Influence of Footwear Features on Oxygen Consumption and Running Economy: A Review

en reported that the new technology applied to current racing shoes has increased the performance of runners who use this kind of footwear. This improvement has been proven in the scienti c literature in relation to oxygen consumption. Nevertheless, as it is a novel topic, there is a lack of knowledge about which speci c features achieve a decrease in oxygen consumption during running. Thus, the purpose of this study was to determine the in uence of the features of footwear, speci cally the shoe mass, the cushioning system, the longitudinal bending stiffness and the comfort feeling on running economy. This review was carried out from the bibliographic search in the main databases such as PubMed, Cochrane Plus and Medline and considering the PRISMA statement as a reference so that an analysis of the results has been obtained together with the methodological quality and risk of bias

cushioning system, the longitudinal bending stiffness and the comfort feeling on running economy. This review was carried out from the bibliographic search in the main databases such as PubMed, Cochrane Plus and Medline and considering the PRISMA statement as a reference so that an analysis of the results has been obtained together with the methodological quality and risk of bias of the studies. Nineteen articles met the inclusion criteria, which presented a moderate/high methodological quality, and an analysis of their results was carried out. Footwear features such as the shoe mass, the cushioning system and the longitudinal bending stiffness produce advantages compared to other footwear that does not include this technology. Due to the lack of evidence, the in uence of comfort feeling on oxygen consumption has not been proved. Keywords: oxygen consumption; shoe mass; cushioning system; longitudinal stiffness; comfort feeling 1. Introduction Worldwide, running may be considered one of the most practiced sports activities, particularly when considering it as a natural task that has always been part of human existence [1]. In addition, this sport modality presents a low-cost activity from an economic point of view as it does not require much more specialized equipment than footwear and may be performed outdoors. Numerous health bene ts have been reported for those who practice running, as it can reduce the prevalence of vascular and neurological diseases [2] and even different types of cancer like colorectal or lung cancer [3,4], as well as other diseases related to a sedentary lifestyle such as cardiovascular function or increased adi- posity [5,6]. Nevertheless, running may cause injuries, mainly on the lower limb [7,8] (i.e., medial tibial stress syndrome, Achilles tendinopathy, or plantar fasciitis). The inci- dence of injuries associated with running has risen with the increased popularity of the sport among those middle/long-distance runners who practice it [9]. Nowadays there are studies that set the incidence of injuries in the lower limb at between 19.4 and 79.3% [9]. It is known that the origin of these injuries is multifactorial (i.e., factors such as age, history of previous injury, or perception of risk should be

the increased popularity of the sport among those middle/long-distance runners who practice it [9]. Nowadays there are studies that set the incidence of injuries in the lower limb at between 19.4 and 79.3% [9]. It is known that the origin of these injuries is multifactorial (i.e., factors such as age, history of previous injury, or perception of risk should be considered) [10] and there are diverse risk factors that may predispose to injury in the lower limb. These risk factors may be Appl. Sci.2023,13, 23.

Appl. Sci.2023,13, 23 2 of 20 classi ed into three areas, namely (1) personal factors (i.e., age, sex, or height), (2) run- ning/training factors (i.e., weekly running days, distance, or running shoes), and (3) health and lifestyle-related factors (i.e., smoking, a history of comorbidity and previous injuries). Among the characteristics of training, footwear plays an important role [11]. Coinciding with the increase in popularity of running races from 1970 onward, research on sports shoes started in two different directions, the prevention of injuries and the improvement in performance during the race. Despite the investment that has been made in these two areas, the injury rate has barely decreased and the improvement in sports performance has not undergone a marked change until recent years [12,13]. The present review aimed to analyze the scienti c literature on the in uence of footwear on running economy at a medium/long distance. In order to understand how this improvement in running performance is quanti ed, it is important to know the following concepts. Three physiological parameters are usually studied to predict the speed that an athlete can maintain in competitive events greater than 3000 m, the maximal rate of oxygen consumption (VO2max), the blood lactate threshold and the energy cost of run- ning [14,15]. From these data, we can obtain the oxygen cost of running at a given speed, which is known as running economy and is measured in ml O2/kg/min [15]. This is the parameter that has traditionally been used to measure the performance of athletes and even today many studies continue to assess improvement in running by measuring oxygen consumption [16,17]. At the same time, it should be noted that there has recently been a proposal to express running economy in terms of metabolic cost measured in kJ/kg/min since this value would have greater sensitivity than oxygen consumption [18]. So, if an athlete has a greater running economy, that is, a lower oxygen cost/metabolic cost, he or she will be able to run at the same speed with less physiological effort, which will translate into an improvement and greater distance traveled in less

