Hamstring strain injuries comprise a substantial percentage of acute musculoskeletal injuries incurred during sporting activities. They are the most prevalent muscle injuries reported in sport. Hamstring injuries account for between 6 and 29% of all injuries reported in Australian Rules football, rugby union, soccer, basketball, cricket and track sprinters (Mendiguchia and Brughelli, 2010). Participants in athletics, football and rugby are especially prone to this injury given the sprinting demands of these sports, while dancers have a similar susceptibility due, in part, to the extreme stretch incurred by the hamstring muscles. Hamstring strain re injury rates have been shown to be 12-30% (Mendiguchia and Brughelli, 2010). With some of world’s most high profile sportsmen including Lionel Messi, LeBron James, Darren Clarke and Ashley Cole recently being sidelined due to hamstring injuries it is still a major problem today. This post will aim to go through how hamstring strains occur and hamstring exercises to improve prevention and rehabilitation. Part 1 goes through the anatomy, mechanism and assessment of hamstring strain injuries. Part 2 goes through the best evidence based exercises to prevent and rehabilitate hamstring strain injuries.
The hamstring muscle group consists of the semimembranosus, semitendinosus and bicep femoris muscles. All three muscles originate from the ischial tuberosity apart from the short head of bicep femoris which originates from the linea aspera and lateral supercondylar ridge of the femur. The semimembranosus inserts onto the medial condyle of the tibia. The semitendinosus inserts onto the superior medial surface of the tibia and the oblique popliteal ligament and both heads of the bicep femoris muscle insert onto the head of fibular. All 3 muscles are innervated by the tibial nerve with the short head of the bicep femoris being innervated by the common peroneal nerve. The hamstrings have a fascial connection to the peroneus brevis muscle linking to actions at the foot and the ankle, and the sacrotuberous ligament linking it with the pelvis and thoracolumbar fascia (Hoskins and Pollard, 2005).
Mechanism of Injury
The hamstrings can be injured by two main mechanisms, a sprinting type injury, that occurs at high-speed running and/or acceleration or by a stretching type injury that occurs during movements with large joint stretch moments that include; high kicking, split positions and glide tackling. The late swing phase of running is when the hamstrings are most prone to injury during. Yu et al. (2005) suggested that hamstring muscles were at risk from a strain injury during the late stance phase as well as during the late swing phase. However, hamstrings may have higher risk for strain injury during the late swing phase than during the late stance phase because the lengths of the hamstring muscles are significantly longer during the late swing phase than during the late stance phase.
The Bicep femoris muscle is the most commonly injured of the three hamstring muscles. It has two different nerve supplies and it reaches the greatest length and also greatest increase in length when eccentrically decelerating the anterior displacement of the lower leg during high speed running. It is the most commonly injured muscle in sprinting type mechanisms which is sometimes associated with a eemitendinosus tear. The semimembranosus is the most commonly affected muscle in over stretching type mechanism hamstring strains.
In a recent literature review it was found that the most significant and consistent predisposing factors for getting a hamstring strain were: age, weight and previous hamstring injury. With more research needed to identify other predisposing factors including: quadriceps peak torque, hamstring flexibility, weight, hip flexor flexibility, ankle dorsiflexion ROM, hamstring peak torque, previous sacroiliac joint dysfunction and lumbar spine injury to determine whether they correlate fully with hamstring strain injuries (Freckleton and Pizzari, 2010).
They could feel a tear or a popping sensation at the back of their leg during high speed running, sprinting, change of direction, deceleration or kicking, overstretching activity. Sudden onset with pain and swelling on the posterior thigh.
Walking gait, functional tests
Clear joints above and below: Lumbar spine with active movements and passive overpressure if active is pain free. Pelvis and Ankle with active and passive range of motion
Active Range of Motion
Prone knee flexion; hip extension with the leg extended, will be painful, reduced strength
Straight leg raise (SLR); hip flexion with knee extension with internal and external rotation of the tibia, will show reduced ROM and pain
Passive Range of Motion
SLR with ankle in plantarflexion to limit neural involvement, will be painful, reduced ROM
Hip flexion with knee extension and internal / external tibial rotation
Manual Muscle Tests (MMT)
Knee flexion at 15 and 90 degrees of flexion with internal and external rotation of the tibia to help differentiate what muscle is injured
Hip extension with knee extended, could show reduced strength and pain
Palpation from ischial tuberosity down the muscle, most pain usually felt up to the musculotendinous junction and mid belly of the muscle.
This concept acknowledges the role that altered neural motion and physiology may have in the production of soft tissue dysfunction. During human motion the nervous system moves against adjacent tissue and is subjected to compressive and tensile forces. An alteration in the ability of the neural system to tolerate these forces has been suggested as a contributing factor in musculoskeletal dysfunction.
The patient lies supine and the clinician passively raises the patient’s leg, keeping the patient’s knee in extension. At the point of slight discomfort, the clinician adds in sensitising manoeuvres that further increase the mechanical and physiological stress on the neural tissue but which, theoretically, do not change the stress in the hamstring tissue.
These are: cervical ﬂexion, internal rotation of the hip and ankle dorsiﬂexion.
The patient sits on the edge of the couch. The clinician asks the patient to slump their spine whilst keeping their head up and looking forwards. The clinician then passively extends the patient’s knee to the point of mild discomfort. The clinician adds in sensitising manoeuvres that further increase the stress on the neural tissue but these are: cervical ﬂexion, internal rotation of the hip and ankle dorsiﬂexion.
These two neurodynamic tests are important in trying to resolve the issue of whether a patient’s posterior thigh pain/hamstring pain is hamstring or neural in origin.
(Hunter and Speed, 2007)
Posterior thigh pain from sciatic nerve damage
Piriformis syndrome causing radicular posterior thigh pain
Adductor strain; due to adductor magnus having a hamstring portion that shares the same origin at the ischial tuberosity and nerve supply from the tibial nerve.
Isokinetic Testing can be helpful in quantifying reductions in strength and differences in strength between injured and non injured hamstrings and eccentric hamstring / quadriceps ratio
MRI and Diagnostic Ultrasound to help determine size of lesions and whether full healing has occurred prior to return to play.
Hamstring Strain Classification
According to the Munich consensus muscle strains can be categorized into functional and structural strains (Mueller-Wohlfahrt et al. 2013). Functional strains show no physical signs of muscle fibre damage on ultrasound or MRI scans but present with increased hamstring tone on palpation and the person reporting a feeling of tightness in the posterior thigh. This type of injury normally resolves in a week with treatment consisting of methods to decrease hypertonicity, decrease swelling and increase function. On the other hand structural strains show muscle fibre damage on MRI and ultrasound, pain on palpation and take longer to resolve.