Hamstrings: Seated, lying, or standing curl?

Hamstring training is essential, whether to increase their size, improve performance, or reduce the risk of injury. Do you train them with leg curls?

Although most of the hamstrings can be worked with hip-extension movements such as the deadlift, fully developing the muscle group requires knee flexion, as with a ham curl, but not all of these exercises are equal.

A little anatomy lesson

Because the short head of the biceps femoris does not cross the hip, the hip position involved in a knee-flexion exercise such as a leg curl will not influence its training response, but it will affect the other three tendons of the hamstring muscles.

The long head of the biceps femoris, the semitendinosus, and the semimembranosus cross the hip and knee joints and are biarticular muscles.

The monoarticular short head of the biceps femoris crosses only the knee joint and can be trained only through knee flexion.

Consequently, seated, lying, and standing leg curls will develop the short head of the biceps femoris similarly, but the seated position provides different benefits for the semitendinosus, semimembranosus, and long head of the biceps femoris.

The science of tension

This technical knowledge will help you understand the anatomy and physiology of movement and hamstring hypertrophy.

Tension is a primary determinant of the magnitude of hypertrophy and the improvement in strength induced by resistance training. Therefore, proper exercise selection should aim to maximize the tension experienced by the target muscle fibers.

The total tension experienced by a given muscle fiber is the sum of:

• The active force produced by the actin-myosin cross-bridge cycle.
• The passive force produced by the stretching of its elastic elements.

This ability of passive tension to contribute to total tension allows greater force to be produced when a muscle lengthens during an eccentric action than when it shortens during a concentric action or contracts statically during an isometric action.

 

What happens with the sarcomere

The sarcomere is each functional unit of a muscle fiber that contains thin actin filaments and thick myosin filaments.

The degree of overlap between actin and myosin determines how much active force a sarcomere can produce, and actin-myosin overlap is a function of sarcomere length.

• At very short or long sarcomere lengths, actin-myosin overlap is low, so little active force can be produced.
• At intermediate sarcomere lengths, actin-myosin overlap and active force production are greater.

However, because of the contributions of passive tension, total tension is greatest at fairly long sarcomere lengths, generally as is the case with the hamstrings.

As a sarcomere lengthens beyond an intermediate length, passive tension develops as titin, a spring-like protein named for its immense size, stretches considerably.

When initially moving from an intermediate length to a moderately long length, the rate at which active force production decreases is greater than the rate at which passive force production increases, resulting in a smaller net reduction in total tension.

When it lengthens further from a moderately long sarcomere length to a very long length, passive force production increases more rapidly than active force production decreases.

A net increase in total tension then occurs, allowing peak tension to develop at very long sarcomere lengths.

Repeatedly exposing muscle fibers to this peak tension while they lengthen can induce stretch-mediated hypertrophy, thereby facilitating greater muscle growth than could be produced by training at shorter lengths.

The best curl for the hamstrings

Because the biarticular hamstrings are both hip extensors and knee flexors, a position of simultaneous hip flexion and knee extension is required to train them at long muscle lengths, where total tension can be maximized.

Think about the position you are in during seated ham curls: your hips are flexed and your knees extend and bend.

In a lying or standing leg curl, where the hip is nearly in a neutral position, the biarticular hamstrings operate at moderate to short muscle lengths, where passive tension is minimal.

At the end of your concentric phases, when maximum knee flexion is reached, the biarticular hamstrings shorten at both the hip and knee joints.

• When shortened at both joints, a biarticular muscle's ability to produce active force may be impaired.
• This phenomenon, called active insufficiency, results from reduced actin-myosin overlap within the sarcomeres of the shortened muscle.

In contrast, in a seated leg curl, the flexed-hip position allows the biarticular hamstrings to operate at moderate to very long muscle lengths, where passive tension can develop and total tension can be maximized.

Research has demonstrated this by finding that peak knee-flexion torque is significantly greater in a seated position.

Over time, exposing the hamstrings to this greater magnitude of tension with the seated leg curl may produce greater gains in size and strength than could be achieved with the lying or standing leg curl.

Leg curls: is seated always better?

This ability of the exercise to achieve superior hypertrophy was demonstrated by a recent study by Maeo (2020).

The study compared 12-week leg-curl training interventions in which each subject had one limb assigned to the seated intervention and the contralateral limb assigned to the lying curl.

For each biarticular hamstring muscle, the increase in muscle volume with the seated curl was greater than with the lying curl.

The greatest difference was experienced by the long head of the biceps femoris, which showed an increase in volume with the seated curl that was more than twice that observed with the lying curl.

An earlier study by Guex (2016) also found that ham curls performed with a flexed hip produced greater strength gains than ham curls in a neutral-hip position.

In this study, the seated ham-curl group experienced an increase in peak eccentric knee-flexion torque that was approximately 39% greater than that of the supine group.

How to train your hamstrings

That said, this does not mean you should avoid standing and lying leg curls, since exercise variety is beneficial both psychologically and from the perspective of reducing the risk of injury.

The key is to spend most of your training time on exercise variations that produce the greatest benefits, and in this case, the seated leg curl is the best option for stimulating the hamstrings.