Estimated cardiorespiratory response during marathon running

Mechanical Energy Changes and the Oxygen Cost of Running

The relationship between the oxygen cost of running at submaximal speeds and running mechanics was investigated in a group of trained athletes by means of an energy analysis.

Subjects were filmed while running on a motorized treadmill at speeds of 3.58, 4.02, 4.47, 4.92, 5.36, and 5.81 m/s. Segmental potential and kinetic energies were determined using a three-dimensional link-segmental model. Intra-stride changes in the energy of the whole body were computed with no allowance for energy transfer and with various energy transfer constraints imposed on the model. Oxygen consumption was determined by expired air analysis and used to estimate energy expenditure.

For each transfer condition, net energy expenditure was more highly correlated with the magnitude of intra-stride energy changes than with running speed per se. The more economic running patterns were characterized by greater within-segment energy transfers.

Given the limitations of the kinematic energy model, it is suggested that individual patterns of running are a significant factor in the determination of energy expenditure.

Thermoregulation and marathon running: biological and environmental influences

The extreme physical endurance demands and varied environmental settings of marathon footraces have provided a unique opportunity to study the limits of human thermoregulation for more than a century. High post-race rectal temperatures (Tre) are commonly and consistently documented in marathon runners, yet a clear divergence of thought surrounds the cause for this observation. A close examination of the literature reveals that this phenomenon is commonly attributed to either biological (dehydration, metabolic rate, gender) or environmental factors. Marathon climatic conditions vary as much as their course topography and can change considerably from year to year and even from start to finish in the same race. The fact that climate can significantly limit temperature regulation and performance is evident from the direct relationship between heat casualties and Wet Bulb Globe Temperature (WBGT), as well as the inverse relationship between record setting race performances and ambient temperatures. However, the usual range of compensable racing environments actually appears to play more of an indirect role in predicting Tre by acting to modulate heat loss and fluid balance. The importance of fluid balance in thermoregulation is well established. Dehydration-mediated perturbations in blood volume and blood flow can compromise exercise heat loss and increase thermal strain. Although progressive dehydration reduces heat dissipation and increases Tre during exercise, the loss of plasma volume contributing to this effect is not always observed for prolonged running and may therefore complicate the predictive influence of dehydration on Tre for marathon running. Metabolic heat production consequent to muscle contraction creates an internal heat load proportional to exercise intensity. The correlation between running speed and Tre, especially over the final stages of a marathon event, is often significant but fails to reliably explain more than a fraction of the variability in post-marathon Tre. Additionally, the submaximal exercise intensities observed throughout 42 km races suggest the need for other synergistic factors or circumstances in explaining this occurrence. There is a paucity of research on women marathon runners. Some biological determinants of exercise thermoregulation, including body mass, surface area-to-mass ratio, sweat rate, and menstrual cycle phase are gender-discrete variables with the potential to alter the exercise-thermoregulatory response to different environments, fluid intake, and exercise metabolism. However, these gender differences appear to be more quantitative than qualitative for most marathon road racing environments.

Cardio-pulmonary function of cyclists competing on an ascending mountain course between altitudes of 1400 m and 2800 m

Physiological changes were investigated in the cardio-respiratory function of competitors in a bicycle race which involved not a flat course but ascending a mountain, from 1400 m to 2800 m. Heart rate throughout the race, arterial oxygen saturation and pulmonary function before and after the race of well trained competitors were measured. The individual's maximal heart rate during the race was designated as HRmax for the calculations. (1) There were significant correlations between the age and the mean %HRmax during the race, between mean %HRmax and time, and between age and time (n = 15); the mean %HRmax had a 3.90 times greater effect on time than did age. (2) The individuals who performed best had lower values of oxygen saturation just after finishing the race (n = 51). (3) At 1 min after reaching the finishing line, oxygen saturation levels had recovered to the value of 20 min after finishing the race, whereas the heart rate was still in the process of recovery (n = 18). (4) Maximum expiratory flow at 50% vital capacity measured 30 min after reaching the finishing line was significantly higher than at the starting point. The intensity of the load on the cardiac system produced by completion of this course was estimated to be almost the same as that of a full marathon on a flat course. The time depended on both the youth of the cyclist and on his ability to maintain a high value of %HRmax during the race.

