Original researchDoes a run/walk strategy decrease cardiac stress during a marathon in non-elite runners?
Introduction
Benefits of regular running on cardiorespiratory fitness are known to reduce all-cause and cardiovascular mortality.1 In contrast, sudden death in marathon runners with no prior documentation of heart disease shows that prolonged endurance exercise can have the opposite effect in exceptional cases.2 Especially in recreational endurance runners with less training the risk for cardiac dysfunction and injury is increased after completing a marathon.3, 4, 5 In this respect, the steadily growing number of participants in running events6 emphasizes the need to assess biochemical markers that allow the prediction of the cardiovascular risk during prolonged exercise at submaximal intensity.
Previous studies have shown that prolonged running evokes abnormal elevations in creatine kinase MB isoenzyme (CK-MB), cardiac troponin (cTnI), and B-type natriuretic peptide (BNP).5 In clinical settings, increased serum levels of these cardiac markers are strong prognostic indicators of cardiac events.3, 7 However, there is still an ongoing debate whether elevations in CK-MB, TNP and BNP after strenuous exercise reflect irreversible cardiac damage or just a reversible cardiac fatigue.8, 9, 10 In this respect, Fortescue et al.11 argue that high BNP and TNP concentrations after a marathon, particularly in non-elite runners, might be due to an incomplete myocardial adaptation to training in which vulnerable myocytes are selectively eliminated. Furthermore, increases in cardiac markers correlate with post-race diastolic dysfunction, increased pulmonary pressures and right ventricular dysfunction after 2000 m rowing.3
Compared to running, walking is associated with lower energy expenditure and less physiological stress.12 Therefore, fitness experts still recommend walking breaks to make novice runners complete a marathon successfully and safely.13 Referring to the stress on the cardiovascular system, this recommendation is hardly based on evidence, as the effect of intermittent running on selected cardiac markers has not been investigated yet. However, a previous study has shown that regular walking breaks do not reduce fatigue and muscular stress during a 24 km run,14 whereas hormonal (e.g. testosterone and cortisol) responses seem to differ from continuous running.15 Furthermore, a high variability of pacing impairs marathon performance,16 possibly due to a higher energy demand, which is associated with an uneconomical running strategy.
The aim of the study was to compare the effects of a run/walk strategy (RWS) vs running only (RUN) on selected markers of cardiovascular injury and stress (CK-MB, BNP, cTnI & myoglobin) as well as marathon performance. Additionally, it was examined whether or not the pacing strategy during a marathon influences the restoration of maximal aerobic performance. Higher serum concentrations of CK-MB, BNP and myoglobin, which are associated with an increased cardiovascular risk, were expected after the run/walk protocol (RWS).
Section snippets
Methods
In response to a newspaper advertisement, recreational athletes applied for the study by submitting personal data including age, weight, profession and exercise experience. Only runners with a regular training volume of 10–20 km/week, who did not participate in marathons before, were included. Exclusion criteria were any chronic or acute cardiovascular, neuronal and orthopedic diseases that could jeopardize the performance and safety of participants during the marathon. Prior to the study they
Results
Due to cramps two participants in RUN were not able to continue running and cross the finishing line. The RWS and RUN completed the marathon in 04:14:25 ± 00:19:51 (hh:mm:ss) and 04:07:40 ± 00:27:15 (hh:mm:ss), respectively. The difference in marathon time was not significant between the groups (F = 0.80; p = 0.377). Furthermore, participants’ mean (158 ± 7 min−1 vs 154 ± 6 min−1; F = 2.22; p = 0.146) and maximal heart rate (174 ± 8 min−1 vs 173 ± 7 min−1; F = 2.22; p = 0.888) did not differ significantly between RWS and
Discussion
Despite different pacing strategies, both groups completed the marathon with no differences in mean heart rate and finishing time. Consequently, the RWS must have compensated the lower velocity during the walking periods with a higher velocity than RUN during the running phases. Due to the decrease in limb mechanical advantage and increase in knee extensor impulse, running requires higher metabolic cost than walking.18 However, similar mean and maximal heart rates between the groups suggest
Conclusions
Prolonged running elicits elevations in CK-MB, myoglobin and BNP, which are similar to those of patients with acute myocardial infarction. Body of evidence suggests that this increase in cardiac biomarkers is a reversible, physiological response to prolonged exercise, indicating temporary stress on the myocyte and skeletal muscle rather than long-term damage to the heart. A combined run walk strategy does not decrease the magnitude of these elevations. However, lower ratings of exhaustion and
Practical implications
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Prolonged running increases levels of cardiac biomarkers, such as CK-MB, BNP and myoglobin.
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Increased levels of cardiac biomarkers return to baseline 4 days after the marathon.
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Elevations in cardiac biomarkers are not reduced by a run/walk strategy.
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A run/walk strategy reduces perceived fatigue and muscle pain in recreational endurance runners.
Conflict of interest
None.
Acknowledgement
There has been no external funding to support the experimental trial.
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