Modeling Variability of Force During Isometric Contractions of the Quadriceps Femoris

Abstract

The authors modeled variability of force during continuous isometric contractions of the quadriceps femoris. Twenty adults (aged 25 ± 6 years old) performed isometric leg extensions Target forces were 11 percentages of maximum voluntary contraction (%MVC), ranging from 2 to 95%, and 5 absolute levels, from 25 to 225 N. The authors used standard deviation of absolute force, coefficient of variation, and signal-to-noise ratio as measures of variability. The results suggested a nonlinear relationship between variability and level of force, which could best be expressed as %MVC and not as absolute force. Variability for continuous isometric contractions was described best by a sigmoidal logistic function. The sigmoidal pattern of variability as a function of %MVC is consistent with physiological mechanisms.

Key Words:

• force variability
• isometric
• lower body
• modeling
• quadriceps femoris