Influence of Joint Position on Electromyographic and Torque Generation During Maximal Voluntary Isometric Contractions of the Hamstrings and Gluteus Maximus Muscles

Abstract

Study Design: Repeated measures analysis o i joint angle e i i~t s on hip and k n w muscle cltrtromyographic IEMGI activitv. Objectives: To simultan~~usly determine angle-dependent changes in maximal voluntary isometric contraction IMVICI torque and EMG activity during hip extension and knee ilexion. Background: Procedures ior normalizing EMG data and ior determining torque-angle relationships for various joint motions both entail asking suhjects to exert an MVIC. The implicit assumption in t h r w paradigms is that magnitude of the EMG response is at a constant, m.iximum level so that ohservcd angle-tlepcndmt variations in torque are due to mechanical iactors, such as muscle length and muscle moment arm.Methods and Measures: Fifty suhjects (25 men and 25 women1 particip.itcd in this study (age, 23.5 + 4.6 y; range, 18-38 y). Subjects periormed maximal isometric knee ilexion at 4 kncv angles and maximal isometric h~p extension at 4 hip angles. The dependent variahlrr were nnrmalizrd root-mean-square EMG and torque. The process ior normalizing EMG and torque data consisted o i determining the largc3t mean value ior each suhject across tcrting positions for the muscle o i interest. That value was designated as corrcqmnding to 100% MVIC, and all other data ior that muscle were expressed as a percentage of the MVIC value. Repeated measures was used to determine angle-dependent changes in normalized MVICtorque and MVIC-EMG values ior each muscle group. Results: Mean torque-angle relationships were generally consistent with previous r e p m , though ~~n s i d e r d~l e intersuhject variability was observed. There were signiiicant .inglc-dependent diiierenccr in maximal EMG ior Ix)th the hamstring and gluteus maximus muscles. Worrell, Duke Universitv Medical Center, Deptartment oi Physical and Occupational Therapy PO 3965, Durham, NC 27710. E-mail: ~vorreOO6@mc.duke.edu xperimental approache.5 to the study of neuromuscular function frequently entail asking subjects to perform a maximal voluntary isornetric contraction (MVIC) of selected muscle groups. This approach is commonly used for amplitude normalization of electroinyographic (EMG) activity in order to determine the potential efficacv of various strengthening exercises by comparing the relative activity elicited by each e x e r c i~e . " . ' . ' .~"~ Maximal voluntary isometric contraction has also been used to determine in vivo torque-angle relationships of various joint motions by having subjects exert an MVIC at multiple points in the range of lnotion.~.~ t.21.22 The implicit assumption in these paradigms is that the instruction to perform an MVIC elicits a constant, rnaxi~nal level of motor iunit activity in the muscle of interest.The question of whether performance of an MVIC results in a

Lower Extremity Strength and Mechanics during Jumping in Women with Patellofemoral Pain

“…All test positions were based on those identified in the literature and were gravity resisted. [20][21][22][23][24] We chose the test position (30° knee flexion) for knee-extension strength used by Walsworth et al 23 because we felt that this position better tests the ability of subjects to generate force at a knee-flexion angle they would experience during single-leg jumps. Straps were used to stabilize the subject and handheld dynamometer (Lafayette Instruments, Lafayette, IN) to eliminate the influence of tester strength on these measurements.…”

Gluteus maximus and semitendinosus activation during active prone hip extension exercises

“…This highest activity level was probably due to the fact that, during these exercises, the hamstrings were in active insufficiency and their capacity to produce or maintain active tension was diminished. Worrell et al 19 observed increases in gluteus maximus activity during exercises performed with KF at 30° and 60° when compared to 90°. In the present study, the peak activity of the gluteus maximus occurred close to the end of the movement.…”

“…MVIC measurements of the gluteus maximus were carried out with the hip in maximum extension and with 90° of knee flexion for the semitendinosus muscle. Worrell et al 19 recommended that the normalizing contractions should be performed at joint angles close to that assumed during the activity of interest. During the MVIC measures, verbal encouragements were given to the participants to reach maximal muscular activation.…”

Influence of Gluteus Maximus Inhibition on Upper Trapezius Overactivity in Chronic Mechanical Neck Pain With Radiculopathy

“…To record muscle activity, Surface electrodes (Ag/AgCl) were placed parallel to the muscle fibers [18]. Electrodes placement to collect EMG signals were as follow: for UT at the midpoint of a line running between the C7 spinous process and the lateral tip of the acromion [19] and for the GM, at the mid point of a line running from S2 to the greater trochanter [20]. The reference electrode was placed over the right ulnar styloid process.…”

“…The first leg to be assessed was chosen by cards and the patient chose the card randomly, the word written in the card was (right side first or lift side first). The positions of limb and foot were manually and verbally supervised throughout the performance to ensure that the subject maintained neutral hip rotation, full knee extension, and neutral ankle flexion, because outward rotation of the hip joint and ankle dorsiflexion especially facilitated the glutei [20]. Before testing, the participants were familiarized with the standard position and movement.…”