Sports engineering

One of the earliest instances of the use of scientific principles in sports context occurred in 1671 when English mathematician Isaac Newton wrote a letter to German theologian and natural philosopher Henry Oldenburg regarding a tennis ball’s flight mechanics. In the following centuries, German scientist Heinrich Gustav Magnus further examined Newton’s analysis and applied Newtonian theories to the spinning properties of balls. Around 1760, in the midst of the Industrial Revolution, sports engineering was further explored with the acceleration of the manufacturing of sports equipment. During this stage, the manufacturers recognized an increase in sales being directly related to better quality of equipment. As a result, experimentation started to explore new designs and materials for greater athletic performance.^[4]

In modern times, sports engineers, such as Howard Head, applied engineering principles to sports equipment. After finding traditional snow skis to be too heavy, Head developed lighter, more flexible skis in 1947. He used his knowledge from the aircraft industry to create skis with a metal-sandwich construction. After 40 iterations and 3 years, he released his skis commercially, and they soon set the standard for skis. Today, his skis are widely known and recognized under the brand Head, with Head Sportswear International, and the Head Ski Company. Head also developed the Prince Classic tennis racquet. He created a much lighter design, with a bigger frame supporting off-center hits, and a grip that did not twist in players' hands. As with his skis, Head's oversized racquets were embraced by top athletes in the sport.^[5]

In 1998, the International Sports Engineering Association (ISEA) was established and the journal Sports Engineering was published. In 1999, the first international sports engineering conference was organized by Steve Haake called The International Conference on the Engineering of Sports in Sheffield, England. The conference brings world-leading researchers, sports professionals, and industry organizations together to celebrate the profession, showcasing innovations in both research and industry.^[6]

Sports engineering has become an important sub-discipline in modern engineering. The optimization of athlete-equipment interaction and the importance of technology for safety and performance, and therefore success have grown ever since. The Speedo LZR Racer, as a very prominent example, is a swimsuit developed in collaboration with NASA researchers and engineers and launched 2015.^[11] Sports engineers tested different materials and coatings in a wind tunnel to reduce drag and optimized stability and mobility by using layering and joining techniques specific to particular body parts.^[11][12] The LZR Racer was able to reduce skin friction drag by 24% compared to Speedo’s previously most advanced suit, resulting in several new world records. Inventions like this present sports engineering as a field of potential and have popularized it as a discipline of very tangible developments.^[12]

A basic aspect of sports engineering is understanding the materials available and their capabilities. Since material selection directly influences the performance, safety, durability, and sustainability of sports equipment, knowledge of material science forms one of the most important foundations of sports engineering.^[10] The typical classification of materials in engineering consists of metals, polymers, and ceramics. This can be extended by including composites as the mixture of more than one material.^[9][39]

These four groups can be divided into subgroups using the Ashby chart, which sorts the groups according to stiffness and density. Compared to the previous classification, it adds some highly relevant groups for the field of sports engineering, such as wood as a biomaterial and a popular ingredient for a composite material.^[9] Determining their value for sports engineering, the key properties of the materials are:

• Strength
• Density
• Ductility
• Fatigue resistance
• Toughness
• Modulus (damping)
• Cost

To understand the relevance for design, it is vital to consider first the most important requirements of the final product. The variety of sports, including equipment, fields, courts, conditions and so on forces engineers to use a very broad spectrum of the materials shown in the chart from left to right. As a result, the final and optimized products usually consist of a mix of materials.^[40]

Metals

From the group of metals, steel, aluminum, magnesium and titanium are the most commonly used types in sports. They offer the main advantages of high strength, corrosion resistance and formability. Steel, for example, can be found in:^{[8][41][36][42]}

• Golf clubs
• Bike frames
• Horseback riding (horseshoes, ...)
• Winter sports (edges for skis and snowboards, blades, bobsleighs, ...)
• Mountain sports (various climbing and mountaineering gear)
• Water sports (diving gear, pieces of sailing and rowing boats, ...)
• Fencing equipment (additional benefit: conductivity)^[43]

Besides that, steel appears in non-personal equipment, which includes weight lifting machines and equipment like lifting bars or weights in fitness centers and set-ups for gymnastics, like the high bar.^[41] This also applies to facilities like outdoor fitness stations, stadiums, etc.^[8][36][42]

In cases where durability is required but objects are required to be lightweight, aluminum, magnesium, or titanium (or alloys with those elements) are used. The latter, however, mostly appears in high-performance sports due to the price of the material.^[36] These types of metals can be found in:^{[8][36][42][44][45]}

• Baseball bats
• Golf clubs
• Tennis rackets (earlier)
• Badminton rackets
• Bike frames
• Track and field (javelins, hurdles, ...)
• Winter sports (skis, snowboards, poles, ...)
• Mountain sports (climbing, ..)

Similar to steel, these materials also appear in non-personal equipment, like in gymnastics (beam) and team sports (goal frames, basketball hoops, ...), as well as in facilities.^[41][46]

In the context of sports engineering, selecting the appropriate manufacturing process is critical as it dictates the performance, durability, and cost of the final product.^[55][62] While high-performance requirements exist, the methods used are often not unique to sports and are frequently adopted from other sectors such as the aerospace and automotive industries.^[55]

For instance, common industrial methods like injection molding and blow molding are used for various components, such as tennis racket parts and protective gear.^[55] For high-performance composites, engineers apply resin transfer molding (RTM).^[55][58] The use of pre-impregnated materials is also common to simplify processing and guarantee consistent quality.^[58] Other techniques include compression molding for golf ball cores and skis,^[55][58] rotational molding for hollow items like hockey balls, and thermoforming for thermoplastic composites.^[55] Furthermore, additive manufacturing (3D printing) is more frequently employed to produce topology-optimized structures that would be difficult to create with traditional tooling.^[58][10]

In contemporary sports engineering, sustainability is now a fundamental priority that is integrated directly into the initial product creation process, largely because approximately 80% of a product's environmental burden is established during the design phase through decisions regarding materials and manufacturing.^[55][63]

A main challenge in this field is the widespread use of high-performance fiber-polymer composites, which, unlike metals, are notoriously difficult and expensive to recycle in a sustainable manner.^[55][63] Conventional thermal recycling methods for these materials often lead to an 80–95% reduction in the mechanical strength of reclaimed fibers, frequently rendering them unsuitable for reuse in high-performance equipment.^[63]

Although there are obstacles, there are promising developments in the industry, such as the growing adoption of thermoplastic matrices that can be melted and reformed at the end of their life cycle.^[47][58] Engineers are also utilizing innovative bio-based materials like polylactic acid (PLA) derived from corn and developing biodegradable tennis strings made from corn starch to reduce environmental impacts.^[55][58][63] Furthermore, circular economy initiatives like the Eco Circle program now allow for the chemical recycling of polyester textiles back into high-quality new fibers without performance loss.^[55][63] These efforts are complemented by the development of advanced functional materials, including auxetic foams for superior impact protection and sustainable textiles like bamboo charcoal yarns, which try to balance peak athletic performance with ecological responsibility.^[10]

• Biomechanics
• Composites
• Materials science
• Mechanical engineering
• Sports equipment
• Sports medicine
• Sports science
• Physics