The pressure within exercising skeletal muscle rises and falls rhythmically during normal human locomotion, the peak pressure reaching levels that intermittently impede blood flow to the exercising muscle. Speculating that a reciprocal relationship between the timing of peak intramuscular and pulsatile arterial pressures should optimize blood flow through muscle and minimize cardiac load, we tested the hypothesis that heart rate becomes entrained with walking and running cadence at some locomotion speeds, by means of electrocardiography and an accelerometer to provide signals reflecting heart rate and cadence, respectively. In 18 of 25 subjects, 1:1 coupling of heart and step rates was present at one or more speeds on a motorized treadmill, generally at moderate to high exercise intensities. To determine how exercise specific this phenomenon is, and to refute the competing hypothesis that coupling is due to vertical accelerations of the heart during locomotion, we had 12 other subjects cycle on an electronically braked bicycle ergometer. Coupling was found between heart rate and pedaling frequency in 10 of them. Cardiac-locomotor coupling appears to be a normal physiological phenomenon, and its identification provides a fresh perspective from which to study endurance.

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This report presents the early results of a new technique, using a solid-state transducer intracompartmental (STIC) catheter, developed to measure dynamic pressure changes in the anterior compartment of the leg in patients with exercise-induced anterior compartment syndrome. Nine male volunteers (15 limbs) with a history of exercise-induced anterior compartment pain were studied and compared to eleven asymptomatic male controls matched for age, weight and height. After catheter insertion, anterior compartment pressures were recorded with the subjects walking and running on a treadmill and performing several static maneuvers before and after the exercise period. The most statistically significant value between the two groups was the difference in mean pressure during running (P less than 0.001). Presently, all mean running pressures greater than 85 mm Hg are considered abnormal. This new technique offers the investigator the opportunity to measure dynamic intracompartmental pressures in symptomatic patients and provides an objective measurement for selection of patients for fasciotomy.

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