Interlimb asymmetries of lower limb isometric strength for predicting plantar fasciitis in male amateur marathon runners: a prospective cohort study.

Background: Plantar fasciitis (PF) is the third most common type of running-related injuries. However, there are few studies on the association between interlimb asymmetry of lower limb isometric strength and PF among marathon runners. The present study aims to investigate whether the interlimb asymmetry of lower limb isometric strength could predict PF in male amateur marathon runners.

Methods: 172 male amateur marathon runners were tested for lower limb isometric strength using the MicroFet 3 muscle testing dynamometer and inclinometer. The interlimb asymmetry of the lower limb isometric strength were calculated. Subsequently, the subjects were followed up for 3-month to record the incidence of PF. Statistical analysis was performed using independent-sample t test, logistic regression analysis and receiver operating characteristic (ROC) curve analysis.

Results: During the 3-month follow-up, a total of 12 runners experienced PF. The results of logistic regression analysis showed that the interlimb asymmetry of hip abduction isometric strength was significantly correlated with PF development (OR = 3.646; 95%CI:1.193-11.148; P = 0.023). The ROC curve analysis revealed that the area under the ROC curve was 0.717 (95% CI: 0.544-0.889, P = 0.012), and the sensitivity and specificity of the interlimb asymmetry of the hip abduction isometric strength for diagnosing PF were 0.667 and 0.238, indicating good discrimination. In addition, the Hosmer-Lemeshow fitting test showed that the model has statistical significance (X² = 14.365, P = 0.001).

Conclusions: The interlimb asymmetry of hip abduction isometric strength was associated with a greater likelihood of developing PF, and interlimb asymmetry of hip abduction isometric strength greater than 32.5% was a significant risk factor for the development of PF in male amateur marathon runners. The risk of PF occurence increased by 3.646 times if the interlimb asymmetry of hip abduction isometric strength greater than 32.5%. For clinicians, it is suggested to pay attention to the balanced development of bilateral muscle strength in the process of PF rehabilitation treatment, and regard the improvement of the interlimb asymmetry of hip abduction isometric strength as one of the rehabilitation therapies. Moreover, for runners and coaches, it is suggested that they should appropriately add unilateral or bilateral strength training (such as side-lying hip abduction training, clamshell exercise, supine bridge, etc.) in the daily training to ensure the balanced development of hip abduction strength, so as to prevent the occurrence of PF.