An examination of the true reliability of lower limb stiffness measures during overground hopping

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Evidence suggests reports describing the reliability of leg-spring (k ) and joint stiffness (k ) measures are contaminated by artifacts originating from digital filtering procedures. In addition, the intraday reliability of k and k requires investigation. This study examined the effects of experimental procedures on the inter- and intraday reliability of k and k . Thirty-two participants completed 2 trials of single-legged hopping at 1.5, 2.2, and 3.0 Hz at the same time of day across 3 days. On the final test day a fourth experimental bout took place 6 hours before or after participants' typical testing time. Kinematic and kinetic data were collected throughout. Stiffness was calculated using models of k and k . Classifications of measurement agreement were established using thresholds for absolute and relative reliability statistics. Results illustrated that k and k exhibited strong agreement. In contrast, k and k demonstrated weak-to-moderate consistency. Results suggest limits in k reliability persist despite employment of appropriate filtering procedures. Furthermore, diurnal fluctuations in lower-limb muscle-tendon stiffness exhibit little effect on intraday reliability. The present findings support the existence of k as an attractor state during hopping, achieved through fluctuations in k variables. Limits to k reliability appear to represent biological function rather than measurement artifact. leg joint leg joint leg joint leg joint leg ankle knee hip joint leg joint joint

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Journal of Applied Biomechanics

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