Running-specific prostheses enable athletes with lower limb amputations to run by emulating the spring-like function of biological legs. Current prosthetic stiffness and height recommendations aim to mitigate kinematic asymmetries for athletes with unilateral transtibial amputations. However, it is unclear how different prosthetic configurations influence the biomechanics and metabolic cost of running. Consequently, we investigated how prosthetic model, stiffness, and height affect the biomechanics and metabolic cost of running. Ten athletes with unilateral transtibial amputations each performed 15 running trials at 2.5 or 3.0 m/s while we measured ground reaction forces and metabolic rates. Athletes ran using three different prosthetic models with five different stiffness category and height combinations per model. Use of an Ottobock 1E90 Sprinter prosthesis reduced metabolic cost by 4.3 and 3.4% compared with use of Freedom Innovations Catapult [fixed effect (β) = -0.177; < 0.001] and Össur Flex-Run (β = -0.139; = 0.002) prostheses, respectively. Neither prosthetic stiffness ( ≥ 0.180) nor height ( = 0.062) affected the metabolic cost of running. The metabolic cost of running was related to lower peak (β = 0.649; = 0.001) and stance average (β = 0.772; = 0.018) vertical ground reaction forces, prolonged ground contact times (β = -4.349; = 0.012), and decreased leg stiffness (β = 0.071; < 0.001) averaged from both legs. Metabolic cost was reduced with more symmetric peak vertical ground reaction forces (β = 0.007; = 0.003) but was unrelated to stride kinematic symmetry ( ≥ 0.636). Therefore, prosthetic recommendations based on symmetric stride kinematics do not necessarily minimize the metabolic cost of running. Instead, an optimal prosthetic model, which improves overall biomechanics, minimizes the metabolic cost of running for athletes with unilateral transtibial amputations. The metabolic cost of running for athletes with unilateral transtibial amputations depends on prosthetic model and is associated with lower peak and stance average vertical ground reaction forces, longer contact times, and reduced leg stiffness. Metabolic cost is unrelated to prosthetic stiffness, height, and stride kinematic symmetry. Unlike nonamputees who decrease leg stiffness with increased in-series surface stiffness, biological limb stiffness for athletes with unilateral transtibial amputations is positively correlated with increased in-series (prosthetic) stiffness.

Inspired by the springlike action of biological legs, running-specific prostheses are designed to enable athletes with lower-limb amputations to run. However, manufacturer's recommendations for prosthetic stiffness and height may not optimize running performance. Therefore, we investigated the effects of using different prosthetic configurations on the metabolic cost and biomechanics of running. Five athletes with bilateral transtibial amputations each performed 15 trials on a force-measuring treadmill at 2.5 or 3.0 m/s. Athletes ran using each of 3 different prosthetic models (Freedom Innovations Catapult FX6, Össur Flex-Run, and Ottobock 1E90 Sprinter) with 5 combinations of stiffness categories (manufacturer's recommended and ± 1) and heights (International Paralympic Committee's maximum competition height and ± 2 cm) while we measured metabolic rates and ground reaction forces. Overall, prosthetic stiffness [fixed effect (β) = 0.036; = 0.008] but not height ( ≥ 0.089) affected the net metabolic cost of transport; less stiff prostheses reduced metabolic cost. While controlling for prosthetic stiffness (in kilonewtons per meter), using the Flex-Run (β = -0.139; = 0.044) and 1E90 Sprinter prostheses (β = -0.176; = 0.009) reduced net metabolic costs by 4.3-4.9% compared with using the Catapult prostheses. The metabolic cost of running improved when athletes used prosthetic configurations that decreased peak horizontal braking ground reaction forces (β = 2.786; = 0.001), stride frequencies (β = 0.911; < 0.001), and leg stiffness values (β = 0.053; = 0.009). Remarkably, athletes did not maintain overall leg stiffness across prosthetic stiffness conditions. Rather, the in-series prosthetic stiffness governed overall leg stiffness. The metabolic cost of running in athletes with bilateral transtibial amputations is influenced by prosthetic model and stiffness but not height. We measured the metabolic rates and biomechanics of five athletes with bilateral transtibial amputations while running with different prosthetic configurations. The metabolic cost of running for these athletes is minimized by using an optimal prosthetic model and reducing prosthetic stiffness. The metabolic cost of running was independent of prosthetic height, suggesting that longer legs are not advantageous for distance running. Moreover, the in-series prosthetic stiffness governs the leg stiffness of athletes with bilateral leg amputations.

Limited available information describes how running-specific prostheses and running speed affect the biomechanics of athletes with bilateral transtibial amputations. Accordingly, we quantified the effects of prosthetic stiffness, height and speed on the biomechanics of five athletes with bilateral transtibial amputations during treadmill running. Each athlete performed a set of running trials with 15 different prosthetic model, stiffness and height combinations. Each set of trials began with the athlete running on a force-measuring treadmill at 3 m s, subsequent trials incremented by 1 m s until they achieved their fastest attainable speed. We collected ground reaction forces (GRFs) during each trial. Prosthetic stiffness, height and running speed each affected biomechanics. Specifically, with stiffer prostheses, athletes exhibited greater peak and stance average vertical GRFs ( = 0.03; < 0.001), increased overall leg stiffness ( = 0.21; < 0.001), decreased ground contact time ( = -0.07; < 0.001) and increased step frequency ( = 0.042; < 0.001). Prosthetic height inversely associated with step frequency ( = -0.021; < 0.001). Running speed inversely associated with leg stiffness ( = -0.58; < 0.001). Moreover, at faster running speeds, the effect of prosthetic stiffness and height on biomechanics was mitigated and unchanged, respectively. Thus, prosthetic stiffness, but not height, likely influences distance running performance more than sprinting performance for athletes with bilateral transtibial amputations.

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.

Purpose Sixty-five years of age typically marks the onset of impaired walking economy. However, running economy has not been assessed beyond the age of 65 years. Furthermore, a critical determinant of running economy is the spring-like storage and return of elastic energy from the leg during stance, which is related to leg stiffness. Therefore, we investigated whether runners over the age of 65 years retain youthful running economy and/or leg stiffness across running speeds. Methods Fifteen young and fifteen older runners ran on a force-instrumented treadmill at 2.01, 2.46, and 2.91 m·s−1. We measured their rates of metabolic energy consumption (i.e. metabolic power), ground reaction forces, and stride kinematics. Results There were only small differences in running economy between young and older runners across the range of speeds. Statistically, the older runners consumed 2–9% less metabolic energy than the young runners across speeds (p=0.012). Also, the leg stiffness of older runners was 10–20% lower than that of young runners across the range of speeds (p=0.002) and in contrast to the younger runners, the leg stiffness of older runners decreased with speed (p<0.001). Conclusion Runners beyond 65 years of age maintain youthful running economy despite biomechanical differences. It may be that vigorous exercise, such as running, prevents the age related deterioration of muscular efficiency, and therefore may make everyday activities easier.