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.
Purpose: The purpose of the study was to investigate changes in lower extremity joint energy absorption for different landing heights and landing techniques.
Methods: 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).
Results: 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.
Conclusions: 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.
During foot contact with ground in vigorous locomotion, the body experiences tremendous impact forces. Maximum vertical ground reaction force values as high as 14.4 times body weight (BW) have been reported (20) for single-leg landings from a double back somersault. Stacoff et al. (25) showed that the first peak (F1) of the vertical component of ground reaction force (GRF) ranged from 1000 to 2000 Newtons (N), whereas the second peak (F2) values ranged from 1000 to 6500 N in landings after a volleyball block jump. McNitt-Gray (17) demonstrated that the maximum vertical ground reaction forces for trained gymnasts were 3.9, 6.3, and 11.0 times BW for landing from heights of 32, 72, and 128 cm, respectively. Accumulation of high impact forces may pose a threat to the integrity of the lower extremity and related overuse injuries are often direct consequences of these impacts (22,23). Many of these injuries are often associated with the knee-joint structure and reported as common in running (16), basketball (19), tennis (24), football (15), volleyball (12), skiing (10), and the triathlon (3). Fifty-eight percent of all injured female basketball players were engaged in landing from a jump at their time of injury (13) and 40% of high-level volleyball players experienced knee problems during their playing careers (11). James et al. (16) reported knee pain as the most common problem for runners.
The studies on biomechanical behaviors of the lower extremity in landing have been focused on prediction of impact forces (9), comparisons of landing techniques (4), effects of landing velocities (18), and manipulations of landing distances, heights, and techniques (8). Dufek and Bates (8) demonstrated greater peak moments of the proximal extensors (i.e., hip extensors) compared with the distal extensors (i.e., plantarflexors). Few studies, however, investigated the contributions of various lower extremity muscle groups to the total energy dissipation. DeVita and Skelly (4) suggested that the ankle joint plantar flexors absorbed more energy in a stiff landing, whereas the hip and knee extensors absorbed more energy in the soft landing. McNitt-Gray (18) demonstrated that elite gymnasts dissipated more energy with ankle and hip extensors at the higher height compared with their recreational counterparts, whereas the latter group adjusted their strategy by increasing hip flexion and by prolonging the landing phase. Different views still exist in the literature regarding the various contributions made by the lower extremity muscle groups to the reduction of impact and energy. The femur and tibia are among the longest bones in human body and significantly greater loading at the knee joint are expected. High mechanical output by the knee musculature should be experienced consequently. Research in this area, however, still fails to agree on the issue. Therefore, the purpose of the study was to investigate changes in energy absorption of lower extremity joints for different landing heights and landing techniques.
Exercise Science Unit, Biomechanics/Sports Medicine Laboratory, The University of Tennessee, Knoxville, Knoxville, TN 37996; and University of Oregon, Eugene, OR
Submitted for publication February 1998.
Accepted for publication September 1998.
Address for correspondence: Song-Ning Zhang, Department of Exercise Science and Sport Management, Biomechanics/Sports Medicine Laboratory, The University of Tennessee, Knoxville, 1914 Andy Holt Ave., Knoxville, TN 37996; E-mail: firstname.lastname@example.org.