Endurance Exercise: Normal Physiology and Limitations Imposed by Pathological Processes (Part 1)

In brief: Endurance exercise induces significant and rapid changes in many physiological functions. To maintain homeostasis, adaptations in the oxygen transport and delivery chain are necessary. Increases in minute ventilation and diffusion across the alveolar-capillary membrane enhance oxygenation of blood in the lungs. Parallel changes in cardiac output, muscle blood flow, and arteriovenous oxygen difference increase oxygen transport and delivery. Pulmonary and cardiovascular diseases can limit oxygen transport and/or delivery, while muscle diseases can impair oxygen delivery.

The Physiology of Marathon Running

In brief: The marathon is one of the greatest tests of human endurance. This review article describes the physiological demands and responses of the respiratory, cardiovascular, and muscular systems to marathon running, focusing on the chain of oxygen transport needed to fulfill the aerobic requirements of marathon running. During the race, runners use about 75% of VO2 max. Increased levels of ventilation (> 80 liters· min(-1)) have been observed during the marathon. This can lead to decrements in forced vital capacity and respiratory muscle fatigue. Prolonged muscle activity during the run can cause muscle injury such as inflammation and necrosis of muscle fibers. Techniques for augmenting performance include endurance and interval training, diet manipulation, and racing strategy.

Cardiac arrest and jogging

Cardiac arrest related to jogging usually occurs in the setting of a structural cardiac abnormality. The patients often have no prodromal symptoms. Certain aspects of these cases, such as delayed entrance into the medical care system and exercise-induced lactic acidosis, make successful resuscitation difficult. We describe three such patients under the age of 36 who died after running.

A Physiological Profile of Four Wheelchair Marathon Racers

In brief A profile of four wheelchair marathon racers (WMRs) is presented including an athletic history, dietary habits, maximal oxygen uptake, and average race pace oxygen uptake (Vo₂) values. These values were compared with those of able-bodied marathon runners matched for age and race time. The WMRs had lower Vo₂ max, maximal heart rates, and higher respiratory exchange ratios, and they used a higher percentage of their Vo₂ max and maximal heart rate at race pace. The authors suggest that a high degree of training is required to perform the grueling marathon.

Assessment of cardiac function in marathon runners by graphic noninvasive techniques

The volume overload type of heart often observed in endurance athletes, was simulate a diseased heart. We used a battery of noninvasive graphic techniques, i.e., echocardiogram, apexcardiogram, carotid pulse, electrocardiogram, vectorcardiogram, phonocardiogram, systolic time intervals, and treadmill stress testing in 12 professional marathon runners, mean age 33.8 +/- 11.1. Twenty nonathletes matched for age, height, sex, and weight served as a control group. Left ventricular (LV) end-diastolic dimension in marathon runners averaged 5.53 +/- 0.5 cm compared to 4.81 +/- 0.04 cm in nonathletes (p less than 0.001), LV end-diastolic volume was 172.69 +/- 43.3 ml compared to 113.57 +/- 30.41 ml in nonathletes (p less than 0.001), stroke volume was 122.27 +/- 32.8 ml compared to 78.42 +/- 20.44 ml in non-athletes (p less than 0.001), the thickness of the posterior LV wall was 1.0 +/- 0.2 cm compared to 0.7 +/- 0.1 cm in nonathletes (p less than 0.001), and LV mass was significantly increased, 212.43 +/- 55.8 g compared to 123.48 +/- 24.54 g in non-athletes (p less than 0.01). Left atrium and aortic root were also relatively larger in athletes (p less than 0.01). Right ventricular end-diastolic dimension was enlarged in marathon runners (2.02 +/- 0.65 cm). No statistically significant differences were noted in ejection fraction, percentage of internal diameter shortening (% delta D) and PEP/LVET. The carotid tracing had a bisferiens pulse in five marathon runners. The apexcardiogram showed a bifid systolic thrust in three and absence of abnormal A wave. These abnormalities were related to the overload type of heart as proven by echocardiogram. "Early repolarization syndrome" (abnormal RS-T segment elevation) and notched T waves in ECG had a counterpart a semilunar configuration in the VCG. Three athletes met ECG criteria and one met VCG criteria of LVH. The treadmill exercise ECG was negative in all 12 athletes. Biventricular enlargement and increased left ventricular mass are present in the marathon runner's heart. Myocardial contractility at rest was, however, not statistically different from nonathletes.