and the assisted, single handed asymmetric lifting.
Due to the asymmetric nature of the one-handed lifting an increase of 19% was recorded for one muscle group (the Contralateral Iliocostalis Lumborum) while using the Ergogripper™. Reductions in muscular activity of 46%, 6%, and 45% were recorded, respectively, for the rest of the muscle groups (Ipsilateral Iliocostalis Lumborum, Contralateral Longissimus Dorsi, and Ipsilateral Longissimus Dorsi) while using the Ergogripper™.
Another comparison method consisted in the use of a static strength prediction modeling software to simulate the static strength requirements for tasks such as lifts, presses, pushes, and pulls. The program provides an approximate job simulation that includes posture data, force parameters and male & female anthropometry. In the Ergogripper™ evaluation a program called 3DSSPP, developed by the University of Michigan (see figures at right), was used to predict compression and shear force around the lower back (L4-L5 disc) and at the sacrolumbar vertebrae L5-S1. Anterior-Posterior shear forces were also predicted for the gripping posture along with an estimate of ligament strain percentage.
Body posture input angles were calculated with a computer aided drafting program by superimposing representations of limb segments over digitally recorded views of the actual postures. See pictures below at left for both assisted and unassisted lifting scenarios.
The Ergogripper™ reduced compression force for the lower back (L4-L5 disc) in 28% (from 715lb or 324kg to 514lb or 233kg). It also reduces compresion force at the sacrolumbar vertebrae (L5-S1) in 38% (from 723lb or 324kg to 445lb or 202kg). Lateral shear increase in 15lb (or 6.8kg) at L4-L5 and saggital shear increase in 5lbs (or 2.2kg) at L5-S1 were recorded as expected due to the asymmetric nature of the one-handed lifting. A reduction of 3% in estimated ligament strain is also provided by the use of the Ergogripper™.
Ergogripper Assisted Lifting
|Low Back (L4-L5)
Shear at L4-L5 disc
at L4-L5 disc
Shear at L5-S1
The fourth and last form of performance comparison of assisted versus unassisted lifting is through a subjective questionnaire. The study participants were asked to perform material handling tasks that included the lifting of a load, passing through a closed door and climbing up and down a stair while carrying the load. The participants were asked to indicated the agreement/disagreement level towards a set of statements grouped to assess their perception on three aspects of the load handling tasks. The statements would measure the amount of effort perceived to be required for load lifting, perceived comfort during handling, and perceived degree of safety involved in the handling of the load. The results were as follows:
- 83.3% of the participants perceived the use of the tool required less effort to lift the load than using both arms.
- 90.0% of the participants perceived that the tool provided more comfort during the handling than using both arms.
- 93.3% of the participants perceived that the tool provided increased safety during the handling than using both arms.