The purpose of the study is to compare the effect of two rehabilitation protocols with different emphasis on eccentric exercises after acute hamstring muscle strain injuries on the time to return to sports (RTS) and the rate of re-injuries in male athletes.

The hypothesis is that the addition of early eccentric hamstring exercises being performed at longer muscle-tendon length towards end range of motion alter the outcomes RTS and re-injuries in a rehabilitation protocol after acute hamstring muscle strain injuries.

Background and rationale:

Acute hamstring muscle strain injuries represent the most prevalent non-contact muscle injury reported in sports. Despite the high prevalence and a rapidly expanding body of literature investigating hamstring muscle strain injuries, [1] occurrence and re-injury rates have not improved over the last three decades [2]. Therefore, rehabilitation and secondary prevention are of particular concern, and the primary objective of all rehabilitation protocols is to return an athlete to pre-injury level as soon as possible with a minimal risk of injury recurrence.There is still a lack of consensus and clinical research regarding the effectiveness of various rehabilitation protocols for acute hamstring injuries in athletes participating in sports with high sprinting demands [3,4]. To our knowledge, there are no prospective, randomised trials investigating the effect of different rehabilitation protocols in a Middle-Eastern athletic population. Eccentric strength training has shown to reduce the risk of both new acute hamstring injuries as well as re-injuries [5,6], whereas hamstring exercises being performed at longer muscle-tendon length, preferentially mimicking movements occuring simultaneously at both the knee and hip are reported to be more effective than a protocol containing conventional exercises [7], and are suggested to be a key strategy in the management of hamstring injuries. However, the preventive effect related to the eccentric training remains unclear and is still debated and the optimal intensity of eccentric training in rehabilitation of acute hamstring strain injuries and prevention of re-injuries is yet unknown [8].

The primary objective in this study is therefore to compare the effect of two rehabilitation protocols after acute hamstring muscle strain injuries on the time to return to sports (RTS) and the rate of re-injuries in male athletes in a prospective single-site randomized controlled trial.

The investigators aim to include 90 male athletes with clinical signs and MRI abnormalities consistent with an acute hamstring muscle strain injury. The injured athletes will be randomised into one of two different rehabilitation protocols with unlike emphasis on eccentric exercises.

Inclusion Criteria:

• Male athletes

• Age 18-50 years

• Acute onset posterior thigh pain when training or competing, identified as:

  1. Patient reported sudden event
  2. Patient reported pain in posterior thigh

• Clinical diagnosis of an acute hamstring muscle strain injury, defined as:

  1. Localised pain during palpation of hamstring muscle
  2. Increasing pain during isometric contraction
  3. Localised pain when performing a passive straight leg raise test

• MRI confirmed isolated hamstring lesion (increased high signal intensity on fat saturated sequences)

• MRI performed ≤5 days from injury

• Available for ≥3 physiotherapy sessions per week at Aspetar

• Available for follow-up

Exclusion Criteria:

• Patients with verified or suspected previous hamstring injury within the last 6 months in the same leg
• Chronic hamstring complaints >2 months
• Grade III injury including complete hamstring disruption or avulsion of all tendons
• Contraindications to MRI
• Patients that do not have an intention to return to full sport activity
• Patients that do not want to receive one of the two therapies