ZHANG, S-N., B. T. BATES, and J. S. DUFEK. Contributions of lower extremity joints to energy dissipation during landings. Med. Sci. Sports Exerc., Vol. 32, No. 4, pp. 812–819, 2000. The purpose of the study was to investigate changes in lower extremity joint energy absorption for different landing heights and landing techniques. Nine healthy, active male subjects volunteered to perform step-off landings from three different heights (0.32 m, 2.5 m-s; 0.62 m, 3.5 m-s; and 1.03 m, 4.5 m-s) using three different landing techniques (soft, SFL; normal, NML; and stiff landing, STL). Each subject initially performed five NML trials at 0.62 m to serve as a baseline condition and subsequently executed five trials in each of the nine test conditions (3 heights × 3 techniques). The results demonstrated general increases in peak ground reaction forces, peak joint moments, and powers with increases in landing height and stiffness. The mean eccentric work was 0.52, 0.74, and 0.87 J·kg−1 by the ankle muscles, and 0.94, 1.31, and 2.15 J·kg−1 by the hip extensors, at 0.32, 0.62, and 1.03 m, respectively. The average eccentric work performed by the knee extensors was 1.21, 1.63, and 2.26 J·kg−1 for the same three heights. The knee joint extensors were consistent contributors to energy dissipation. The ankle plantarflexors contributed more in the STL landings, whereas the hip extensors were greater contributors during the SFL landings. Also a shift from ankle to hip strategy was observed as landing height increased.

Individuals jump higher when they adopt an external focus of attention, relative to an internal focus or no focus of attention ( G. Wulf, T. Zachry, C. Granados, & J. S. Dufek, 2007 Wulf, G. , Zachry, T. , Granados, C. and Dufek, J. S. 2007. Increases in jump-and-reach height through an external focus of attention. International Journal of Sports Science & Coaching, 2: 275–284. [Crossref] [Google Scholar] ). In the present study, the authors determined the underlying cause of this effect. Participants performed a vertical jump-and-reach task for (a) an external focus condition (i.e., participants focused on the rungs of a Vertec [Perform Better, Cranston, RI] measurement device that they touched) and (b) an internal focus condition (i.e., participants focused on the finger with which they touched the rungs). Participants’ jump height, center-of-mass displacement, jump impulse, and lower extremity joint moments were greater with an external focus compared with an internal focus. These results suggest that participants jump higher by producing greater forces when they adopt an external focus. This finding adds to evidence that an external focus facilitates the production of effective and efficient movement patterns.