What Is A Hamstring Injury?

Overview

Did you know hamstring muscles are three in number, just like the letters in “ham”? Place your palm on the back of your thigh, and glide your fingers across the length and breadth of that big muscle mass that’s your hamstrings.

The hamstrings are a group of three large muscles located at the back of the thigh. These muscles run from the hip to the knee. They play a crucial role in various movements involving the hip and knee joints.

The three hamstrings work together and aid in the extension (stretching straight) of the hip and in the flexion (bending) of the knee. Hence, they are called hip extensors (stretchers) and knee flexors (benders). The term "hamstring" also refers to the tendons that connect these muscles to the leg bones. These tendons are string-like bands of fibrous tissue.

The hamstring muscles are active and involved in everyday activities such as walking, climbing, running, and jumping. However, they are susceptible to injuries. 

Hamstring strain or pulled hamstring as it is sometimes called, occurs when one or more of the hamstring muscles are overstretched and begin to tear. Athletes are highly prone to hamstring muscle strains or muscle tears because of their frequent heavy use of these muscles.^1,3

How does hamstring injury occur?

The hamstrings consist of three big muscles — biceps femoris, semitendinosus, and semimembranosus at the back of the thigh. They run the length of the hip to the knee. These muscles help perform movements at the hip and knee joints. The three muscles work together in a coordinated manner to extend (stretch) the hip and flex (bend) the knee.

The term “hamstring” also refers to the string-like bands of tissues called tendons that attach these big thigh muscles to the bones of the leg.

Hamstrings are active during and play an important role in such activities as walking, climbing, running, and jumping. Athletes are highly prone to hamstring muscle strains or muscle tears because of their frequent heavy use of these muscles.^1,3

Hamstring injury is a condition in which one or more of the hamstring muscles or tendons are strained or torn. Hamstrings work to slowly reduce flexion (bending) of the hip and extension (stretching or straightening) of the knee. This facilitates the switch to their primary action to flex (bend) the knee and extend (stretch or straighten) the hip joint. When there is a disruption of the smooth transition between these two phases of muscle action, a strain or tear may result. 

A hamstring muscle strain occurs when the hamstrings lengthen at the same time as they are working hard to contract  (shorten to produce movement). Imagine you have a super stretchy spring. If you hang a heavy weight on it and slowly pull it down, the spring gets longer and stretches. The spring coils upward to resist the downward pull of the heavyweight, but because the weight is heavier, its downward force tends to overstretch the spring. This is how eccentric contraction works in muscles. When our muscles are working and trying to resist an opposing force, e.g., when holding something heavy, such as a backpack, and slowly lowering it to the ground, they get longer and overstretch, just like the spring. This eccentric contraction happens in hamstring muscles during abrupt stops and starts (such as those in movements involved in some sports manoeuvres), and if the force due to the weight of the body exceeds the resisting force produced by the hamstrings, it can result in hamstring muscle injuries.

A hamstring tear that involves one or two hamstring muscles is called a partial hamstring tear, while a tear that involves all three muscles is called a complete hamstring tear. 

The majority of hamstring injuries happen either in the thick, central region of the muscle known as the muscle belly or at the tapering ends of the muscle belly where the muscle fibres merge with the tendon fibres.

Grades of hamstring injury

Hamstring injuries are graded according to their severity.² All these grades are often observed in athletes and are listed below:

• Grade 1 – mild hamstring muscle pull or strain resulting in mild pain or swelling, with a recovery time of a few days. You may experience minimal pain or discomfort when you try using the affected leg
• Grade 2 – partial hamstring muscle tear with notable swelling and loss of function. You may experience pain when you move the affected leg
• Grade 3 – complete hamstring muscle tear with severe pain and significant swelling; there is loss of function with a recovery time lasting from a few weeks to months. Walking will be very difficult and may require the use of crutches

In cases of severe hamstring injury, an avulsion injury or hamstring tendon avulsion fracture can occur, which is when the tendon tears from its attachment completely, pulling a part of the bone along with it.

The healing curve and recovery time of a hamstring injury is dependent on the severity.

Causes of hamstring injury

The most common cause of hamstring injury is muscle overload, resulting from the overstretching of the hamstring muscles and/or tendons or the sudden introduction of a load as in sports involving abrupt and rapid starts and stops.² In sports involving sprinting, athletes commonly stretch out their hamstring muscles during movement. However, when they abruptly stop, they place the full weight of their bodies on these stretched muscles, which may lead to overstretching and ultimately cause hamstring injuries.⁴

The biceps femoris is the hamstring muscle most susceptible to strain or tear during sprinting because of its arrangement on the outside of the thigh. 

