T Distribution in the Forearm Muscles and the T Threshold for Defining Activated Muscle.

PURPOSE

In order to detect exercised muscles by the increase in T, we have defined a Gaussian T distribution and reference values (T and SD) in resting state muscles, and a threshold for detecting exercised muscles.

METHODS

The subjects were healthy adult volunteers (14 males and 12 females). Multiple-spin-echo (MSE) MR images were obtained with 10 TE values from 10 to 100 ms using a 0.2T MRI system. T values for 10 forearm muscles were obtained in the resting state and after isometric wrist flexion exercise with 5%, 15%, and 25% of the maximum voluntary contraction (MVC). Z values were obtained by (T - T)/SD, where T was T after exercise. Based on sample size calculations, three thresholds (Z = 1.00, 2.56, and 3.07) were applied to agonist and antagonist muscles.

RESULTS

A normal distribution of T was detected in resting muscles at 34 ± 3 ms (mean ± standard deviation [SD]) in 26 subjects using the Kolmogorov-Smirnov test, the Shapiro-Wilk test, and the Jarque-Bera test (P > 0.05). No gender differences were shown between the T or SD, and a similar result was obtained in 12 measurements on a single subject (P < 0.01). The T and SD were used for reference values. The threshold Z = 1.00 showed the highest sensitivity (0.86) even with 5% MVC, but it showed a lower specificity (0.85) than the other thresholds. Z = 3.07 showed the highest specificity (1.0), but it showed a lower sensitivity (0.36) with the 5% MVC, compared with Z = 2.56 (0.50). The receiver operating characteristics analysis also supported these results.

CONCLUSION

We found that the T distribution in muscles was Gaussian, suggesting that a one-sample t-test can be applied, and that Z = 2.56 could cover low-intensity exercise with high specificity and a low false-positive rate.