Adaptations to Resistance Training

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. Muscle Actions • 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.