metabolic cost measured in kJ/kg/min since this value would have greater sensitivity than oxygen consumption [18]. So, if an athlete has a greater running economy, that is, a lower oxygen cost/metabolic cost, he or she will be able to run at the same speed with less physiological effort, which will translate into an improvement and greater distance traveled in less time [19]. Therefore, in this review, running economy may be considered as the metabolic cost measured in kJ/kg/min whenever possible because, although this measurement may be more reliable, this fact has only been con rmed in recent years and the vast majority of previous studies [15–17] use running economy as a reference in relation to oxygen consumption in ml O2/kg/min. There are several factors that affect running economy [20] and that may be improved or modi ed in the life of an athlete, such as strength training, altitude training, or the environment where they practice sports [21]. It is interesting to note that there are other variables that we could qualify as extrinsic factors since they do not depend directly on the athlete, which provides the possibility to improve running economy. These are the surface on which the race takes place [22] and footwear [23–25]. Since the podiatrist is considered the specialist in the anatomy and biomechanics of the foot and the lower limb, whether in walking or running, his/her role in the research and development of sports footwear acquires great importance in order to prevent injuries or increase running economy [11–13]. Although most runners use sports footwear for their daily activity, running barefoot or with minimal foot protection (minimalist footwear) has been described in humans for about 2 million years [1] and it was not until the beginning of the 19th century that footwear began to be used in order to protect the foot from the surface on which the wearer was walking. Nevertheless, modern sports footwear is a relatively recent development and it's only in the last 40 years that most of the running shoe companies have been founded and most of the scienti c advances in this

the 19th century that footwear began to be used in order to protect the foot from the surface on which the wearer was walking. Nevertheless, modern sports footwear is a relatively recent development and it's only in the last 40 years that most of the running shoe companies have been founded and most of the scienti c advances in this eld have been made [26]. Simultaneously, more technology and sophistication have been added to running shoes. In 2005, the rst modern minimalist footwear (Nike Free) was developed by the sneaker brand Nike. In 2006, it was proposed that a style of footwear used by yacht crews, the Vibram brand FiveFingers, could be the ideal footwear to imitate barefoot racing [26]. However, the turning point that popularized minimalist footwear was the publication of Christopher McDougall's book “Born To Run”. Many of the people who have read the book are convinced that this type of footwear could be the solution for injuries and could even increase their performance [26]. These af rmations have been widely discussed in the scienti c literature and there is great controversy. Indeed, there is no evidence that running in minimalist footwear causes a

Appl. Sci.2023,13, 23 3 of 20 signi cant decrease in injury rate [27]. In addition, we must keep in mind that minimalist running has certain risks, from skin injuries caused by minimal foot protection to muscle- tendon injuries associated with poor adaptation to minimalist footwear [28]. Taking this latter fact into account, the adaptation to minimalist footwear must be progressive and controlled by a specialist who will guide wearers in this process [27,28]. Regarding the improvement in running economy thanks to minimalist footwear, there are studies that support this hypothesis but these studies present a limitation in that the tests are carried out on subjects experienced in minimalist running [29,30]. This fact must be taken into account, as a person used to a given activity seems to have lower physiological demands to perform that activity than someone who performs the same activity for the rst time. In fact, in a study with 15 subjects without previous experience with minimalist footwear, a 4-week adaptation to minimalist footwear was carried out and running economy tests were performed before and after adaptation, comparing them with tests with standard footwear. In the tests prior to adaptation, no differences were found in oxygen consumption between barefoot running and standard footwear. Conversely, after adaptation, the results supported the theory that minimalist footwear reduces oxygen consumption [31]. This improvement in running economy with minimalist footwear is based on the weight of the shoe, as, for every 100 g added to the shoe, there is a loss of approximately 1% in running economy [32,33]. Nevertheless, when we use a light shoe (approximately 220 g per pair of shoes) with a good cushioning system, no differences are found between running barefoot and with shoes due to what is known as the cushioning cost that must be carried out by the muscles to cushion the impact when we run wearing minimalist footwear [32]. In order to study running economy in terms of the parameters mentioned above and continue with the trend of looking for footwear that improves performance in a race, a review of the features of the shoe with

