Quantitative intramuscular myoelectric activity of lumbar portions of psoas and the abdominal wall during a wide variety of tasks.

PURPOSE: Since most previous reports of EMG activation profiles from psoas and the abdominal wall have been qualitative, the objective of this work was to document myoelectric activity from these deep muscles. This knowledge is required to assist in choosing specific training exercises and for making rehabilitation decisions that require knowledge of normalized and calibrated muscle activation levels in different tasks. METHODS: Intramuscular EMG was collected from five men and three women, in whom amplitudes were normalized to maximum contraction efforts and reported over a wide variety of clinical and rehabilitation tasks. Electrodes were inserted into vertebral portions of psoas and the three layers of the abdominal wall. Normalized signal amplitudes were reported as peak levels and time histories. RESULTS: All forms of sit-ups activated psoas (15-35% MVC) more than the curl-up (<10%); psoas was not highly activated during barbell lifting of loads up to 100 kg (< 16% MVC); psoas was most active during maximal hip flexion efforts; push-ups activated psoas up to 25% MVC. Several isometric abdominal exercises were evaluated using the criteria of maximizing abdominal activation while minimizing psoas activity: the side (bridge) support exercise proved the best training method for the abdominal wall. CONCLUSIONS: Consideration of deep muscle activity, provided in this report, is important for choosing the most appropriate rehabilitation and training program for an individual. Specific guidance is provided for choosing the best abdominal exercise, together with activation profiles during lifting, during twisting, and during hip rotation.

Appropriately placed surface EMG electrodes reflect deep muscle activity (psoas, quadratus lumborum, abdominal wall) in the lumbar spine.

This study tested the possibility of obtaining the activity of deeper muscles in the torso-specifically psoas, quadratus lumborum, external oblique, internal oblique and transverse abdominis, using surface myoelectric electrodes. It was hypothesized that: (1) surface electrodes adequately represent the amplitude of deep muscles (specifically psoas, quadratus lumborum, external oblique, internal oblique, transverse abdominis); (2) a single surface electrode location would best represent the activation profiles of each deep muscle over a broad variety of tasks. We assumed that prediction of activation within 10% of maximum voluntary contraction (RMS difference between the surface and intramuscular channels), over the time history of the signal, was reasonable and acceptable to assist clinical interpretation of muscle activation amplitude, and ultimately for modeled estimates of muscle force. Surface electrodes were applied and intramuscular electrodes were inserted on the left side of the body in five men and three women who then performed a wide variety of flexor tasks (bent knee and straight leg situps and leg raises, curl ups), extensor tasks (including lifting barbells up to 70 kg), lateral bending tasks (standing lateral bend and horizontal lying side support), twisting tasks (standing and sitting), and internal/external hip rotation. Using the criteria of RMS difference and the coefficient of determination (R2) to compare surface with intramuscular myoelectric signals, the results indicated that selected surface electrodes adequately represent the amplitude of deep muscles-always within 15% RMS difference, or less with the exception of psoas where differences up to 20% were observed but only in certain maximum voluntary contraction efforts. It appears reasonable for spine modelers, and particularly clinicians, to assume well selected surface electrode locations provide a representation of these deeper muscles-as long as they recognize the magnitude of error for their particular application.

Correcting trunk muscle geometry obtained from MRI and CT scans of supine postures for use in standing postures.

Many studies have reported the geometry of the trunk muscles for use in models to predict spine loads. However, all have reported data collected from subjects positioned in a prone or supine posture which is required by CT or MRI scan techniques. This study compared the abdominal and extensor muscle moment arms obtained with muscles relaxed and activated and in both supine and upright postures. Both internal ultrasound measurements and external anthropometer measurements were collected. The anterior abdominal wall increased its flexor moment arm by approximately 30% when in a standing posture compared to the supine posture. The effect of an upright posture on the moment arm of erector spinae at the level of L3 was much smaller (3% increase in males and 12% increase in females). There was no moment arm change due to activating the muscles when compared to the relaxed condition for either posture. Modelers should be aware of the need to scale muscle moment arms obtained from MRI/CT scans in order to more accurately predict spine loads in upright postures.

Quantitative intramuscular myoelectric activity of quadratus lumborum during a wide variety of tasks.

Intramuscular fine-wire electrodes monitored the electromyographic activity of quadratus lumborum in four young adults. A wide variety of tasks were performed including flexion tasks, lateral bending, twisting, extension, and lifting tasks. Heavy lifts of barbell weights up to 70 kg activated the quadratus lumborum 74% of their maximum on average while surface recording of erector spinae (L(3)) were only 62% of their maximum activation. The quadratus lumborum was more active (54%) than other muscles during isometric side support postures where the body is held horizontally almost parallel to the floor as the subjects supported themselves on one elbow on the floor together with both feet. Furthermore, it increased activation in response to increasing compression in static upright standing postures. RELEVANCE:--Electromyographic evidence, together with architectural features make the quadratus lumborum a better stabilizer of the spine than psoas. Use of horizontal 'side support' exercise to train this muscle would appear to be a wise choice.