Extrapolating Metabolic Savings in Running: Implications for Performance Predictions

Training, footwear, nutrition, and racing strategies (i.e., drafting) have all been shown to reduce the metabolic cost of distance running (i.e., improve running economy). However, how these improvements in running economy (RE) quantitatively translate into faster running performance is less established. Here, we quantify how metabolic savings translate into faster running performance, considering both the inherent rate of oxygen uptake-velocity relation and the additional cost of overcoming air resistance when running overground. We collate and compare five existing equations for oxygen uptake-velocity relations across wide velocity ranges. Because the oxygen uptake vs. velocity relation is non-linear, for velocities slower than ∼3 m/s, the predicted percent improvement in velocity is slightly greater than the percent improvement in RE. For velocities faster than ∼3 m/s, the predicted percent improvement in velocity is less than the percent improvements in RE. At 5.5 m/s, i.e., world-class marathon pace, the predicted percent improvement in velocity is ∼2/3rds of the percent improvement in RE. For example, at 2:04 marathon pace, a 3% improvement in RE translates to a 1.97% faster velocity or 2:01:36, almost exactly equal to the recently set world record

Commentaries on viewpoint : physiology and fast marathons

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The mechanics and energetics of the aging pulmonary system during exercise

As a part of healthy aging, older individuals experience a decline in respiratory function making breathing more difficult, especially during exercise. Purpose: Here, I comprehensively examine the combined effects of healthy aging and biological sex on respiratory mechanics and the metabolic cost of breathing during exercise. Methods: In study #1 (Chapter-2), we validated a newer technology, optoelectronic plethysmography (OEP), which allows us to measure how different groups of respiratory muscles contribute to breathing and proposed a method for quantifying the mechanical work done by the ribcage and abdomen. In study #2 (Chapter-3) we used OEP with healthy adults to understand how differences in regions of the chest-wall contribute to breathing mechanics during exercise with respect to age and sex. In study #3 (Chapter-4) we used voluntary hyperpnea to estimate the metabolic cost of breathing and understand the physiological consequences of different respiratory mechanics across age and sex. Conclusion: Ventilation increases during exercise to meet the metabolic demands of the working muscles and is accompanied by an increased work to breathe. Older individuals and females have a higher work of breathing for a given ventilation and use different regional respiratory muscle to meet those demands relative to younger individuals and males, respectively. With exercise, there is an ample increase in the oxygen uptake by the respiratory muscles. Specifically, both younger and older females have a higher cost to breathe than their male counterparts during moderate and high-intensity exercise and older individuals incur a higher cost to breathe than younger individuals for a given ventilation. Our results suggest that both sex differences and normal age-related changes in respiratory structure and function, appear to have a significant effect on the ventilatory responses during exercise. Collectively, the results of this thesis suggest that sex differences in respiratory mechanics persist throughout healthy aging and contribute to the increased metabolic cost to breathe during exercise in healthy older females relative to males. Understanding the demands of the respiratory system during exercise of healthy older adults is especially important from a clinical perspective given that many diseases of the heart and lungs occur in older individuals.Education, Faculty ofKinesiology, School ofGraduat

Why Does Metabolic Rate Increase Curvilinearly with Running Velocity?

The ‘cost of generating force’ model proposes that a major determinant of metabolic rate during running is the rate of muscular force production. However, the amount of muscle force needed during running is affected by the effective mechanical advantage (EMA), the ratio of the ground reaction force moment arm (R) to the muscle moment arm (r), R/r. The ‘cost of generating force’ model assumed that EMA and active muscle volume remain constant across velocity. With this assumption, the cost of generating force hypothesis explains 80% of the linear increase in metabolic rate in human runners across a moderate velocity range. Additionally, many studies have demonstrated a linear relationship between metabolic rate and running velocity for a diverse assortment of species. However, in humans there is less of a consensus of how to mathematically characterize the relationship. Using 7 sub-elite male runners, I performed a more systematic analysis of EMA over 6 different velocities (8, 10, 12, 14, 16 and 18km/hr) to explain both the remaining 20% and the curvilinear increase in metabolic rate. I hypothesized that the curvilinear metabolic rate pattern observed in elite runners at fast sub-maximal velocities can be explained by a decrease in EMA at the hip, knee and ankle joints, which necessitates a greater volume of active muscle recruitment. Over the velocity range, all subjects demonstrated a curvilinear increase in metabolic rate. Ankle EMA decreased by 14.5 ± 4.1%, while hip EMA showed the largest magnitude decrease of 51.2 ± 30.2%. Accordingly, the active volume of hip extensor muscles increased 50.1% from 448 ± 245 cm3 to 898 ± 250cm3 across the velocity range. The ankle extensor active muscle volume increased by 32.8% from 713 ±145cm3 to 1061 ± 159cm3. I extended the cost of generating force model and found that in human runners, metabolic rate is proportional to the rate of force generation multiplied by the volume of muscle activated

What Determines the Metabolic Cost of Human Running Across a Wide Range of Velocities?

The cost of generating force hypothesis proposes that the metabolic rate during running is determined by the rate of muscle force development (1/tc, tc=contact time) and volume of active leg muscle. A previous study assumed a constant recruited muscle volume and reported that the rate of force development alone explains ~70% of the increase in metabolic rate for human runners across a moderate velocity range (2-4 m s-1). PURPOSE: We performed a more systematic analysis of the effective mechanical advantage (EMA) of the lower leg over a wide velocity range to determine if we could more completely explain the increase in metabolic rate that human runners are capable of sustaining aerobically. We hypothesized that over a wide range of velocities, the EMA of the lower leg joints would overall decrease, necessitating a greater volume of active muscle recruitment. METHODS: Ten high-caliber male human runners (mean max = 72.7 ± 3.9 mlO2/kg/min) ran on a force-measuring treadmill at 8, 10, 12, 14, 16 and 18 km hr-1 while we analyzed their expired air to determine metabolic rates. We measured ground reaction forces and joint kinematics to calculate contact time and estimate active muscle volume. RESULTS: From 8 to 18 km hr-1, metabolic rate increased 132% from 9.01 to 20.92 W kg-1. All subjects completed the speed range with an RER-1 = 0.937 +/- 0.04, and mean blood [La] at 18 km hr-1 = 3.51 ± 0.31 mmol/L). Contact time (tc) decreased from 0.280 sec to 0.190 sec, and thus the rate of force development (1/tc) increased by 48%. Ankle EMA decreased by 19.7±11%, knee EMA increased by 11.1±26.9% and hip EMA decreased by 60.8±11.8%. Estimated active muscle volume per leg increased 54.1% from 1663±152 cm3 to 2550±169 cm3. CONCLUSION: Overall, 97% of the increase in metabolic rate across the velocity range was explained by just two factors: the rate of generating force and the volume of active leg muscle. These results link the biomechanics and metabolic costs of human running and the approach may give greater insight into understanding individual differences in metabolic rate

Calculating metabolic energy expenditure across a wide range of exercise intensities: the equation matters

We compared ten published equations for calculating energy expenditure from oxygen consumption and carbon dioxide production using data for 10 high-caliber male distance runners over a wide range of running velocities. We found up to a 5.2% difference in calculated metabolic rate between two widely used equations. We urge our fellow researchers abandon out-of-date equations with published acknowledgments of errors or inappropriate biochemical/physical assumptions.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author