Magnetic resonance imaging and electromyography as indexes of muscle function

Abstract

1992.-Electromyography (EMG) is commonly used to determine the electrical activity of skeletal muscle during contraction. To date, independent verification of the relationship between muscle use and EMG has not been provided. It has recently been shown that relaxation-(e.g., T 2 ) weighted magnetic resonance images (MRI) of skeletal muscle demonstrate exercise-induced contrast enhancement that is graded with exercise intensity. This study was conducted to test the hypothesis that exercise-induced magnetic resonance (MR) contrast shifts would relate to EMG amplitude if both measures reflect muscle use during exercise. Both MRI and EMG data were collected for separate eccentric (ECC) and concentric (CON) exercise of increasing intensity to take advantage of the fact that the rate of increase and amplitude of EMG activity are markedly greater for CON muscle actions. Seven subjects 30 ± 2 (SE) yr old performed five sets of 10 CON or ECC arm curls with each of four resistances representing 40, 60, 80, and 100% of their 10 repetition maximum for CON curls. There was 1.5 min between sets and 30 min between bouts (5 sets of 10 actions at each relative resistance) . Multiple echo, transaxial T 2 -weighted MR images (1.5 T, TR/TE 2,000/30) were collected from a 7-cm region in the middle of the arm before exercise and immediately after each bout. Surface EMG signals were collected from both heads of the biceps brachii and the long head of the triceps brachii muscles. CON and ECC actions resulted in increased integrated EMG (IEMG) and T 2 values that were strongly related (r = 0.99, P < 0.05) with relative resistance. The rate of increase and absolute value of both T 2 and IEMG were greater for CON than for ECC actions. IEMG and T 2 for both CON and ECC actions were correlated (r = 0.99, P < 0.05). The results suggest that J) surface IEMG accurately reflects the contractile behavior of muscle and 2) exercise-induced increases in MRI T 2 values reflect some processes that scale with muscle use. muscle function MAGNETIC RESONANCE SPECTROSCOPY (MRS) has become an accepted tool for in vivo biochemical studies of muscle tissue. Magnetic r esonance (MR) imaging (MRI) is a variant of this methodology that is rapidly becoming the standard for many clinical diagnostic applications because it provides unparalleled visualization of anatomic detail of soft tissues such as muscle, tendon, cartilage, and various organs. MRI has also begun to be used in basic muscle research. For example, MR images of skeletal muscle show exercise-induced contrast enhance-1578 ment, which appears to be graded with exercise intensity (7). This has been used to infer which muscles were used during the activity and the extent of their contribution.Electromyography (EMG) has long been the noninvasive method of choice for analyses of muscle activation during exercise (2). It entails sampling electrical activity from a muscle region of interest with needle or surface electrodes. There is good relation between EMG amplitude and force development for a variety of...

Maximal strength training and increased work efficiency: contribution from the trained muscle bed

“…Second, following high-intensity resistance training, less muscle is required to lift a given absolute load, as documented by a reduction in magnetic resonance image contrast shift (29). Such a reduction in muscle recruitment is associated with an alteration in metabolic demand (1,11). Third, the kinetics of force development can also play a role in altering metabolic demand of the exercising muscle (36).…”

Dynamic MRS and MRI of skeletal muscle function and biomechanics

“…It is well known that exercise leads to a change in the distribution of water within skeletal muscle, and this shift in water distribution is considered to be at the basis of the above T 2 change in exercise (208). The T 2 changes correlate well with electromyography (EMG) recordings of muscle activity (209) and increase with increased exercise intensity (210). The prime advantage of the MRI read-out is its ability to produce a three-dimensional view of the entire muscle (or groups of muscles), non-invasively, while the EMG is limited to a superficial recording.…”

Surface electrical stimulation of skeletal muscle after spinal cord injury

“…The extent of T 2 contrast shift of muscle is correlated with previous contractile activity. The extent of T 2 contrast shift of muscle is correlated with integrated electromyography activity 15 and increases with exercise intensity. 15,16,19,22 ± 24 Adams et al 25 utilized contrast shifts in MR images to re¯ect the territory and extent of muscle contraction induced by surface ES.…”