Last week we discussed the importance of aerobic and anaerobic training and this week we will focus on the importance of incorporating strength training into your exercise regimen. Basically, there are several different categories of exercise: Isometric Exercises, Isotonic Exercises and Isokinetic Exercises. By combining the first two types of exercises during your weekly workout regimen, you will attain synergistic benefits that both these exercises provide.

One of the main reasons for exercise is for weight loss and to improve your body composition. According to a study done at UCLA School of Medicine by Dr. Srikanthan published in July 2011 in the Journal of Clinical Endocrinology and Metabolism, building higher muscle mass may improve insulin sensitivity and decrease the risk for both pre-diabetes and diabetes. This finding is quite significant because provides motivation for those who have difficulty “losing weight”. By adding resistance (strength training) into your exercise programwe are still building muscle mass and therefore, decreasing our risk for pre-diabetes and diabetes and contributing to positive changes in our metabolic profile. In addition, several studies have demonstrated that strength training may improve our self-esteem and body image more so than aerobic exercises alone.

So what are the different types of exercises we perform?

Isotonic Exercises:
In this type of exercise, thereis no change in the muscle tone or degree of muscle tension throughout the exercise.In simpler terms, during these exercises, the muscle contracts and causes the body part to which it is connected to move. These exercise result in a change in the joint angle that the muscle crosses. A bicep curl results in bending and straightening of the elbow joint. Typically, isotonic exercises are more vigorous types of exercises such as cycling, swimming, running, tennis, etc. In general, isotonic exercises tend to burn more calories, improve bone density and lower risk of heart disease. Isotonic exercises can be further classified by the type of contraction that occurs in the muscle.

Concentric Isotonic Exercises:
In this type of exercise, (i.e. the upward motion of a bicep curl with weights), the force the muscle generates is greater than the resistance placed on the muscle (weight in the hand) leading to a shortening of the muscle. Concentric exercises always decrease the angle of the joint that the muscle crosses. For example, the upward motion of a bicep curl — starting with the arm fully straight with the hand and weight by the thigh and ending when the arm is fully bent with the hand and weight by the shoulder — is the concentric portion of this exercise.

The Benefits of Concentric Exercises Include:

• Allows for specific muscle strengthening and repair of muscle damage
• Improvement in the range of motion in the joint and muscles exercised
• Improvement in strength in the muscle exercised

Eccentric Isotonic Exercises:
Eccentric exercises occur when the muscle is contracting but lengthening at the same time. In this case the force of the weight may be greater than the force that the muscle can generate. Examples of eccentric isotonic exercises include slowly putting down a heavy object, or the downward portion of the bicep curl — beginning with the hand and weight at the shoulder and slowly straightening the arm and elbow and ending with the hand and weight at the thigh. In eccentric exercises the joint angle that the muscle crosses gets larger. Eccentric exercises are the main cause of muscle soreness and are more likely to result in injury. This is because the muscle is contracting but lengthening at the same time which results in more micro-tears in the muscle belly. It is not the tearing of the muscle that builds muscle, but instead the repairing of these muscle tears which increase protein production and causes muscle growth and hypertrophy (swelling or enlargement). Eccentric exercises are thought to provide greater muscle strengthening as compared to concentric exercises because of the higher tension the muscle is under during the exercise.

Exercises such as cycling, swimming, weight lifting (upwards and downwards motion of the weight), and stair climbing all provide benefits of both concentric and eccentric exercise as the muscles are shortening and lengthening throughout the exercise.

In contrast, Isometric Exercises, occur when the muscle contracts but there is no change in the length of the muscle. It neither lengthens nor shortens throughout the exercise. In this case the force generated by the muscle is equal to the opposing force (such as a hand weight). Therefore, neither the muscle nor the joint moves. An example of an isometric exercise is holding a weight out in front of the body in a fixed position, or holding a squat in a fixed position. Isometric exercises can be further divided into:

Yielding Isometric exercises are those in which the weight is neither dropped nor lifted, despite the fact that the muscle has the ability to move the weight.

Overcoming Isometric exercises are those that no matter how much force is exerted by the muscle, the weight will not move. For example, attempting to move a 2000 pound boulder by pushing against it is an overcoming isometric exercise. The terms yielding and overcoming are somewhat of semantics as the benefits of both types are isometric exercises are fairly equal.

Benefits of Isometric Exercises:

• Can be used in cases of arthritis when joint movement is painful
• Used to heal injured muscles without much strain being placed on the joints
• Improves muscle strength and size
• Less chance of injury when performing these exercises
• Ability to isolate certain muscles to allow for strength training and muscle healing
• Increased bone density
• Increase in lean muscle mass
• Decreased blood flow during the prolonged muscle contraction may contribute to increased muscle growth because growth factors remain in the muscle tissues longer
• Holding the contractions longer increases muscle mass
• Increasing the number of contractions increases muscle strength

Risks/Caveats of Isometric Exercises:

• Blood pressure rises during contractions which can be risky in individuals with high blood pressure or increased risk of stroke
• Increases in strength are angle specific therefore it helps to hold the exercise in several positions. For example, an isometric bicep curl should be held with the elbow joint at approximately 45 degrees, 90 degrees and 135 degrees to strengthen different parts of the muscle belly.
• No improvement in muscle speed, agility or power
• If body alignment is poor, injury is more likely

Another type of exercise that exists is an Isokinetic Exercise. In this exercise, usually machines are used which control the speed of the muscle contraction within a specific range of motion. Essentially, these machines can control the resistance placed on the muscles and keep the speed of the muscle movement fairly constant. These machines combine the benefits of isotonic and isometric exercises. Examples of these machines include the stationary bicycle, and the Cybex arm machine.

Benefits of Isokinetic Exercise:

• Used to rehabilitate muscles
• Uses uniform resistance that adapts to the body
• Less stressful on the body
• Increases range of motion without muscle fatigue or muscle strain
• Muscles are allowed to rest which avoids lactic acid build up

Typically, isokinetic exercises are utilized by Physical therapists and Occupational therapists for rehabilitating muscles after injury, or for treating muscle imbalances which may lead to injury. As with all exercise programs, it is important to start with little to no resistance and build up slowly both your resistance and your repetition count. If you have injuries, you should seek medical attention to determine which exercises are right for you and which can lead to worsening of your injuries.