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.

Keywords: Acceleration; Fascicle length; Guinea fowl; Ontogeny; Training.

Figure 1.

Experimental housing set-up. EXE birds were housed in large, dual-circle pen (A) with ~0.35 m² of space per bird and the ability to undertake spontaneous running exercise. Each circle contained a rotating boom that turned on for 10 minutes per hour during the lighted hours. EXE pen also contained perches and hurdles that promoted acceleration movements. SED birds were initially housed in small, square pens (B, solid lines) with ~0.05 m² of space per bird. SED birds were split between the two pens. At week 6 of the protocol, SED pens were expanded (dashed lines) with ~0.10 m² of space per bird, in accordance with Animal Care regulations.

Figure 2.

Muscle dissection protocol. Anatomical location of ILPO (black) and LG (gray) muscles (top left). ILPO was divided into anterior and posterior sections (top right). LG was split longitudinally (bottom left) and then divided into proximal, middle, and distal sections (bottom right).

Figure 3.

Line graph showing changes in body mass throughout the protocol. Mean ± SD body mass for each group. EXE: solid line / filled circles. SED: dashed line / open circles. * p < 0.05 between groups.

Figure 4.

Boxplots for optimal fascicle length (left) and limb length normalized optimal fascicle length (right) in ILPO. Data shown are averaged across both anterior and posterior portions of the muscle. Box represents 25th-75th percentiles. Line within box represents median. * indicates statistical significance between groups from blocked ANOVA.

Figure 5.

Boxplots for optimal fascicle length (left) and limb length normalized optimal fascicle length (right) in LG. Data shown is averaged across proximal, middle, and distal portions of the muscle. Box represents 25th-75th percentiles. Line within box represents median. Open circle represents outlier (>3 mean absolute deviations from the mean). * indicates statistical significance between groups from blocked ANOVA.