Abstract
he introduction of advanced footwear technology (AFT) in 2017, numerous world records from 5 km to the marathon have been broken. Among these innovations, carbon- plated shoes have received particular attention. Previous research indicates improvements of 2–4% in running economy (RE), which translates into an approximate 1–2% improve- ment in running performance when running in these shoes. The rapid progression of performance has generated significant scientific interest; however, a clear understanding of the mechanisms driving the effectiveness of AFT remains limited. Despite widespread adoption and remarkable results, the mechanisms underlying the effectiveness of AFT are still not fully understood, which is why optimising its potential benefits continues to be an ongoing challenge. This review summarises current knowledge on AFT and critically evaluates the biomechanical and physiological mechanisms underlying their effects on RE and performance. It also highlights the interaction between shoe design features and individual biomechanics, supporting evidence-based approaches to footwear selection and training strategies tailored to athletes’ needs. A clearer understanding of these mechanisms may provide valuable insights for researchers, coaches, and athletes and help maximise the potential benefits of AFT. Keywords:running shoes; advanced footwear technology; carbon-plated shoes; running biomechanics; running economy; running performance 1. Introduction Running shoes can be categorised into several types based on their function and intended use, including minimalist, conventional, carbon-plated, motion control, support, and other types [1,2]. All of these can influence running economy (RE) and performance in long-distance runners [3–5] and may also alter running biomechanics [6–9]. In recent years, increasing attention has been paid
economy; running performance 1. Introduction Running shoes can be categorised into several types based on their function and intended use, including minimalist, conventional, carbon-plated, motion control, support, and other types [1,2]. All of these can influence running economy (RE) and performance in long-distance runners [3–5] and may also alter running biomechanics [6–9]. In recent years, increasing attention has been paid to carbon-plated shoes—running shoes with an embedded carbon fibre plate in the midsole combined with multiple layers and specialised foam structures [10,11]. There remains some ambiguity regarding how to categorise these shoes. In the literature, terms such as “plated shoes”, “4% shoes”, “super shoes”, “super spikes”, “neoteric shoes”, “carbon shoes”, and “ergogenic shoes” are used [1]. In this review, we refer to this category collectively as advanced footwear technol- ogy (AFT), with carbon-plated models representing the most widely recognised type. Introduced by Nike in 2016 [12] and commercially available since 2017 [13], AFT has gained significant scientific and public interest due to its potential to enhance RE [10,14,15] Muscles2026,5, 2 https://doi.org/10.3390/muscles5010002
Muscles2026,5, 2 2 of 28 and endurance race performance [16–18]. The growth in performance, especially in female athletes [19–23], has led some to compare AFT to the barefoot and minimalist running era of the 2000s [1]. Although a growing number of studies have analysed different brands and models of AFT, there is still no clear consensus on the mechanisms that explain their effectiveness. Moreover, questions remain about how these shoes can be optimally applied to individual athletes, considering biomechanical and physiological variability [24,25]. A clear under- standing of AFT mechanisms is crucial both to optimising athlete-specific performance outcomes and to informing regulations that ensure fairness as footwear technologies con- tinue to advance. This raises broader questions: How far will technological advances go? How will they influence the evolution of performance outcomes and the nature of sport? Could they even be considered a form of “technological doping” [26]? The purpose of this review is to summarise and critically evaluate the dominant factors determining the working mechanisms of AFT, highlighting their role in shaping RE and performance. It further identifies key considerations for future research design and interpretation and provides practical insights for coaches and athletes on effective AFT use tailored to individual needs. The ultimate goal is to support the development of evidence-based and practically applicable guidelines for the assessment and use of AFT in sport. To ensure comprehensive coverage of the literature, we conducted a broad narrative search across multiple databases, including PubMed, Scopus, Web of Science, and Pro- Quest. The primary focus was on publications from the past five years to capture the most recent developments, while earlier studies were included to illustrate the underly- ing mechanisms of advanced footwear technology (AFT) and its historical evolution in running footwear. Searches were conducted using combinations of key terms such as running AND shoes, running shoes, advanced footwear technology AND running econ- omy, carbon-plated shoes, advanced footwear technology AND running biomechanics, and advanced footwear technology AND running performance. Only articles published in English were considered. Studies were selected based on their relevance to running economy, biomechanics, and performance. The final synthesis
