Page 92 - Journal of Special Operations Medicine - Summer 2014

Figure 3 Means (solid lines) and standard deviations (dashed movement of the hands and arms. Previous studies ex-
lines) of the amount of frequencies during fast-roping with a amined the effects of mechanical vibrations on hands
slightly molded (black) and a deeply molded rope (gray). and arms. 11,13,14,20–22 It was shown that exposure to vi-
brations manipulates sensation and sensibility of the
muscle–nerve system. In particular, vibrations to muscles
and tendons of the wrist result in inaccurate movements
of hands and arms. The reasons for that phenomenon
are so-called segmental kinesthetic illusions. These illu-
sions provoke misinformation about the real joint angle
position and therefore cause errors in the precision of
movement. 13,20–22 Kinesthetic illusions are found not
only during exposure to vibration but also seconds to
minutes after vibration.

Wierzbicka et al. analyzed oscillations of the center
23
of force application after an exposure to vibration (80
Hz) of 30 seconds to the Achilles tendon and tibialis
anterior muscle. The results of the study showed that
Notes: *Statistically significant (p < .05) difference between the ropes. kinesthetic illusions were found 19 to 180 minutes after
***statistically significant (p < .001) difference between the ropes.
exposure to vibration. The most distinctive oscillations
of the center of force application occurred immediately
geometry, and shape of the rope, the purpose of this after completion of vibration.
work was to determine the frequency spectrum that oc-
curred with a slightly molded compared with a deeply In the study by Rogers et al., vibrations of either the
15
molded rope. To the best of our knowledge, no other biceps brachii muscle or the triceps brachii muscle for
studies have previously investigated mechanical vibra- 60 seconds (100 Hz) provoked disturbances in forearm
tions during fast-roping maneuvers with different ropes. matching task performances. The alignment errors occur
However, it was found that the construction (especially immediately following the 60-second period of muscle
geometry) of a rope plays a substantial role in releasing vibration and last for up to 4 minutes. Cordo et al. re-
13
vibrations. Because fast-roping is a rappelling technique ported that 40-Hz vibrations applied to the tendon of the
without a hook-up to the rope, the hands provide the biceps brachii muscle 5 seconds before movement onset
main contact to the rope and regulate the velocity of the and then stopped at movement onset caused target over-
maneuver by opening and closing fingers. Therefore, one shooting. The authors concluded that muscle spindle af-
can assume that the vibrations caused by the ropes are ferents, which are activated by tendon vibration, are an
transferred mainly to the Soldier’s hands and arms. The important source of the dynamic position and velocity
results of the study showed that frequencies between information that the central nervous system uses to co-
5 and 10 Hz occurred when Soldiers used a slightly ordinate the movement sequence tasks. Further, vibration
molded rope. By changing the rope into a deeply molded influences the production of finely graded forces.
one, frequencies between 18 and 60 Hz were measured.
The frequencies between the ropes differed significantly A study by Bock et al. showed that force responses
14
(p < .001) between 20 and 50 Hz (Figure 3). of the hand were 22% smaller with than without wrist
vibrations of 18 to 80 Hz. The authors concluded that
Negative effects of vibration on humans are well docu- afferent feedback plays a substantial role in the produc-
mented but are most often observed in the workplace tion of finely graded forces. In consideration, because
through exposure to large vibration loads or chronic precise movements of the arms and hands during aim-
exposure to vibration. 16–19 In this environment, expo- ing and shooting are of high relevance to maintain per-
sure to vibration has been shown to damage several sonal and tactical safety after fast-roping maneuvers,
biologic structures (e.g., peripheral nerves, blood ves- the choice of equipment of the Special Forces should be
sels, joints, and perceptual function). Animal studies considered with caution.
also reported changes in endocrine and cardiovascular
function, respiratory responses, central nervous system It should be mentioned that in this study the ropes were
patterns, and metabolic processes. Exposure to vibra- fixed with a dummy of a helicopter cockpit at a height
1
tion affects several physiological systems (e.g., neuro- of 12 m. The duration of the maneuver lasted 3 to 5 sec-
endocrine, cardiovascular, musculoskeletal, and sensory onds. During operation, the ropes have a length up to 28
systems), but there is limited reliable information on the m, which increases the duration of the maneuver to 7 to
aftereffects of mechanical vibrations on the precision of 12 seconds. Further, the flying helicopter might transfer

82 Journal of Special Operations Medicine Volume 14, Edition 2/Summer 2014