Ultrasound Measurements of Hamstring Muscles Thickness Are a Valid Tool

X healthy volunteers, from an amateur football team, and X football players with previous history of hamstring injury from an orthopaedic clinic, comprised the subjects in this study. Hamstring muscle injury was defined as "a traumatic distraction or overuse injury to the hamstring muscle leading to a player being unable to fully participate in training or match play".

The Control Group (CG) were healthy, had neither surgery/trauma in their lower extremities, nor history of hamstring injury, and there were no abnormal findings in their physical examination. The exclusion criteria included participants who: (1) had metal implants or pace makers, (2) weighted more than 200 kg (MRI table limitations), and (3) were unable to complete testing. In the Injured Group, patients were also excluded if their previous injury was originated from a non-muscular source (e.g., inguinal or femoral hernia, nerve entrapment, lumbosacral pathology), or if still had symptoms, had not returned to practice and had not been participating in track and field since their last injury.

The Study Group (SG) had history and diagnosis of hamstring injury assessment with diagnosis image technique (ultrasound or MRI), and at least 2 of the next criteria: 1. When the injury happened disability to practise with the team at least one week; 2. Lost at least one match; 3. Felt pain when trying to kick the ball or run fast; 4. Receive specific treatment (medical or physiotherapy) for the injury; 5. Needed a period plan to return to play.

Participants were screened for contraindications to MRI before ultrasound assessment and an MRI scan of the hamstring muscles of both legs were performed. MRI was performed within 24 h of the ultrasound scan. The subjects were instructed not to consume alcohol or perform any moderate to heavy exercise for 24 hours prior to each imaging session.

Muscle thickness was defined as the distance between the bone-muscle interface and the adipose tissue-muscle interface. The measurement was made from the most superficial edge of the bright line representing the interface of the bony cortex and the muscle to the most superficial edge of the bright line representing the interface of the outer fascial layer of the muscle and the subcutaneous adipose tissue. When the bone was not in contact of the muscle the two fascial layer were used.