Searches were conducted using combinations of key terms such as running AND shoes, running shoes, advanced footwear technology AND running econ- omy, carbon-plated shoes, advanced footwear technology AND running biomechanics, and advanced footwear technology AND running performance. Only articles published in English were considered. Studies were selected based on their relevance to running economy, biomechanics, and performance. The final synthesis integrates findings from experimental, observational, and review papers to provide a balanced overview of current knowledge and its practical implications. 2. The Evolution of Advanced Footwear Technology Although AFT is commonly associated with recent decades, carbon fibre plates were already used in running shoe construction in the 1980s [27]. At that time, the concept was discussed under the term “energy return shoes” [28,29]. Early models such as Brooks’ Fusion and Fission and later Fila’s racing shoes embedded flat carbon plates in the midsole, but a more significant technological shift occurred when Adidas introduced a curved geometry-specific carbon fibre plate (ProPlate), which advanced the principle of bending– stiffness manipulation of the midsole. This design was associated with Haile Gebrselassie’s 2007 marathon record of 2:04:26 [27]. The modern era of carbon-plated footwear began in 2016 (commercially available from 2017) when Nike released the ZoomX Vaporfly 4% [12]. The name reflected the manufac- turer’s claim of up to 4% improvement in RE, which was later supported by independent studies [10,14,15]. Vaporfly 4% incorporated a carbon fibre plate embedded in the midsole together with other design elements intended to increase bending stiffness [11] and re- duce movement in the metatarsophalangeal joint (MTPJ), facilitating more efficient energy transfer [30] and contributing to forward propulsion, often described as a “springboard effect” [31]. https://doi.org/10.3390/muscles5010002
Muscles2026,5, 2 3 of 28 Subsequent innovations, including Nike Air Zoom AlphaFly Next %, added fea- tures such as “Air pods,” intended to return up to 90% of stored energy according to the manufacturers—technological extensions rather than conceptual departures. Wearing this model, Eliud Kipchoge broke the 2-hour marathon barrier in 2019 during the INEOS 1:59 Challenge, although the result was unofficial under World Athletics regulations [32]. More recently, the evolution of these design principles continued with Nike Alphafly 3, used by Kelvin Kiptum Cheruiyot to set the 2023 world record of 2:00:35. Significant improvements in performance and multiple record-breaking results have led other companies to adopt similar carbon-plate and high-energy-return midsole tech- nologies. As a result, nearly all major brands, including Nike, Adidas, Asics, New Bal- ance, Saucony, and Hoka One One, now incorporate these design principles into their racing footwear, and technological development continues to accelerate [33]. This his- torical progression of design principles directly informs ongoing scientific debates about the mechanisms underlying AFT effectiveness and their implications for performance and regulation. 3. Regulatory Responses to Advanced Footwear Technology in Elite Athletics Opinions on the rapid development of AFT and its impact on performance are divided. On one hand, AFT can be viewed as a technological advancement that enables elite athletes, whose physiological limits are already near their peak, to further enhance performance. On the other, concerns have been raised about fairness and whether such external interven- tions align with the fundamental nature of sport, which traditionally centres on human physiological and technical abilities. In the early stages of AFT development, not all athletes had equal opportunities to access these models. Initially, prototypes were provided only to select elite runners in high-profile competitions, creating potential inequalities. Even after their public release, some athletes continued to have access to the latest prototype models before they became commercially available, leading to situations where runners switched sponsors to obtain perceived performance advantages [31]. To address these concerns, World Athletics introduced regulations in 2020 governing the use and design of AFT in elite competitions [34]. According to the updated competition technical rules [35,36],
public release, some athletes continued to have access to the latest prototype models before they became commercially available, leading to situations where runners switched sponsors to obtain perceived performance advantages [31]. To address these concerns, World Athletics introduced regulations in 2020 governing the use and design of AFT in elite competitions [34]. According to the updated competition technical rules [35,36], the sole thickness of AFT shoes must not exceed 40 mm (Table). Previous studies have suggested that even relatively small changes in stack height within a 20 mm range can meaningfully affect performance [37]. In addition, the shoe must not contain more than one carbon fibre plate, or any other material with similar properties, regardless of whether it spans the full length of the sole or only part of it [36]. These restrictions do not apply, however, to the National Collegiate Athletic Association or high school athletics, where all types of running shoe construction remain permitted [38]. For athletics spikes, regulations allow an additional carbon plate only for attaching the spikes, and the sole thickness must not exceed 30 mm [36]. To uphold fairness, World Athletics also mandated that all innovative shoes released after 30 April 2020 must be commercially available to all athletes for at least four months before a relevant competi- tion. Shoes not meeting this requirement are considered prototypes and are prohibited in competition [36]. These regulations were designed to safeguard equality and fair play while establishing reasonable boundaries for technological innovation in sport-related performance enhance- ment. They also clearly reflect ethical considerations of technological fairness, ensuring that access to innovation does not compromise the integrity of competition. https://doi.org/10.3390/muscles5010002
