Tonic stretch reflexes in older able-bodied people

It is a general assumption that, in able-bodied persons, tonic stretch reflex (TSR) activity is not elicited during stretching of relaxed muscles and that the presence of TSR activity following brain damage is, therefore, indicative of spasticity. However, a variety of studies have reported age-related changes in reflex activity, raising the question of whether this assumption is justified in older subjects. The aim of this study was to determine if TSRs were activated in the relaxed elbow flexors of able-bodied people in an age-group at risk of stroke. Electromyographic (EMG) activity was recorded in 30 able-bodied subjects aged 46 to 78 years when their relaxed elbow flexors were subjected to ramp and sinusoidal stretches of different amplitudes and velocities. It was found that these subjects did not exhibit TSR activity under these conditions. Therefore, the practice of measuring TSR activity as a means of quantifying spasticity in stroke patients appears justified.