Fitness Articles

Reference Guide to Strength Training

An In-Depth Look


4 Principles of Strength Training
The four principles of strength training are guidelines that will help you strength train safely and effectively to reach your goals.

1. The Tension Principle: The key to developing strength is creating tension within a muscle (or group of muscles). Tension is created by resistance. Resistance can come from weights (like dumbbells), specially-designed strength training machines, resistance bands, or the weight of your own body. There are three methods of resistance:
  • Calisthenics (your own body weight): You can use the weight of your own body to develop muscle, but using body weight alone is less effective for developing larger muscles and greater strength. However, calisthenics adequately improve general muscular fitness and are sufficient to improve muscle tone and maintain one’s current level of muscular strength. Examples include: pushups, crunches, dips, pull ups, lunges, and squats, just to name a few.
  • Fixed Resistance: This method of resistance provides a constant amount of resistance throughout the full range of motion (ROM) of a strength training exercise. This means that the amount of resistance/weight you are lifting does not change during the movement. For example, during a 10-pound curl, you are lifting 10 pounds throughout the motion. Fixed resistance helps to strengthen all the major muscle groups in the body. Examples include: Exercises that use dumbbells (free weights), resistance bands and tubes, and some machines.
  • Variable Resistance: During exercises with variable resistance, the amount of resistance changes as you move through the range of motion. This creates a more consistent effort of exertion throughout the entire exercise. For example, when lifting weights, it is harder to lift up against gravity and easier to lower the weight down with gravity. Specially-designed machines (like Nautilus and Hammer Strength brands) take the angle, movement, and gravity into account so that the release of a biceps curl feels just as hard as the lifting phase of the curl.
2. The Overload Principle: In order to build strength, your muscles must work harder than they are accustomed to. This “overload” will result in increased strength as the body adapts to the stress placed upon it. Everyone begins at a certain level of strength. To become stronger, you must regularly increase the tension (weight or resistance) that your muscles work against, causing them to adapt to a new level. As the muscles respond to an overload, they will grow in size and strength. There are two types of strength overloads:
  • Isometric means “same length.” This is a high-intensity contraction of the muscle with no change in the length of the muscle. In other words, your muscles are working hard but the muscle itself remains static. Isometric exercises are good for variety and some strength maintenance, but they don’t challenge your body enough to build much strength. Learn more about isometric exercise here.
  • Isotonic means “same tension.” When you lift weights or use resistance bands, your muscles are shortening and lengthening against the resistance. This challenges your muscles throughout the entire range of motion. However, the amount of force the muscle generates will change throughout the movement (Force is greater at full contraction/shortening of the muscle). Unlike isometric exercises, this type of contraction does help build strength. Continued ›
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About The Author

Jen Mueller Jen Mueller
Jen received her master's degree in health promotion and education from the University of Cincinnati. A mom and avid marathon runner, she is an ACE-certified personal trainer, health coach, medical exercise specialist and behavior change specialist. See all of Jen's articles.

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