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.
Systematic review process
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), nonrunning 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 Tables 1 to 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).
Overview of review data
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.
Effects of shoelace
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).
Effects of shoe midsole
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 (Stef-anyshyn 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).
Effects of heel flare
Only one included article (Table 3, Figure 2) investigated the effects of heel flare construction (lateral heel flare of 25[degrees], no lateral heel flare 0[degrees], 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).
Effects of heel--toe drop
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...