It is not surprising that 80% of adults will experience some form of back pain in their lifetime. Maintaining a healthy back and proper posture can be difficult when you are required to work at a computer station or a desk for the majority of the day. Lesson 3.2 gives you some biomechanical principles for lifting and moving objects. The U.S. Division of Occupational Health and Safety has information for maintaining a healthy back in your workplace or your parents’ workplace. Check it out!
An understanding of the basic laws of motion can help you to move efficiently and avoid injury. Sir Isaac Newton’s three laws of motion provide the basis for an understanding of the application of force in physical activity and sports as well as for maintaining good posture and preventing injury to the back and other body parts.
Force (the effect that one body has on another) is important in physical activity because it causes the body’s levers (bones) to move. Outside forces can cause the body to move, but the muscles of the body are the primary means of producing the force necessary for movement.
Newton’s three laws relate to the effective use of force and can be applied in a variety of settings. The first law states that a resting object or body will stay at rest until a force causes it to move, and a moving object or body will move in a straight line based on the force that created the movement except when another force causes a change in the direction of movement. Your muscles contract and exert force to get you moving when you run in a straight line, but additional muscle action is necessary if you are to change the direction of the movement, as in playing defense in basketball or changing direction to hit a tennis ball. As pointed out in chapter 2, force applied inappropriately or the use of excessive force can cause injury.
The second law states that an object or body accelerates in proportion to the force that causes it. For example, when you kick a football, the greater the contraction of the muscles that move the levers of the leg, the greater the amount of force applied to the football. The force created by the contraction of the muscles accelerates the movement of the leg, and the force of the foot hitting the ball accelerates the movement of the football.
The third law states that for every action there is an equal and opposite reaction. Rocket propulsion illustrates this basic law. When the rocket blasts off, the blast (away from the rocket) causes the rocket to move upward in the direction opposite the blast. When you hit the ball with your racket in tennis, the racket causes the ball to move toward the net; but at the same time, the ball causes an opposite reaction against the racket. You must grip the racket firmly to resist the opposite reaction on the racket.
Many other factors affect your ability to move efficiently and effectively, but Newton’s laws of motion are fundamental. The way force is applied to levers is important (for example, leverage and methods of applying force). When you’re moving in the water, the principles of hydrostatics apply; when you’re moving through the air (jumping, applying force to a ball or other object), the principles of aerodynamics apply.
