Over the past 50 years, running shoes have experienced tremendous changes. That is, from very minimal to highly supportive and cushioned shoes, and then to very minimal and finally back to highly cushioned shoes (Krabak et al., 2017). Shoes with various functionality were released because of technological advancements (e.g., structural and material engineering) used in running shoe development, such as cushioned, stability and minimalist running shoes. Although cushioned midsoles can theoretically reduce the impact forces by influencing the stiffness of one’s impact attenuation system and reducing the body’s deceleration (Shorten and Mientjes, 2011), the reported injury rate and performance of running have not remarkably improved over the years (Nigg, 2001). Therefore, reducing injuries and improving performances by using running shoes have become a focus in both sport industries and academia.

Running shoes are designated to improve shoe comfort, enhance running-related performance and reduce the injury potentially. To identify the appropriate functionality of running shoes, previous research has examined different shoe constructions, which included shoelaces (Hong et al., 2011), midsole (TenBroek et al., 2014), heel flare (Stacoff et al., 2001), heel-toe drop (Malisoux et al., 2017), minimalist shoes (Fuller et al., 2015), Massai Barefoot Technology (MBT) ((Boyer and Andriacchi, 2009), heel cup (Li et al., 2018), shoe upper (Onodera et al., 2015), and bending stiffness (Stefanyshyn and Wannop, 2016). For one example, shoelace regulate the tightness of the shoe opening to allow a geometrical match between the foot and the shoe based on the individual’s preference. Good fit is considered a prerequisite for shoe comfort (Ameersing et al., 2003). A shoelace system, heel counter or any other systems that can secure the foot within the footbed should be integrated in running shoes.

For another example, the midsole is an important shoe component for cushioning and shock absorption of running impacts. Midsole thickness is considered important to influence plantar sensations and alter foot strike pattern for shod and minimalist shoes running (Chambon et al., 2014). A wide range of heel-toe drops used in running shoes (e.g., 0 mm to 12 mm) has been shown to influence foot strike pattern and injury risk (Malisoux et al., 2016). Technically, minimalist shoe is defined as the footwear with high flexibility and low shoe mass, stack height and heel-toe drop (Esculier et al., 2015). The minimalist shoe index is the combined scores of shoe quality, sole height, heel-toe drop, motion control, and stabilisation techniques, flexibility, longitudinal flexibility and torsional flexibility (Esculier et al., 2015). Recently, forefoot bending stiffness has received more attention because it has the potential to influence both running-related injury and performance (Stefanyshyn and Wannop, 2016). Softer and thicker running shoes (Sterzing et al., 2013; Teoh et al., 2013) were claimed that reduced impact in order to reduce impact-related injuries. However, Theisen et al., (2014) found that there was no difference in running-related injury between softer and harder shoes. Such a relationship between biomechanics and injury not well established in the literature.

While different shoe constructions showed the remarkable changes in running biomechanical and performance-related variables, no consistent findings on running biomechanics can be found for most shoe constructions. For example, shoe cushioning properties are interplayed with multiple footwear constructions including midsole hardness, midsole thickness, heel-toe drop, and crash-pad. The efficacy of isolated footwear constructions on running performance requires further investigation. Furthermore, analysing the development trend of running shoes can provide valuable guidelines to understand the roles of various footwear constructions in lower extremity biomechanics. Therefore, the current review aimed to examine the effect of different footwear constructions on running biomechanics and review the development status of running shoes related to injury, performance and applied research.

