Dataset Information

Mechanical Determinants of the U-Shaped Speed-Energy Cost of Running Relationship.

ABSTRACT: Purpose: The aim of this study was to investigate the relationship between the energy cost of running (Cr) and speed and its mechanical determinants by comparing running in normal [100% body weight (BW)] and reduced (20% and 60% BW) gravity conditions at several speeds (2.25, 3.17, 4.08, and 5.00 m·s-1) in experienced runners. Methods: Twelve experienced runners (24.6 ± 5.4 year) ran on an AlterG treadmill in a partially randomized order at the four running speeds and at the three gravity conditions in order to assess Cr, spatiotemporal parameters, spring-mass characteristics and elastic energy (EL) during running. Results: For the three gravity conditions, the speed-Cr per kg of body mass relationship was curvilinear (significant speed effect: P < 0.001) and was significantly downward shifted with reduced gravity (100%>60%>20% BW; P < 0.001). EL, expressed in J·step-1, was significantly higher at 100% BW than at 60 and 20% BW and at 60% BW than at 20% BW (significant gravity effect: P < 0.001) with a significant increase in EL per step at faster speeds for the 3 gravity conditions (P < 0.001). EL, expressed in J·kg-1·m-1, was significantly downward shifted with gravity (100%>60%>20% BW; P < 0.001), with no significant speed effect (P = 0.39). Conclusions: Our findings showed that, for the three gravity conditions, the speed-Cr relationship was curvilinear, and the optimization of the stretch-shortening cycle and muscle activation in the muscle-tendon unit may be involved to explain these U-shaped relationships, especially at normal terrestrial gravitational conditions (100% BW). The U-shaped speed-Cr per kg of the body mass relationship was shifted downward in hypogravity conditions, which was characterized by decreased EL compared to 100% BW. These mechanisms may contribute to the less than proportional decrease in Cr per kg of body mass relative to gravity.

SUBMITTER: Carrard A

PROVIDER: S-EPMC6305502 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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Mechanical Determinants of the U-Shaped Speed-Energy Cost of Running Relationship.

Carrard Apolline A Fontana Elisa E Malatesta Davide D

Frontiers in physiology 20181218

Purpose: The aim of this study was to investigate the relationship between the energy cost of running (Cr) and speed and its mechanical determinants by comparing running in normal [100% body weight (BW)] and reduced (20% and 60% BW) gravity conditions at several speeds (2.25, 3.17, 4.08, and 5.00 m·s-1) in experienced runners. Methods: Twelve experienced runners (24.6 ± 5.4 year) ran on an AlterG treadmill in a partially randomized order at the four running speeds ...[more]

PMID: 30618803

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Project description:Psychological variables such as motivation, self-efficacy, and anxiety have been widely studied in marathon runners, usually within the framework of Bandura's theory of self-efficacy. It is also assumed a link between self-perceived fitness and physiological performance parameters such as speed at ventilatory thresholds and running economy. The purpose of this paper is to describe longitudinal trends of self-perceptions and examine their link to physiological performance parameters over time. Sixteen healthy recreational marathoners (8 males and 8 females), aged M = 37.6 (SD = 3.9) who were about to participate in a major marathon agreed to participate. After 3 months of regular training and competition in shorter distances, all participants trained during a 16-week macrocycle under the supervision of the same coaching staff. At 4-week intervals, the participants responded five times the Podium questionnaire, measuring self-perceived psychological state relative to the upcoming race, and performed five exercise performance parameters tests. Linear mixed-effects models were used to analyze the trends and associations. In general, Podium questionnaire scores were within the standard range, with the lowest values at the beginning and the highest values closer to race day. Although only perceived fitness (p < 0.001, Cohen's f 2 = 1.19) and somatic anxiety (p < 0.001, f 2 = 0.32) showed large effect sizes for the whole longitudinal period, other partial increases were found between time points. All physiological performance parameters presented significant improvements over time (Aerobic Threshold speed, p < 0.001, f 2 = 1.04; Anaerobic Threshold speed, p < 0.001, f 2 = 0.498; Running Economy in VO2, p < 0.001, f 2 = 0.349; Running Economy in energy, p = 0.024, f 2 = 0.197). The analysis of changes between consecutive time points revealed that improving perceived physical condition predicted improving self-efficacy (p < 0.001, f 2 = 1.33), and improvements in motivation were predicted by improvements in either self-efficacy (p < 0.001, f 2 = 0.36) or perceived physical condition (p = 0.003, f 2 = 0.17). Improvements in perceived fitness, self-efficacy and motivation were associated with small effect-size improvements (decreases) in anxiety. None of the physiological performance parameters was shown to predict changes in psychological variables, although their general trends over time correlated. The results have practical implications for sport psychologists and running coaches, supporting the need for integrated working.

Project description:BackgroundReducing the energy cost of running with exoskeletons could improve enjoyment, reduce fatigue, and encourage participation among novice and ageing runners. Previously, tethered ankle exoskeleton emulators with offboard motors were used to greatly reduce the energy cost of running with powered ankle plantarflexion assistance. Through a process known as "human-in-the-loop optimization", the timing and magnitude of assistance torque was optimized to maximally reduce metabolic cost. However, to achieve the maximum net benefit in energy cost outside of the laboratory environment, it is also necessary to consider the tradeoff between the magnitude of device assistance and the metabolic penalty of carrying a heavier, more powerful exoskeleton.MethodsIn this study, tethered ankle exoskeleton emulators were used to characterize the effect of peak assistance torque on metabolic cost during running. Three recreational runners participated in human-in-the-loop optimization at four fixed peak assistance torque levels to obtain their energetically optimal assistance timing parameters at each level.ResultsWe found that the relationship between metabolic rate and peak assistance torque was nearly linear but with diminishing returns at higher torque magnitudes, which is well-approximated by an asymptotic exponential function. At the highest assistance torque magnitude of 0.8 Nm/kg, participants' net metabolic rate was 24.8 ± 2.3% (p = 4e-6) lower than running in the unpowered devices. Optimized timing of peak assistance torque was as late as allowed during stance (80% of stance) and optimized timing of torque removal was at toe-off (100% of stance); similar assistance timing was preferred across participants and torque magnitudes.ConclusionsThese results allow exoskeleton designers to predict the energy cost savings for candidate devices with different assistance torque capabilities, thus informing the design of portable ankle exoskeletons that maximize net metabolic benefit.

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Mechanical Determinants of the U-Shaped Speed-Energy Cost of Running Relationship.

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Mechanical Determinants of the U-Shaped Speed-Energy Cost of Running Relationship.

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