Differences in quadriceps but not hamstrings strength in runners with varying durations of patellofemoral pain

Patellofemoral pain (PFP) is a common injury among runners. The quadriceps and hamstrings strength in patients with different durations of PFP is still unclear. The purpose of this study is to evaluate the isokinetic strength characteristics of quadriceps and hamstrings and the symmetry of muscle strength in runners at different stages of PFP, providing a theoretical basis for the prevention and rehabilitation of PFP.

Ten patients with a short PFP duration (short-term group, <3 months), eleven patients with a long PFP duration (long-term group, >12 months), and sixteen healthy runners (control group) participated. Bilateral quadriceps and hamstrings isokinetic strength data were collected from all individuals. A one-way ANOVA was performed to evaluate the effect of disease duration on knee joint isokinetic strength and the strength symmetry index.

The short-term group had significantly lower peak quadriceps torque than the long-term (P = 0.009) and control groups (P = 0.015). However, peak quadriceps torque did not significantly differ between the long-term and control groups (P = 0.639). The strength symmetry index of the quadriceps (P = 0.250) and hamstrings (P = 0.541), as well as the peak torque of the hamstrings (P = 0.087), did not differ significantly across the three groups. No significant differences in the H/Q ratio among the short-term group, the long-term group, and the control group (P = 0.440).

Quadriceps strength varied across stages of PFP, with individuals in the short-term group showing weaker strength than the healthy, while those in the long-term group exhibited strength comparable to the healthy. Runners with different durations of PFP demonstrate little difference in hamstring strength, H/Q ratio, and muscle symmetry from healthy.