Neuromotor synergies of the ligamentously injured knee

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Abstracts

SESSION 12: MUSCLE FUNCTION Chairperson: Roger Enoka COACTIVATION

OF THE HAMSTRINGS

L.F. Draganich”‘,

R.J. Jaeger**l

AND QUADRICEPS

DURING

EXTENSION

OF THE KNEE

and A.R. Kralj3*’

‘The University of Chicago Medical Center, Section of Orthopaedic Surgery and Rehabilitation Department of Surgery, Box #421, Chicago, Illinois 60637. ‘Pritzker Institute of Medical Engineering, Illinois Institute of Technology, Chicago, Illinois. 3Faculty of electrical Engineering, Edvard Kardelj University, Ljubljana, Yugoslavia.

Medicine,

The electromyographic activities of six of the muscles of the thigh during active extension of the knee were recorded in six healthy adult males using bipolar surface electrodes. The signal amplitudes were normalized to those recorded during isometric maximum voluntary contractions. Knee extension from 90 to 0 degrees (full extension) was performed at the rate of 10 degrees per second with leg weight alone and with ankle weights. Coactivation of all three hamstrings was found to occur at joint angles up to 9 degrees, with the maximum at full knee extension, the strength of their signals ranging up to 20%. The signals of all of the flexors and extensors increased with increasing loads on the ankle and also increased as the knee extended. The results supoort the hypothesis that the hamstrings function synergistically with the anterior cruciate ligament to prevent interior tibia1 displacement produced by active contraction of the quadriceps in the terminal degrees of extension of the knee.

NEUROMOTOR M.D. Grabiner’, ‘Department Foundation,

SYNERGIES G.G.

Weiker,

OF THE LIGAMENTOUSLY T.E. Anderson,

of Musculoskeletal Research Cleveland, Ohio, 44106

INJURED

KNEE.

J.A. Bergfeld

and Department

of Orthopaedic

Surgery,

The Cleveland

Clinic

This investigation determined the effect of knee ligament injury on knee joint muscular synergies. Subjects having undergone anterior cruciate ligament reconstruction (n = 12) or having nonsurgically treated anterior cruciate ligament insufficiency (n = 9) performed a previously standardized isometric knee extension protocol. Both groups of patients demonstrated clinically relevant differences from previously established patterns on normal knees. Compared to the normal data, disruption in synergies was generally characterized by increased cocontraction of the hamstrings musculature during knee joint extension, increased quadriceps excitation during submaximum contraction intensities, and inhibition of the quadriceps femoris components at maximum knee joint extension contraction intensities. It is concluded that ligamentous injury can be associated with disrupted neuromotor relationships despite the presence of a clinically stable joint and normal muscular strength levels. Presently, it is of interest to determine if patients demonstrating disrupted neuromotor synergies are predisposed to long-term joint dysfunction.

THE QUANTITATIVE GASTROCNEMEIUS James J. Dowling Dept. of Exercise

ASSESSMENT MUSCLES

OF EMG CROSSTALK

and Susan R. Kennedy Science, Concordia University,

Montreal,

IN HUMAN

Canada,

SOLEUS

AND

H4B IR6

The surface EMG allows a measure of the global activity of a muscle but is also susceptible to volume conducted signals from other sources (crosstalk). The purpose of this study was to assess the amount of crosstalk in two of the triceps surae muscles using a modified double differential technique. A three electrode configuration was used to collect two bioolar EMG signals from each of the soleus and medial nastrocnemius muscles. A second differential was obtained for each muscle by simulating a differential ampIif?er with a micro-computer. The results yielded crosstalk values of 7.5% on the soleus and 12.4% on the gastrocnemius muscles of 10 subjects. indicated that While these means were relatively low, values as large as 45% were seen. The large variability caution should be used in the quantification of soleus muscular activity from the traditional, single bipolar surface EMG arrangement.

MUSCLE

ACTIVITY

PATTERNS

AND CONTROL

OF TEMPOROMANDIBULAR

Gaylord S. Throckmorton, Scott Boyd, and Greg Groshan, Department of Surgery, University of Texas Southwestern

JOINT

LOADS.

Department of Cell Biology and Anatomy and Medical Center, Dallas, Texas 75235, USA.

Theoretical studies and experimental measurements in animals suggest that the working and balancing side temporomandibular joints are unevenly loaded during unilateral biting. However, previous electromyographic studies in humans suggest an attempt to balance the distribution of the two joint forces. The current study measured bilateral activity in the anterior temporalis, posterior temporalis, and superficial masseter muscles of 35 subjects during isometric bites and chewing at five different positions along the tooth row. The resulting ratios of working/balancing side muscle activity were compared to ratios required to maintain equal joint forces and estimates of the ratio of working/balancing side joint forces at each tooth position were made. Our results indicate that the muscle activity patterns do not maintain equal joint forces, nor are the muscles responding to joint forces exceeding critical limits. The muscle activity patterns appear to be more important for maintaining mandible position than in controlling temporomandibular joint forces.