Muscle contractions are the foundation of human movement and strength. Among the various types of contractions, eccentric and concentric muscle contractions play a significant role in exercise performance, rehabilitation, and daily activities. Understanding the differences between these two types of contractions is crucial for optimizing training strategies and improving muscle function.
What Are Eccentric and Concentric Contractions?
Eccentric Contraction: This occurs when the muscle lengthens under tension. For example, when lowering a weight during a bicep curl, the biceps muscle performs an eccentric contraction.
Concentric Contraction: This occurs when the muscle shortens while producing force. For instance, lifting a weight during a bicep curl involves concentric contraction of the biceps.
Key Characteristics of Eccentric and Concentric Contractions
Force Production: Eccentric contractions produce more force compared to concentric contractions under the same conditions.
Energy Efficiency: Eccentric contractions are more energy-efficient than concentric contractions, as they require fewer motor units to generate the same amount of force.
Muscle Damage: Eccentric contractions are more likely to cause muscle microtrauma, leading to delayed onset muscle soreness (DOMS). However, this microtrauma is a stimulus for muscle growth.
Strength Development: Concentric contractions are associated with improved muscle strength, while eccentric contractions contribute significantly to muscle hypertrophy and control.
Exercise Load and Strength Gain
Force and Load: Maximum concentric contraction produces less force than maximum eccentric contraction under the same conditions. This is why greater loads can be lowered than lifted.
Lowering a Load (Eccentric Contraction): When a load is lowered, the force exerted by the external load is controlled by both the active contractile components and the non-contractile components of the muscles.
Lifting a Load (Concentric Contraction): When a load is lifted, the force exerted by the external load is controlled only by the active contractile components of the muscles.
Motor Inputs: Concentric contractions require a higher number of motor inputs to control the same load compared to eccentric contractions.
Load Handling: When a load is lifted and lowered, maximum resistance during concentric contraction does not equate to maximum load during eccentric contraction.
Velocity and Its Impact
Effect of Velocity: The velocity of a segment directly affects the force-generating capacity of the neuromuscular unit.
Isometric Phase: When external resistance provides zero velocity, the contraction is isometric.
Concentric Contraction:
When resistance is slightly decreased, concentric contraction begins with slow velocity and high tension.
As resistance decreases further, concentric contraction occurs with high velocity but lower tension.
Eccentric Contraction:
When resistance increases, eccentric contraction starts with slow velocity and high tension.
Misconception About Eccentric Phases: There is a misconception that lifting weights quickly and lowering them slowly increases strength due to greater tension. However, the reality is that the load is constant, and less tension is generated during the eccentric phase. The only way to increase strength during eccentric contraction is by increasing the weight.
Cross-Training Effect
Definition: A slight increase in strength over time in the same muscle group of the contralateral unexercised extremity.
Mechanism: This can occur due to repeated contractions of the unexercised extremity to stabilize the body during high-effort exercises.
Limitations: No evidence suggests that this effect positively influences individual performance significantly.
Exercise-Induced Muscle Soreness
DOMS: Repeated and rapidly progressed high-intensity eccentric exercises can lead to Delayed Onset Muscle Soreness (DOMS).
Cause: DOMS occurs due to greater damage to the muscle and connective tissue when heavy loads are controlled and lowered.
Applications in Training and Rehabilitation
Incorporating both eccentric and concentric contractions in training regimens can enhance overall muscle function. For example:
Eccentric Training: Used to improve muscle control and prevent injury. It is commonly employed in rehabilitation programs, particularly for tendon injuries.
Concentric Training: Focused on building muscle strength and explosiveness. It is widely used in sports performance training.
By strategically combining these two types of contractions, individuals can achieve a well-rounded approach to strength and conditioning.
Stay tuned for more insights and principles related to eccentric and concentric muscle contractions. Next, we will explore advanced strategies and practical applications for different populations, from athletes to rehabilitation patients.
