Meeting Abstract
We explored whether animals exhibit musculoskeletal plasticity that correspond to different locomotor requirements during growth. Specifically, we tested the hypothesis that a growth period marked by either a) high-level exercise or b) minimal exercise (consisting primarily of standing) result in musculoskeletal modifications that are advantageous for power production or body-weight support, respectively. To test this, guinea fowl were raised from 2 – 26 wks in either 1) large pens that allowed spontaneous running and high-power perch jumps in addition to daily automated forced exercise (EX group, n=16) or 2) small pens that restricted movement to standing/walking (SED group, n=16). We found that optimal fiber lengths in the parallel-fibered iliotibialis lateralis pars postacetabularis were 25% longer in EX vs. SED (p < 0.05) post growth but that muscle cross-sectional area was 10% larger in SED (p < 0.05). No differences in muscle architecture were found in the pennate fibered gastrocnemius, but joint morphology indicated larger tendon moment arms at the ankle in the SED group post growth. These modifications favor power production in the EX group by minimizing force-length-velocity constraints and body weight support in the SED group by improving static joint moment generation. This interpretation was supported by greater mass-specific maximal jumping power in the EX group (p<0.05). Surprisingly, there was no effect on standing or running metabolic cost, including pilot data from animals that underwent sedentary growth with further local muscle disuse via botulinum toxin injections. These findings suggest that energy expenditure may be highly conserved compared to other locomotor performance criteria.
