NDLI: Lower extremity extension force and electromyography properties as a function of knee angle and their relation to joint torques: implications for strength diagnostics.

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Lower extremity extension force and electromyography properties as a function of knee angle and their relation to joint torques: implications for strength diagnostics.

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Lower extremity extension force and electromyography properties as a function of knee angle and their relation to joint torques: implications for strength diagnostics.

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Hahn, Daniel
Description	Country affiliation: Germany Author Affiliation: Hahn D ( Department of Biomechanics in Sports, Faculty of Sport Science, Technical University of Munich, Munich, Germany. d.hahn@sp.tum.de)
Abstract	The purpose of this study was to evaluate whether and how isometric multijoint leg extension strength can be used to assess athletes' muscular capability within the scope of strength diagnosis. External reaction forces (Fext) and kinematics were measured (n = 18) during maximal isometric contractions in a seated leg press at 8 distinct joint angle configurations ranging from 30 to 100° knee flexion. In addition, muscle activation of rectus femoris, vastus medialis, biceps femoris c.l., gastrocnemius medialis, and tibialis anterior was obtained using surface electromyography (EMG). Joint torques for hip, knee, and ankle joints were computed by inverse dynamics. The results showed that unilateral Fext decreased significantly from 3,369 ± 575 N at 30° knee flexion to 1,015 ± 152 N at 100° knee flexion. Despite maximum voluntary effort, excitation of all muscles as measured by EMG root mean square changed with knee flexion angles. Moreover, correlations showed that above-average Fext at low knee flexion is not necessarily associated with above-average Fext at great knee flexion and vice versa. Similarly, it is not possible to deduce high joint torques from high Fext just as above-average joint torques in 1 joint do not signify above-average torques in another joint. From these findings, it is concluded that an evaluation of muscular capability by means of Fext as measured for multijoint leg extension is strongly limited. As practical recommendation, we suggest analyzing multijoint leg extension strength at 3 distinct knee flexion angles or at discipline-specific joint angles. In addition, a careful evaluation of muscular capacity based on measured Fext can be done for knee flexion angles ≥ 80°. For further and detailed analysis of single muscle groups, the use of inverse dynamic modeling is recommended.
File Format	HTM / HTML
ISSN	10648011
Issue Number	6
Volume Number	25
e-ISSN	15334287
Journal	Journal of Strength and Conditioning Research
Language	English
Publisher	Lippincott Williams & Wilkins
Publisher Date	2011-06-01
Publisher Place	United States
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Discipline Sport Sciences Knee Physiology Leg Muscle Strength Muscle, Skeletal Adult Electromyography Humans Isometric Contraction Male Torque Journal Article
Content Type	Text
Resource Type	Article
Subject	Orthopedics and Sports Medicine Physical Therapy, Sports Therapy and Rehabilitation Sports Science

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