1. Adaptations to Resistance Training

2. Key Points Eccentric muscle action adds to the total work of a resistance exercise repetition.

3. Key Point The use of typical concentric-eccentric repetitions in heavy resistance training by using only concentric muscle actions, at least twice as many concentric-only repetitions may be required.

4. Key Point Further research is needed to characterize the adaptations to resistance training strategies that incorporate extremely high intensity eccentric muscle actions.

5. Introduction Understanding the roles of concentric and eccentric actions and the training adaptations that they promote are important when designing a resistance training program.

6. Introduction Changes in muscle size, strength, and power may all be affected by the choice of exercise employed, and particularly by the type(s) of muscle action(s) that are utilized.

7. Introduction Many times, the muscle actions will be predetermined by the choice of a particular type of resistance training equipment.

8. Introduction Accordingly, understanding the capabilities of various types of resistance equipment to train specific muscle actions is vital for the proper selection of the “tools” of resistance training.

9. Introduction The training adaptations that are achieved will be directly related to the decisions made regarding the muscle action(s) used during each repetition of an exercise.

10. Introduction Such program design decisions should be dependent upon specific program goals (e.g., strength gain versus strength maintenance) of a resistance training program.

11. Muscle Actions There are three types of muscle action: isometric concentric eccentric

12. Muscle Actions An isometric muscle action is one in which force is produced with no change in the length of the whole muscle and with no joint movement.

13. Muscle Actions An example of an isometric muscle action is attempting to lift from the floor a barbell that is too heavy to move (i.e., the maximal force produced by the muscles is less than the downward force of gravity on the barbell).

14. Muscle Actions Note that a submaximal attempt to lift the barbell would also produce an isometric muscle action.

15. Muscle Actions A concentric muscle action is a dynamic action in which the whole muscle shortens and joint movement occurs.

16. Muscle Actions Raising a barbell in an elbow flexion (curl) movement is an example of a concentric action of the biceps and other elbow flexors.

17. Muscle Actions Lowering the barbell in a controlled manner back to the starting point is an example of an eccentric muscle action of the biceps.

18. Muscle Actions In this case, the active muscle (e.g., biceps of the arm) is forcibly lengthened as it resists the force of gravity in lowering the barbell.

19. Muscle Actions Both concentric and eccentric muscle actions can be performed maximally or at specific submaximal percentages of their respective one repetition maximums (1RM).

20. Muscle Actions Furthermore, the eccentric 1 RM is greater than the concentric 1 RM.

21. Muscle Actions It is important to note that most resistance training programs involves exercises at some percentages of the concentric 1 RM.

22. Muscle Actions Thus, for each repetition, the percentage of the eccentric 1 RM is lower than the percentage of the concentric 1 RM.

23. Muscle Actions This article primarily examines the influence of eccentric muscle actions in resistance training programs.

24. Muscle Actions The maximal force a muscle can develop concentrically at a given length varies inversely with the velocity of the movement (i.e., the faster the velocity of movement, the lesser the maximal force that can be produced).

25. Muscle Actions Within a certain range of velocities, eccentric actions develop greater force at faster velocities of lengthening.

26. Muscle Actions

27. Several concepts emerge from an analysis of figure 1.

28. Muscle Actions First, maximal concentric muscle actions at any velocity always result in lower force development than do either maximal isometric or maximal eccentric contractions.

29. Muscle Actions Second, force development for eccentric actions attains a plateau at the greater velocities of lengthening.

30. Muscle Actions Third, maximal force production for concentric actions is greatest just below the isometric point on the curve (i.e., zero velocity); thus, a concentric 1 RM exertion for many exercise movements is a low speed exertion.

31. Increasing Muscle Strength One of the primary goals of most resistance training programs is to increase the strength of various muscles or muscle groups.

32. Increasing Muscle Strength Strength is defined as the maximal force or torque a muscle or muscle group can generate at a specified velocity of movement.

33. Increasing Muscle Strength Improved strength provides an individual with a greater functional capacity.

34. Increasing Muscle Strength It appears that a combination of concentric and eccentric actions in resistance exercises produces the greatest net gains in strength.

35. Increasing Muscle Strength The mechanisms responsible for the significant role of the eccentric component of resistance training exercises are not clear.

36. Increasing Muscle Strength Potential mechanisms include: an enhancement of neural adaptations with eccentric muscle actions caused by increased activation of the CNS, improved synchronization of motor units, and/or decreased input from neural inhibitory reflexes that limit strength in untrained subjects.

37. Increasing Muscle Strength Further research is needed to clarify optimal strategies of eccentric loading for different muscle groups.

38. Increasing Muscle Strength One of the major issues concerning maximal or near maximal eccentric training is the delayed muscle soreness and the tissue injury that accompanies such training.

39. Increasing Muscle Strength To minimize excessive muscle damage, there should be a slow progression in resistance as well as careful monitoring of the athlete’s perceived soreness when prescribing eccentric training against great resistance (I.e., 105-120% concentric 1 RM).

40. Strength Maintenance During a four week detraining period, strength was maintained above pre-training values only when both concentric and eccentric phases of the exercises had been employed during the training phase.

41. Muscle Pain As one becomes progressively better trained with predominantly eccentric based exercises, soreness and tissue damage are reduced.

42. Muscle Pain The mechanisms responsible for these adaptations remain speculative but may include better neural control of muscle actions, enhanced strength of muscle and connective tissue, and/or improved structural organization of the contractile elements within the muscle.

43. Summary Eccentric muscle actions appear to be crucial for optimal adaptations in muscle strength and hypertrophy in resistance training programs employing multiple set, 6-10 RM regimens in which both concentric and eccentric phases of resistance exercises are performed.

44. Summary Furthermore, concentric plus eccentric actions better preserve strength during brief periods of detraining than do training programs utilizing only concentric muscle actions.

45. Summary On the other hand, eccentric training using exceptionally high resistance exercise has produced mixed results on muscular adaptations.

46. Summary Further research is needed to determine the efficacy of high force eccentric training with or without accompanying eccentric actions.