Much attention has been focused on eccentric contraction exercises (also known as negatives) in which the muscle yields to an outside force. As the muscle yields to the outside force, an eccentric contraction takes place during which, the muscle lengthens and develops tension. The greater the resistance, especially when it is over 100%, the greater is the muscle tension.
The Russians have done considerable research on the eccentric contraction and have found it to be very effective for strength gains. However, it is not used for most of the workout because of its intensity and it does not replace the concentric contraction.
Part of the reason for this is that even though the eccentric contraction is very effective, it takes too long to prepare the body for such intense and offer prolonged loads. When doing eccentrics, it is necessary to have the overload principle in effect. This means that you use up to 50% more weight than in the maximum concentric contraction exercise.
Because of the great stress and the amount of time needed, the eccentric contraction is not foremost in training. The concentric contraction still remains supreme in the training of athletes, powerlifters, bodybuilders and weightlifters. The concentric, or the typical exercise done by most individuals, is used for up to 60 to 70% of all the total lifts done in the course of a year.
Isometric or static contractions should be used fairly extensively in the training of athletes. The isometric contraction is less intense than the eccentric but has up to 20% greater stress than the concentric contraction. This means that you can use up to 20% more weight in the isometric exercise. Isometric exercises play an important role in developing greater stability for better execution of skills as well as strength exercises.
According to the Russians it is possible to use all three muscle contraction regimens in one session. For example, on any given day the athlete may work out with eccentric, isometric and concentric exercises. There may also be days when the workout is devoted to isometrics or the eccentric or concentric contraction type exercise.
One of the most promising and effective methods that the Russians developed is the combination of muscle contraction regimens in one exercise. For example, when doing the squat, you load the bar so you are using 20-40% greater than the concentric max in the eccentric contraction.
As you lower the body the muscles undergo an eccentric contraction. As soon as you hit the bottom position, you hold the position in an isometric contraction while your assistants slide the extra weights off the barbell. You then rise up quickly in the concentric regimen.
Research has shown that lowering a barbell with weights of 120 to 140% of the maximum concentric, is more effective than lifting a near maximum weight from a deep squat position. The reason for this is that in regimens without the eccentric, there is no preliminary muscle tension, which is needed for utilization of the stretch reflex.
From the research and practical experiences, doing combinations of muscle contraction regimens is the key to getting the greatest gains in muscle strength.
See Secrets of Soviet Sports Fitness and Training, for more details.