# Influence of Footwear Features on Oxygen Consumption and Running Economy: A Review
## 1 Introduction
There are several factors that affect running economy [20] and that may be improved or modified 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; 24; 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; 12; 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 19 th 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 scientific advances in this field have been made [26]. Simultaneously, more technology and sophistication have been added to running shoes. In 2005, the first 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 [PERSON]'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 affirmations have been widely discussed in the scientific literature and there is great controversy. Indeed, there is no evidence that running in minimalist footwear causes a significant 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 first 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].