Signs and symptoms of hamstring injury

A grade 1 hamstring injury may not hurt much, but severe hamstring injury can be identified by the following cardinal signs and symptoms:

1. Pain during movement – pain accompanied by a popping sensation is felt at the back of the thigh during movements such as walking, jumping and running, making movement difficult and discomforting
2. Walking with a limp – during the shortening and lengthening of hamstring muscles, a hamstring injury elicits pain, which causes affected individuals to limp while walking
3. Swelling and bruising – there may be swelling of the back of the thigh after a few hours, along with a noticeable alteration in the skin colour, which manifests as a purplish or bluish patch
4. Tenderness – there is increased sensitivity when pressure is applied to the injured area, indicating inflammation or damage to the muscle tissue

Numbness, tingling, and weakness in the distal extremities (lower legs and feet) are symptoms that may occur infrequently. If this occurs, it warrants the additional examination necessary to investigate irritation of the sciatic nerve.

Management and treatment for hamstring injury

Mild and moderate hamstring injuries are managed without surgery by adopting the RICE 

(Rest, ice, compression, elevation) method within the first 3 to 5 days to control swelling, pain and any bleeding. Pain and inflammation can also be managed using non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen.

• Rest – the affected leg must be rested, and weight-bearing on it must be avoided as much as possible
• Ice – ice packs should be applied for up to 20 minutes every 2 to 3 hours to reduce pain and swelling. Ice should not be directly applied to the skin to avoid skin irritation and damage
• Compression – compress the back of the thigh using elastic bandages to minimise swelling and immobilise the affected area
• Elevation – raise the leg using a pillow support to reduce swelling

After carefully following the procedures above, physical therapy should then be used to slowly reintroduce movement and mobility to assist healing, recovery and rehabilitation.

Severe hamstring injury is managed surgically to restore the functionality of the torn muscle.⁶

The main aim of hamstring rehabilitation, or the management of the injury, is to restore muscle function as completely as possible, returning the affected leg as close as is achievable to the optimum level of performance it had before the injury. Management of hamstring injury is of paramount importance in sports medicine as it seeks to ensure the restoration of muscle full activity and minimise the risk of injury recurrence.¹

Diagnosis

Taking a comprehensive history and thorough physical examination helps in the accurate diagnosis of hamstring injuries. Severe hamstring injury may require imaging to determine an accurate diagnosis and assessment of injury severity and extent.

Risk factors

• Age – age has an impact on the flexibility and strength of muscle, and this influences the rate of hamstring injury and injury recurrence
• Previous injury – prior injury predisposes the hamstring muscle to future incidents of injury
• Sports involving sprinting - sports like football,⁵ basketball, and rugby predispose their players to hamstring injuries
• Tight or tired muscles – lack of muscle flexibility, as well as fatigued muscles, may result in hamstring injury 
• Muscle imbalance – when muscles in front of the thigh become disproportionately tighter or stronger relative to the hamstrings, this may lead to an imbalance of forces around the knee joint, resulting in hamstring muscle strain or tear

Complications of hamstring injury

The following complications are associated with hamstring injuries:

• Returning to play too soon is associated with long-term chronic hamstring pain and injury
• Hamstring syndrome can occur which is when scar tissue forms and compresses the sciatic nerve after the healing of a prior hamstring injury
• Reinjury is often associated with the presence of calcification and inflammation in the hamstring area following the initial injury²

FAQs

How can I prevent hamstring injury?

Do adequate warm-up exercises before physical activities. Also, strengthen and stretch hamstring muscles and surrounding muscles. Gradually increase the intensity and avoid overtraining.

How common is hamstring injury?

Hamstring injury is common among athletes who engage in frequent bouts of sudden rapid acceleration and deceleration, such as footballers, sprinters, basketballers, and rugby players. 

When should I see a doctor?

See a doctor if you think your injury is severe when your symptoms are getting worse or are not improving with time. If in any doubt, consult a physician.

Summary

The hamstrings comprise three large muscles at the back of the thigh. They are involved in hip and knee movements. Hamstring injuries can be mild (Grade 1), partial (Grade 2), or complete (Grade 3) tears. Rest, ice, compression, elevation, and physical therapy are common conservative initial treatments. Risk factors include age, previous injury, sports involving sprinting, muscle tightness, and muscle imbalances. Complications can include chronic pain, hamstring syndrome, and reinjury. Treatment and management include rest, physical therapy, medication, and, in severe cases, surgery.