Locomotor activity, growth hormones, and systemic robusticity: An investigation of cranial vault thickness in mouse lines bred for high endurance running

Abstract

Our results fail to provide support for the systemic robusticity hypothesis, suggesting it is important to rethink the long-standing theory that increased CVT in Homo erectus reflects increased physical activity compared other hominin species.

Exercise‐induced loading increases ilium cortical area in a selectively bred mouse model

“…Our results are broadly similar to previous studies on long bones of the HR mice that show an inconsistent effect of increased chronic wheel‐running activity on bone cross‐sectional properties. Neither femoral nor humeral midshaft cross‐sectional properties demonstrated a statistically significant effect of activity in other studies of these particular mice (Copes et al, ) or those sampled from another generation (Middleton et al, ). Middleton et al () document some significant differences in femoral cross‐sectional properties (maximum second moment of area and section modulus) by linetype, and also in relation to the mini‐muscle phenotype, but none by activity.…”

“…This study uses a two‐way experimental design, in which female HR and control mice ( N = 74) from the 57th generation were divided into four experimental groups at weaning based on access to a running wheel attached to individual housing cages (i.e., each mouse was housed in its own cage; these are the same individuals included in Copes et al, , ). Thus, mice were assigned to one of four experimental groups: control mice without access to a wheel ( N = 19), control mice with access to a wheel ( N = 20), HR mice without access to a wheel ( N = 17), and HR mice with access to a wheel ( N = 18).…”

“…This experimental design is uniquely situated to differentiate evolved differences from individual‐level differences (i.e., bone functional adaptation). A 12‐week experiment on this sample of mice collected data on total wheel revolutions, daily minutes of activity, mean running speed, and maximum speed, and has shown that HR mice with wheel access ran for significantly greater distances, duration, and at higher mean speeds than control mice with wheel access (Copes et al, ; Copes et al, ). These variables were analyzed at week eight and the results demonstrate that HR mice ran 2.31 times farther, 1.31 times as long, and 1.91 times faster (average speed) than control mice (Copes et al, ).…”

“…These variables were analyzed at week eight and the results demonstrate that HR mice ran 2.31 times farther, 1.31 times as long, and 1.91 times faster (average speed) than control mice (Copes et al, ). In addition to wheel‐running activity, all physical activity within the home cage, regardless of wheel access, was collected daily via infrared motion detection sensors and summed over a 23.5 hr period (Copes et al, ). In this sample of mice, HR mice without wheel access exhibited significantly greater total home cage activity (1.5 times greater) than control mice without wheel access (Copes et al, ).…”

“…In addition, comparing loading versus non‐loading experimental conditions is difficult in primates because it requires preventing the use of a limb, and does not easily allow for testing the effects of increased loads. One way around this difficulty has been to use mice as models in studies of primate bone biology because it is feasible to manipulate their loading environments through various types of forced or voluntary exercise (e.g., Copes et al, ; Copes, Schutz, Dlugsoz, Judex, & Garland Jr, ; Green, Richmond, & Miran, ; Wallace et al, ). In this study, we test the hypothesis that increased physical activity results in ilium cross‐sectional properties that are indicative of greater resistance to loading.…”