Muscle structure governs joint function: linking natural variation in medial gastrocnemius structure with isokinetic plantar flexor function

Abstract

Despite the robust findings linking plantar flexor muscle structure to gross function within athletes, the elderly and patients following Achilles tendon ruptures, the link between natural variation in plantar flexor structure and function in healthy adults is unclear. In this study, we determined the relationship between medial gastrocnemius structure and peak torque and total work about the ankle during maximal effort contractions. We measured resting fascicle length and pennation angle using ultrasound in healthy adults (N=12). Subjects performed maximal effort isometric and isokinetic contractions on a dynamometer. We found that longer fascicles were positively correlated with higher peak torque and total work (R 2 >0.41, P<0.013) across all isokinetic velocities, ranging from slow (30°/s) to fast (210°/s) contractions. Higher pennation angles were negatively correlated with peak torque and total work (R 2 >0.296, P<0.067). These correlations were not significant in isometric conditions. We further explored this relationship using a simple computational model to simulate isokinetic contractions. These simulations confirmed that longer fascicle lengths generate more joint torque and work throughout a greater range of motion. This study provides evidence that ankle function is strongly influenced by muscle structure in healthy adults.

Torque-producing capacity is affected by moment arm in the human knee extensors

“…Previous studies determined that greater pennation angles of individual muscles among the quadriceps femoris correlated with higher knee extensor isometric torque in healthy adults [14,17]. Furthermore, previous studies reported a potential relationship between longer fascicle length and higher joint torque [20,21]. However, whether the magnitudes of pennation angle and fascicle length would be related to torque-producing capacity remains unclear.…”

Differential changes in muscle architecture and neuromuscular fatigability induced by isometric resistance training at short and long muscle-tendon unit lengths

“…However, despite the numerous studies using this paradigm, something that has not been considered with this approach is that the imposed isotonic resistance will represent different relative levels of maximal strength throughout a given range of motion. This would be particularly true at the starting and end points of the range of motion, owing to the distinct torque-angle relationship of the muscle group tested (11,24). This novel assumption may be one potential explanation for divergent neuromuscular fatigability across various populations such as young versus old (21,68,71,76), male versus female (18,50,66,67), or trained versus untrained (37).…”

Relationship of the knee extensor strength but not the quadriceps femoris muscularity with sprint performance in sprinters: a reexamination and extension

“…As another explanation in terms of morphological factors, the muscle fascicle length may be involved in determining muscle strength [ 11 , 14 , 32 ]. Blazevich et al [ 11 ] reported that the fascicle length of the quadriceps femoris muscle (i.e., vastus lateralis) was a positive predictive variable for the fast-velocity isokinetic strength, but not the isometric and slow-velocity isokinetic strengths, of knee extensors in untrained individuals.…”