Reliability of a novel procedure to monitor the flexibility of lower limb muscle groups in highly-trained adolescent athletes

ObjectivesTo evaluate the reliability level of an innovative method using a standardized stretch force to assess the flexibility of lower limb muscle groups in highly-trained adolescent athletes and to examine whether interchanging the examiners affects the reliability of the measures.DesignRandomized test–retest study.Setting and participantsIn ten athletes, the flexibility of eight lower limb muscle groups was examined on two occasions on both sides and in two phases: a video capture by three distinct operators and an analysis by three distinct analysers. The reliability of the measures was assessed by the coefficient of variation (CV, 90% CI). Between-analysers and between-operators standardized differences (i.e., Cohen's d) were calculated.ResultsCV (%, 90% CI) were 8.3% (7.5; 9.3) for quadriceps, 3.3% (3.0; 3.7) for hamstrings, 7.2% (6.5–8.0) for adductors, 5.7% (5.1; 6.3) for gastrocnemius, 4.5% (4.0; 5.0) for soleus, 2.6% (2.3; 2.9) for hip flexors, 9.6% (8.6; 10.8) for hip medial rotators and 12.4% (12.2; 14.0) for hip lateral rotators. There was no substantial (i.e., Cohen's d < 0.2) difference in CV between all the possible operators/analysers combinations.ConclusionThis method has a moderate-to-good reliability level and is examiner-independent. It may be implemented in future injury prevention programs, in order to monitor the flexibility of highly-trained adolescent athletes.