Humans Optimize Ground Contact Time and Leg Stiffness to Minimize the Metabolic Cost of Running

Abstract

Trained endurance runners appear to fine-tune running mechanics to minimize metabolic cost. Referred to as self-optimization, the support for this concept has primarily been collated from only a few gait (e.g., stride frequency, length) and physiological (e.g., oxygen consumption, heart rate) characteristics. To extend our understanding, the aim of this study was to examine the effect of manipulating ground contact time on the metabolic cost of running in trained endurance runners. Additionally, the relationships between metabolic cost, and leg stiffness and perceived effort were examined. Ten participants completed 5 × 6-min treadmill running conditions. Self-selected ground contact time and step frequency were determined during habitual running, which was followed by ground contact times being increased or decreased in four subsequent conditions whilst maintaining step frequency (2.67 ± 0.15 Hz). The same self-selected running velocity was used across all conditions for each participant (12.7 ± 1.6 km • h −1). Oxygen consumption was used to compute the metabolic cost of running and ratings of perceived exertion (RPE) were recorded for each run. Ground contact time and step frequency were used to estimate leg stiffness. Identifiable minimums and a curvilinear relationship between ground contact time and metabolic cost was found for all runners (r 2 = 0.84). A similar relationship was observed between leg stiffness and metabolic cost (r 2 = 0.83). Most (90%) runners self-selected a ground contact time and leg stiffness that produced metabolic costs within 5% of their mathematical optimal. The majority (n = 6) of self-selected ground contact times were shorter than mathematical optimals, whilst the majority (n = 7) of self-selected leg stiffness' were higher than mathematical optimals. Metabolic cost and RPE were moderately associated (r s = 0.358 p = 0.011), but controlling for condition (habitual/manipulated) weakened this relationship (r s = 0.302, p = 0.035). Both ground contact time and leg stiffness appear to be self-optimized characteristics, as trained runners were operating at or close to their mathematical optimal. The majority of runners favored a self-selected gait that may rely on elastic energy storage and release due to shorter ground contact times and higher leg stiffness's than optimal. Using RPE as a surrogate measure of metabolic cost during manipulated running gait is not recommended.

Limitations of Foot-Worn Sensors for Assessing Running Power

“…[ 23 , 27 ])). The same holds true for varying the ground contact time [ 28 ]. Reducing the ground contact time additionally alters both step length and frequency.…”

Predicting Temporal Gait Kinematics: Anthropometric Characteristics and Global Running Pattern Matter

“…Similarly to SF, inter-individual differences in the spontaneous choice of DF was depicted by a greater = 97.7% than =69.3% ( Table 1 ), and by the ICCs of the random effects which were excellent for the intercept and moderate for speed ( Table 1 ). Therefore, DF variability on an individual level might also be related to self-optimization, as this was shown to be present in t c ( Moore, 2016 ; Moore et al, 2019 ), but again, using the same linear mixed effects model on a dataset with a larger speed range would be needed to validate this assumption.…”

Relationship between Biological, Training, and Physical Fitness Variables in the Expression of Performance in Non-Professional Runners

“…Moreover, it was found that a higher stride frequency decreases the time spent to cover 1 km. Although there is no consensus, this may occur since a higher stride frequency shortens the time of ground contact, resulting in a more economic running [ 46 , 47 ]. Expert runners usually have higher step rates and shorter stride length than the novice ones, aiming to optimize energy expenditure and to reduce injury risk–in a mechanism called “self-optimization” [ 46 , 48 , 49 , 50 , 51 ].…”