Volumetric muscle loss (VML) injury is associated with persistent functional deficits in the remaining muscle and uninjured bone adjacent to the injury. Thus far, rehabilitative interventions to restore musculoskeletal function, such as running, have not shown efficacy. In some cases, these interventions have further impaired function compared to leaving VML to the natural sequela. The goal of this study was to determine if weight-bearing asymmetry changes following VML and whether the lack of response to rehabilitation could be explained by limb loading asymmetry. We hypothesized that 6 weeks of voluntary wheel running would result in functional deficits in both muscle and bone, and that weight-bearing asymmetry would not differ between running and sedentary experimental groups. At ~12 weeks of age, C57Bl/6J mice (n=24; equal male/female) were randomized to the following groups: Naïve+Run, VML, and VML+Run. Mice that received VML had an ~20% volume injury to the plantar flexor muscles (gastrocnemius, soleus, plantaris) of the left hind limb. Two weeks post-VML, mice allocated to running were given free access to wheels for 6 weeks. Weight-bearing asymmetry was evaluated prior to injury, and biweekly thereafter, for a total of 5 times. At ~20 weeks of age, the plantar-flexor muscle group was tested for in vivo maximal isometric torque, and muscles and bones were harvested for functional and biochemical analyses. Data were analyzed by one-way ANOVA and one-way repeated measures ANOVA as appropriate. Mice ran ~279km over 6 weeks, with an average of ~6.5km per day. There was no difference in daily, weekly, or total distance run between groups (p≥0.494). Preceding injury, there was no difference in weight-bearing asymmetry across groups (p=0.302). Two weeks post-VML, before running, there was no difference in weight-bearing asymmetry between the VML-injured mice allocated to sedentary or running experimental groups, but there was a deficit of 7.4% of the weight distributed to the injured (left) limb in VML-injured compared to Naïve mice (p< 0.0001). After 6 weeks of running (i.e., 8 weeks post-VML), there was no difference in weight-bearing asymmetry between the running groups (p=0.810; Naïve+Run vs. VML+Run). Conversely, the VML sedentary group had a deficit of 5.4% of weight distributed to the injured (left) limb leg compared to the other groups (p=0.005). As expected, the VML injury resulted in a 21.1% lower gastrocnemius mass-to-body ratio compared to the Naïve group (p< 0.0001). Terminally, in vivo maximal torque of the posterior compartment muscle group indicated that the VML-injured groups had a torque deficit of 41.5% compared to the Naïve group (p=0.044). Thus, while the running intervention provided significant stimuli (i.e., running load) to impart positive adaptations to weight-bearing ability following VML, there is a noted inability to physiologically respond to the intervention. Although this cannot be explained by a lack of mechanical loading of the limb, changes in gait following injury may lead to a different loading pattern on the limb that does not impart the same physiological adaptations expected in uninjured muscle. Future research should specifically evaluate gait and loading patterns during running to further understand the limitations of rehabilitation after VML. Funding: NIH R01-AR078903 (JAC and SMG), K02-AG081488 (SMG), T32-AR007612 (ASB); and CDMRP W81XWH-20-10885 (JAC and SMG) This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Weberg et al. (2026) studied this question.