as the cushioning cost that must be carried out by the muscles to cushion the impact when we run wearing minimalist footwear [32]. In order to study running economy in terms of the parameters mentioned above and continue with the trend of looking for footwear that improves performance in a race, a review of the features of the shoe with regard to the consumption of oxygen and running economy was carried out in this review. These features are the weight of the shoe [32], the cushioning system [17], increased dorsi exion stiffness [34] and the comfort feeling [35]. Among the features that may explain this phenomenon, previous studies suggest that different changes in these shoe properties result in an improved running economy [16,36]. The addition of carbon ber plates into the midsole increases the longitudinal bending stiffness, reducing the energy cost of running; however, it depends on the plate design ( at or curved and length) [36]. If the plate design is correct, it may result in a force during push-off that acts at the right location, time and frequency, improving running economy [37]. The combination of this plate with the right cushioning system and the light weight of the shoes cause an improved running economy [25]. This improved running economy may be interesting for long-distance performance, as a better running economy is directly translated into less physiological effort at the same speed [19], although the same improvements have not been shown in previous research [16,25]. These controversial ndings highlight the necessity to carry out this review. The development of a new type of shoe by sports shoe companies that provides a clear bene t compared to previous shoes [16] has caused repercussions in recent years necessitating the modifying of the regulations regarding its use [38]. Due to the scarce evidence on this subject and the interest that it arouses in the sports community and at the research level by different professionals, it is considered necessary to review the available bibliography in relation to the improvement in performance in long-distance races due to the characteristics of the footwear that decrease

the regulations regarding its use [38]. Due to the scarce evidence on this subject and the interest that it arouses in the sports community and at the research level by different professionals, it is considered necessary to review the available bibliography in relation to the improvement in performance in long-distance races due to the characteristics of the footwear that decrease the metabolic cost [17,32,34,35] in an attempt to know the true impact of the new sports footwear. Consequently, the effect of different characteristics of footwear in improving running performance has been investigated by reviewing observational studies, clinical trials and randomized controlled trials. In order to reach a conclusion about the subject to study, two hypotheses have been established. We hypothesized that the features of the footwear such as the shoe mass, the cushioning system, the longitudinal bending stiffness and the comfort feeling produce a positive in uence on running economy in trained athletes. The main purpose was to

Appl. Sci.2023,13, 23 4 of 20 determine the in uence of the characteristics of the footwear on the running economy in trained athletes and the secondary aim was to detail the shoe mass, the cushioning system, the longitudinal bending stiffness and the comfort feeling in uence on running economy in trained athletes. 2. Methods 2.1. Study Design This review followed the Preferred Reporting Items for Systematic Review and Meta- Analyses (PRISMA) criteria [39]. A bibliographic search of scienti c literature was carried out from December 2020 to December 2022. Most of the studies used for this work have been published in the last ten years. Nevertheless, certain articles which have not been published in the last decade were included in order to be able to perform a complete review regarding the study purposes. From these studies, the most relevant information was collected to carry out each section of the work. Observational studies, clinical trials and randomized clinical trials were included. 2.2. Selection Criteria Studies were included in this review if [24,40]: (1) the studies presented running economy data (measured in kJ/kg/min or mL O2/kg/min) on at least one of the char- acteristics of interest for this work (shoe mass, cushioning system, longitudinal bending stiffness and comfort feeling); (2) running economy should be evaluated on a treadmill or a running track; and (3) studies that were indexed at scienti c journals that presented an impact factor as a hallmark for international citations. The exclusion criteria were [23,24]: (1) articles that were not written in English or Spanish; (2) articles that included in their sample patients with some type of musculoskeletal or neurological disorder that could affect their performance; (3) investigations carried out in some unusual environment that affects performance (on the beach, in water or on steep slopes); and (4) articles that do not study running economy in the units mentioned above. 2.3. Search Strategy The databases used to carry out this bibliographic review were PubMed, Cochrane Plus and Medline offered by the services of the library of the Complutense University of Madrid. The search terms were based on the following

