Biomechanics

• 1 Biomechanics in Sport
• 1.1 Center of Gravity
• 1.2 Overuse injuries
• 1.3 Pregnancy
• 1.4 Knees
• 2 Athletic Equipment Design and Apparel

Muscles govern range and speed of movement in all complex animals. To power movement, muscles must exert forces to support, forces to accelerate or decelerate, and forces to overcome inertia and the resistance of air or water through which movement occurs. The action of forces is studied in mechanics whereas the action of forces in living things is examined in biomechanics.
Biomechanics is a relatively new subdiscipline of kinesiology, although some people use the terms biomechanics and kinesiology interchangeably. Kinesiology means “the study of motion,” which has a broad focus. In contrast, according to the American Society of Biomechanics, biomechanics means “the application of the principles of mechanics to the study of biological systems.” Biomechanics views the human body as a machine— a mechanical system subject to the restrictions of the laws of physics. The body is divided into a collection of body segments connected to one another and pivoting at the joints, moved by muscular and/or externally applied forces.
The subdiscipline of biomechanics has grown rapidly and steadily during the past fifteen to twenty years because of, in large part, improvements in instrumentation in general and in high-speed computers in specific. Pennsylvania State University and Indiana University were perhaps the first two universities to design a laboratory for biomechanics during the 1960s.Today, however, biomechanics is a part of every curriculum, and almost all departments of kinesiology have biomechanics laboratories.
Although biomechanics is a relatively new subdiscipline, the first “biomechanic” was probably the Italian painter, sculptor, architect, and engineer Leonardo da Vinci (1452–1519). Leonardo’s works demonstrated his knowledge of the musculoskeletal system as he described the mechanics of movement. During the nineteenth century the photographer Edward Muybridge used a system of multiple cameras to document the movement of racehorses. During the 1990s high-speed cinematography became a cornerstone of data collection and analysis of many athletic activities.
Biomechanics incorporates many other fields (physics, engineering, biology, computer science, zoology, and physical and occupational therapy), and human biomechanics can be divided into many areas of study. For example, some biomechanics experts are interested in the elderly and mobility impairments. Others are interested in the development patterns of children. Clinical biomechanics experts might study the gait of people with cerebral palsy or the daily living activities of people with disabilities, whereas occupational biomechanics experts focus on work-related injuries and the prevention of those injuries and are particularly interested in safety factors in the workplace.

Biomechanics in Sport

In sport biomechanics is especially concerned with how the human body applies forces to itself and to other bodies with which it comes into contact and, in turn, how the body is affected by external forces. A sound knowledge of biomechanics equips the physical educator, the coach, and the athlete to choose appropriate training techniques and to detect and understand faults that may arise in their use. Joseph Hamill, a professor at the University of Massachusetts, listed the major categories of interest for the sport-biomechanics expert as improvement of health and physical fitness, injury prevention, equipment design, and improvement of athletic performance.
During recent years the number of girls and women participating in competitive sport, fitness activities, and recreational activities has grown rapidly.Women’s demand for more information about new performance techniques and exercise regimens, accompanied by a willingness to spend money on scientifically designed running shoes, tennis rackets, exercise equipment, or health-promoting foods and diets, has brought even more support to sports research. Once considered the weaker sex, women are playing with speed, precision, explosiveness, and power.
Perhaps because of women’s increased involvement in sports, people are beginning to rely less on the male body as a medical norm or athletic-performance yardstick. Biomechanical and physiological factors relative to women should be a primary concern for people who teach, coach, and participate in exercise and sports. However, although much has been said about the woman athlete, little research has addressed her performance. With the increasing number of women participating in sports and other physical activities, the need for such research is paramount. Concepts of biomechanics particularly relevant to women include the following.

CENTER OF GRAVITY

Perhaps the most important concept in biomechanics is equilibrium and stability. People often use the terms equilibrium and stability synonymously.However, equilibrium is that point around which the body freely rotates in any direction with all the opposing forces equal, whereas stability is the resistance to the disruption of equilibrium. Balance is the ability to control movements. Many factors affect stability and balance. For example, when the line of gravity is within the base of support, the body is more stable. Because of a slightly wider pelvic girdle and narrower shoulders, women have a lower center of gravity than men and are, therefore, more stable. In balance-related activities women have an advantage because of their lower center of gravity.

