Adaptations to Resistance
Training
Key Points
Eccentric muscle action adds to the total work of
a resistance exercise repetition.
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.
Key Point
Further research is needed to characterize the
adaptations to resistance training strategies that
incorporate extremely high intensity eccentric
muscle actions.
Introduction
Understanding the roles of concentric and
eccentric actions and the training adaptations
that they promote are important when designing
a resistance training program.
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.
Introduction
Many times, the muscle actions will be
predetermined by the choice of a particular type
of resistance training equipment.
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.
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.
Introduction
Such program design decisions should be
dependent upon specific program goals (e.g.,
strength gain versus strength maintenance) of a
resistance training program.
Muscle Actions
There are three types of muscle action:
isometric
concentric
eccentric
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.
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).
Muscle Actions
Note that a submaximal attempt to lift the barbell
would also produce an isometric muscle action.
Muscle Actions
A concentric muscle action is a dynamic action in
which the whole muscle shortens and joint
movement occurs.
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.
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.
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.
Muscle Actions
Both concentric and eccentric muscle actions
can be performed maximally or at specific
submaximal percentages of their respective one
repetition maximums (1RM).
Muscle Actions
Furthermore, the eccentric 1 RM is greater than
the concentric 1 RM.
Muscle Actions
It is important to note that most resistance
training programs involves exercises at some
percentages of the concentric 1 RM.
Muscle Actions
Thus, for each repetition, the percentage of the
eccentric 1 RM is lower than the percentage of
the concentric 1 RM.
Muscle Actions
This article primarily examines the influence of
eccentric muscle actions in resistance training
programs.
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).
Muscle Actions
Within a certain range of velocities, eccentric
actions develop greater force at faster velocities
of lengthening.
Muscle Actions
Force
Force - Velocity Curve
10
9
8
7
6
5
4
3
2
1
0
Force
8
6
4
2
0
Velocity
2
4
6
8
Muscle Actions
Several concepts emerge from an analysis of
figure 1.
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.
Muscle Actions
Second, force development for eccentric actions
attains a plateau at the greater velocities of
lengthening.
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.
Increasing Muscle Strength
One of the primary goals of most resistance
training programs is to increase the strength of
various muscles or muscle groups.
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.
Increasing Muscle Strength
Improved strength provides an individual with a
greater functional capacity.
Increasing Muscle Strength
It appears that a combination of concentric and
eccentric actions in resistance exercises
produces the greatest net gains in strength.
Increasing Muscle Strength
The mechanisms responsible for the significant
role of the eccentric component of resistance
training exercises are not clear.
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.
Increasing Muscle Strength
Further research is needed to clarify optimal
strategies of eccentric loading for different
muscle groups.
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.
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).
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.
Muscle Pain
As one becomes progressively better trained
with predominantly eccentric based exercises,
soreness and tissue damage are reduced.
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.
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.
Summary
Furthermore, concentric plus eccentric actions
better preserve strength during brief periods of
detraining than do training programs utilizing
only concentric muscle actions.
Summary
On the other hand, eccentric training using
exceptionally high resistance exercise has
produced mixed results on muscular
adaptations.
Summary
Further research is needed to determine the
efficacy of high force eccentric training with or
without accompanying eccentric actions.