Biology subjects

Kram, R.

Publications and source records attributed to Kram, R..

4 recordsLinked to original sources

bioRxiv2025

Metabolic energy expenditure during level, uphill, and downhill running

PurposeTo extend the Running Energy Expenditure Estimation (RE3) model for predicting metabolic rates during uphill and downhill running as well as to enhance the Hoogkamer-Taboga-Kram (HTK) equation for estimating metabolic rates during level and uphill running. MethodsWe combined running metabolic data from an original dataset (n=63) with individual subject data from 26 studies (n=424) and group mean data from 12 studies (n=187). Using this integrated dataset, we derived a new graded running term for the empirical RE3 model and updated the HTK equation coefficients for level and uphill running. We then compared the accuracy and precision of these new equations with the established American College of Sports Medicine (ACSM) and Minetti et al. equations based on the root-mean-square deviation (RMSD). ResultsAccuracy and precision of estimating level [M] were high for the Minetti et al. (RMSD, 1.44 W{middle dot}kg-1), HTK (1.30 W{middle dot}kg-1), and RE3 (1.27 W{middle dot}kg-1) equations but much worse for the ACSM equation (1.82 W{middle dot}kg-1). Agreement on uphill slopes was highest for the HTK (RMSD, 1.45 W{middle dot}kg-1) and RE3 (1.41 W{middle dot}kg-1) equations with less precision noted for the ACSM (2.17 W{middle dot}kg-1) and Minetti et al. (2.18 W{middle dot}kg-1) equations. When estimating [M] during downhill running, the RE3 equation performed marginally better (RMSD, 1.45 W{middle dot}kg-1) than the Minetti et al. equation (1.57 W{middle dot}kg-1). ConclusionThe improved RE3 and HTK equations estimate metabolic rates during level and graded running with improved accuracy and precision. We provide a publicly available web-based metabolic rate calculator that simplifies estimation for researchers, practitioners, and runners alike.

physiology↗

bioRxiv2024

Could a female athlete run a 4-minute mile with improved aerodynamic drafting?

In 2023, Faith Kipyegon set the female world record for running one mile (4:07.64). Here, we quantitively explore if improved aerodynamic drafting could allow her to run just 3.19% faster and thus break the 4-minute mile barrier. Drafting involves other athletes (pacers) running in formation around a designated athlete to reduce the aerodynamic drag force acting on the designated runner. Drafting allows the designated athlete to run faster at the same rate of metabolic energy consumption. Our overall approach was to estimate Kipyegons metabolic energy consumption during her mile world record performance. Then, we used empirically established relationships between horizontal resistive force, running velocity and metabolic power to estimate how much faster she could run at the same metabolic power if the aerodynamic force was reduced via drafting. Our calculations suggest that Kipyegon could run [~]3:59.37 with drafting provided by one pacer in front and one in back who change out with two other pacers at 800 m.

physiology↗

bioRxiv2021

The metabolic cost of overcoming air resistive forces in distance running

We lack a mechanistic understanding of the relationship between aerodynamic drag forces and metabolic power during running. Further, the energetic and time savings possible from reducing aerodynamic drag (drafting) are still unclear due to the different methods previously assumed for converting from force reductions to metabolic power savings. Here, we quantified how small horizontal impeding forces (equivalent to aerodynamic forces) affect metabolic power and ground reaction forces over a range of velocities in competitive runners. In three sessions, 12 runners completed six 5-minute trials with 5 minutes of recovery in-between. We tested one velocity per session (12, 14 and 16 km/h), at three horizontal impeding force conditions (0, 4 and 8 N). On average, metabolic power increased by 6.13% per 1% body weight of horizontal impeding force but varied considerably between individuals. With greater horizontal impeding force, braking impulses decreased while propulsive impulses increased (p < 0.001). Across running velocities, the changes in braking and propulsive impulses with greater impeding force were correlated (r = -0.97; p < 0.001), but were not related to individual changes in metabolic power. We estimate that at [~]2-hour marathon pace, overcoming air resistive force comprises 8.52% of the gross metabolic power on average.

physiology↗

bioRxiv2018

Preferred walking speed on rough terrain; is it all about energetics?

Humans have evolved the ability to walk very efficiently. Further, humans prefer to walk at speeds that approximately minimize their metabolic energy expenditure per unit distance (i.e. gross cost of transport, COT). This has been found in a variety of population groups and other species. However, these studies were performed on smooth, level ground or on treadmills. We hypothesized that the objective function for walking is more complex than only minimizing the COT. To test this idea, we compared the preferred speeds and the relationships between COT and speed for people walking on both a smooth, level floor and a rough, natural terrain trail. Rough terrain presumably introduces other factors, such as stability, to the objective function. 10 healthy men walked on both a straight, flat, smooth floor and on an outdoor trail strewn with rocks and boulders. In both locations, subjects performed 6-8 trials at different speeds relative to their preferred speed. The COT-speed relationships were similarly U-shaped for both surfaces, but the COT values on rough terrain were approximately 215% greater. On the smooth surface, the preferred speed (1.24+/-0.14 m/sec) was 5.1% faster (p>0.05) than the speed that minimized COT (1.18 m/sec) but on rough terrain, the preferred speed (1.06+/-0.07 m/sec) was 6.2% slower (p>0.05) than the COT minimum speed (1.13 m/sec). This suggests that the objective function when walking on rough terrain includes additional factors such as stability.\n\nSummary statement: On rough terrain, humans do not choose their walking speed based on metabolic energy minimization alone.

evolutionary biology↗