Insulin growth factors may explain relationship between spasticity and skeletal muscle size in men with spinal cord injury

The major objectives of this cross-sectional study were to (1) measure insulin-like growth factor-1 (IGF-1) in individuals with complete spinal cord injury (SCI) and spasticity and (2) determine the relationships between IGF-1 and cross-sectional areas (CSAs) of thigh skeletal muscle groups. Eight individuals with motor complete SCI underwent magnetic resonance imaging to measure the CSA of the whole thigh, knee extensor, and knee flexor skeletal muscle groups and dual-emission X-ray absorptiometry to measure fat-free mass. After participants fasted for 12 h, we measured their IGF-1 levels and determined spasticity using the Modified Ashworth Scale (MAS). Spearman rho correlations were used to test for the relationships among the tested variables, and independent t-tests were used to determine the difference in plasma IGF-1. Plasma IGF-1 was 44% greater in those with MAS scores of 2 or higher (p < 0.05). Plasma IGF-1 was positively related to knee extensor skeletal muscle CSA (r = 0.83, p < 0.01). IGF-1 was strongly related to knee extensor and flexor spasticity (r = 0.88,p < 0.004). The findings suggest that IGF-1 is greater in SCI individuals with increased spasticity, and this may explain the strong positive relationships that were noted between spasticity and skeletal muscle CSA.