842 Back and Hip Extensor Muscle Function During Therapeutic Exercises Jari EA. Arokoski, MD, PhD, Markku KankaanpZiSi, MD, Taru Valta, PT, Ilkka Juvonen, PT, Juhani Partanen, MD, PhD, Simo Taimela, MD, PhD, Karl-August Lindgren, MD, PhD, Olavi Airaksinen; MD; PhD ABSTRACT. Arokoski JPA, Kankaanpaa M, Valta T, Ju- vonen I, Partanen .I, Taimela S, Lindgren K-A, Airaksinen 0. Back and hip extensor muscle function during therapeutic exercises.Arch Phys Med Rehabil 1999;80:842-50. Background: Therapeutic exercises are widely used in the treatment of low back problems. Clinical knowledge about targeting the load in these exercises, however, is insufficient. This study assessed the L2 and L5 level paraspinal and gluteus maximus muscle activities in different therapeutic exercises. Intramuscular and surface electromyography (EMG) measure- ments were obtained to study whether surface EMG measure- ments can be used in the assessment of multifidus muscle function. Methods: Eleven healthy subjects (5 men, 6 women) 21 to 38 years of age volunteered for the study. The subjects performed 18 different therapeutic exercises. During the exer- cises paraspinal EMG was recorded using fine wire and surface electrodes. The normalized peak and average muscle EMG activities (percentage of amplitude in maximal voluntary con- traction [MVC]) during each task were determined. Results: The correlations between the average intramuscular and surface activities of the normalized EMG (% of MVC) at the L2 and L5 levels were .928 and .950, respectively. The peak and average EMG amplitudes of the exerciseswere below 50% and 25% of MVC, respectively. At the L5 level, the multifidus peak and average EMG amplitudes (% MVC) were higher in women than in men, whereas no significant difference was found at the L2 level. In women, the normalized multifidus EMG amplitude was higher at the L5 level than at the L2 level, whereas no significant difference was found in men. In both sexes, the normalized EMG amplitude was higher in the multifidus than in the longissimus muscle. Conclusion: Surface EMG measurements may be used in the assessment of multifidus muscle function. Simple therapeutic exercises are effective in activating the lumbar paraspinal muscles. 0 1999 by the American Congress of Rehabilitation Medi- cine and the American Academy of Physical Medicine and Rehabilitation From the Deoartment of Phvsical and Rehabilitation Medicine (Drs. Arokoski, KankaanpLSi, Airaksinen, Mr. Galta, Mr. Juvonen), the Rehabilitation Clinic (Dr. Arokoski, Mr. Valta), and the Department of Clinical Neurophysiology (Dr. Partanen), Kuopio University Hospital, Kuopio; DBC International, Vantaa (Dr. Taimela); and ORTON Rehabilitation Centre, Invalid Foundation, Helsinki (Dr. Lindgren), Finland Submitted for publication May 27, 1998. Accepted in revised form February 10, 1999. Supported by grants from Kuopio University Hospital, Kuopio, Finland. No commercial party having a direct or indirect interest in the subject matter of this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated. Reorint reauests to Jari Arokoski. MD. PhD. Rehabilitation Clinic. Kuooio University Ho’spital, IO Box 1777, FlN:7021i Kuoiio, Finland. A 0 1999 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation 0003-9993/99/8007-5045$3.00/O L UMBAR SPINE STABILITY is provided by bone, disc, ligamentous, and muscle restraints. Segmental instability of the lumbar spine may cause functional disorders and strain as well as pain.1,2 It is supposed that paraspinal and abdominal muscles have the greatest capacity for enhancing the stabiliza- tion of the spine. Paraspinal and abdominal muscles also have importance in pain modulation and prevention.3-7 The interseg- mental lumbar multifidus, the most medial of the lumbar back muscles, has been shown to be more important than the longissimus thoraci and ilicostalis lumborum muscles in stabi- lizing the lumbar spine.*-lo The stabilizing function of the multifidus muscle is disturbed by disuse, pain, or injury. Dysfunction of the lumbar back muscles has been suggested to be related to back pain, and can be described in terms of loss of lumbar back muscle11~12 and loss of strength and endurance.13 The aim of restoring the stabilizing role of the paraspinal muscles is to protect the articular structures, discs, and liga- ments from excessbending, strains, and injury. Stabilization of hypermobile segments requires functional multifidus muscles, which stabilize the aberrant motion produced by the trunk muscles during rotation and flexion.14,15 The potential for exercise to prevent and reduce low back disorders involves changes in muscle physiology. Reduced intramuscular density in chronic back pain patients is attributable to atrophy of muscle fibers secondary to disuse or long loop reflex inhibition of back musculature.16s1g Furthermore, deconditioned muscles have a decreased capacity to withstand perturbation and repetitive load, causing strain in the annular fibers of the lumbar disc and potentially leading to back pain.11s20 Many comprehensive exercise programs have been proposed to enhance lumbar stability.7,21-30 The literature yields some evidence that stabiliza- tion exercises are beneficial for patients with lumbar segmental instability,7 chronically symptomatic spondylolysis or spondy- lolisthesis31 and segmental dysfunction.27 Specific exercise techniques have been suggested to activate multifidus muscles.21-30 However, the back and hip extensor muscle activity levels in these exercises are unknown. Muscle activity can be assessed by electromyography (EMG).32 Surface electrodes are convenient and detect muscle EMG signals from a fairly large detection area and thus from many motor units. 32The disadvantage of surface electrodes is that they may be used effectively only with superficial muscles. Using wire electrodes, the kinesiology and neurophysiology of deep muscles can be studied. The pick-up area of wire electrodes is much smaller than that of surface electrodes and is less affected by cross talk. The frequency alterations of the EMG signal obtained from both surface and wire electrodes are suggested to be valid measures of local muscle fatigue.33-35 In general, increased force output of the muscle results in corre- sponding changes in EMG amplitude, although the relationship is not always linear. Joint angle, muscle length, contraction type, and fatigue level may affect the behavior of the EMG/ force relationship.36-38 The aim of this study was to assessthe L2 and L.5 level paraspinal and gluteus maximus muscle activities, using wire Arch Phys Med Rehabil Vol 80, July 1999