Muscles2026,5, 2 4 of 28 Table 1.Summary of World Athletics Footwear Regulations (2020). Maximum stack height, plate count, and availability requirements categorised by Advanced Footwear Technology type: road racing shoes and track spikes. Footwear Type Maximum Stack Height Plate Count Availability Requirements Road racing shoes 40 mm Maximum of one plate or similar device Must be available for purchase at least four months before competition Track spikes 30 mm One functional plate permitted Must comply with the four-month commercial availability requirement NCAA and high school (USA) Not restricted unless regulated by WA No WA plate restriction No WA availability requirement 4. Design Elements of AFT The construction of carbon-plated shoes can be conceptualised as a layered structure, often described as a “sandwich”, consisting of multiple layers of varying types and thick- nesses compressed together [17]. Each of the elements—plate geometry, foam properties, longitudinal bending stiffness, toe spring, and stack height—has its role and should be evaluated in terms of their multi-factorial interactions (Figure). In the following section, the main design components of AFT and their interdependence will be discussed. Figure 1.Conceptual schematic illustration of the key design elements of AFT and their interrelations. 4.1. Plate Geometry and Midsole Material Properties Usually defined as a “key structural element” of AFT, the carbon fibre plate [1,17] is either embedded within the shoe midsole or inserted directly into the shoe [39]. These two placements differ significantly. Insertable carbon soles, not surrounded by cushioning foam, are stiffer and may alter both the running feel and perceived comfort [40,41]. However, they tend to last longer and may be a more economical option than purchasing a new pair of carbon-plated running shoes [42]. Curved carbon plates are generally associated with greater improvements in RE and performance compared with flat plates [43–49]. A distinctive feature of many AFT models is rocker geometry, characterised by a slight forefoot elevation (“toe spring”) that creates an S-shaped sole design, in which the heel sits slightly higher than the forefoot. In interaction with increased midsole longitudinal bending stiffness (LBS), this configuration has been consistently associated with improve- ments in RE [9,40,42,43,50,51].
compared with flat plates [43–49]. A distinctive feature of many AFT models is rocker geometry, characterised by a slight forefoot elevation (“toe spring”) that creates an S-shaped sole design, in which the heel sits slightly higher than the forefoot. In interaction with increased midsole longitudinal bending stiffness (LBS), this configuration has been consistently associated with improve- ments in RE [9,40,42,43,50,51]. However, recent research indicates that the benefits may https://doi.org/10.3390/muscles5010002
Muscles2026,5, 2 5 of 28 be runner-specific [52,53], and an “optimal shoe bending stiffness” may exist for different individuals [54]. In addition, some evidence suggests potential injury-prevention benefits due to increased stability and support for the foot and ankle joints [47]. The specific feature “toe spring” facilitates a faster and more efficient heel-to-toe tran- sition, often described as a “rollover” or “spring-like” sensation, which helps to maintain a straighter alignment of the hallux, reduces energy expenditure during push-off, and shortens ground contact time [9,14,44,47,55]. In contrast, flatter shoe soles require greater muscular force and energy to complete this transition, leading to less efficient rollover mechanics [56]. Furthermore, it may help reduce overuse injury risk by decreasing peak pressure on the forefoot without increasing loads in the metatarsal region and by lowering demands on the ankle plantar flexors compared with flat-plate or non-plated shoes [45,47,48]. Mechanically, this effect is explained by the "teeter–totter" mechanism, in which the stiff carbon plate and curved sole act as a lever to reduce muscular effort during ankle dorsiflexion and push-off [24,37,56]. However, the design must be optimised to ensure that the teeter-totter effect occurs at the correct location (heel of the foot), time (push-off), and frequency (determined by running velocity and ground contact time) [56,57]. According to Nigg, Cigoja, and Nigg [56], three conditions must be met to achieve the effect: 1. 2. Proper pivot point placement, ensuring that it is not positioned too far forward, so that the heel can act as a support point. 3. Appropriate forefoot curvature, enabling effective lever action and smooth rollover mechanics. As noted by Willwacher et al. [58], translating these theoretical mechanisms into real- world running conditions is complex. Nonetheless, they provide valuable insights into critical design features that influence the effectiveness of AFT. Plate location is also an important factor, particularly in models with increased stiffness [41]. The design of the forefoot plate—whether full-length or segmented—can substantially alter running biomechanics and, consequently, performance outcomes [59]. In contrast, inappropriate plate curvature or stiffness may increase the risk of foot in- juries [41,47,51]. 4.2. Foam Construction Foam construction has
