Hölmich 1999.

Methods	Study design: single‐blinded randomized controlled trial Setting: Clinic of Sports Medicine, Department of Orthopaedic Surgery, Amager University Hospital, Copenhagen, Denmark
Participants	N = 68 (exercise therapy group, n = 34; physiotherapy without active training group, n = 34) Athletes Age range: 18 to 50 years Gender: males Groin pain at least 2 months Desire to continue sports at the same level of competition as before the injury Pain at palpation of the adductor tendons or the insertion on the pubic bone, and during active adduction against resistance
Interventions	1. Exercise therapy (AT): 8 to 12 weeks; 3 times a week Module 1: first 2 weeks ‐ Static adduction against soccer ball placed between feet when lying supine (10 rep. of 30s, each) ‐ Static adduction against soccer ball placed between knees when lying supine (10 rep. of 30s, each) ‐ Abdominal sit‐ups both in straightforward direction and in oblique direction (5 series of 10 rep.) ‐ Combined abdominal sit‐ups and hip flexion, starting from supine position and with soccer ball between knees (5 series of 10 rep.) ‐ Balance training on wobble board (5 min) ‐ One‐foot exercises on sliding board, with parallel feet as well as with 90 angle between feet (5 sets of 1 min continuous work with each leg and in both positions)   Module 2: 2 to 6 weeks ‐ Leg abduction and adduction exercises performed in side lying (5 series of 10 rep. of each exercise ‐ twice) ‐ Low‐back extension exercises prone over end of couch (5 series of 10 rep. – twice) ‐ One‐leg weight pulling abduction/adduction standing (5 series of 10 rep. for each leg – twice) ‐ Abdominal sit‐ups both in straightforward direction and in oblique direction (5 series of 10 rep. – twice) ‐ One‐leg coordination exercise with flexing and extending knee and swinging arms in same rhythm (5 series of 10 rep. for each leg – twice) ‐ Training in sideways motion on mini‐skateboard (5 min) ‐ Balance training on wobble board (5 min) ‐ Skating movements on sliding board (5 sets of 1 min continuous work) 2. Conventional physiotherapy (PT): 8 to 12 weeks; twice a week ‐ Laser treatment with a gallium aluminium arsen laser. All painful points of the adductor‐tendon insertion at the pubic bone received treatment for 1 min, receiving 0·9 mJ per treated point. The probe was in contact with the skin at 90° angle. The laser was fitted with an 830 nm (±0·5 nm) 30 mW, diode beam divergence was 4° and area of probe head was 2·5 mm2 ‐ Transverse friction massage for 10 min on painful area of adductor‐tendon insertion into pubic bone ‐ Stretching of adductor muscles, hamstring muscles, and hip flexors. The contract‐relax technique was used. The stretching was repeated three times and the duration of each stretch was 30 s ‐ Transcutaneous electrical nerve stimulation was given for 30 min at painful area. The apparatus used was a Biometer, Elpha 500, frequency 100 Hz and a pulse width of one and a maximum of 15 mA (100% effect) Treatment was given or instructed by physiotherapists and in both groups a return to running program was done after 6 weeks.
Outcomes	Successful treatment ‐ No pain at palpation of the adductors tendon or during resisted adduction ‐ No pain in connection with or after athletic activity in the same sport and at the same level of competition ‐ Return to sports at the same level without groin pain If all three measures above were reached, the result was labelled excellent, if two measures were reached, the result was good, if one measure was reached, the result was fair and if no measures were reached, the result was poor. Patients' subjective global assessment Return to sports at the same level without pain Outcomes were evaluated at 16 weeks and long‐term (8 to 12 years) follow‐up.
Notes	‐ The participants from AT group were treated in groups with two to four patients, while in PT group the treatment was individual ‐ A longer‐ term follow‐up of Hölmich 1999 (8 to 12 years from the original study) was included (Hölmich 2011) ‐ Percentage of lost participants (follow‐up of 16 weeks): 13% (9/68); 5 losses from AT group and 4 from PT group ‐ Reasons for withdrawn (follow‐up of 16 weeks): knee injury (one patient); immigration to Australia (one); loss to follow‐up at 4 months (two); did not want the treatment they were assigned (two patients assigned AT); could not get sufficient time off from work to complete the study (three) ‐ Percentage of lost participants (follow‐up of 8 to 12 years): 31% (21/68); 10 losses from AT group and 11 from PT group ‐ Reasons for withdrawal (follow‐up of 8 to 12 years): 5 individuals could not be located; 4 because of lack of current address 1 because of emigration; 5 were not interested primarily because they would have to take time off work to attend the examination, and 2 could not participate because they had suffered serious disability due to an accident not related to their groin problem
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Patients were randomly allocated by sealed, opaque, and serially numbered envelope to AT or PT group by means of block randomisation (block size four)"
Allocation concealment (selection bias)	Low risk	Quote: "Patients were randomly allocated by sealed, opaque, and serially numbered envelope to AT or PT group by means of block randomisation (block size four)" Quote: "The examining physician was not involved in the randomisation procedure and remained unaware of the treatment allocation"
Blinding of participants and personnel (performance bias) All outcomes	High risk	Participants and physiotherapists could not be blinded to allocation treatment
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	While the examining physician was not involved in the randomization procedure and remained unaware of the treatment allocation, there were subjective outcomes (successful treatment and patients' subjective global assessment) assessed by the trial participants, who were not blinded
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	While the study participant flow was clear and the missing data were balanced across groups, with reasons for missing data provided, the characteristics of lost participants were not described. The analyses were not entirely 'intention to treat', nor were sensitivity analyses to address decisions regarding handling missing data. Quote: "The subjective global assessment of the effect of treatment in the two groups based solely on results from patients completing the study (per‐protocol analysis)"
Selective reporting (reporting bias)	Unclear risk	Function (an important primary outcome) was not evaluated. No protocol available.
Other bias	High risk	There was no explicit information about supplementary treatment and physical activity of participants during the follow‐up period (8 to 12 years).