Original contribution
A Novel Method for Measuring Electromechanical Delay of the Vastus Medialis Obliquus and Vastus Lateralis

https://doi.org/10.1016/j.ultrasmedbio.2008.06.011Get rights and content

Abstract

Electromechanical delay (EMD) of the vastus medialis obliquus (VMO) and vastus lateralis (VL) is determined by measuring the interval between the time of onset of muscle activities and the time of onset of mechanical output. However, individual mechanical output of the VMO or the VL cannot be obtained with the conventional method because of the knee extension force as the mechanical output. Therefore, the objective of the present study was to develop a new method for measuring EMD of the VMO and VL individually. Twelve healthy volunteers participated in the experiment. The motor point of the target muscle was electrically stimulated to evoke a muscle twitch. Simultaneously, the electrical stimulation signal was transmitted to ultrasound apparatus via the electrocardiography input channel. The ultrasound apparatus was used to capture the patellar movement elicited by the muscle twitch. EMD was measured from the onset of the electrical stimulation to the onset of patellar movement. The results showed that the intraclass correlation coefficients for the reproducibility of the EMD measurements of the VMO and VL were greater than 0.8. The EMDs of the VMO and VL were 18.3 ± 2.2 ms and 24.8 ± 5.8 ms, respectively. This new method provides a more precise measurement of EMD in the VMO and VL than does the conventional method because of the use of patellar movement as the mechanical output. (E-mail: [email protected])

Introduction

Electromechanical delay (EMD) is defined as the interval from the time of electrical activities to the time of mechanical response of the muscle (Cavanagh and Komi 1979). Some researchers believe that the EMD is a component of the stretch reflex and is related to sports performance and protective reflex (Georgoulis et al 2005, Samozino et al 2007, Stemper et al 2006). The shorter the EMD, the better the sports performance and protective reflex. Some studies have reported that strength training (Kaneko et al 2002, Kubo et al 2001, Linford et al 2006), braces and tapping decrease the EMD of the surrounding muscle of the affected joint (Stanek et al. 2006). The conventional method for measuring EMD involves recording the time interval between the onset of muscle activity and the onset of mechanical output (such as force production) of the detected muscle contraction. Researchers have measured EMD in the peroneal muscle, gastrocnemius and biceps brachii on the basis of foot eversion (Mora et al 2003, Vaes et al 2001), ankle plantar flexion (Muraoka et al. 2004) and elbow flexion (Vint et al. 2001), respectively. However, the validity of measuring the vastus medialis obliquus (VMO) and vastus lateralis (VL) in the conventional way is questionable.

The common tendon of the VMO and VL passes over the patella and through the tibial tubercle. Conventionally, EMD of the VMO and VL is measured as the interval from the time of stimulation of the femoral nerve (Kaneko et al. 2002) or voluntary quadriceps contraction to the time of onset of knee extension force (Chan et al 2001, Georgoulis et al 2005, Kubo et al 2000, Yeung et al 1999, Zhou et al 1995). Three important issues concerning the measurement of EMD of the VMO and VL require clarification: (1) the VMO and VL cannot be activated individually by stimulating the femoral nerve or with voluntary quadriceps contraction, (2) the earlier firing muscle has the longest EMD because the measured EMD ends at the same time as the onset of mechanical output and (3) the EMD measurement of the VMO and VL is likely confounded by the patella and patellar tendon because they are situated between the muscle and the tibial tubercle. Therefore, we believe that it is more accurate to measure the EMD of the VMO and VL individually by stimulating the VMO and VL directly instead of stimulating the femoral nerve and by determining the onset time of patellar movement instead of the onset time of knee extension force.

Ultrasonography was used to observe real-time patellar movement in vivo; the intrarater reliability was excellent (intraclass correlation coefficient [ICC] = 0.9 ∼ 0.99) (Herrington et al 2006, Shih et al 2003, Shih et al 2004). Because the onset time of electrical stimulation of the VMO and VL and the initiation of patellar movement were synchronized on the same ultrasonographic screen, the “real” EMD of the VMO and VL could be measured. The purpose of this study was to develop a novel method for measuring the EMD of the VMO and VL individually.

Section snippets

Subjects

Seven men (age: 27.6 ± 6.3 y; height: 171.1 ± 8.2 cm; and weight: 73.3 ± 7.3 kg) and five women (age: 28.4 ± 5.1 y; height: 154.0 ± 2.0 cm; and weight: 50.0 ± 4.6 kg) voluntarily participated in the study. None of the subjects had knee pain, a history of injury in the past 6 months or any neurological deficit that might affect the functions of the lower extremities. The subjects were examined on the dominant limb, resting on a bed in full muscle relaxation with their knees slightly flexed. All

Results

The results of test-retest ICC for the measurement of the EMD of VMO and VL are summarized in Table 1. The reproducibility of the EMD of both the VMO and VL was good (ICC > 0.8). The CV for the EMD measurement of the VMO was also less than that of the VL.

The power of the paired t test was 0.97 for the effect of muscle types. The mean difference of the EMDs between the VMO and VL was 6.46 ms. The result of the paired t test demonstrated that the EMD of the VMO was significantly less than that of

Discussion

EMD of the VMO and VL is conventionally determined by measuring the interval between the time of onset of muscle activities and the time of onset of knee extension force after stimulation of the femoral nerve or voluntary quadriceps contraction. Thus, the earlier firing muscle had a longer EMD because the initiation of the same mechanical output was detected as the terminal point of the EMD. Therefore, the current study proposed a novel technique for measuring EMD by detecting patellar movement

Summary

A novel, feasible and more precise method for measuring the EMD of the VMO and VL individually was developed in this study. For the purpose of measuring the EMD of individual muscles in the quadriceps, it is recommended that the motor point of the target muscle be stimulated directly. It is also suggested that the mechanical output of the VMO or VL twitch should be based on patellar movement rather than on knee extension force. The EMD data derived with the use of this new method was more

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