The effects of jump strategy modification on energetics during dance jumps

Coordinated movement of the entire body and significant energetic contributions are required for dynamic, high-load movements such as jumping. Variations in either the vertical or horizontal components of a jump will result in modifications in the trajectory and velocity of the center of mass; lower extremity joint demands may also be altered. Examination of the role and function of lower extremity joints and the impact of modification of task goals during jumping will provide insight regarding skilled athletic performance and implications for lower extremity injuries. The purpose of this dissertation was to examine the influence of modified task goals on an entire jump including the takeoff, flight, and landing phases. The general hypothesis was that lower extremity demands during takeoff and landing would be redistributed in response to modified task goals without altering task performance during flight. ❧ Thirty healthy, experienced female dancers with an average 20.8±4.9 years of dance training performed saut de chat leaps (split jumps involving vertical and horizontal movement) in two conditions: traveling as far as possible (FAR) and jumping as high as possible (UP). A three-dimensional motion analysis system and force plates were used to collect kinematic and kinetic data. A four-segment lower extremity model was used to analyze the takeoff, flight, and landing phases of the leap. Horizontal ground reaction force (GRF) impulses and sagittal plane mechanical energy expenditure (MEE) of the metatarsophalangeal (MTP), ankle, knee, and hip joints were calculated. Peak net joint moments at the MTP, ankle, knee, and hip were identified. The lower extremity contact angle (LECA) was calculated as the angle between the floor and a line connecting the L5S1 marker and the center of pressure at the beginning of the landing phase. All dependent variables were compared between conditions using paired samples t-tests. The angle between the legs was determined at the time when the center of mass reached its peak height during the leap. The split angle was considered unaltered and performance was considered successful if the mean difference between conditions fell within the standard error of measure for this variable (4.7°). ❧ During takeoff, braking GRF impulse was lower (p<0.001) and propulsive GRF impulse was greater (p<0.001) in the FAR condition compared to the UP condition. MEE at the MTP, ankle, and hip joints was greater in the FAR condition, and MEE at the knee was lower in the FAR condition (MTP p<0.001; ANKLE p<0.001; KNEE p<0.001; HIP p<0.001). During flight, split angle changed by an average of 0.42±3.37° in the FAR condition and 0.68±4.89° in the UP condition, which both fall within the standard error of measure for split angle, indicating consistent performance. During landing, dancers demonstrated greater, or more vertical, lower extremity contact angles in the UP condition compared to the FAR condition (p<0.001). Braking GRF impulse was lower in UP compared to FAR (p=0.002). MEE at the knee was greater in UP compared to FAR (p=0.012). Peak knee abductor net joint moments were lower in the UP condition (p=0.005). ❧ Biomechanical demands on the lower extremity joints during takeoff and landing were altered in response to modified task goals without altering task performance during flight. Alterations were exhibited in the horizontal component of the ground reaction force as well as in individual joint energetics. When the goal of the jump was to focus on distance, demands were increased at the distal joints during takeoff, and braking ground reaction force impulse and frontal plane peak knee abductor net joint moment were higher during landing. When the goal of the jump was to focus on height, sagittal plane demands were increased at the knee during both takeoff and landing, while braking ground reaction force impulse and peak knee abductor net joint moment were reduced during landing. These results suggest focusing on increased distance during saut de chat leaps may not be an optimal movement strategy for dancers. This dissertation was designed to allow for a thorough examination of the consequences of jump strategy modification as exhibited in the lower extremity energetics during both takeoff and landing and the kinematics during flight. Lower extremity demands during takeoff and landing were redistributed in response to modified task goals without altering task performance during flight.