that influence the effectiveness of AFT. Plate location is also an important factor, particularly in models with increased stiffness [41]. The design of the forefoot plate—whether full-length or segmented—can substantially alter running biomechanics and, consequently, performance outcomes [59]. In contrast, inappropriate plate curvature or stiffness may increase the risk of foot in- juries [41,47,51]. 4.2. Foam Construction Foam construction has been shown to play a particularly important role when inter- acting with carbon fibre plates [33,60,61] and may also influence shoe durability depending on the foam’s microstructure [62]. Aimar et al. [62] compared five commercial midsole foams derived from three of the most commonly used polymers in carbon-plated shoes—ethylene-vinyl acetate (EVA), polyether block amide (PEBA), and thermoplastic polyurethane (TPU) [60]—plus one modified sample obtained from an additional insert of the same midsole to capture struc- tural variability. Under mechanical fatigue testing, EVA foams reinforced with microfillers demonstrated improved mechanical strength but reduced rebound properties and acceler- ated wear, likely due to weak cohesion between fillers and the polymer matrix. In contrast, denser foams with hierarchical microstructures exhibited slower damage progression and enhanced durability; however, they were associated with poorer initial mechani- cal properties. Lloria-Varella et al. [63] examined whether shoe wear and degradation after a fatiguing trail run influenced biomechanics and whether switching to a fresh pair of shoes could restore mechanics altered by worn footwear. After the race, the participants’ own shoes https://doi.org/10.3390/muscles5010002
Muscles2026,5, 2 6 of 28 showed reduced midsole thickness and increased stiffness, confirming degradation. Run- ning mechanics also changed: contact time and step frequency increased, while flight time and tibial peak-to-peak acceleration amplitude decreased. Contrary to their hypothesis, replacing the worn shoes with new ones did not significantly alter the main biomechanical variables, although it did affect shoe × time interaction. 4.3. Stack Height Foam construction in modern AFT serves not only to provide additional cushioning but also to increase the stack height of the shoe [60,61]. Stack height is a critical design parameter, as it determines the thickness of the midsole and, consequently, the shoe’s capacity to store and return mechanical energy. Functionally, stack height acts like a compliant spring: a thicker midsole allows for greater elastic deformation during foot strike (via sole compression) and subsequent energy release during push-off, assisting propulsion [14]. This mechanism not only influences RE and biomechanics but also affects comfort and impact attenuation [37,61,64–66]. It may also contribute to fatigue resistance and reduced muscle damage or soreness over longer distances [16,67]. When comparing the Nike Zoom Vaporfly prototype (heel height: 31 mm; forefoot height: 21 mm) with two similar-technology shoes—the Adidas Adios Boost and the Nike Zoom Streak 6—Hoogkamer et al. [14] reported that the prototype deformed nearly twice as much (11.9 mm; energy return: 87%) compared with the Adios Boost, with 6.1 mm (75.9%), and the Zoom Streak 6, with 5.9 mm (65.5%). A recent study by Baumann et al. [61] confirmed that adding an additional 10 mm of stack height to the current 40 mm limitation improved running economy (RE) by 0.6% during treadmill running and 0.7% during overground running. Interestingly, this modifi- cation did not significantly affect perceived exertion ratings or running kinematic variables (step frequency, flight time, ground contact time, duty factor, etc.). Moreover, the shoes with the highest stack height (50 mm) were rated the lowest in terms of subjective comfort. One possible explanation for this could be the reduced running stability, primarily resulting from lateral instability associated with greater ankle eversion—a factor previously linked to an increased risk
running kinematic variables (step frequency, flight time, ground contact time, duty factor, etc.). Moreover, the shoes with the highest stack height (50 mm) were rated the lowest in terms of subjective comfort. One possible explanation for this could be the reduced running stability, primarily resulting from lateral instability associated with greater ankle eversion—a factor previously linked to an increased risk of injury [37,65,66,68,69], particularly among runners with pre-existing foot conditions or excessive pronation [65]. However, evidence supporting this remains limited, and further research is needed. 5. Working Mechanisms of AFT Understanding the underlying working mechanisms of AFT is essential to explaining the improvements in RE, biomechanics, and performance observed in recent years. The interaction of shoe geometry, material properties, and runner-specific biomechanics de- termines how effectively mechanical energy is stored, transferred, and returned during the gait cycle. Collectively, it illustrates that the effectiveness of AFT arises from vari- ous multiple-element interactions. A deeper understanding of it may contribute to more effective performance outcomes. 5.1. Energy Return Mechanisms of Running Footwear: Implications for AFT Performance The storage and release of elastic energy is recognised as one of the main factors contributing to RE in both humans and animals. When analysing the role of mechanical energy in performance, three strategies are commonly identified [43,58]: 1. 2. 3. https://doi.org/10.3390/muscles5010002
Description
The review evaluates advanced footwear technology's impact on running economy and performance.