TIBIALIS ANTERIOR FASCICLE LENGTH AND PENNATION ANGLE DURING SUBMAXIMAL CONCENTRIC, ECCENTRIC, AND ISOMETRIC ACTIONS

Abstract

Fascicle length (FL) and pennation angle (PA) change during isometric contractions as a function of joint angle and force. However, changes in FL and PA have not been investigated during dynamic movement. PURPOSE To measure in vivo FL and PA of the human tibialis anterior (TA) during concentric (CON), eccentric (ECC), and isometric (ISO) muscle actions using ultrasonography (US). Changes in FL and PA were compared between these three muscle actions at predetermined joint angles and force outputs. METHODS 13 subjects volunteered (23.0 ± 1.1 years, 5 males, 8 females). Subjects sat on a table with the hips at 90 deg, the tibia at a 45 deg angle from the femur, and the right foot secured to a custom designed footplate. A strin gaguge in the footplate measured the dorsiflexion maximum voluntary isometric contraction (MVIC) with the ankle at 90 deg. US images of the TA were recorded during ISO and dynamic (CON and ECC) contractions at 20% and 50% of MVIC. The subjects moved from 25 deg plantarflexion to 10 deg dorsiflexion for electromyographic (EMG) and US data collection. Images were then still framed at 5 deg increments to measure FL and PA. Average angular velocity across subjects during dynamic contractions was 12 deg/sec. EMG activity of the TA was recorded with surface electrodes at each angle, intergrated and averaged over ±2 deg to each angle, then normalized to the subject's MVIC. A multificatorial repeated measures ANOVA was used to analyze the results. RESULTS PA increased (42%) and FL decreased (31%) significantly from plantarflexion to dorsiflexion in each type of contraction. FL and PA at a given joint angle did not change as force production increased regardless of contraction type. There was no change in FL and PA across contraction types despite a significant EMG decrease of 39% in ECC actions and 49% in ISO actions when compared to CON actions. CONCLUSIONS Despite the significant difference in the level of TA muscle activation between the types of contractions, FL and PA are similar whether the muscle action is CON, ECC, or ISO.