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Bodyweight versus external resistance

This is an excerpt from Exercises for Resistance Training by Lauren R. Tapp,Joshua Wludyga.

Most of the exercises we tend to see performed in gym settings involve the use of external resistance. External resistance can be applied through free weights, machines, cable pulleys, or various other implements. All of these are great tools but not always necessary for a resistance workout. Bodyweight training can also be an effective method for improving strength and fitness by applying the weight of one’s own body as the resistance. By positioning the body in specific ways, the muscles will work to overcome the earth’s gravitational pull. The position of the body can be modified to increase or decrease resistance, still only using one’s own body weight.

GRAVITY

Due to the earth’s gravitational pull, the resistance a human body exerts on itself is equal to the mass of the body multiplied by the gravitational acceleration. In other words, the mass of the body is being pulled toward the earth, which creates a resistance; thus, gravity is an important component of resistance training. Without gravity, body weight would not be an adequate resistance training tool. In addition, due to the direction of gravitational pull, the angle or position of the body can affect the degree of resistance, or difficulty, of an exercise. This is called leverage. Leverage can be modified by changing the body position to make exercises harder or easier.

GROUND REACTION FORCES

Ground reaction forces (GRFs) are a representation of Newton’s third law of motion—for every action there is an equal and opposite reaction. Therefore, when our body makes contact with the ground, the ground reacts against the body in an equal magnitude. For bodyweight exercises, the resistance exerted against the ground will equal the resistance exerted on the body. Therefore, to make a bodyweight exercise more difficult, more force needs to be exerted by the body on the ground. Without external resistance, this can be accomplished by increasing the acceleration of the body toward the ground in a countermovement. An example of this would be comparing a squat with a squat jump. During a bodyweight squat, we exert the force of the body weight onto the ground when we move downward, and that equal force exerted back against us allows us to stand up. However, when we jump, the first movement we perform is the countermovement, a faster, more powerful squat that prepares us for a jump. That increased force production allows us to jump higher than if we just performed a bodyweight squat. More simply put, if we want to make a bodyweight exercise more difficult without adding external resistance, we can add an “explosive” component to it.

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