The effect of knee flexor and extensor fatigue on shock absorption during cutting movements after a jump landing.

BACKGROUND

Sporting situations include instances of continuous and/or integrated movements. However, the effect of fatigue on the performance of these movements remains unclear.

PURPOSE: To investigate the effect of knee flexor and extensor fatigue on the shock absorption strategy of the lower limb during cutting movements performed after jump landings.

METHODS

Twenty-four healthy participants performed cutting movements following jump landings from two heights - 30cm and 40cm - and under three levels of lower limb fatigue: pre-fatigue (100% peak knee extension torque), and post-fatigue 50% (post-50%) and 30% (post-30%) peak knee extension torque. Fatigue was induced by repeated isokinetic flexion/extension of the knee (60°/s).

RESULTS

Compared to the pre-fatigue condition, power and work at the knee joint decreased under both post-50% and post-30% conditions (P<0.001), while the work performed by the ankle (P<0.001) increased significantly. An increase in height from 30cm to 40cm was associated with an increase in the range of motion of the ankle (P<0.001) and knee (P=0.022), peak vertical ground reaction force (P<0.001), rate of loading (P<0.001), knee stiffness (P=0.026) and peak power of the knee (P<0.001), as well as the work performed by the knee (P<0.001) and hip (P<0.001) joints.

CONCLUSIONS

Under substantial muscle fatigue the proportion of shock absorption contributed by the knee for cutting movements performed after jump landings from a height of 40cm decreased; there was an adaptive increase in the contribution by the ankle.