We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for this systematic review (Alessandro et al., 2009). A standardised electronic literature search strategy was performed using the following keyword combinations: “running shoes” OR “running footwear” AND (“upper” OR “shoe lace” OR “midsole” OR “minimal shoes” OR “minimalist” OR “stiffness” OR “bending stiffness” OR “heel flare” OR “heel cup” OR “friction” OR “traction” OR “Masai Barefoot Technologies” OR “MBT”) AND PUBYEAR from 1994 to September 2018 via the five databases (Elsevier, Ebsco, WoS, SAGE Knowledge e-book database, and PubMed Central) and Footwear Science. WKL and WJF agreed on the use of the search terms. Figure 1 summarises the search and selection processes. All articles were input into Endnote to eliminate duplicates. Then, the original research articles in peer-reviewed journals that investigated the effect of shoe constructions on biomechanical changes during running were included. The exclusion criteria included duplicates, orthotics, non-biomechanical related (i.e., only physiological-, biochemical-, and medical-related), non-running shoe related, non-English or non-full text articles.

This systematic review included mainly laboratory-based biomechanical studies, a Physiotherapy Evidence Database (PEDro) scale (Macedo et al., 2010) was used to assess the quality of each included study. Studies with a PEDro score of less than 6 were deemed as low quality and were not included in the review. Two independent raters (authors XLS and XNZ) performed each step of the search and the PEDro quality assessment. When the steps or the quality scores differed between the raters, it would be discussed and consulted with the third rater (author WJF) to reach a final consensus.

The effects of different running shoe constructions on athletic performance-related and injuries variables were shown in Table 1, Table 2, Table 3, Table 4, Table 5, Table 6, Table 7, Table 8 and Table 9 respectively. The injury-related variables included cushioning, motion control, reduce sprain, lower pronation, lower plantar pressure in the braking phase. Meanwhile, the performance-related variables included energy consumption, running efficiency, kinematics, GRF, and plantar pressure in the propulsion phase (Wing et al., 2019).

The full search yielded 1260 articles (Figure 1). After excluding the articles which were duplicates, irrelevant and low PEDro scores (i.e., less than 6), a total of 63 articles were included into subsequent analysis.

Four included articles (Table 1) investigated the effects of shoelace on running biomechanics. Three articles compared the effect of different shoelace patterns (6 eyelets-regular lacing, 6 eyelets-tight lacing, all 7 eyelets) on the biomechanics during overground running (Hagen and Feiler, 2011; Hagen and Hennig, 2009; Hagen et al., 2010). One article investigated different running mechanics between laced and elastic-covered running shoes (Hong et al., 2011). As shown in Table 1, 6 eyelets-regular lacing was the most unstable than other patterns, and showed higher loading rate and heel peak pressure than all 7 eyelets patterns (Hagen and Hennig, 2009; Hagen et al., 2010). Additionally, 6 eyelets-tight lacing was considered as the most uncomfortable (Hagen et al., 2010).

Nineteen included articles investigated the hardness (n = 13), thickness (n = 2), and material properties (n = 4) of the midsoles, which would influence lower extremity biomechanics that is related to injury or athletic performance (Table 2). The PEDro score was “8” for only one, all of the other articles were equal to “6. 4”. Out of 13 studies (Stefanyshyn and Nigg, 2000; Willwacher et al., 2014; Maclean et al., 2009; Hardin et al., 2004) demonstrated that the increase in the stiffness/hardness of midsoles from Asker C40 to Asker C70 would be related to running performance as indicated by the reduced energy lost at metatarsophalangeal and maximum rearfoot eversion velocity, and increased positive work at metatarsophalangeal and peak ankle dorsiflexion velocity in running. However, 4 out of 13 studies (Hardin and Hamill, 2002; Nigg and Gerin-Lajoie, 2011; Teoh et al., 2013; Wakeling et al., 2002) showed no significant effects on peak tibial acceleration, running velocity, stride duration and all frequency spectral or time domain parameters of gastrocnemius medialis, biceps femoris and vastus medialis variables. Among the related studies, two included studies (Sterzing et al., 2013; Teoh et al., 2013) demonstrated soft midsoles could reduce impact forces and loading rates, thereby minimising the risk of impact-related injuries.

