Common Methods of Muscular Strength and Endurance Training

In a group exercise setting, exercises will involve either concentric, eccentric, or isometric muscular contractions.

Concentric Muscular Contraction: A concentric contraction occurs when tension generated by the muscle is sufficient to overcome a resistance, and moves (at a joint) a body segment of one attachment toward the segment of its other attachment (e.g., the upward or shortening phase of a biceps curl).

Eccentric Muscular Contraction: An eccentric contraction occurs when a muscle slowly lowers a resistance (lengthening phase) as it returns from its shortened phase to normal resting length.

Isometric Muscular Contraction: An isometric contraction describes a static (held) position in which tension is developed in the muscle, but the muscle length and joint angle do not change.

NOTE: The following methods and exercises use one or both types of muscle contraction(s).

Muscle Isolation (Prime Movement)
Isolation exercises are used to target a specific muscle group by utilizing the primary movement (joint action) of that particular muscle. Examples include biceps curls, calf raises, and deltoid raises.

As the name implies, multi-joint exercises involve more than one joint and target several muscle groups in the same exercise. In a squat, for example, movement occurs at several joints (hip, knee, and ankle) and many muscles (quadriceps, gluteal muscles, and hamstrings) are targeted simultaneously.

Torso Stabilization
Commonly referred to as torso, core, or spinal stabilization, these exercises will enhance the ability to maintain proper spinal alignment and posture. The primary focus of these exercises is to keep the axial skeleton (torso) stable, whether in a held position against gravity (e.g., modified V-sit) or resisting the movement of an extremity (e.g., supine alternating toe taps, with low back held in neutral). To be executed correctly, the abdominal and back muscles must work together in a co-contracting isometric manner.

Functional Training
Functional training describes exercises that replicate movements commonly used in activities of daily living. A narrow stance squat, for example, duplicates the action of getting in and out of a chair. In many cases (e.g., the squat), functional exercises are not always separate or distinct from multi-muscle /multi-joint or stabilization exercises.

NOTE: A combination of the aforementioned training techniques can be used in most fitness programs. Each technique challenges the body differently and offers distinct training benefits. The key to exercise selection is based on the participants’ goals, their ability to maintain proper form and alignment, and the amount of available training time.

Special Considerations

Muscle Balance
Muscle balance is achieved when muscles on all sides of a joint are properly trained for proper posture, body mechanics, and injury prevention. Thus, for every primary muscle worked (agonist), the opposing muscle group (antagonist) should also be worked. It is important to note that although both agonist and antagonist muscles should be trained, not all muscles have the equal capacity of their op posers (e.g., calves and anterior tibialis).

It is important for the instructor to be familiar with the most common muscle imbalances so that class time is used wisely. In general, weak, loose muscles (thoracic and upper back) need to be strengthened or tightened and excessively tight muscles (chest and anterior deltoids) need to be stretched or lengthened.

Range of Motion
Isotonic exercises should be taken through a full ROM. This will allow the muscle to function at its best throughout its usable range, as well as to maintain adequate joint mobility. Care should be taken not to overload a muscle past its ability to control the movement. Control is often compromised when working at either end of the range of motion-the beginning and end of the motion are often weaker than mid-range.

Speed and Control
Muscle conditioning exercises should be performed at slow to moderate speeds that allow full range of motion and concentrated work in proper alignment. Performing an exercise too quickly often relies on momentum; this is both less effective and more likely to lead to joint or muscle injury.

Train a muscle or muscle group to the point of muscle fatigue. Adjust the resistance so that the muscle is fatigued within a reasonable number of repetitions (generally 8 to 15). In group exercise, adjustments of training variables, such as the number of repetitions (up to 25), sets ( 1-4), or sequencing, may be necessary if the equipment does not offer sufficient resistance.

Torso Stabilization Exercises
If inadequate abdominal strength is present, certain torso stabilization exercises may place inappropriate stress on the spine. ln a group exercise setting, extreme care should be used and sufficient modifications properly cued to accommodate individual needs with these torso stabilizing exercises. Properly performed stabilization exercises can be a positive complement to traditional isotonic forms of abdominal training (e.g., crunches and curls). Both methods may be included in a complete training program.

Resistance Equipment Techniques
Participants should not use external resistance (e.g., weights or resistance tubing) until they can perform the given exercises with proper alignment and technique without resistance. When all the repetitions can be completed comfortably with proper form, the amount of resistance should be gradually increased in order to continue to overload the muscles and stimulate improvement. Some general points to keep in mind when cueing exercises that use resistance equipment are as follows:

  • Keep the hands relatively relaxed. Avoid a tightly clenched fist; this can potentially cause blood pressure elevation.
  • Maintain a neutral wrist. Avoid flexing or extending the wrists while gripping weights, bands, or tubes. Excessive repetitive wrist flexion or extension can increase the risk of carpal tunnel-syndrome and tennis elbow.
  • Teach participants to bend over and pick up their equipment properly for low-back pain prevention. One hand is on the thigh for support, while the other hand picks up the weight or tubing. For picking up heavier items, use correct squatting technique and a two-handed lift.
  • For exercises that are not equipment-based, position the muscle so that it is directly opposed by gravity for the most effective and time-efficient work.
  • When using elastic resistance, it is important to control the eccentric, or return, phase of the exercise; “rebounding,” or suddenly returning to the starting position without control, can cause injury. Additionally, for healthy joint mechanics, the instructor needs to be attentive to utilizing tubing only when there is correct line of pull.

Muscle Conditioning Exercises in the Water
Water exercise differs from land exercise in several important ways. Instead of gravity constantly exerting a downward force (as on land), there is the upward force of buoyancy in the water. In addition, muscle actions are different; all actions in the water are concentric (shortening), whereas on land the actions are both concentric and eccentric (lengthening). Because of these differences, instructors may need additional training or experience in working in water.

Sample Exercises
The following chart is a compilation of a variety of common exercises. The exercises listed are organized into several approaches to exercise selection. It may also be used as a reference chart to primary muscles and their joint actions.


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