Sensitivity was 10–20 μV/division, low-frequency filter was 32 Hz, high-frequency filter was 3.2 kHz, sweep speed was 1 ms/division, and duration of pulse was 0.2 ms. Rate of pulse and the machine used were not specified.

This study was performed in the supine position.

Following the orthodromic method [1], surface electrodes of felt (8 mm pads, 25 mm apart) soaked in 0.9 % saline were placed at the wrist for both the median and radial nerve sensory recordings. For the median nerve recording (R1), the electrodes were placed on the course of the median nerve, the active (A) electrode was placed proximal to the distal wrist crease, and the reference (R) was placed proximally. For the radial nerve recording (R2), the electrodes were placed on the course of the radial nerve, the active (A) electrode was placed proximal to the radial styloid, and the reference (R), like for the median nerve, was placed proximally. Recording electrodes from the median and radial nerves (R1 and R2) were placed at the same distance from the distal stimulating cathode to the digit I (Fig. 1). No fixed distance was used by the author; electrodes were placed at a distance range of 6.7–10.5 cm (mean distance was 8.5 cm). Ground (G) electrode was taped on the palm or dorsum of the hand; the figure shows the ground electrode placed on the palm. The median (R1) and radial (R2) nerve recordings were made separately.

Stimulation was applied distally to the digit I (thumb). The author used ring electrodes for stimulating both median and radial nerves: the stimulating cathode (−) was placed proximal to the proximal interphalangeal joint of the digit I and anode (+) electrode was placed distally. The median and radial nerves were stimulated separately by the supramaximal stimuli.

Peak latency (ms) was measured from the onset of the stimulus to the peak of the negative deflection of the sensory nerve action potential (SNAP). Negative peak amplitude (μV) was measured from the baseline to the peak of the negative deflection. The author reported only peak latencies (ms) of the median nerve SNAPs; he measured the peak latency difference (ms) between the median and the radial distal sensory latencies. The surface distance between the stimulating and recording sites was measured with a tape measure to the nearest 0.1 cm. Each subject was studied at one session at room temperature. The temperature at the wrist, measured with a surface thermistor, was kept above 30 °C. A total of 100 hands from 50 healthy subjects (Table 1) were studied (24 women and 26 men, age range 16–82 years, mean age 46.7 years). Controls were divided into three groups according to age (16–39 years, 40–59 years, and 60–82 years).