Background Knee injuries often occur due to biomechanical factors such as knee joint laxity. Individuals with Generalised Joint Hypermobility (GJH) frequently have knee joint hypermobility. Thus, GJH has been proposed as an intrinsic risk factor for knee injuries in adults and adolescents. To potentially compensate for reduced passive joint stability, adequate neuromuscular knee joint control is required before and during loading of the lower extremities.

Objective To determine whether there is a difference in the neuromuscular pre and post activation landing patterns of the knee in adolescents with GJH and without GJH (NGJH) in the Single leg Hop for Distance test.

Design Case-control study with groups matched on age and sex.

Participants 54 adolescents (10–15 years), 25 with GJH and 29 with NGJH. GJH inclusion criteria were Beighton score ≥5/9 and hypermobility of at least one knee, and no current pain in the lower extremities.

Main outcome measurements EMG of Vastus Medialis (VM), Vastus Lateralis (VL), Biceps Femoris (BF), Semitendinosus (ST), Gastrocnemius Medialis (GM) and Lateralis (GL) of the most hypermobile knee for the GJH group was used to determine pre- and post impact activation levels in % MVE before and during landing of the Single leg Hop for Distance test.

Results Age and sex-adjusted analysis showed that GJH pre-activated ST 30% less compared with NGJH (22.1 (±12.6) vs 31.4 (±16.6.), P=.02). Conversely, GJH had a 28% higher GM pre-activity level than NGJH (32.5 (±14.8) vs 23.2 (±15.6), P=.02). There was no difference in performance (P=.67).

Conclusions Lower ST but higher GM pre-activation levels were found in adolescents with GJH and knee joint hypermobility compared with NGJH. This latter is likely a compensatory strategy to enhance joint stability. For adolescents with GJH and knee joint hypermobility, intensive knee injury preventive training could be important, focusing among others on the ST.