Bilateral deficit of voluntary quadriceps muscle activation after unilateral ACL tear

• Published in: Medicine and science in sports and exercise 1999-12, Vol.31 (12), p.1691-1696
• Main Authors: URBACH, D, NEBELUNG, W, WEILER, H.-T, AWISZUS, F
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Anterior Cruciate Ligament Injuries; Biological and medical sciences; Humans; Injuries of the limb. Injuries of the spine; Male; Medical sciences; Middle Aged; Muscle Contraction; Muscle, Skeletal - physiopathology; Rupture; Space life sciences; Thigh; Traumas. Diseases due to physical agents
• ISSN: 0195-9131; 1530-0315
• DOI: 10.1097/00005768-199912000-00001

The inability to fully activate the quadriceps femoris muscle voluntarily is known to accompany several different knee-joint pathologies. The extent of a voluntary-activation deficit in patients after isolated rupture of the anterior cruciate ligament (ACL), however, has been reported to be small or nonexistent, making it questionable if a voluntary-activation deficit is a relevant factor for these patients at all. In this study the ability to voluntarily activate the quadriceps femoris muscles was quantified in 22 male patients with arthroscopically-proven isolated ACL ruptures using an established highly sensitive twitch-interpolation technique. Furthermore, the maximal voluntary contraction force of the quadriceps muscle was obtained by isometric knee-joint torque measurements. The results were compared with an age-, gender-, and activity-matched control group. There was a moderate but significant mean reduction in maximal voluntary activation (VA) in both the injured (VA: 83.9 +/- 2.3%, mean +/- SEM) and uninjured side (VA: 84.7 +/- 2.2%) in comparison with controls (VA: 91.1 +/- 0.8%). However, of the patients the 23% who presented a considerably reduced voluntary-activation of less than 80% were mainly responsible for the significant mean deficit. The deficit of isometric muscle strength on the injured side compared with that of controls was explained by the voluntary-activation deficit and a true muscle weakness. On the other hand, the diminished muscle strength of the uninjured side was explained sufficiently by the voluntary-activation deficit alone. Considering the bilateral voluntary-activation deficit, functional muscle tests might not be valid when the uninjured extremity serves as reference.