5.3. Postures

The trunk inclination varied across the conditions. On average, the inclination was
greatest during the pull trials at the initiation of motion and during the push trials during

Figure 7. Average initial and sustained forces for each of the transfer devices during a
‘push’ transfer. Arrow lines represent the transfer devices that are significantly different
from each other. * represents those transfer devices in which the sustained force is
significantly different from the initial force.


Figure 8. Average initial and sustained forces for each of the transfer devices during a
‘pull’ transfer. Arrow lines represent the transfer devices that are significantly different
from each other. * represents those transfer devices in which the sustained force is
significantly different from the initial force.


the sustained motion. However, in general, trunk inclination was highly variable both
across subjects and across trials. Overall, there was no association between trunk angle
and transfer device. Trunk angle ranged from 17 to 678. This high level of variability can
be explained by the fact that technique was not controlled in this study. Rather, using a


Figure 9. Average initial and sustained forces for each of the transfer devices during a
‘twist’ transfer. Arrow lines represent the transfer devices that are significantly different
from each other. * represents those transfer devices in which the sustained force is
significantly different from the initial force. In this condition the control trial was
eliminated from this analysis. No subject was able to successfully move the manikin with
a pure pulling force without lifting.

self-selected technique inherently increased content validity by allowing the experienced
patient handlers to lift as they would in real life.

5.4. Electromyographic profile

The peak electromyographic profile of the 14 tested muscles was averaged across subjects
and is shown in figures 10, 11 and 12 for the conditions of push, pull and twist
respectively. Some general observations can be made. A high degree of variability existed
between the peak EMG amplitudes for the different muscles. However, overall a general
trend was observed in certain muscles. As expected, as the external force required to
perform the transfer increased so did the peak EMG amplitude. This trend was
particularly evident in the back extensors during the push and pull transfers and in the
obliques during pull and twist transfers. Across the different transfer types, push transfers
led to the highest levels of peak EMG across muscles, suggesting higher levels of muscle
co-contraction. Pull and twist transfers produced much lower levels. One note is that in
the push and pull transfers, only the RollboardTM and BubbleboardTM were successful in
preventing subjects to produce levels of activation above 100% of their isometric
maximum voluntary contraction. With the twist transfers, the highest levels of activation
were observed in the right internal obliques, which is consistent with twisting to the right.

6. Discussion

The initial study to quantify the friction-reducing properties of the transfer devices was
relatively easy to control and appropriate for statistical analysis. In contrast, by having
real workers perform the tasks it was not easy to vary conditions due to ethical/safety
concerns. Thus, while analysis of the devices may be considered a typical paradigm, the
testing with three workers simply forms a proof of principle. All three transfer devices
tested were successful at reducing the static and kinetic coefficients of friction during the
patient transfer task. The three workers showed that their choice of technique was also
important.

The limited results obtained from EMG data also showed a slight association with the
patient transfer device; however, a large amount of variability in peak EMG amplitude
existed. Skotte et al. (2001) also reported that during manual tasks performed by health
care workers, EMG was found to be more dependent on the health care worker than on a
specific transfer device. In the present limited study of just three workers, the ‘proof of
principle’ conclusions substantiate the Skotte findings. It is very possible that a more
robust pool of workers would have demonstrated a wider variety of transfer techniques.
However, this would not change the conclusions reached here. In addition, the
conclusions may not be generalized to much heavier patients. Even though different
applied loads did not appear to affect the coefficient of friction of the devices, moving
heavier patients may need different postures for the patient handlers. Finally, the
observations were under ‘ideal conditions’ since all other factors were controlled, such as
time pressures, uncooperative patients, etc.
In summary, both the RollboardTM and the BubbleboardTM successfully reduced the
coefficient of friction and hand forces. But what is clear is that worker transfer technique
remains a critical determinant of back load. The proof of principle obtained in this work
demonstrates that directing the hand force vector through the low back diminished the
magnitude of this force to influence back load. This would be considered good form. This
relegates the variables of trunk inclination and forward reach to dominate the magnitude
of the back load. The full potential effectiveness of these devices requires some education
on these manual patient transfer techniques, recognizing these variables.