Abstract
Cardiolocomotor synchronization, when step rate and heart rate naturally occur with a 1:1 ratio, has been well-described in studies of running and walking. A proposed explanation for this phenomenon is that the frequency match enables cardiac counterpulsation via diastolic stepping, a potentially adaptive physiological behavior that may improve hemodynamic efficiency during ambulation. PURPOSE: Highly trained runners were studied to assess the prevalence of cardiolocomotor synchronization and whether the step-to-heart phase timing preferentially occurred during diastole, facilitating natural counterpulsation.We hypothesized that unprompted heart rate and step rate entrainmentwould be present in our cohort of elite runners and the synchronization would occur during the diastolic phase of their cardiac cycles. METHODS: Eleven elite male endurance athletes completed three stages of over-ground running separated by ample recovery. The stages consisted of 12 min at 17.06 km/h (5:40 min/mi), 11 min at 18.67 km/h (5:10 min/mi), and 5 min at 21.08 km/h (4:35 min/mi), for a total running time of 28 minutes. A chest strap-based sensor transmitted and recorded real-time ECG and three-axis accelerometry data. Proprietary software was then used to analyze data for timing comparison of step rate, heart rate and the step-to-heart cycle phase relationship. RESULTS: When the frequencies of step and heart rates were matched, six of the eleven athletes displayed episodes of prolonged (>30 sec) diastolic stepping during at least one of the three speeds. Three runners exhibited prolonged diastolic stepping for 18 ± 6% of the first stage. All six runners exhibited prolonged diastolic stepping for 26 ± 15% of the second stage. Three runners exhibited prolonged diastolic stepping for 28 ± 15% of the third stage. Five of the eleven athletes did not experience any episode of cardiolocomotor synchronization, due to heart rate being consistently lower than step rate. Only one episode of prolonged systolic stepping was observed. CONCLUSIONS: Unprompted cardiolocomotor synchronization occurs with highly trained runners and is associated with diastolic stepping and natural counterpulsation, suggesting that the entrainment for hemodynamic advantages may be a driving force behind the coupling of heart rate and step rate.
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