Validity and reliability of a novel instrumented one-legged hop test in patients with knee injuries

Background: Conventional one-legged hop tests simply evaluate the total hop distance, thus neglecting important temporal and spatial parameters related to the strategy of execution, such as foot contact time.

Aim: To examine the validity and reliability of an instrumented one-legged hop test, the "four hops, three contacts" (4H3C) test, in patients with knee injuries.

Methods: The 4H3C test consists of four consecutive one-legged hops, of which individual hop distance and foot contact time are recorded by a validated floor-based photocell system. We examined the test-retest reliability, discriminant validity (involved vs. uninvolved side) and convergent validity (relation with maximal voluntary strength) of consecutive hop distance and foot contact time parameters in 50 patients with unilateral knee injuries.

Results: Test-retest reliability was very high for hop distance (intraclass correlation coefficients: 0.91 to 0.97) and high for contact time variables (intraclass correlation coefficients: 0.75 to 0.88). The difference between the involved and the uninvolved side was significant for all hop distance and contact time parameters (p<0.05). Maximal voluntary strength was correlated to both hop distance (r=0.67; p<0.001) and contact time (r=-0.42; p<0.01) variables.

Conclusion: The 4H3C is a valid and reliable test for the evaluation of single hops in patients with knee injuries and may be useful in sport and clinical settings. The interpretation of foot contact time data requires however some caution.