Two out of 19 articles found that thicker midsoles can provide better cushioning effects and attenuate shock during impacts but may also decrease plantar sensations of a foot (Robbins and Gouw, 1991).

Only one included article (Table 3, Figure 2) investigated the effects of heel flare construction (lateral heel flare of 25°, no lateral heel flare 0°, rounded heel) on running biomechanics. However, there were no significant differences in tibiocalcaneal and ankle kinematics (initial inversion, maximal eversion velocity) among heel flare conditions (Stacoff et al., 2001).

Seven included articles (Table 4) investigated the effects of heel-toe drop on running. The PEDro scores of 5 articles were 6 and the other two were 7. As shown in Table 4, all these studies investigated different performance-related variables. Shoes with higher drops were found to be related to increase knee adduction (Malisoux et al., 2016), knee excursion, knee flexion at midstance, stance time (TenBroek et al., 2014) and reduce tibial acceleration, initial ankle plantarflexion, initial knee extension angle (TenBroek et al., 2014). For running mechanics, shoes with higher drops would increase net knee flexion moment in the push-off, but reduced net joint ankle flexion moment during braking phase (Besson et al., 2017). In a randomized controlled study (Malisoux et al., 2016), cox proportional hazards regression was used to compute the hazard rates in the exposure groups, using first-time injury as the primary outcome and concluded that there was no significant difference of overall injury risk among different heel-toe drops.

Twenty included articles (Table 5) investigated the effects of minimalist shoe on running. The PEDro scores of 18 articles were 6 and the other two were 7. Three included studies showed that minimalist shoes would improve running economy (Fuller et al., 2017b; Michael et al., 2014; Warne et al., 2014) and other three included studies indicated that minimalist shoes would increase the cross-sectional area, stiffness and impulse of Achilles tendon compared with the conventional shoes (Histen et al., 2017; Joseph et al., 2017; Sinclair and Sant, 2016). Furthermore, participants wearing minimalist shoes promote midfoot and/or forefoot running, with smaller footstrike angles (Fuller et al., 2016; Moore et al., 2014), more anteriorly shift of center of pressure (Bergstra et al., 2015), greater metatarsophalangeal and ankle loading but smaller knee loading (Firminger and Edwards, 2016), compared to conventional shoes.

Only one included article (Table 6) investigated the effects of MBT on running kinematics and kinetics with a PEDro score of 6. Specifically, running in MBT shoes was related to larger dorsiflexion at initial contact and mid-stance, reduced peak ankle moments and power, and smaller medial and anterior GRF peak than the conventional shoes (Boyer and Andriacchi, 2009).

Two included articles (Table 7) investigated the effects of heel cup on running tasks. Both PEDro scores were 6. Li and colleagues (2018) investigated the effect of 3D printed and customised heel cup on plantar pressure, stress, and pain score variables. Their results showed that heel cup reduced peak plantar pressure, stress on plantar fascia and calcaneus bone and self-reported pain significantly after wearing heel cups for 4 weeks. Another article reported that plastic heel cup increased heel pad thickness than rubber heel cup and that rubber and plastic heel cup increased shock absorption of heel than no heel cup condition (Wang et al., 1994).

Two included articles (Table 8) investigated the effects of shoe upper on running biomechanics. Both PEDro scores were equal to 6. These articles investigated the influence of different shoe upper constructions on the plantar pressure distribution (Onodera et al., 2015), joint angle in sagittal, frontal, and transversal planes, and ground reaction force (Onodera et al., 2017). Structured shoe upper increased contact time and peak pressure at midsole than minimalistic shoe upper (Onodera et al., 2015).

