RESUMO
Objectives: Ski and snowboard-related injuries are common among Canadian youth. Analyzing the role of risky behaviours that contribute to injury risk is essential for gaining an understanding of injury prevention opportunities. The objective was to determine if rates of risky behaviour seen at the ski hill were lower for children and adolescents exposed to an educational injury prevention video. Methods: This single-blinded cluster randomized controlled trial included students (ages 7-16) from 18 Calgary schools who were enrolled in novice levelled school-sanctioned ski and snowboard programs. Consenting schools were randomly assigned to the intervention or control. The control group followed standard preparation including watching a general ski hill orientation video that was created by the ski hill. The intervention group viewed the intervention video focussed on injury prevention. The Risky Behaviour and Actions Assessment Tool was used by blinded research assistants to observe and record students' risky behaviours at an Alberta ski hill. Results: In total, 407 observations estimated the rate of risky behaviour. The overall rate of risky behaviour was 23.31/100 person runs in the control group and 22.95/100 person runs in the intervention group. The most commonly observed risky behaviours in both groups were skiing too close to other skiers/snowboarders and near collision with an object/person. Conclusions: Both groups showed similar rates of risky behaviour and demonstrated the same most common type of behaviour. Practical applications: future work should focus on mitigating common risky behaviours.
RESUMO
Residual force enhancement (rFE) describes the increase in isometric force following muscle stretching compared to the corresponding isometric force. Even though rFE is consistently observed in isolated muscle preparations, it is not always observed in human skeletal muscle. This inconsistency might be associated with disociations between length changes in muscle tendon units (MTUs) and fibres. This prompted the question if there is rFE for conditions where the MTU is stretched while fibres shorten. Rabbit tibialis anterior (TA) MTUs (n = 4) were stretched and the isometric forces following stretching were compared to corresponding forces from isometric reference contractions. Unique combinations of stretch speed and activation were used to create conditions of continuous fibre shortening during MTU stretch. Mean force was increased (18 ± 2%) following MTU stretching compared to the isometric reference forces. Without fibre length measurements, this result would be referred to as rFE. However, fibre shortening in the reference contractions was always greater than for the eccentric stretch contractions, suggesting that the observed increase in force might be caused by less residual force depression (rFD) in the stretch tests compared to the reference contractions. However, the work performed by fibre shortening was similar between the reference and the MTU stretch contractions, suggesting that rFD was similar for both experimental conditions. Therefore, we conclude that we observed rFE in the absence of contractile element stretching. However, a lack of knowledge of the molecular mechanisms that distinguish rFE from rFD prevents an unequivocal pronouncement of what caused the enhanced forces after active muscle stretching.
