Hamstring Curls: Concentric vs. Eccentric Contraction, Training Benefits, and Injury Prevention

What is the difference between a concentric and eccentric hamstring curl?

A concentric hamstring curl involves shortening the hamstring muscles as they contract to lift a weight, while an eccentric hamstring curl focuses on lengthening the hamstring muscles under tension as they control the lowering of that weight.

Understanding Muscle Contraction: The Foundation

To understand the difference between concentric and eccentric hamstring curls, it's essential to first grasp the fundamental types of muscle contractions. Muscles generate force through three primary actions:

• Concentric Contraction: The muscle shortens as it generates tension, overcoming resistance. This is the "lifting" phase of most exercises.
• Eccentric Contraction: The muscle lengthens under tension as it resists a load, acting as a "brake." This is the "lowering" or "negative" phase.
• Isometric Contraction: The muscle generates tension without changing length. This occurs when holding a position against resistance.

For the hamstring curl, we are primarily concerned with the concentric and eccentric phases. The hamstrings, a group of three muscles (biceps femoris, semitendinosus, and semimembranosus) located on the posterior thigh, are primarily responsible for knee flexion and hip extension. In a hamstring curl, their main action is knee flexion.

The Concentric Hamstring Curl: The "Lifting" Phase

A concentric hamstring curl is the action of actively shortening the hamstring muscles to bring your heels towards your glutes (or a pad towards your body).

• Action: As you initiate the movement, the hamstring muscles contract concentrically, shortening to pull the lower leg up against gravity or resistance.
• Force Production: The muscles are actively generating force to overcome the external load.
• Energy Expenditure: Concentric contractions are metabolically more demanding than eccentric contractions for the same amount of work.
• Training Focus: Primarily targets muscle hypertrophy (growth) and the ability to generate propulsive force. It's the most common focus in traditional strength training.
• Example: Lying hamstring curl machine: You push the pad towards your buttocks.

The Eccentric Hamstring Curl: The "Lowering" Phase

An eccentric hamstring curl is the action of slowly and controllably lengthening the hamstring muscles as you return your heels (or the pad) to the starting position.

• Action: The hamstring muscles are still under tension, but they are lengthening as they resist the force of gravity or the machine's resistance, preventing the weight from dropping quickly.
• Force Production: Eccentric contractions can generate significantly more force (up to 1.5 times more) than concentric contractions.
• Muscle Damage & Soreness: Eccentric contractions are known to cause greater microscopic muscle damage, which is a key stimulus for muscle growth and strength adaptation, but also leads to more delayed onset muscle soreness (DOMS).
• Training Focus: Highly effective for increasing muscle strength, hypertrophy, power, and critically, enhancing injury prevention, especially for hamstring strains.
• Example: Lying hamstring curl machine: You slowly and deliberately allow the pad to return to the starting position, resisting its descent. The Nordic hamstring curl is an advanced eccentric-focused exercise where you lower your body from a kneeling position, resisting the fall with your hamstrings.

Key Differences Summarized

Why Differentiate? Training Implications and Benefits

Understanding these differences is crucial for effective program design and achieving specific fitness goals.

• Enhanced Strength Gains: Eccentric training can lead to greater strength improvements, particularly in the ability to resist external forces. This translates to better control and stability.
• Superior Hypertrophy: Both concentric and eccentric contractions stimulate muscle growth, but the increased mechanical tension and muscle damage from eccentric training provide a potent stimulus for hypertrophy.
• Injury Prevention, Especially for Hamstrings: The hamstrings are notoriously prone to strains, particularly in sports involving sprinting and rapid changes in direction. Eccentric training, especially with exercises like the Nordic hamstring curl, significantly strengthens the hamstrings' ability to absorb force during lengthening, which is critical during the terminal swing phase of sprinting. This makes them more resilient to injury.
• Improved Power and Speed: Eccentric strength is a prerequisite for powerful concentric contractions. Stronger eccentrics allow for a more forceful stretch-shortening cycle, contributing to greater power output in activities like jumping and sprinting.
• Rehabilitation: Eccentric exercises are often incorporated into rehabilitation programs to rebuild strength and tissue resilience following injuries.

Incorporating Concentric and Eccentric Training

For most individuals, a balanced approach incorporating both concentric and eccentric phases within each repetition is ideal. However, there are specific strategies to emphasize one over the other:

• Standard Repetitions: Perform a controlled concentric lift (1-2 seconds) followed by a controlled eccentric lower (2-3 seconds). This balances both stimuli.
• Eccentric Overload:
  • Slower Negatives: Deliberately slow down the lowering phase of your hamstring curls (e.g., 4-6 seconds).
  • Supra-maximal Eccentrics: Use a weight that is heavier than you can concentrically lift, and have a spotter assist you with the concentric phase, then perform a slow, controlled eccentric lower. This is advanced and requires careful supervision.
  • Dedicated Eccentric Exercises: Incorporate exercises like the Nordic hamstring curl, where the entire movement emphasizes eccentric control.
• Concentric Emphasis: Explosively lift the weight during the concentric phase, then control the eccentric phase normally. This is often used for power development.

Conclusion

While often performed as a single, fluid movement, dissecting the concentric and eccentric phases of a hamstring curl reveals distinct physiological demands and training benefits. A concentric curl is about generating force to shorten the muscle, while an eccentric curl is about resisting force to lengthen the muscle under tension. Both are vital for comprehensive hamstring development, but eccentric training holds a unique and critical role in enhancing strength, promoting hypertrophy, and significantly reducing the risk of hamstring injuries, making it an indispensable component of any serious fitness regimen.