Seven included articles (Table 9) investigated shoe bending stiffness on running. All the PEDro scores were equal to 6. In performance perspective, 5 out of the 7 included studies (Hoogkamer et al., 2018; Stefanyshyn and Nigg, 2000; Roy and Stefanyshyn, 2006; Stefanyshyn and Fusco, 2004; Madden et al., 2015) showed that increasing bending stiffness could improve running performance and economy, as indicated by the reduction of energetic cost, maximum VO₂, energy lost at metatarsophalangeal joint, and sprint time in stiffer shoes. One of the included studies (Madden et al., 2015) found that there was no difference in running economy among tested shoe conditions. The other two studies (Oh and Park, 2017; Willwacher et al., 2013) showed that stiffer shoes reduced stance time, negative work and flexion of metatarsophalangeal joint, and increased GRF lever arms for all joints.

This study summarised the effect of various footwear constructions on running biomechanics that is related to performance and injury potentials. The main results were: 1) increasing the stiffness of running shoes at the optimal range can benefit performance. Some included studies showed stiffer shoe would reduce energetic cost (Hoogkamer et al., 2018), maximum VO₂, energy lost at metatarsophalangeal joint (Roy and Stefanyshyn, 2006; Stefanyshyn and Nigg, 2000), and sprint time (Stefanyshyn and Fusco, 2004); 2) softer midsoles can reduce the impact forces and loading rates (Sterzing et al., 2013; Teoh et al., 2013); 3) thicker midsoles could provide better cushioning effects and attenuate shock during impacts but might also decrease plantar sensations of a foot (Robbins and Gouw, 1991); 4) minimalist shoes can improve running economy (Fuller et al., 2017b; Michael et al., 2014; Warne et al., 2014; Ridge et al., 2013), increase the cross-sectional area and stiffness of Achilles tendon but it would increase the metatarsophalangeal and ankle joint loading compared to the conventional shoes (Histen et al., 2017; Joseph et al., 2017; Sinclair and Sant, 2016); 5) the shoe constructions included shoe lace, heel flare, heel-toe drop, Masai Barefoot Technologies, heel cup, and shoe upper did not show clear influence on biomechanics (Hong et al., 2011; Stacoff et al., 2001; Malisoux et al., 2017; Boyer and Andriacchi, 2009; Li et al., 2018; Onodera et al., 2015).

Amongst the included articles, Hagen and Hennig (2009) typically examined the influence of the number of laced eyelets used (e.g. 1, 2, 3, 6 and 7) and lacing tightness (e.g. weak, regular and strong) on foot biomechanics in running. The tightest (strong) and highest lacing (i.e., seven-eyelet) conditions reduced loading rates and pronation velocities of rearfoot motion. The lowest peak pressures at the heel and lateral midfoot regions were observed in the high lacing pattern than in the lower lacing patterns. They (Hagen et al., 2010) also found that the shoe comfort and stability perception scores were related to the runners’ level and experience. In contrast with the regular six-eyelet lacing pattern (REG 6), low-level runners perceived A57 (the laces were pulled from the outside from the fifth to the seventh eyelet) with better stability and comfort perception. However, high-level runners demonstrated poor comfort perception in A57 condition. Future studies should investigate the practicability of various shoe lacings (Figure 3) in runners with different arch height, muscle level (Lieber, 2018), and running experience (Clermont et al., 2019).

For midsole hardness, the increase of midsole hardness from Asker C40 to Asker C70 would reduce the impact peak (Baltich et al., 2015), minimize energy loss (Stefanyshyn and Nigg, 2000) and increase the contact time (Willwacher et al., 2013); whereas other studies found that the impact peak increased (Chambon et al., 2014) while contact time did not change (Sterzing et al., 2013) across different midsole hardness. These inconsistent results may be due to the different tested speeds (3.3 ± 0.1 m/s vs. 3.5 ± 0.18 m/s) (Willwacher et al., 2013), hardness (0.6-17.10 N/mm vs. 40-65 Asker C vs. 47.1-62.8 Asker C) (Baltich et al., 2015) across the included studies.

