Loading conditions in the spine, hip and knee during different executions of back extension exercises.

BACKGROUND: Back extension (BE) is a strength exercise for training the dorsal trunk and hip muscles. To optimise training recommendations that avoid overloading and possible injury, the aim of this study was to determine the loading conditions and the influence of different execution forms of BE on spine, hip and knee ranges of motion (RoMs), joint moments and muscle activity. METHODS: The kinematics, kinetics and muscle activity (EMG) of two execution types (BEh: dynamic hip, BEs: dynamic spine) and two versions (one-legged and two-legged) of BE were measured in 16 subjects. RoMs and external joint moments were calculated using an inverse dynamics approach and analysed with a linear mixed model. RESULTS: Although lumbar spine flexion was observed in both execution types, thoracic spine flexion predominantly occurred during BEs, whereas thoracic spine extension was observed during BEh. Larger maximal back and hip moments were observed for BEh than for BEs. The activity of the dorsal back and hip muscles, as observed using EMG, was increased for one-legged executions. CONCLUSION: To strengthen the hips and lower back, BEh seem to be more efficient due to the higher moments, with higher or similar RoMs in the hip and lower back. One-legged BEs seem to provide an effective training for the hamstrings and hip regions without subjecting the spine to excessive loading, possibly promoting this as an effective exercise during training and rehabilitation.

Investigating physical fitness and race performance as determinants for the ACL injury risk in Alpine ski racing.

BACKGROUND: ACL ruptures in Alpine ski racers are frequently observed. This study analysed the association between physical fitness, race performance and the knee injury history. METHODS: A retrospective study was conducted to investigate the influence of physical fitness and performance on the knee injury outcome. As part of this study an injury data base (covering 2004-2013) was established that recorded information about the athletes, their fitness status as determined by a standardised fitness test (Swiss Ski Power Test, SSPT) as well as medical information related to injuries. The performance of athletes who sustained knee injury was compared to athletes who suffered no injury or a different injury. RESULTS: Twenty-seven (19f, 8 m) of 70 athletes sustained a knee injury. ACL ruptures accounted for 71 % of these knee injuries. While more females sustained a knee injury, the difference between males and females was not statistically significant. It was shown that athletes with a better FIS (Fédération Internationale de Ski) rank were more prone to knee injury. However, none of the parameters related to physical fitness was linked to a history of knee injury. CONCLUSIONS: A general fitness test as SSPT is not associated with a history of knee injury in Alpine skiing. More specific physical fitness test procedures should be investigated to determine relevant fitness factors.