Low-frequency filter was 2 Hz, high-frequency filter was 2 kHz, and the machine used was a TECA MS20 EMG device. Sensitivity, sweep speed, duration of pulse, and rate of pulse were not specified.

This study was performed in the supine position.

Following the antidromic method [1], signals were recorded using surface electrodes from the median and ulnar nerves separately. For the median nerve (R1), the active recording electrode (A) was placed between the proximal interphalangeal joint and the metacarpophalangeal joint of digit II; the reference electrode (R) was placed 3 or 4 cm (depending on the size of the hand) distal to the active electrode over the same digit (Fig. 1). For the ulnar nerve (R2), the active recording electrode (A) was placed between the proximal interphalangeal joint and the metacarpophalangeal joint of digit V; the reference electrode (R) was placed 3 or 4 cm (depending on the size of the hand) distal to the active electrode over the same digit. The ground (G) electrode position was not specified in the text; the figure shows the ground electrode placed on the palm. The median and ulnar nerves were stimulated separately; the cathodes were placed proximally.

Stimulations were applied over the median and ulnar nerves at the wrist. The median nerve was stimulated at a fixed 13 cm distance from the active recording electrode (A) placed to the proximal interphalangeal joint. The ulnar nerve was stimulated at 11 cm from the active recording electrode (11 cm). The median and ulnar nerves were stimulated separately.

Peak to peak amplitude (μV) of the sensory nerve action potentials (SNAPs) of the median and ulnar nerves was measured from negative peak to the positive peak of the SNAP. In each limb studied, the ratio of the median nerve SNAP amplitude to ulnar nerve SNAP amplitude (peak to peak median to ulnar SNAP amplitude ratio, MUSAR) was determined. For example, if the median SNAP amplitude value was 36 and the ulnar SNAP amplitude value was 24, then the MUSAR would be calculated by dividing the former by the latter value (36 divided by 24) giving a MUSAR value of 1.5. The limb temperature was measured with a surface thermistor; a warm water bath was used to maintain limb temperature at or above 32 °C. Normal values (Table 1) were obtained from 46 apparently healthy male veterans (age range 18–45 years).