Alena Marie Grabowski

Metabolic cost reductions for stationary hopping on elastic compared with rigid surfaces are frequency dependent. We found that the surface stiffness that minimized metabolic cost was stiffer at faster hopping frequencies. Leg stiffness and contact time increased as surface stiffness decreased, and this effect was amplified at faster hopping frequencies. These findings suggest that the stiffness of passive-elastic devices, like elastic surfaces and footwear, should be tuned to movement frequency to minimize metabolic cost.

Purpose: The aim of this study was to investigate the running economy and biomechanics of runners wearing Advanced Footwear Technology (AFT) spiked shoes (spikes) and AFT shoes relative to traditional spikes. Methods: 17 (7 female & 10 male) competitive distance runners completed two sessions of eight (four shoes × two replicates), five-minute trials at 15 km*hr ⁻¹ (females) or 17 km*hr ⁻¹ (males) wearing Nike ZoomX Dragonfly (NDF) and On Cloudspike 10,000 m (OCS) AFT spikes, Nike Vaporfly Next % 2 (NVN) AFT shoes, and Nike Zoom Victory 3 (NZV) traditional spikes. We measured metabolic rates and ground reaction forces and compared average running economy (W*kg ⁻¹ ) and biomechanical variables from four trials per shoe per runner. Results: When runners wore NDF and OCS AFT spikes and NVN AFT shoes, running economy improved by 2.1%, 2.3%, and 1.9%, respectively, compared to NZV traditional spikes (p < 0.001). These improvements coincided with 6.1%, 4.5%, and 8.9% increases in leg stiffness and 1.5%, 2.2%, and 2.3% increases in ground contact time for the NDF, OCS, and NVN, respectively, compared to NZV traditional spikes (p < 0.002). Conclusion: Running economy improved by 2.1% for athletes wearing compliant AFT spikes and shoes compared to traditional spikes. Future generations of AFT spikes that are designed with further increases in midsole compliance and energy return could improve race performance by eliciting potentially favorable biomechanical changes, such as increased leg stiffness and/or ground contact time.

Individuals with unilateral transtibial amputation walked while using an energy storage and return prosthesis and the BiOM prosthesis and were provided with visual feedback of peak propulsive horizontal force (hGRF). Visual feedback increased affected leg peak propulsive hGRF and decreased peak propulsive hGRF asymmetry, but participants incurred a greater metabolic cost when using either prosthesis. Future device designs should explore biofeedback and device control to help individuals more effectively use a powered prosthesis.

People with unilateral transtibial amputation (uTTA) using a passive-elastic prosthesis typically walk with contact time (t_c) and first and second peak vertical ground reaction force (F₁ and F₂) asymmetry and greater first peak external knee adduction moment in their unaffected versus affected leg. A previous study found that use of stance-phase powered prosthesis (BiOM) at a recommended power setting compared to a passive-elastic prosthesis can reduce t_c asymmetry at self-selected speed and unaffected leg first peak external knee adduction moment at 1.50–1.75 m/s. However, the BiOM includes a passive-elastic prosthesis that can have different stiffness categories and can be tuned to different power settings, which may affect t_c and F₁ and F₂ asymmetry and unaffected leg first peak external knee adduction moment. Thirteen people with uTTA used 16 different passive-elastic prosthetic foot stiffness categories and BiOM power settings to walk at 0.75–1.75 m/s. We found that use of the stiffest compared to least stiff category reduced F₂ asymmetry. Use of the BiOM reduced t_c asymmetry compared to a passive-elastic prosthesis and the effects of power setting on F₁ and F₂ asymmetry depended on walking speed. To minimize biomechanical asymmetry during walking at 1.25 m/s, people with uTTA should use the BiOM with power settings up to 20% greater than those that match biological ankle joint biomechanics. Such prosthetic settings could potentially reduce unaffected leg joint pain and/or osteoarthritis risk.

For individuals with unilateral transtibial amputation, powered ankle-foot prostheses have the potential to reduce the metabolic rate of walking, which could contribute to improvements in mobility and quality of life; however, physiological improvements have not been consistently demonstrated in experimental studies. To improve our understanding of the biomechanical mechanisms that drive metabolic rate outcomes, we used a machine learning approach to model the relationship between multimodal biomechanical factors and the metabolic rate of walking with a powered ankle-foot prosthesis. Our model included 50 features describing spatiotemporal parameters, step-to-step transition work, joint kinematics, muscle activity, ground reaction forces, prosthesis settings, and subject characteristics, and resulted in a pseudo-R ² of 0.986. Accumulated local effects plots were used to visualize the direction and magnitude of the relationship between each feature and the metabolic rate of walking. The features with the largest effect on metabolic rate were peak unaffected side ankle inversion angle, leading affected leg positive work during the step-to-step transition, and peak affected knee extension angle. This work furthers our knowledge about the biomechanical and physiological response to powered ankle-foot prosthesis use and could assist in developing new strategies to drive reductions in metabolic rate.

The incidence of lower extremity injuries in collegiate distance runners is ∼20%. Identification of a runner sustaining a potential injury remains challenging. This exploratory, cross-institutional study sought to determine whether ground reaction force (GRF) characteristics during steady-state running could identify competitive collegiate distance runners who would later sustain lower extremity injuries. Normative boundaries for 10 GRF variables during braking and propulsion were established for noninjured runners using median ± scaled median absolute deviation. A subanalysis was conducted on runners with and without impact peaks in vertical GRF to mitigate the influence of impact peaks on GRF variables. We hypothesized that prior to injury, runners who later developed an injury would have more GRF variables outside of the normative boundaries than noninjured runners. Using Cliff’s method, a rank-based, nonparametric method for comparing 2 independent groups, we found no statistically significant difference between the number of variables outside the boundaries for injured and noninjured runners overall (P = .17). However, injured runners without impact peaks had more variables outside the normative boundaries than noninjured runners (P < .001). This novel analytical approach demonstrates the potential for preidentifying collegiate distance runners without impact peaks who may be at risk for injury.

After accounting for historical race time trends, average race times from the top 100 elite male and female athletes competing in the 800-m to 10,000-m events have improved since the introduction of advanced footwear technology spikes. However, the percentage performance improvement is smaller at faster average running speeds. Thus, future research is warranted to determine the interaction of footwear compliance, running speed, and performance for elite runners.

Females with unilateral transtibial amputation can improve running performance through reductions in net metabolic power by using a running-specific prosthesis (RSP) that is less stiff than manufacturer-recommended. Lower RSP stiffness values are associated with greater leg stiffness and contact time asymmetry, and lower stance-average vertical ground reaction force asymmetry. However, we found that adding mass to the RSP did not affect net metabolic power and stance-phase biomechanical asymmetries during running.