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Bio Engineering Department - University of Milan
EFFECT OF DIFFERENT
HANDLEBAR HAND POSTURES ON FAST BRAKE LEVER REACHING MOVEMENTS IN
CYCLING.
INTRODUCTION
AND PURPOSE OF THE STUDY
Aim of the present study was to evaluate
the effect of different kinds of handlebar hand postures on fast
brake lever reaching movements.
More specifically, it was investigated
whether the use of clip-on handlebars significantly altered the
time taken to reach brake levers compared to times obtained with
traditional hand postures on the handlebar.
The underlying assumption motivating
the study, is that riding postures providing quick access to brake
levers, allow the athletes to more easily manage the braking operation,
when he is forced to suddenly decrease bicycle speed or change direction
for avoiding an unexpected obstacle.
For this reason, an additional goal
of this research was to evaluate whether the time spent in reaching
the brakes, regardless of the riding position, is a factor of great
or minor importance in influencing the distance needed for a bicycle
to be brought to a stop in an emergency.
For the braking action monitoring,
it was decided for the use of the ELITE optoelectronic motion capture
system, which has gained growing popularity in the international
market for its unique powerful FPSR (Fast Processor for shape recognition)
image processor. The high system accuracy, precision, and acquisition
speed, even in difficult experimental conditions, are proved by
more than 250 scientific communications in various research areas,
and were considered adequate for the purpose of this study.
Beside the accurate measures of action
times, the used methodology, by monitoring the posture assumed by
all upper limb segments during the hand travel to the brake lever,
allowed the collection of data that could be used to further the
analysis of the motor strategies adopted by cyclists in performing
this movement.
METHODS
Experimental protocol
Experiments were conducted in the Sport
Movement Analysis Laboratory (LAMS) of the Bioengineering Center
(Politecnico di Milano-Fondazione Don Gnocchi) in Milan.
Three high level road cyclists were
the subjects of this study. Each athlete was tested while pedalling
on his own racing bicycle mounted on an air braked roller simulator.
The bikes were equipped with a Cinelli Spinaci clip-on handlebar.
While pedalling, the athletes were
asked to reach, as quickly as possible, the brake levers (as they
should brake their bike in the shortest time as possible) from the
following starting pre-defined handlebar hand postures:
- on the lower ends of the handlebar
bend (on the drops) (Fig. 1)
- on the lateral side of the handlebar
bend (Fig. 2)
- on the upper lateral side, with
the hands around the top of the brake lever mounts (Fig. 3)
- the most comfortable top-bar position
for each athletes (Fig. 4)
- on the middle section of the top
handlebar bend with the hand spaced (Fig. 5).
- on the clip-on handlebar (Fig. 6)
- on the top of the handlebar bend
with the hands close to the stem (Fig. 7)
These positions were randomly varied
from trial to trial with the limitation that each of them was used
equally often for each subject. Further, the subjects performed
the braking actions under the following trigger conditions: responding
to a visual stimulus, to an acoustic stimulus, and free to choose
when starting the movement. For each of the resulting 21 experimental
conditions, data of 10 trials were acquired for a total of 630 trials
(230 for each subject).
Data recording equipment
At a sampling rate of 100 Hz, the ELITE
motion analysis system was used to collect the 3-D kinematic variables
(displacements, velocities and accelerations) of the right upper
limb segments respect to the handlebar and right brake lever frame.
To this end, the configuration of the
ELITE system was the following: two TV cameras paired off on the
right side of the subject, while the calibrated volume for the 3-D
coordinates computing was 1.25 long, 1.25 high and 0.5 wide.
Five small retroreflective markers
(8 mm in diameter) were glued on the subject skin in correspondence
of the following anatomical repere points (Fig. 8):
mb1 the lateral side
of the arm at deltoid insertion
mb2 lateral ephicondyle
mb3 distal end of
the radio-ulnar joint
mb4 distal end of
the 3rd metacarpal
m1 distal end of
the 3rd phalanx
Two additional markers were located
on a stick rigidly fixed to the handlebar (m0)
and on a stick rigidly fixed to right brake lever (m2)
To verify the measurement accuracy
of the system, a test was carried out before each experimental session:
a stick with two spherical markers fixed on its extremities at the
distance of 400 mm were moved along the whole field of view. The
mean differences between the measured and actual distance of the
markers fixed on the rigid bar was within 0.4 mm, in agreement to
the values declared by the manufacturer.
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