In an attempt to improve their distance-running performance, many athletes race with carbon fiber plates embedded in their shoe soles. Accordingly, we sought to establish whether, and if so how, adding carbon fiber plates to shoes soles reduces athlete aerobic energy expenditure during running (improves running economy). We tested 15 athletes as they ran at 3.5 m/s in four footwear conditions that varied in shoe sole bending stiffness, modified by carbon fiber plates. For each condition, we quantified athlete aerobic energy expenditure and performed biomechanical analyses, which included the use of ultrasonography to examine soleus muscle dynamics in vivo. Overall, increased footwear bending stiffness lengthened ground contact time (p = 0.048), but did not affect ankle (p ≥ 0.060), knee (p ≥ 0.128), or hip (p ≥ 0.076) joint angles or moments. Additionally, increased footwear bending stiffness did not affect muscle activity (all seven measured leg muscles (p ≥ 0.146)), soleus active muscle volume (p = 0.538; d = 0.241), or aerobic power (p = 0.458; d = 0.04) during running. Hence, footwear bending stiffness does not appear to alter the volume of aerobic energy consuming muscle in the soleus, or any other leg muscle, during running. Therefore, adding carbon fiber plates to shoe soles slightly alters whole-body and calf muscle biomechanics but may not improve running economy.

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Human locomotion is remarkably robust to environmental disturbances. Previous studies have thoroughly investigated how perturbations influence body dynamics and what recovery strategies are used to regain balance. Fewer studies have attempted to establish formal links between balance and the recovery strategies that are executed to regain stability. We hypothesized that there would be a strong relationship between magnitude of imbalance and recovery strategy during perturbed walking. To test this hypothesis, we applied transient ground surface translations that varied in magnitude, direction, and onset time while eight healthy participants walked on a treadmill. We measured stability using integrated whole-body angular momentum (iWBAM) and recovery strategy using step placement. We found the strongest relationships between iWBAM and step placement in the frontal plane for earlier perturbation onset times in the perturbed step (R2=0.52, 0.50) and later perturbation onset times in the recovery step (R2=0.18, 0.25), while correlations were very weak in the sagittal plane (all R2 <= 0.13). These findings suggest that iWBAM influences step placement, particularly in the frontal plane, and that this influence is sensitive to perturbation onset time. Lastly, this investigation is accompanied by an open-source data set to facilitate research on balance and recovery strategies in response to multifactorial ground surface perturbations, including 96 perturbation conditions spanning all combinations of three magnitudes, eight directions, and four gait cycle onset times.

Trunk postural control (TPC) has been investigated in several populations and tasks. Previous work observed targeted training of TPC via isolated trunk control tasks may improve performance in other activities (e.g., walking). However, the nature of this relationship remains unknown. We therefore investigated the relationship between TPC, at both the global (i.e., response to finite perturbations) and local (i.e., resistance to continuous perturbations) levels, during walking and unstable sitting, both at varying levels of task demand. Thirteen individuals (11 Male, 2 Female) with no recent history (past 12 months) of illness, injury, or musculoskeletal disorders walked on a dual-belt treadmill at four speeds (-20%, -10%, +10%, and + 20% of self-selected walking speed) and completed an unstable sitting task at four levels of chair instability (100, 75, 60, and 45% of an individual's "neutral" stability as defined by the gravitational gradient). Three-dimensional trunk and pelvic kinematics were collected. Tri-planar Lyapunov exponents and sample entropy characterized local TPC. Global TPC was characterized by ranges of motion and, for seated trials, metrics derived from center-of-pressure time series (i.e., path length, 95% confidence ellipse area, mean velocity, and RMS position). No strong or significant correlations (-0.057 < ρ < 0.206) were observed between local TPC during walking and unstable sitting tasks. However, global TPC declined in both walking and unstable sitting as task demand increased, with a moderate inter-task relationship (0.336 < ρ < 0.544). While the mechanisms regulating local TPC are inherently different, global TPC may be similarly regulated across both tasks, supporting future translation of improvements in TPC between tasks.

In an attempt to improve their distance-running performance, many athletes race with carbon fiber plates embedded in their 20 shoe soles. Accordingly, we sought to establish whether, and if so how, adding carbon fiber plates to shoes soles reduces athlete 21 aerobic energy expenditure during running (improves running economy). We tested 15 athletes during running at 3.5 m/s in four 22 footwear conditions that varied in shoe sole carbon fiber plate bending stiffness. For each condition, we quantified athlete aerobic 23 energy expenditure and performed biomechanics analyses, which included the use of ultrasound imaging to examine soleus muscle 24 dynamics in vivo. Overall, increased footwear bending stiffness lengthened ground contact time (p=0.048), but did not affect ankle 25 (p≥0.060), knee (p≥0.128), or hip (p≥0.076) joint angles or moments. Additionally, increased footwear bending stiffness did not affect 26 muscle activity (all seven measured leg muscles (p≥0.146)), stride averaged active soleus volume, (p=0.068) or aerobic power 27 (p=0.458) during running. Hence, footwear bending stiffness does not appear to alter the volume of aerobic energy consuming muscle 28 in the soleus, or any other leg muscle, during running. Therefore, adding carbon fiber plates to shoe soles slightly alters whole-body 29 and calf muscle biomechanics but does not improve running economy. 30 31 In competitive athletics, marginal differences distinguish champions from their competitors. For instance, if any of the top-five 2016 33Olympic women's marathon finishers ran 0.51% faster, they would have been crowned Olympic champion. Such miniscule 34 differences highlight the importance for athletes to optimize all factors that influence race performance. One way to further optimize 35 athletic performance is to don the best footwear. Using footwear that reduces athlete aerobic energy expenditure at a given running 36 speed (improves their running economy) can augment distance-running performance by decreasing their relative aerobic intensity. 1-3 37An established method of improving footwear to augment athlete distance-running performance is to reduce its mass. 1,2,4,5 Based on 38 literature values, if an aforementioned Olympic marathoner re-raced in shoes that were 100 g less than their original footwear, they 39 would have expended aerobic energy at an ~0.8% slower rate, 5 run the marathon ~0.56% faster, 6 and taken the gold medal back to 40 their home country. 42A longstanding footwear technology that has recently polarized the running community is the use of carbon fiber plates in shoe soles. 7 43Despite the rampant use of carbon fiber plates in athletics, 8-10 many seek to regulate the use of these plates in distance-running 44 footwear based on the notion that they provide wearers an 'unfair advantage' over competitors without such technology. 11 These 45 views persist even though it is inconclusive whether adding carbon fiber to shoe soles improves running economy. [12][13][14][15][16] To date, two 46 studies have reported that...