Title : Association between eccentric knee flexor–extensor performance and knee proprioception in para-athlete runners with cerebral palsy
Abstract:
Background: Cerebral palsy is associated with neuromuscular impairments such as muscle weakness, spasticity, altered muscle-tendon properties, and impaired selective motor control, including alterations in flexor-extensor muscle synergies. Proprioceptive deficits have also been described and may affect the sensory information required for postural control, locomotion, and movement regulation. In para-athlete runners, these alterations may be particularly relevant because running requires continuous integration between muscle force production and joint-position information. At the knee, the hamstrings and quadriceps contribute to flexion and extension control, respectively; however, the relationship between their eccentric performance and proprioceptive accuracy in para-athlete runners with cerebral palsy remains insufficiently characterized.
Objective: To investigate the association between eccentric knee flexor and extensor performance and knee proprioceptive accuracy in para-athlete runners with cerebral palsy, with emphasis on differences between these muscle groups.
Methods: This observational, analytical, cross-sectional study included 17 male and female para-athlete runners with cerebral palsy evaluated at the Brazilian Paralympic Training Center in São Paulo, Brazil. Muscle performance was assessed using an isokinetic Biodex dynamometer. Eccentric knee flexor and extensor torque were analyzed at an angular velocity of 60°/s. Knee proprioception was assessed using a joint position sense test with a target angle of 45°, and proprioceptive accuracy was expressed as the absolute repositioning error. For participant-level analysis, torque and proprioceptive measurements were summarized as mean values per participant. The flexor-extensor torque difference was calculated as flexor torque minus extensor torque. Associations with proprioceptive error were examined using Spearman’s correlation coefficient. Flexor and extensor torque values were compared using the Wilcoxon signed-rank test, with statistical significance set at p < 0.05.
Results: Median eccentric knee flexor torque was 182.1 Nm (IQR 131.1–223.0), compared with 120.1 Nm (IQR 100.1–155.4) for eccentric knee extensor torque (p < 0.001). Eccentric flexor torque showed a significant negative correlation with absolute proprioceptive error (ρ = −0.626; p = 0.007), indicating that greater flexor torque was associated with lower repositioning error and, consequently, greater proprioceptive accuracy. In contrast, eccentric extensor torque was not significantly associated with proprioceptive error (ρ = −0.280; p = 0.277). The flexor-extensor torque difference was also significantly correlated with proprioceptive error (ρ = −0.521; p = 0.032), indicating that a greater difference in favor of flexor torque was associated with lower repositioning error.
Conclusion: Eccentric knee flexor performance was significantly associated with proprioceptive accuracy in para-athlete runners with cerebral palsy, whereas eccentric extensor performance was not. The significant association between the flexor-extensor torque difference and repositioning error further suggests that differences in eccentric performance between these muscle groups may be related to knee joint position sense. Given the small sample and cross-sectional design, these findings should be interpreted as exploratory and do not establish a causal relationship.