beach, in water or on steep slopes); and (4) articles that do not study running economy in the units mentioned above. 2.3. Search Strategy The databases used to carry out this bibliographic review were PubMed, Cochrane Plus and Medline offered by the services of the library of the Complutense University of Madrid. The search terms were based on the following keywords combined with Boolean operators “VO2” OR “running economy” OR “metabolic cost” OR “oxygen consumption” AND “shoe mass” OR “cushioning running shoes” OR “soft soled shoes” OR “longitudinal bending stiffness” “shoe bending stiffness” OR “footwear comfort”. Table results of this search strategy for each database. 2.4. Methodological Quality Assessment The methodological quality of the studies was assessed using the Spanish Critical Reading Skills Program (CASPe Criteria) which allowed evaluation of observational studies and clinical trials [41]. This program is one of the most widely used tools to carry out this type of assessment being an effective system currently used by many authors in the article selection process [42–44]. As it is a scale that allows the evaluation of a wide variety of types of articles, there is no perfectly de ned ranking, so in this work, a score of 0–5 was considered as a low methodological quality and a score greater than or equal to 6 was considered as moderate/high methodological quality. 2.5. Impact Factor Assessment The impact factor of the articles was obtained using the Journal Citations Report (JCR) tool. This quality indicator, which can be found on the Web of Science platform, measures the impact factor of each journal using a formula that takes into account the number of citations received by the articles published in the previous two years divided by the total number of articles published in those two years [45]. Although the impact factor is the

Appl. Sci.2023,13, 23 5 of 20 main quality indicator, the position and quartile (Q) in the range of journals of the same category were also provided. Table 1.Search strategy results. Search Terms Selection Criteria Results Selection PubMed VO2OR running economy OR metabolic cost OR oxygen consumption AND shoe mass 10 years English and Spanish 62 6 VO2OR running economy OR metabolic cost OR oxygen consumption AND cushioning running shoes OR soft soled shoes 10 years English and Spanish 22 2 VO2OR running economy OR metabolic cost OR oxygen consumption AND longitudinal bending stiffness OR shoe bending stiffness 10 years English and Spanish 6 1 VO2OR running economy OR metabolic cost OR oxygen consumption AND footwear confort 10 years English and Spanish 16 1 Cochrane Plus VO2OR running economy OR metabolic cost OR oxygen consumption AND shoe mass 10 years English and Spanish 113 1 VO2OR running economy OR metabolic cost OR oxygen consumption AND cushioning running shoes OR soft soled shoes 10 years English and Spanish 70 1 VO2OR running economy OR metabolic cost OR oxygen consumption AND longitudinal bending stiffness OR shoe bending stiffness 10 years English and Spanish 66 1 VO2OR running economy OR metabolic cost OR oxygen consumption AND shoe mass 10 years English and Spanish 156 1 Medline VO2OR running economy OR metabolic cost OR oxygen consumption AND longitudinal bending stiffness OR shoe bending stiffness 10 years English and Spanish 65 1 2.6. Risk of Bias Assessment The recommendations of the Cochrane Handbook of Systematic Reviews of Inter- ventions were followed to assess the risk of bias in the included articles. The evaluation of the risk of bias was carried out through a domain-based assessment, since, as stated in this manual, assessing the risk of bias using scales is not recommended, since these assessments included considerations that could be dif cult to support. The most practical way to perform an assessment of this type was to use criteria that may be speci ed objec- tively. Therefore, six domains were evaluated classifying them as “low risk”, “high risk” or “unclear risk” in order to obtain a summary

The study reviews how footwear characteristics affect running performance.