european college of sport science

PP-AP01 Adapted Physical Activity 1
Women’s gymnastics in seventies and eighties was sport for children. The central meaning was put to achieve the biggest international
trophies for any price. With intention to avoid such abuses of children in elite sport in the future is urgently to raising the age limitation for
the senior artistic women’s gymnastics competitions to the majority, like is usual praxis in other Olympic competitive sports.
A WEARABLE SYSTEM TO TIME GATE CROSSING DURING ALPINE SKIING SLALOM
CHARDONNENS, J., FAVRE, J., CATTIN, S., JOLLES, B.M., GREMION, G., AMINIAN, K.
1. ECOLE POLYTECHNIQUE FÉDÉRALE DE LAUSANNE, 2. FISCHER SPORTS GMBH, 3. CENTRE HOSPITALIER UNIVERSITAIRE VAUDOIS & UNIVER-
SITY OF LAUSANNE
INTRODUCTION: In alpine skiing, chronometry analysis is currently the most common tool to assess performance. It is widely used to rank
competitors during races, as well as to manage athletes training and to evaluate material. Usually, this measurement is accurately
realized using timing cells. Nevertheless, these devices are too complex and expensive to allow chronometry of every gates crossing. On
the other side, differential GPS can be used for measuring gate crossing time (Waegli et al). However, this is complex (e.g. recording gate
position with GPS) and mainly used in research applications. The aim of the study was to propose a wearable system to time gates
crossing during alpine skiing slalom (SL), which is suitable for routine uses.
METHODS: The proposed system was composed of a 3D accelerometer (ADXL320®, Analog Device, USA) placed at the sacrum of the
athlete, a matrix of force sensors (Flexiforce®, Tekscan, USA) fixed on the right shin guard and a data logger (Physilog®, BioAGM, Switzerland).
The sensors were sampled at 500 Hz. The crossing time were calculated in two phases. First, the accelerometer was used to
detect the curves by considering the maximum of the mediolateral peak acceleration. Then, the force sensors were used to detect the
impacts with the gates by considering maximum force variation. In case of non impact, the detection was realized based on the acceleration
and features measured at the other gates. In order to assess the efficiency of the system, two different SL were monitored twice
for two world cup level skiers, a male SL expert and a female downhill expert.
RESULTS AND DISCUSSION: The combination of the accelerometer and force sensors allowed to clearly identify the gate crossing times.
When comparing the runs of the SL expert and the downhill expert, we noticed that the SL expert was faster. For example for the first SL,
the overall difference between the best run of each athlete was of 5.47s. At each gate, the SL expert increased the time difference slower
at the beginning (0.27s/gate) than at the end (0.34s/gate). Furthermore, when comparing the runs of the SL expert, a maximum time
difference of 20ms at each gate was noticed. This showed high repeatability skills of the SL expert. In opposite, the downhill expert with a
maximum difference time of 1s at each gate was clearly less repeatable. Both skiers were not disturbed by the system.
CONCLUSION: This study proposed a new wearable system to automatically time gates crossing during alpine skiing slalom combining
force and accelerometer sensors. The system was evaluated with two professional world cup skiers and showed a high potential. This
system could be extended to time other parameters.
REFERENCES
Waegli A, Skaloud J (2007). Inside GNSS, Spring, 24-34.
INFLUENCE OF WORKLOAD AND POSTURE ON HANDCYCLING EFFICIENCY
GAFFURINI, P., GOBBO, M., BISSOLOTTI, L., CALABRETTO, C., ORIZIO, C.
LABORATORY OF NEUROMUSCULAR REHABILITATION (LARIN), UNIVERSITY OF BRESCIA/DOMUS SALUTIS CLINIC
Introduction: Handbike (HB) is an arm propelled device of locomotion for subjects with lower limbs disabilities. Handcycling has become
a Paralympics discipline, increasing the need to study how lesion level may influence posture on HB and energy cost during exercise. The
aim was also to test how postures different from the free chosen one might influence functional parameters during exercise.
Methods: We studied 20 handbikers: 14 DivB (lesions T1-T10), 6 DivC (lesions T11-L5). The HB was placed on a computerized roller to
measure speed (km/h), frequency of revolutions (rpm) and power (Watt). The arm-crank unit was equipped with a load cell to measure
horizontal (Fh)/vertical (Fv) forces and an infrared encoder to transduce angular position (15° resolution). VO2 and VCO2 were measured
by a portable metabolic system Cosmed K4 b2 and heart rate (HR) by Polar monitor. The main muscles involved in cranking (Biceps
Brachii, Triceps Brachii, Deltoid Anterior, Trapezius, Latissimus Dorsi) were studied by a portable EMG system.
1) The subject sat on the HB and chose his favourite posture (seat-crank distance and adjustable backrest inclination). The elbow angle (α)
was measured when crank was in 90° position (maximal arm extension during cranking).
2) The athlete was asked to cycle at 65 rpm with 3 different chain gears: L1, L2, L3, corresponding to 32x28, 32x21 and 32x16 gear ratios,
respectively.
3) The gear ratio determining 60-70% of HRmax, named threshold gear (Lt), was used to test two other positions with elbow angles of
α+10° and α-10°.
Each bout lasted 4 min. Averaged Force and EMG envelope profiles were derived for a complete revolution.
Results: The increase of external workout from L1 to L3 determined an increase of both Fh and Fv. In particular, an increase of about 100%
and 60% of Fh in DivB and DivC, respectively, took place. EMG activity in DivC increased less than in DivB subjects to obtain the same
increase of external workload from L1 to L3. Considering exercise at Lt, no variations in EMG envelopes were founded passing from α-10°
to α+10°. An increase in Fh was observed only in DivB group from α (41.2±21.6 N) to α+10° (56.9±27.5 N). VO2 was influenced by posture
changes only in DivC: higher values for α-10° and α+10° than α position (α-10°: 23±7.5; α+10°: 22±6.9; α: 20±6.7 ml/kg•min).
Discussion: The different increase of both Fh and EMG with incrementing workload suggests different biomechanics and muscle recruitment
in the two groups. Indeed, DivC subjects can recruit abdominal muscles leading to a higher exercise efficiency.
The increase of energy cost in DivC for α-10° and α+10° cranking positions, without concomitant changes in force and EMG, indicates
lesser efficient postures compared to the free chosen one. For DivB, the more stable α+10° position determines even a more advantageous
biomechanical condition, that is probably not spontaneously adopted by the subject for the uncomfortable sustained flexion of the
head required to look forward.
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ANNUAL CONGRESS OF THE EUROPEAN COLLEGE OF SPORT SCIENCE