PT - JOURNAL ARTICLE AU - Einarsson, Einar AU - Thomson, Athol AU - Sas, Bart AU - Hansen, CLint AU - Gislason, Magnus AU - Whiteley, Rodney TI - Lower medial hamstring activity after ACL reconstruction during running: a cross-sectional study AID - 10.1136/bmjsem-2020-000875 DP - 2021 Mar 01 TA - BMJ Open Sport & Exercise Medicine PG - e000875 VI - 7 IP - 1 4099 - http://bmjopensem.bmj.com/content/7/1/e000875.short 4100 - http://bmjopensem.bmj.com/content/7/1/e000875.full SO - BMJ OPEN SP EX MED2021 Mar 01; 7 AB - Objective Anterior cruciate ligament reconstruction (ACLR) predisposes footballers for subsequent ACL and hamstring (HS) injury. This case series examines HS muscle activation patterns during the running in ACLR patients (bone-patellar tendon-bone (BTB) and (HS) graft) after completion of functional criteria allowing return to training.Methods Electromyography (EMG) recorded from medial and lateral HS bilaterally during treadmill running (12, 14 and 16 km/hour) from 21 male ACLR patients on average 7 months from surgery (5-9) that underwent (HS) (n=12) or BTB reconstruction (n=9) were compared with 19 healthy runners. Main outcome measures: EMG signal was normalised to peak during the running. Pairwise comparisons were made for each muscle group examining stance and swing activation for mean and peak EMG for each patient group and leg.Results Significantly lower relative peak activation in stance (not swing) phase for medial HS was seen for all conditions with effect sizes ranging from −0.63 (controls, BTB non-injured leg) to −1.09 (HS injured). For lateral HS only BTB injured were significantly lower in stance phase (−1.05)Conclusion ACLR patients show neuromuscular alterations during different phases of running. The finding of reduced medial HS activity in stance phase might have implications for knee instability and HS muscle injury on resumption of sport.