Variability of human biceps brachii spinal stretch reflexes: Control conditions

Area of Science:

• Neuromuscular physiology
• Human motor control

Background:

• The variability of the human biceps brachii spinal stretch reflex (SSR) is not well understood.
• Previous research using tendon taps indicated significant variability in biceps SSR.

Purpose of the Study:

• To quantify the variability of biceps SSR elicited by rotational stretches within and across sessions in able-bodied individuals.
• To assess if four baseline sessions are adequate for comparison with intervening variables.

Main Methods:

• Ten able-bodied subjects underwent multiple baseline sessions (four initially, with five subjects continuing for eight additional sessions).
• Each session involved 250 rotational stretches, divided into five bins.
• Data analysis included calculating means, standard deviations, coefficients of variation, and using nested analysis of variance.

Main Results:

• Within-session variance was at least five times greater than day-to-day variability.
• Within-session coefficients of variation were approximately 60% during the baseline phase.
• Within-session variability increased in an extended baseline phase, while across-session variability remained stable.

Conclusions:

• Biceps SSRs elicited by rotational stretches exhibit substantial variability, particularly within sessions.
• Researchers must conduct multiple trials and sessions to obtain meaningful and reliable data on biceps SSR.
• The findings highlight the importance of considering within-session variability in experimental design.