Only a few longitudinal studies examined the relationship between midsole and running injuries. Theisen et al. (2014) randomly assigned soft (Asker 64C) and hard (Asker 57C) midsole shoes to 247 runners to wear for five months. The same injury rates were found between soft and hard midsole shoes used in training. However, Dixon et al. (2015) found that shoes with hard lateral stiffness (Asker 70C) had larger peak knee abduction moment and peak loading rates than softer midsoles (i.e., 52 and 60 Asker) during running, suggesting the increase the risk of running-related injuries (Dixon et al., 2015).

With regard to the material used, EVA and PU were widely used in footwear industry and related studies (Brückner et al., 2010). PU material exhibited lower relative changes of damping parameters than EVA and thus recommended as the alternative use of midsole material in running, even though PU material showed better durability than EVA (Brückner et al., 2010). From the running economy perspective, Wang et al. (2012) found that EVA shoes had higher capability of energy return than PU shoes at all running distances (e.g. 50 km, between 200 to 300 km and 500 km). A larger percentage of energy return could be related to improved running economy (Thomson et al., 2010). Future studies should investigate whether the varying hardness of the midsole would be related to the risk of injuries to provide sports scientists, coaches, and footwear manufacturers an insight into running shoe developments for injury prevention.

Minimalist shoes were suggested to improve running economy by changing a runner's strike and performance-related variables (Fuller et al., 2015). Most included studies have found that minimalist shoes showed remarkable differences in lower extremity biomechanics when compared with traditional running shoes (Table 5). In addition, the effect of minimalist shoes on the changes and adaptations in Achilles tendon became a popular research topic. One included article reported that participants who wore minimalist shoes developed greater cross-sectional area, stiffness and Young's modulus of Achilles tendon than those who used the conventional running shoes (Joseph et al., 2017). A consensus has been reached on running with minimalist shoes can improve running economy. For example, Warne et al., (2014) found that four-week habituation to simulated barefoot running would improve running economy (VO_2max) compared with shod running. Similarly, Fuller et al. (2017a) randomly assigned 61 runners gradually increased the amount of running when wearing either minimalist (n=31) or conventional (n=30) shoes during a six-week training program and found that minimalist shoes during training improved running economy compared to training in conventional shoes.

Although the concept and functionality of running shoes have dramatically evolved in recent years, the injury rate remains high and is still the focus in running research. A prospective cohort study demonstrated that running in minimalist footwear appears to increase the likelihood of experiencing pain and injury at the shin and calf (Michael et al., 2014).

Increased forefoot plantar pressure in minimalist shoes with minimal cushioning is one of the main causes of forefoot stress fracture. Bergstra et al.’s study (2015) minimalist shoes induced higher peak pressures on the medial, middle and lateral sides of the forefoot and maximum mean pressures, which were associated with metatarsophalangeal joints fractures than traditional running shoes. Another study (Ridge et al., 2013) examined the stress fracture injury risks by measuring the presence of bone marrow edema in the foot after runners transitioned to minimalist shoes (i.e., Vibram FiveFinger) throughout a 10-wk transition period. Their results indicated the Vibram group experienced a significantly greater incidence of bone marrow edema after the training period than the traditional shoes. From these studies, it confirmed that minimalist shoes may increase the injury risk. For runners with habitual conventional shoes, transition to minimalist shoes should progressively take time and training process.

To date, only a few included articles investigated the effect of shoe upper on performance-related and injuries-related variables (Table 8). The reason may be due to the large variety of upper materials used, the lack of mainstream upper materials and the difficulty of experimental control. Shoe upper has stronger influence over fit and comfort, which would alter the kinematic and kinetic strategies of runners. It was demonstrated that firmer foot contact within a shoe would result in lower loading rates due to a better coupling of foot-footwear (Hagen and Hennig, 2009). For example, Onodera et al. (2015) found that participants who wore shoes with minimalist upper would experience higher peak pressures in total area, rearfoot and medial forefoot regions but lower peak pressure at midfoot region; whereas those who wore shoes with structured upper demonstrated longer contact time for total area midfoot and lateral forefoot regions (Onodera et al., 2015). It is argued that the structured upper shoes would provide greater maneuverability and robustness, resulting in a uniformly distributed foot pressure and reduced foot plantar loading (Onodera et al., 2015). From the anthropometry perspective, better shoe upper fit and/or comfort can make the runner’s foot coupled better with the sole (Onodera et al., 2017). Furthermore, various running speeds may have different requirements for the tightness of the shoe upper. However, the effects of shoe upper on comfort and running biomechanics included plantar pressures would require further investigation.

