Activity-related energy expenditure during lower limb cast immobilization in children

Independent of physical activity, volumetric muscle loss injury in a murine model impairs whole-body metabolism

Volumetric muscle loss (VML) injuries result in a non-recoverable loss of muscle tissue and function due to trauma or surgery. Reductions in physical activity increase the risk of metabolic comorbidities over time, and it is likely that VML may reduce whole-body activity. However, these aspects remain uncharacterized following injury. Our goal was to characterize the impact of VML on whole-body physical activity and metabolism, and to further investigate possible muscle-specific metabolic changes. Adult male C57Bl/6J (n = 28) mice underwent a standardized VML injury to the posterior compartment of the hind limb, or served as injury naïve controls. Mice underwent longitudinal evaluation of whole-body physical activity and metabolism in specialized cages up to three times over the course of 8 weeks. At terminal time points of 4- and 8-weeks post-VML in vivo muscle function of the posterior compartment was evaluated. Additionally, the gastrocnemius muscle was collected to understand histological and biochemical changes in the muscle remaining after VML. The VML injury did not alter the physical activity of mice. However, there was a noted reduction in whole-body metabolism and diurnal fluctuations between lipid and carbohydrate oxidation were also reduced, largely driven by lower carbohydrate utilization during active hours. Following VML, muscle-specific changes indicate a decreased proportion of fast (i.e., type IIb and IIx) and a greater proportion of slow (i.e., type I and IIa) fibers. However, there were minimal changes in the capillarity and metabolic biochemical activity properties of the gastrocnemius muscle, suggesting a miss-match in capacity to support the physiologic needs of the fibers. These novel findings indicate that following VML, independent of changes in physical activity, there is whole-body diurnal metabolic inflexibility. Supporting future investigations into the chronic and overlooked co-morbidities of VML injury.

What is the real impact of upper limb cast immobilisation on activity-related energy expenditure in children?

Background

Upper limb fractures and subsequent cast immobilisation constitute a potential cause of reduction in childhood levels of physical activity (PA), with subsequent decrease of energy consumption. The main objective of this study was thus to quantify the decrease of activity-related energy expenditure (AEE) due to upper limb cast immobilisation.

Methods

We conducted a longitudinal matched case-control study that included 35 children and teenagers with a first episode of upper limb fracture and 35 healthy cases. PA was assessed during cast immobilisation by accelerometer. AEE was the calculated using an equation based on the total counts per day measured by accelerometers.

Results

AEE in children and teenagers with upper limb fractures was estimated to be 7.4 % lower than healthy controls. The mean difference corresponded to 1.35 kcal/kg per mean valid recorded time (750  min), that is, the waking hours. When converted in kcal per mean subjects’ weight, the difference in AEE amounted 63.5 kcal/day, which corresponds approximately to 26  min of walking at a speed of 4  km/hours. In comparison with the mean AEE in healthy controls (18.2 kcal/kg), the noted decrease (1.35 kcal/kg) represents only 7.4 % of AEE.

Conclusion

Reduction of AEE in children and teenagers with upper limb fractures may lead to a slight positive energy balance, as there is usually no compensatory reduction of energy intake. An increase of light PA has to be counselled in this situation or patients should be advised to reduce their energy intake during the immobilisation period.

Level of evidence

Level I: high-quality prospective study (all patients were enrolled at the same point in their disease with ≥80 % follow-up of enrolled patients).