Question

Which of the following is an example of an eccentric muscle contraction? a. Doing a "curl" with a dumbbell b. Doing a breast stroke in a swimming pool c. Extending the arms when bench-pressing a weight d. Flexing the arms when bench-pressing to allow the weight to return to the chest

Short answer

The best example of an eccentric muscle contraction among the given options is d. Flexing the arms when bench-pressing to allow the weight to return to the chest. In this phase, the pectorals and triceps lengthen while still under tension.

Step-by-step solution

Option (a) - Doing a "curl" with a dumbbell

During a bicep curl, the muscle primarily involved is the bicep. In the curl's upward phase (concentric contraction) when we are lifting the dumbbell, the bicep muscle shortens. During the downward phase (eccentric contraction) when we lower the dumbbell, the bicep muscle lengthens but is still under tension.

Option (b) - Doing a breaststroke in a swimming pool

In the breaststroke, the muscles of the arms, legs, and back are all engaged. During the recovery phase of the stroke (eclectic contraction), when the swimmer extends their arms forward, these muscles can lengthen under tension. However, since numerous muscles are involved and the stroke as a whole doesn't focus on eccentric muscle contraction specifically, it may not be the best example.

Option (c) - Extending the arms when bench-pressing a weight

When extending the arms while bench-pressing a weight, the main muscles involved are the pectoral and tricep muscles. During this concentric contraction phase, these muscles shorten as they lift the weight. In the opposite phase (eccentric contraction), when the arms are flexing, the muscles lengthen as the weight returns to the chest.

Option (d) - Flexing the arms when bench-pressing to allow the weight to return to the chest

When flexing the arms during bench-press and allowing the weight to return to the chest, the muscles that primarily lengthen under tension are the pectorals and triceps. This phase represents an eccentric muscle contraction as the muscles involved are lengthening while still under tension.

Conclusion

Out of the given options, the example that most clearly represents an eccentric muscle contraction is: d. Flexing the arms when bench-pressing to allow the weight to return to the chest

Key concepts

Muscle Physiology

Muscle physiology is the study of how muscles function and enable movement in the body. Muscles are highly specialized tissues that have the ability to contract and produce force. There are three main types of muscle tissues: skeletal, cardiac, and smooth. Each type performs unique roles in the body, but for our focus on eccentric muscle contractions, we'll concentrate on skeletal muscles.

Skeletal muscles are composed of long, fibrous cells called muscle fibers, which contain smaller units known as myofibrils. Myofibrils are packed with proteins like actin and myosin, which are crucial for muscle contraction.

• Actin and Myosin: These are the primary proteins involved in muscle contraction. Their interaction results in the sliding filament model, which describes how muscles contract and relax by sliding past one another.
• Sarcoplasmic Reticulum (SR): This organelle regulates calcium ions, essential for muscle contraction. The release of calcium from the SR triggers the interaction between actin and myosin.

Skeletal muscles can contract in three main ways: concentric, eccentric, and isometric contractions. Understanding these different types of contractions helps in designing effective training regimens.

Bench Press Exercise

The bench press is a popular training exercise that targets the upper body, particularly the chest, shoulders, and triceps. It involves lying on a bench, usually with weights held on a barbell above the chest, and lowering it towards the chest before pushing it back up to the starting position.

During the bench press, two main types of muscle contractions occur: concentric and eccentric. In the upward phase of the lift, where the weights are pushed away from the chest, the muscles perform concentric contractions, shortening as they generate the needed force. Conversely, in the downward phase, as the weights are lowered back to the chest, the muscles stretch while maintaining tension, which is characteristic of eccentric contractions.

• Core Muscles Involved: Major muscles include the pectoralis major, anterior deltoids, and triceps brachii.
• Safety Tips: Always use a spotter when lifting heavy weights to avoid injury.

Performing the bench press with proper form increases strength and muscle mass while also engaging stabilizer muscles that aid in balance and coordination.

Types of Muscle Contractions

Understanding different types of muscle contractions is fundamental in muscle physiology and exercise science. Each contraction type serves a specific role and has distinct characteristics.

• Concentric Contractions: This occurs when muscles shorten while generating force. An example is lifting a dumbbell during a bicep curl. The upward movement shortens the muscle as it works against resistance.
• Eccentric Contractions: These occur when muscles lengthen under tension, often seen when lowering weights back to the ground. As with the bench press, when lowering the barbell towards the chest, the pectorals and triceps undergo eccentric contractions.
• Isometric Contractions: This involves muscle tension without any visible change in muscle length. It can happen when holding a static position, such as maintaining a plank hold.

Eccentric contractions are particularly important in resistance training as they can increase muscle strength and size more effectively than concentric contractions alone. They can also minimize the risk of injury by improving muscle control and endurance.