Effect of sand on knee load during a single-leg jump task: implications for injury prevention and rehabilitation programs

The purpose of the study was to determine potential differences in landing strategies and subsequent joint loads at the knee (knee abduction moment [KAM], anterior-posterior [AP] tibial translation, and total knee shear force) when jumping onto sand and firm ground from both a level surface and a 30-cm height. Firm ground would act as the control for the study. Seventeen subjects (age: 23.6 ± 3.7 years; body mass: 67.7 ± 10.3 kg; height: 168.5 ± 7.4 cm) performed 3 single-leg jumps on their dominant leg for each of the 4 conditions tested (ground level, sand level, ground height, and sand height). A repeated-measures design investigated the effect of sand on KAM, AP tibial translation, and total knee shear force. Data were analyzed using magnitude-based inferences and presented as percentage change with 90% confidence limits. Results indicated that sand had a clear beneficial effect on KAM, which was possibly moderate during a drop jump (30 cm) and possibly small from a level jump. Sand also had a possibly moderate beneficial effect on AP tibial translation from a level jump. The effect of sand on total knee shear force was unclear. These results suggest that sand may provide a safer alternative to firm ground when performing jump tasks commonly used in anterior cruciate ligament and patellofemoral joint injury prevention and rehabilitation programs. Sand may also allow for an accelerated rehabilitation program because jumping activities could potentially be implemented more safely at an earlier stage in the process.