Lower extremity joint angles associated with exercise.

Introduction: The squat and forward step-up activities are common exercises used in research and rehabilitation. In unweighted and weighted conditions, the difficulty of these exercises is typically standardized by limiting the maximum anterior knee joint angle (KJA) during the activity. Methods of KJA limitation include: 1) the use of a stool or box to provide a barrier, preventing further depth increases during the squat; and 2) verbal instruction by the researcher or clinician, either asking the individual to squat as deep as comfortable or verbally guiding the individual to stop descending when the desired KJA is attained. Subject specific measurements, such as movement depth and movement height measured as a percentage of leg length (%LL), may also be valid and easily quantifiable methods of standardizing exercise difficulty. Purpose: To examine the associations among %LL squatting depth, %LL stepping height, and KJA in healthy, young adults. Methods: KJAs were measured using a goniometer during the bilateral squat and forward step- up exercises in 4 men and 5 women volunteers. A tape ruler was used to measure the distance from the ASIS to the center of the ipsilateral medial malleolus for both limbs while the subject lay supine on a plinth. The length of the dominant limb was used to calculate the %LL used during the exercises. The height of the bar when resting on the subject's shoulders was marked on the squat rack during quiet standing and %LL was marked on the rack measuring down from the bar height. The step height consisted of a mobile force platform that was raised using fixed height spacers. Squatting depth and stepping height were increased in 10% increments from 10%LL to 70%LL for the squat and 10%LL to 50%LL for the step-up. The average of three KJA measurements was calculated for each squat depth and step height. Linear regression models were used to fit KJA with squatting depth and stepping height. Results: Both the bilateral squat and step-up exercises demonstrated a strong linear relationship with KJA, [r.sup.2]=0.859 and [r.sup.2]=0.917 respectively (p<0.001), showing that as squatting depth and step height increased, KJA positively increased. Conclusion: Determining angular excursion during an activity is difficult without sophisticated equipment. These findings suggest that linear displacement of the total body is related to KJA, and imply that clinicians can prescribe squatting depth and stepping height using patient-specific LL measures when attempting to limit knee flexion angles. These studies need to be repeated in specific patient populations (ACL repair, joint arthroplasty) to determine if the relations among % LL movement depth/height and KJA are consistent.

Dunn EJ, Kessans K, Salem GJ

Musculoskeletal Biomechanics Research Laboratory, Dept. of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA