Strains in the hamstring muscle or muscles are caused by extensive contraction or a violent stretch that happens too quickly. It is a type of mechanical stress that results in varying degrees of muscle rupture.  

Hamstring strains are common in dynamic sports like sprinting, jumping, water-skiing, and bull riding and are very common in other contact sports like football and soccer. Injuries usually happen in a fully extended knee.

Hamstring tendonitis is the most common lesion in long-distance runners and other sports that involve hurdles or sprinting activities. Other sports like football and hockey, which involve a rapid change of direction, also present hamstring tendonitis.

Hamstring tendonitis may present with tendon degeneration, partial tearing, and inflammatory reactions in the areas surrounding the tendon. Most often, it occurs at the proximal end of the ischial tuberosity of the pelvic bone. That is why the condition is also called insertional tendinopathy or tendonitis.

When the hip is in flexion or adduction, the tendon gets compressed, leading to tendonitis in high-risk cases. Repetitive trauma due to friction between the hamstring attachment and the ischial tuberosity is also a contributing cause.

Anatomy of the hamstrings

A hamstring is a group of three muscles;

• The biceps femoris
• The semitendinosus
• The semimembranosus

The hamstrings muscle group is the most important in running. They actively participate at various stages while walking and running by performing knee flexion and hip extension.

The hamstrings muscles originate from a common point on the lateral side of the ischial tuberosity, a bony prominence of the hip bone.

The semitendinosus and the long head of the biceps femoris from a conjoined tendon. At the same time, the semimembranosus lies deeper and is one of the most commonly affected parts of the proximal hamstring tendinopathy.  Other tendons of the hamstrings are also affected by tendonitis; the common hamstring tendon, biceps femoris, and semitendinosus.

High hamstring tendinopathy affects the junction between the tendons of the hamstrings and the ischial tuberosity.  Factors like tendon thickness, fibrous nature, and poor blood supply impede healing at this locale.

Hamstrings perform three functions during running.

• They keep a check on knee extension when the knee moves forward, usually at the end of the forward swing phase during walking.  This is done via an eccentric contraction, and it helps to stabilize the weight-bearing knee joint.
• The hamstrings elongate at foot strike and facilitate hip extension through an eccentric contraction. This helps to add more stability to the leg when it comes to weight-bearing.
• The hamstrings assist another muscle, the gastrocnemius, in knee extension during the take-off phase of the running cycle.

Causes of a hamstring strain and tendonitis

Some of the causes of hamstring strain include;

• Extreme stretching or overload during a sporting event like soccer, football, and ice hockey
• Any history of a past hamstring injury
• Overtraining of the hamstrings
• Poor flexibility of the hamstrings
• Increased fatigue
• Strength imbalance in the lower limb
• Weak abdominal muscles leading to unstable core
• Tightness of the hip flexors
• Any history of abnormalities in the lumbar spine

In the second half of the swing phase of running, the hamstrings are stretched to their maximum limit and exhibit great tension. At this stage, the hamstrings contraction acts to cut back the hip and leg extension flexion. The hamstring muscle fibers are at their maximum functioning limit at this point.

To avoid injury, the hamstrings need to contract, and the quadriceps needs to relax. Failure of this step while high-speed running can cause muscle tears in the hamstrings affecting the biceps femoris on most occasions.

During running and kicking, hip flexion and knee extension accompany the lengthening of the hamstrings. As a result, the action may surpass the mechanical limits of the muscle, causing a micro-trauma or result in micro-trauma due to the accumulation of microscopic muscle damage.

The difference in the musculature of the biceps femoris is also suggested to play a part in a hamstring strain.

The Biceps femoris has two heads. The short head has longer muscle fibers which make the muscle extensible. The longer fibers also reduce the risk of over lengthening during eccentric contraction. In contrast, the long head of the biceps femoris has shorter fibers which are more prone to undergo repetitive lengthening resulting in added muscle damage.

Similarly, an excessive anterior pelvic tilt results in elongation of the hamstrings, increasing the risk of strain.

The hamstring strain is a mechanical stress injury, while tendinopathy of the muscle-tendon is related to load. The tendinopathy usually starts with micro-trauma without considerable damage. However, predisposing factors can cause further damage and failed healing contributing to tendinopathy.

Some causative factors for hamstring tendinopathy include;

• Overload due to an increase in training volume
• Overload owing to training errors
• an increase in the intensity of exercise
• Excessive static stretching as may happen in yoga or Pilates
• Extended periods of sitting

Some risk factors that predispose to hamstring tendinopathy include;

• Mal-alignments of the musculoskeletal elements
• Length difference of leg
• Imbalance
• Decreased flexibility
• Joint laxity
• Female gender
• Aging
• Overweight and obesity
• Core weakness
• Pelvic dysfunction
• Previous injury of the hamstrings, knee, or groin area
• Hip stiffness
• Tightness or weakness of the hamstrings and quadriceps
• Poor core stability
• Sciatic nerve irritation.
• Inefficient sport equipment
• Insufficient warm
• Fatigue

Signs and symptoms of hamstring strains and tendonitis

Hamstring strain present as;

• Sudden pain in the back of the thigh
• The pain may be minimal or severe depending on the injury
• A "popping" or tearing sensation at the time of injury
• Swelling and bruising of the affected site; immediately after the injury or after some days
• Numbness and tingling of the affected side
• Weakness of the muscles on the affected side
• Tenderness of the affected thigh
• Limited mobility

Hamstring strains are of three grades depending on the amount of pain, weakness, and loss of motion.

Grade 1

• Minimal damage involving few muscle fibers
• The pain appears few days after the injury
• Stiffness on the posterior side of the leg
• Small localized swelling
• Walk is normal

Grade 2

• Half of the muscle fibers are torn
• Acute pain and swelling on the affected side
• Mild function loss on the affected side
• Walk is disturbed  
• Pain on applying pressure on the hamstring or bending the knee against resistance

Grade 3                                                                                                                  

• More than half or complete rupture of the muscle fibers
• Both the muscle belly and the tendon are affected
• Massive swelling
• Severe pain
• Functional loss

The hamstring tendonitis presents as a gradual development of symptoms;

• Pain felt in deep buttocks in the posterior thigh area
• Pain may be felt lower in the gluteal area that radiates along with the muscle
• Pain gets worse on activities that involve hip flexion, for example; squats, lunging.
• Pain is also worse after long periods of sitting, especially on harder surfaces.
• Occasional morning stiffness in the thigh

Diagnosis of a hamstring strain and tendonitis

History of presenting complaints indicates the type of injury, whether arising in muscle or its tendon. X-rays, MRI scans confirm the diagnosis.

On examination, a patient with a strain injury exhibits a shortened walking gait. In addition, swelling and bruising may appear after few days of initial injury in strain.

MRI confirms the diagnosis of tendonitis and is often a necessary test to evaluate the severity of the injury. Tendon thickening, tearing, inflammation, and swelling at the ischial tuberosity can be detected with MRI.

Some tests for tendonitis of the hamstring include;

• Passive Stretch Tests
• Bent-knee stretch test
• Modified bent-knee stretch test

Treatment of hamstring strain and tendonitis

Hamstring strain injuries have a high incidence and recurrence rate with slow healing and persistent symptoms. That presents a challenge for both the athlete and the doctor.

1. Immediately after the injury to few days

1. RICER
2. Medication

Oral NSAIDs, corticosteroid injections, platelet-rich plasma infusions are some medical management techniques.

• TENS
• Surgery

Surgical intervention is rarely required for a hamstring strain, only recommended for complete rupture of the muscle.

Extracorporeal shockwave therapy (ESWT) is also effective as an alternative therapy module.

• After few days to weeks, when symptoms start to resolve

• Massage

Deep stripping massage used as rehabilitation for a hamstring strain is effective at restoring strength. It is done in conjunction with other treatment modules.

• Therapeutic ultrasound

Therapeutic ultrasound is effective for strain as well as tendonitis. It helps to heal and speeds up recovery.

• Active rehabilitation

The primary objective of physical therapy and the rehabilitation program remains the same; that is

• restoring the patient’s functions to the highest degree possible
• returning to the sport with minimal risk of recurrence

A rehabilitation program aimed at improving agility with trunk stabilization exercises is more effective than a program targeting isolated hamstring stretching and strengthening.  

Similarly, the use of load management techniques is important in rehabilitating tendonitis. Resistance training principles along with optimal loading should be applied.

The physical therapist should monitor pain every day with a load test. Though some pain is acceptable during the exercise, it should settle within 24 hours. Progression of symptoms throughout the load training program is not a good indicator.

Treating every patient as an individual is important where the focus should remain on the patient's symptomatic response.

Stage 1: Isometric hamstring load

Isometric load exercises without tendon compression are an effective strategy to load the muscle-tendon unit. These exercises also help to reduce pain in proximal hamstring tendinopathy.  The isometric exercises should be repeated several times every day instead of the severity of symptoms. 

Some appropriate isometric exercises for hamstring tendinopathy include;

• Isometric leg curl

Here is how to do a standing hamstring curl:

Stand with your feet at a width of your hips.

Take support by placing your hand on your waist or a chair.

Begin by shifting your weight onto one of your legs.

Slowly bend you’re the knee of your other leg so that your heel touches your buttocks.

Keep your thighs parallel, and do not mis-align them.

Lower your heels back to the starting position.

Complete at least fifteen reps.

Repeat with the other leg.

• Bridge holds
• Isometric straight leg pulldowns
• Trunk extensions
• Isometric, long leg bridging on two followed by one leg holds

Stage 2: Isotonic hamstring load with minimal hip flexion

Isotonic hamstring loading is started when the pain has resolved to a minimum or nil. Heavy Slow Resistance training (HSR) is suggested that includes eccentric and concentric elements.

Some important exercises in this regard include;

• Single-Leg Bridge

Lay on your back on the floor and keep your hands by your sides.

Bend your knees and keep your feet flat on the floor.  Make sure to keep your feet in line with your knees.

Tighten your abs and muscles of the butt.

Now slowly raise your hips so that they are in line with your knees and shoulders.

Focus on squeezing your core by pulling your belly button towards your spine.

Now slowly raise one of your legs and extend it. Keep your pelvis raised and leveled.

Hold the position.

Return slowly to the starting position keeping your knees bent all the while.

Perform the leg bridge lift with the other leg.

• Prone hip extension
• Prone leg curl
• Nordic hamstring exercise
• Bridging progressions
• Supine leg curl

Stage 3: Isotonic exercises in increased hip flexion at 70° - 90° degrees

Slow and controlled movements are important at this stage. Some exercises include;

• Slow hip thrusts
• Forward step-ups
• Walking lunges
• Deadlifts
• Romanian deadlifts

Hold a bar using an overhand grip. Keep the bar at the level of your hips.

Keeping your back straight, draw your shoulders back.  

Now slowly lower the bar downwards as you push your hips back.  

Come back to the standing position slowly and keep the bar at your thigh level.

Stage 4: Energy storage loading

These exercises are required for patients and athletes who need to return to sports that involve lower limb energy storage or impact loading.

Steady movements with limited hip flexion are adopted. A conservative approach is applied that includes performing exercises on every third day only. Exercises in this stage include;

• Sprinter leg curl
• A-skips
• Fast sled push or pull
• Alternate leg split squats
• Bounding
• Stair or hill bounding
• Kettlebell swings
• Lateral, rotational cutting movements

Prevention of hamstring strains and tendonitis

To prevent hamstring tendonitis and strain recurrence;

• Sports activities should be switched with cross-training exercises or should be adapted to reduce the load. For example, cycling (if the patient tolerates a standing position), swimming, water running, etc.
• Learn to adopt proper posture and form during physical activity and daily life.
• Use shaped cushions to avoid compression on extended sitting.
• Perform regular exercise to maintain cardiovascular and muscle health.
• Warm-up before work out or and cool down after physical activities.
• Perform stretching and strengthening exercises regularly to prevent muscular imbalance.
• Take adequate rest.