A review study summarized that shoe bending stiffness was related to changes in lower limb joint kinematics and kinetics as well as athletic performance (Stefanyshyn and Wannop, 2016). Forefoot bending stiffness of a shoe can be increased by inserting a forefoot plate (Madden et al., 2015) or using harder midsole (Willwacher et al., 2014). This has the potential to enhance sports performance in forward acceleration, jumping and agility tasks (Wannop and Stefanyshyn, 2016). Increasing the bending stiffness within a certain range could benefit runners. However, excessively increased bending stiffness may induce discomfort or hinder the performance benefits (Roy and Stefanyshyn, 2006). Furthermore, some included articles suggested that the reduction in metatarsophalangeal flexion would minimise the magnitude of negative joint power generation, which was beneficial to athletic performance (Stefanyshyn and Fusco, 2004). 5 out of the 7 included studies (Hoogkamer et al., 2018; Stefanyshyn and Nigg, 2000; Roy and Stefanyshyn, 2006; Stefanyshyn and Fusco, 2004; Madden et al., 2015) in Table 10 showed that increasing bending stiffness improved running performance and economy. Specifically, stiffer shoes would reduce energetic cost (Hoogkamer et al., 2018), maximum VO₂ (Roy and Stefanyshyn, 2006), energy lost at metatarsophalangeal joint (Stefanyshyn and Nigg, 2000), and sprint time (Stefanyshyn and Fusco, 2004).

In injury-related perspective, no longitudinal injury studies have been reported for the relationship between bending stiffness and running injury. The optimal bending stiffness of a shoe is currently unknown due to different stiffness measurement across studies, future research should develop standard testing protocols to identify the optimal ranges of forefoot stiffness used in various running level (elite, intermediate and novice), type of foot strikes (rearfoot, midfoot and forefoot) and running conditions (10k, half-marathon and full marathon).

The outcomes related to heel flare, heel-toe drop, MBT, and heel cup were associated with insufficient studies to make strong conclusions and therefore require further investigation. Besides, the findings for heel cup appear to be the most promising across. In general, heel cups can serve as an effective treatment for heel pain because it can provide external support to the heel fat pad, maintain the heel pad thickness, and reduce the heel peak pressure and pain (Li et al., 2018).

Over the past decades, most of the included articles focused on midsole and minimalist constructions. Studies with running shoe constructions confirmed the beneficial effects on athletic performance and running injury: 1) increasing the forefoot bending stiffness of running at the optimal range can benefit performance-related variables; 2) softer midsoles can reduce impact forces and loading rates; 3) thicker midsoles can provide remarkable cushioning effects and attenuate shock during impacts but may decrease plantar sensations at touchdown; 4) minimalist shoes would improve running performance-related including economy and build the cross-sectional area and stiffness of Achilles tendon, but also induce greater loading of the ankle, metatarsophalangeal joint and Achilles tendon compared with the conventional shoes. Notably, progressive training and adaptation seems necessary and recommended when using minimalist shoes. Although research on heel flare, shoelace and heel cup were limited, these constructions showed some potentials to influence running stability. The role and interaction of these shoe constructions would require further investigations. Future research should also develop standard testing protocols to help to establish the scientific guidelines of optimal stiffness, thickness and heel-toe drop across various running shoe studies in the future.