An examination of the relationship between electromechanical delay and muscle quality

Electromechanical delay (EMD) is defined as the time delay between the onset of electrical activity at the muscle and the generation of force. Muscle quality (MQ) is a muscle’s maximal strength relative to its cross-sectional area (CSA). Although both EMD and MQ are related to muscle function, very little research has explored the relationship between the two. PURPOSE: The purpose of this study was to examine the relationship between EMD and MQ in college-aged males. METHODS: Maximal isometric torque and EMD of the knee extensors were assessed in seventeen resistance-trained men (mean age = 22.7 years) using an isokinetic dynamometer. Subjects performed three, 3 s isometric maximal voluntary contractions (MVCs) of the knee extensors, at a knee joint angle of 120° with 1 min of recovery between each contraction. Electrical activity of the vastus lateralis muscle was measured using surface electromyographic electrodes with an interelectrode distance of 20 mm. The onset of contraction was determined as the point when the torque signal reached a threshold of 7.5 Nm and isometric MVC peak torque (PT) was determined as the highest mean 0.5 s epoch during the entire 3 s MVC plateau. The lowest EMD and the highest torque produced during the 3 MVCs were used for subsequent analysis. Anthropometric measures were performed prior to testing. CSA of the quadriceps was estimated using the following regression equation (Housh et al., 1995): Quadriceps CSA = (2.52 × mid-thigh circumference in cm) – (1.25 × anterior thigh skinfold in mm) – 45.13. MQ was calculated as PT/CSA. A correlation was used to assess the strength of the relationship between EMD and MQ. RESULTS: The pearson correlation coefficient demonstrated a weak, and non-significant relationship (r = -.245) between EMD and MQ (p = .344). The removal of CSA produced a stronger (r = -.406) but still non-significant (p = .106) relationship between EMD and PT. CONCLUSION: These data suggest that there is little to no correlation between EMD and MQ, while the relationship between EMD and PT is only moderate. Future research exploring which neuromuscular performance characteristics are related to EMD is warranted