Submitted on September 19, 2006
Accepted on March 6, 2007
Changes in stretch reflexes and muscle stiffness with age in prepubescent children
Jean-Francois Grosset1, Isabelle Mora2, Daniel Lambertz1, and Chantal Perot3*
1 Genie Biologique, Université de Technologie de Compiègne, Compiegne, France
2 UFR STAPS, Université de Picardie Jules Verne, France
3 Genie Biologique, Université de Technologie de Compiègne, France
* To whom correspondence should be addressed. E-mail: chantal.perot{at}utc.fr.
Musculo-articular stiffness of the triceps surae (TS) increases with age in prepubescent children, under both passive and active conditions. This study investigates whether these changes in muscle stiffness influence the amplitude of the reflex response to muscle stretch. TS stiffness and reflex activities were measured in 46 children (7 to 11 years old) and in 9 adults. The TS Hoffmann reflex (H reflex) and T reflex (tendon jerk) in response to taping the Achilles tendon were evaluated at rest and normalized to the maximal motor response, Mmax. Sinusoidal perturbations of passive or activated muscles were used to evoke stretch reflexes and to measure passive and active musculo-articular stiffness.
The children s Hmax/Mmax ratio did not change with age and did not differ from adult values. The T/Mmax ratio increased with age but remained significantly lower than in adults. Passive stiffness also increased with age and was correlated with the T/Mmax ratio. Similarly, the children's stretch reflex and active musculo-articular stiffness were significantly correlated and increased with age.
We conclude that prepubescent children have smaller T reflexes and stretch reflexes than adults, and the lower musculo-articular stiffness is mainly responsible for these smaller reflexes, as indicated by the parallel increases in reflex and stiffness.
