In vivo measurements of the triceps surae complex architecture in man: implications for muscle function

Abstract

The objectives of this study were to (1) quantify experimentally in vivo changes in pennation angle, fibre length and muscle thickness in the triceps surae complex in man in response to changes in ankle position and isometric plantarflexion moment and (2) compare changes in the above muscle architectural characteristics occurring in the transition from rest to a given isometric plantarflexion intensity with the estimations of a planimetric muscle model assuming constant thickness and straight muscle fibres. The gastrocnemius medialis (GM), gastrocnemius lateralis (GL) and soleus (SOL) muscles of six males were scanned with ultrasonography at different sites along and across the muscle belly at rest and during maximum voluntary contraction (MVC) trials at ankle angles of −15 deg (dorsiflexed direction), 0 deg (neutral position), +15 deg (plantarflexed direction) and +30 deg. Additional images were taken at 80, 60, 40 and 20 % of MVC at an ankle angle of 0 deg. In all three muscles and all scanned sites, as ankle angle increased from −15 to +30 deg, pennation increased (by 6–12 deg, 39–67 %, P < 0.01 at rest and 9–16 deg, 29–43 %, P < 0.01 during MVC) and fibre length decreased (by 15–28 mm, 32–34 %, P < 0.01 at rest and 8–10 mm, 27–30 %, P < 0.05 during MVC). Thickness in GL and SOL increased during MVC compared with rest (by 5–7 mm, 36–47 %, P < 0.01 in GL and 6–7 mm, 38–47 %, P < 0.01 in SOL) while thickness of GM did not differ (P > 0.05) between rest and MVC. At any given ankle angle the model underestimated changes in GL and SOL occurring in the transition from rest to MVC in pennation angle (by 9–12 deg, 24–38 %, P < 0.01 in GL and 9–14 deg, 25–28 %, P < 0.01 in SOL) and fibre length (by 6–15 mm, 22–39 %, P < 0.01 in GL and 6–8 mm, 23–24 %, P < 0.01 in SOL). The findings of the study indicate that the mechanical output of muscle as estimated by the model used may be unrealistic due to errors in estimating the changes in muscle architecture during contraction compared with rest.

Can pennation angles be predicted from EMGs for the primary ankle plantar and dorsiflexors during isometric contractions?

“…The reliability of our ultrasound measurements has previously been reported (Manal et al, 2006) and compares favorably with values reported in the literature (Fukunaga et al, 1997;Maganaris et al, 1998). The coefficient of variation for scanning a site multiple times and computing the pennation angle for each scan was 8.5%.…”

“…Results from recent studies using real-time ultrasonography question these inherent assumptions of the planimetric model (Hodges et al, 2003, Maganaris et al, 1998, Muramatsu et al, 2002. For example, Maganaris and colleagues (1998) showed that a planimetric model underestimated pennation angle at MVC by 12° and 14° for the lateral gastrocnemius and soleus compared to in vivo measures recorded using ultrasonography.…”

“…The transducer was placed just inferior to the surface electrode placements of the TA, LG, and MG. Muscle architecture does not change significantly over the length of these muscles (Maganaris et al, 1998;Maganaris and Baltzopoulos, 1999). The insertion of the superficial fibers into the central aponeurosis was used to define the pennation angle for the TA.…”

“…Muscles with large pennation angles such as the soleus allow more fibers to be arranged in parallel within a given cross sectional area, thereby increasing a muscle's force generating potential. Fiber pennation angle varies with muscle contraction intensity and fiber length (Maganaris et al, 1998;Maganaris, 2003;Narici et al, 1996), and thus such changes should be considered when using musculoskeletal models to estimate muscle force.…”

Are Current Measurements of Lower Extremity Muscle Architecture Accurate?

“…The architectural properties of small numbers of human lower extremity muscles have been reported in several studies, some of which used indirect methods to assess the architecture [11,14,23,26]. The two most extensively used data sets representing direct measurements of human lower extremity architecture consist of only five specimens of unknown size, gender, and age [8,30].…”