Effects of ischemic pre-conditioning on electrically stimulated contractions.

Abstract

Ischemic pre-conditioning (IPC) offers protection against future ischemic events and may improve sports performance due to several mechanisms at local and systemic levels. This study investigates the local effects on muscle contractility in electrically induced muscle contractions, thus effectively excluding any uncontrolled change in the motor drive. Twenty-one subjects were divided into two groups: 12 subjects in the IPC group (3 × 5/5min right arm ischemia/reperfusion; cuff pressure 250mmHg) and 9 subjects in the SHAM group (same treatment at 20mmHg). The adductor pollicis was contracted by supramaximal stimulation of the ulnar nerve with single pulses, trains of stimuli (5, 8, 10 and 12Hz, 1-s duration) and bursts (4 pulses, 25Hz), all separated by 5-s intervals. The stimulation sequence was delivered before and 15 and 30min after IPC/SHAM treatment. The isometric contraction force, the superficial electromyographic signal, and tissue oxygenation were continuously monitored. A significant force decrease in time was observed at 8, 10 (p < 0.01) and 12Hz (p < 0.05) along with a decrease in half-relaxation time in single twitches and bursts (p = 0.01), regardless of treatment. This general time-related weakening was more marked in IPC than SHAM at 5-Hz stimulation. No effects were observed on the magnitude of the superficial electromyographic signal. Data indicate that IPC does not increase muscle force during electrically stimulated contractions, supporting the idea that IPC's ergogenic effects are not due to increased muscle contractility.