MRI quantification of muscle activity after volitional exercise and neuromuscular electrical stimulation.
OBJECTIVE
The efficacy, and even the depth, of muscle stimulation during surface electrode neuromuscular electrical stimulation (NMES) is a matter of debate. This study addresses these issues by assessing the utility of a magnetic resonance imaging (MRI) technique in localizing and quantitating changes in the nature of MRI signals in the quadriceps muscle after volitional exercise and NMES.


METHODS
Volitional isometric and NMES-evoked quadriceps muscle activity was evaluated in two controlled trials. In the first, isometric quadriceps strength was determined during NMES and maximal volitional isometric exercise in six healthy men. In the second, changes in the ratio of MRI T2 signal intensities before and after volitional isometric exercise and NMES were used to quantitate MRI signal changes associated with muscle activation in 12 additional healthy men.


RESULTS
MRI clearly detected quadriceps muscle tissue activation after both volitional and stimulated contractions, even though the NMES knee extension torque was only 23.5% that of maximal volitional isometric exercise. In particular, the T2 intensity ratios increased 26.5% +/- 17.3% (mean +/- standard deviation) after volitional exercise and 12.9% +/- 12.8% after NMES. This pattern of volitional isometric exercise, producing larger T2 intensity ratio values than NMES, was present in both deep and superficial layers and throughout the quadriceps muscle.


CONCLUSIONS
Although volitional muscle contractions were several times stronger than those induced by NMES in this study, our findings support the idea that MRI can provide a noninvasive way to quantitate and localize volitional and electrically stimulated muscle activation.
Ogino
Misa
M
Rehabilitation Center, Kurume University, Kurume City, Japan.
Shiba
Naoto
N
Maeda
Takashi
T
Iwasa
Kiyohiko
K
Tagawa
Yoshihiko
Y
Matsuo
Shigeaki
S
Nishimura
Hiroshi
H
Yamamoto
Toshiyasu
T
Nagata
Kensei
K
Basford
Jeffrey R
JR
D000328:Adult; D004558:Electric Stimulation / Q000295:instrumentation / Q000379:methods*; D015444:Exercise; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*