Gastrocnemius Muscle Pennation Variation

Open Access
Mendez, Laura Ximena
Graduate Program:
Master of Science
Document Type:
Master Thesis
Date of Defense:
December 17, 2014
Committee Members:
  • John Henry Challis, Thesis Advisor
  • Gastrocnemius muscle
  • pennation angle
Pennated muscles have their fibers attaching obliquely to their tendon forming an angle which is referred to as the pennation angle. Pennation angles change with muscle length, muscle force, and contractile velocity. The aim in this study was to further understand the function of pennation angle variations during different muscle actions of the gastrocnemius muscle in vivo. The direct action of the gastrocnemius muscle can cause ankle and knee motion. Both heads of the gastrocnemius were imaged in vivo using ultrasound during muscle actions in a dynamometer while ankle moments were recorded. These data were collected for twenty-four healthy subjects (age: 25.8 ± 5.2 years; mass: 68.0 ± 14.6 kg; height: 1.69 ± 0.12 m). Ultrasound images were taken at nine different ankle angles for maximal static plantar-flexions, and for three different angular velocities for dynamic contractions. Both tests were performed with the knee extended and the knee flexed. The ultrasound images were used to measure pennation angles during the static and dynamic tests. Analyses were performed to assess differences in pennation angle between ankle angles and between gastrocnemius heads in the static test, and between the static and dynamic tests. Correlations were analyzed between pennation angle and the inertial parameters of the shank, and ankle moments. A muscle model which included pennation angle in the calculation of tendon force was evaluated based on the experimental data. There were no statistically significant correlations between pennation angle and the segmental inertial parameters, or with normalized peak ankle moment at the two knee angles. Differences in ankle moments between the two knee conditions were not statistically significantly different. The model presented similarities with the experimental data with the knee flexed but not with the knee extended. The predicted ankle moments were higher compared with the experimental data with knee extended, and with the knee flexed the predicted moments were higher than the experimental data in plantar-flexion and lower in dorsi-flexion. Coefficients of variation presented small variability in pennation angle between subjects. Pennation angles between the gastrocnemius heads were not statistically significantly different for both knee conditions. Pennation angles in static and dynamic contractions presented statistically significant differences where in general larger pennation angles were found for the static conditions for all ankle angles. In some cases the lateral head presented larger pennation angles for the dynamic condition compared with the static condition. This study helped in the understanding of in vivo pennation angle changes and is the first study to examine pennation angles and segmental inertial parameters, and to compare pennation angle between static and dynamic conditions for different ankle angles within the normal ankle range of motion.