American Society of Biomechanics Journal of Biomechanics Award 2017: High-acceleration training during growth increases optimal muscle fascicle lengths in an avian bipedal model

Abstract

Sprinters have been found to possess longer muscle fascicles than non-sprinters, which is thought to be beneficial for high-acceleration movements based on muscle force-length-velocity properties. However, it is unknown if their morphology is a result of genetics or training during growth. To explore the influence of training during growth, thirty guinea fowl (Numida meleagris) were split into exercise and sedentary groups. Exercise birds were housed in a large pen and underwent high-acceleration training during their growth period (age 4-14 weeks), while sedentary birds were housed in small pens to restrict movement. Morphological analyses (muscle mass, PCSA, optimal fascicle length, pennation angle) of a hip extensor muscle (ILPO) and plantarflexor muscle (LG), which differ in architecture and function during running, were performed post-mortem. Muscle mass for both ILPO and LG was not different between the two groups. Exercise birds were found to have ∼12% and ∼14% longer optimal fascicle lengths in ILPO and LG, respectively, than the sedentary group despite having ∼3% shorter limbs. From this study we can conclude that optimal fascicle lengths can increase as a result of high-acceleration training during growth. This increase in optimal fascicle length appears to occur irrespective of muscle architecture and in the absence of a change in muscle mass. Our findings suggest high-acceleration training during growth results in muscles that prioritize adaptations for lower strain and shortening velocity over isometric strength. Thus, the adaptations observed suggest these muscles produce higher force during dynamic contractions, which is beneficial for movements requiring large power outputs.

Gastrocnemius fascicles are shorter and more pennate throughout the first month following acute Achilles tendon rupture

“…In addition to our current findings that skeletal muscle architecture is sensitive to tendon rupture, muscle fascicle length can also be affected by loading, pathology, surgical procedures, and immobilization in both humans and animal models. High-acceleration training during maturation in guinea fowl stimulates longer muscle fascicles that contain greater amounts of sarcomeres in series (Salzano et al, 2018). Children with cerebral palsy have shorter gastrocnemius fascicles that can be increased with surgical correction of the plantarflexor contracture (Wren et al, 2010).…”

“…Longer muscle fascicles generate greater power during isokinetic contractions (Drazan, Hullfish & Baxter, 2019b), which is beneficial for activities like sprinting (Lee & Piazza, 2009). Targeted training can increase muscle fascicle length (Salzano et al, 2018), effectively increasing power potential. Although muscle structure has been linked to function in many populations, shorter muscle fascicles have only been reported in a single case report of a patient with poor outcomes following an Achilles tendon rupture (Baxter, Hullfish & Chao, 2018).…”

Gastrocnemius fascicles are shorter and more pennate throughout the first month following acute Achilles tendon rupture

“…In addition to our current findings that skeletal muscle architecture is sensitive to tendon rupture (Figure 3), muscle fascicle length can also be affected by loading, pathology, surgical procedures, and immobilization in both humans and animal models. High-acceleration training during maturation in guinea fowl stimulates longer muscle fascicles that contain greater amounts of sarcomeres in series (28). Children with cerebral palsy have shorter gastrocnemius fascicles that can be increased with surgical correction of the plantarflexor contracture (35).…”

“…Longer muscle fascicles generate greater power at high speeds, which is beneficial for activities like sprinting (20). Targeted training can increase muscle fascicle length (28), effectively increasing power potential. Although muscle structure has been linked to function in many populations, shorter muscle fascicles have only been reported in a single case report of a patient with poor outcomes following an Achilles tendon rupture (2).…”

Gastrocnemius muscle remodeling explains functional deficits three months following Achilles tendon rupture

“…26 Conversely, high velocity training stimulates longer muscle fascicles in a bipedal bird model. 27 However, both tendon elongation and fascicle remodeling appear to occur during the weeks following the initial injury, limiting the potential efficacy of restoring muscle structure after the tendon is fully healed in an elongated position. 6 Therefore, we suggest that future research focus on the interplay between tendon elongation and muscle remodeling throughout healing to identify treatment options that mitigate detrimental changes to structure and function.…”