Automatic measurement of key ski jumping phases and temporal events with a wearable system

Abstract

We propose a new method, based on inertial sensors, to automatically measure at high frequency the durations of the main phases of ski jumping (i.e. take-off release, take-off, and early flight). The kinematics of the ski jumping movement were recorded by four inertial sensors, attached to the thigh and shank of junior athletes, for 40 jumps performed during indoor conditions and 36 jumps in field conditions. An algorithm was designed to detect temporal events from the recorded signals and to estimate the duration of each phase. These durations were evaluated against a reference camera-based motion capture system and by trainers conducting video observations. The precision for the take-off release and take-off durations (indoor < 39 ms, outdoor = 27 ms) can be considered technically valid for performance assessment. The errors for early flight duration (indoor = 22 ms, outdoor = 119 ms) were comparable to the trainers' variability and should be interpreted with caution. No significant changes in the error were noted between indoor and outdoor conditions, and individual jumping technique did not influence the error of take-off release and take-off. Therefore, the proposed system can provide valuable information for performance evaluation of ski jumpers during training sessions.

Association between traditional standing vertical jumps and a soccer‐specific vertical jump

“…The Keimove TM data were sent to a laptop computer via Bluetooth † . The validity and reliability of the device to measure contact/flight times and velocity at take-off variables have been previously demonstrated (Chardonnens et al, 2012;Picerno, Camomilla, & Capranica, 2011;Requena, Requena, García, Sáez-Sáez de Villarreal, & Pääsuke, 2012).…”

Rapid weight loss in the context of Ramadan observance: recommendations for judokas

“…For instance, the London Summer Olympics of 2012 were scheduled during Ramadan. About 25% of the participants came from Muslim-majority countries, although it is less clear how large a proportion of these individuals observed Ramadan [16]. Those who did so would have consumed increased quantities of food and drink during the hours of darkness, largely meeting their fluid and nutrient needs [1, 2, 17].…”

“…The performance decrements associated with Ramadan observance could be explained by several factors [1, 2], including disturbances of circadian rhythms [29], hypohydration [34], altered food intake [17], sleep disturbances [29], a decrease in training [16], alterations of body composition, and fatigue [16]. In a study of 15 male elite judokas, Chaouachi et al [35] found that maximal oxygen intake and performances of the squat jump, counter movement jump, and 30-m sprints were all maintained throughout Ramadan observance; the only decrement of performance was in the mean power developed during repeated 30-s vertical jumping.…”

“…They could reflect differing periods of food and water deprivation, different performance test protocols, failure to allow for exacerbating factors [37], differences in the timing of experimental sessions, training status, the age and sex of the subjects, and environmental conditions. Most of the studies where Ramadan had no adverse effects on sport performance were conducted on athletes living in centres of excellence, where training load, sleeping schedule, and nutritional aspects were well controlled, and body mass was well maintained [16]. …”

Forward acceleration of the centre of mass during ski skating calculated from force and motion capture data

“…They do, however, demonstrate small but acceptable limitations (e.g. [14,35,41]). Advances in measurement systems (e.g.…”