Coupling of cardiac and locomotor rhythms.

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.

The effect of locomotion speed on the anterior tibial intramuscular pressure of normal humans.

We examined the hypothesis that anterior tibial intramuscular pressure increases with the speed of locomotion. A solidstate pressure transducer was placed near the tip of an intramuscular fluid-filled catheter and each of ten normal subjects walked, jogged and ran barefoot, at 1.5, 2.5 and 3.5 m s-1 respectively, on a treadmill to which they had been previously familiarized. The pressure signals during ten gait cycles from each subject were sampled at 600 Hz and were averaged at each speed. The peak pressures increased in magnitude as a function of increasing locomotion speed, while the mean pressure remained constant.

Reliability of walking endurance with an incremental treadmill test.

Treadmill walking endurance is the major outcome measure for intervention studies on patients with intermittent claudication. The measurement properties of this test have not, however, been well documented. We assessed the test-retest reliability of treadmill walking endurance in 10 normal subjects with a mean (+/- 1SD) age of 27.5 (+/- 3.3) years. On four occasions, at intervals of at least one week, each subject walked on a motorized treadmill to the limits of his or her capabilities. With the standard protocol, subjects began at a very low exercise intensity (0.25 m/sec, 0% grade), which increased in either speed or grade at ninety-second intervals through a maximum of fifteen stages to 2.75 m/sec and 20% grade. On the final occasion, 5 of the subjects were tested twice with a fifteen-minute interval, using a truncated protocol starting at stage five (1.25 m/sec, 0% grade). Within-subject standard deviations were low, averaging twenty-three seconds (2.1%). Reliability was very high for the first three tests with the standard protocol (r greater than or equal to 0.98, p less than 0.0001) and for the 5 subjects tested and retested with the short interval and truncated protocol (r = 0.99, p less than 0.0002), while the correlation between the standard protocol and the truncated protocol was somewhat lower (r greater than 0.81, p less than 0.01). For young normal subjects the measurement of walking endurance with an incremental treadmill test is highly reliable, but the limits of reliability need to be considered when conclusions are drawn from such measures.