OVERUSE INJURIES

Overuse injuries result from repetitive stress and/or microtrauma (injury at the miscroscopic level) and can result from both intrinsic and extrinsic factors. Intrinsic factors are those biomechanical aspects specific to each athlete and include bone structure, muscle imbalance and/or weakness, and lack of flexibility. Extrinsic factors are usually specific to a sport, including faulty equipment, incorrect shoes, changes in running surfaces, and improper training. Overuse injuries usually begin as mild or moderate nagging soft-tissue injuries and advance to more severe problems if the person does not receive proper care. Common overuse injuries particular to women who exercise and participate in athletics are Achilles tendonitis, chondromalacia (abnormal softening of cartilage), iliotibial band syndrome, stress fractures, carpal tunnel syndrome, and plantar fascitis. Stress fractures are the most common type of injury for women in sports and occur most frequently with an increase in training. In addition, stress fractures are associated with girls or women who have irregular or no menstrual cycles because of heavy exercise routines.

PREGNANCY

Every pregnancy is unique, but all pregnant women undergo significant and multiple physiological and biomechanical changes that affect the body. Some of these changes start as early as conception, but most occur during the third trimester. In particular, musculoskeletal changes occur as a result of the hormone relaxin. Relaxin causes a progressive relaxation of the joints, which include the ligaments that hold the sacroiliac joint and the symphysis pubis. Women often experience lower back pain as a result of an increase in lordosis (spinal curvature) and upper spine extension. These changes occur to accommodate the enlarged abdomen as the fetus grows.To compensate for this exaggerated lumbar curve, the center of gravity shifts. The woman must, in essence, lean backward to maintain a sense of stability. During the third trimester most women need to modify some of their movement patterns. An outward rotation (toeing out) of the feet and almost a shuffle gait usually occur.

KNEES

The knees are the largest and most vulnerable joints in the body. The combined functions of bearing weight and providing locomotion place considerable stress and strain on the knees. According to several studies,women athletes experience twice the knee injuries of men.This fact seems particularly true in such sports as basketball, soccer, and volleyball, all of which require constant pivoting. As with overuse injuries, the predisposition to a knee injury may fall under either intrinsic or extrinsic factors. Intrinsic factors include ligament size and intercondylar notch width (the distance between the lateral and medial condyle of the femur), joint laxity, and the quadricep angle (Q-angle), which is the angle made by the tendons of the quadriceps femoris and the ligamentum patella with the center of the patella, which is the thick, flat triangular movable bone that forms the anterior point of the knee. Extrinsic factors include motor skill, level of conditioning, muscular strength and coordination, and individual mechanics. Common knee injuries among women are patella femoral pain syndrome, chondromalacia, patella tendonitis, meniscal or cartilage injuries, and ligament injuries. In particular, a disproportionate number of anterior cruciate ligament (ACL) injuries occur in women’s athletics.The anterior cruciate ligaments provide stability to the knee, particularly for forward-backward movement.The greater incidence of ACL injuries stems from interrelated factors, including hamstring-quadriceps strength imbalances, wider Q-angle, and joint laxity. These factors do not necessarily cause the problem together—hamstringquadriceps strength imbalances may add to joint instability.

Athletic Equipment Design and Apparel

For many years women and girls participating in sports and fitness activities have had to use equipment designed for men. Recently, however, some companies have responded to the enormous number of women who are now physically active. Shoe companies and sporting goods and athletic-wear companies are making functional design adaptations to meet the needs of women. In addition, more businesses owned and operated by women are making design changes in athletic equipment for women. Compared to the average man, the average woman is shorter and has longer legs, shorter arms, and a shorter torso. Women also have smaller hands and feet, narrower shoulders, and wider hips.Women have a higher percentage of body fat and less lean muscle mass.
Biomechanical differences also apply to athletic shoes for women. Whereas most men’s athletic shoes are designed on a standard athletic last (mold), many women’s shoes are designed on a special last. Lasts come in two shapes: A straight-lasted shoe is filled in under the medial arch, whereas a curved-lasted shoe is flared medially at the ball of the foot. Also, women’s shoes usually have narrower heels. Although a number of sport-specific athletic-shoe designs exist, all incorporate biomechanical factors such as heel counters, midsoles, and lateral forefoot support.
In summary, biomechanical factors are critical in analyzing and improving the way women execute particular movements. Some factors may also cause an increased predisposition to specific injuries. Therefore, people should understand the principles of biomechanics as they relate to care and prevention of injuries and to the enhancement of motor performance of people.

See also Human Movement Studies; Kinesiology; Sport Science