HMB Supplementation Effects on High‐Resolution Skeletal Muscle Diffusion Tensor Imaging and Intramyocellular Fat Changes during High Intensity Military Training

Abstract

The purpose of this study was to examine the effect of β‐hydroxy‐β‐methylbutyrate Free Acid (HMB) supplementation on muscle morphological and muscle lipid changes during highly intense military training. Thirteen soldiers from an elite combat unit were randomly assigned to either a HMB (n=6) or placebo (PL; n=7) group. Soldiers were provided with 3 g·day−1 of either HMB or PL for 23 days. During the final week of supplementation (days 18 – 23) soldiers participated in extreme physical training, which included night navigation of 6 – 8 hours across difficult terrain with approximately 35 kg of equipment on their back. During daylight hours, soldiers remained in camouflaged positions with minimal recovery. Due to a severe environmental stress (37°C and a sand storm) navigational training was performed on only the first two evenings of the week. Still, soldiers continued to be subjected to excessive physical training. During the 6 days of intense training the soldiers slept a total of 22.5 hours (3.8 ± 3.0 h per night). Prior to and following the supplementation period participants were assessed using a 3‐Tesla magnetic resonance imaging (MRI), which included diffusion tensor imaging (DTI) sequence for muscle fiber tracking analysis. Changes of intramyocellular fat percent, muscle volume, intramyocellular fat, fractional anisotropy (FA) and apparent diffusion coefficient (ADC). Data was analyzed using a two‐way mixed factorial ANOVA. To complement null hypothesis testing, magnitude based inferences were examined to provide inferences on the true effects HMB may have had on muscle morphological, intramyocellular fat and DTI variables, compared to PL, calculated from 90% confidence intervals. Following the 23‐day supplementation period a possible increase was noted for changes in muscle volume for adductor magnus for HMB (77% likelihood for an increase). Differences in muscle volume for the vastus lateralis, rectus femoris and semitendinosus between HMB and PL were unclear. A possible decrease in intramyocellular fat was noted in the rectus femoris (73% likelihood), but a likely increase in intramyocellular fat was observed in the adductor magnus (83% likelihood) in HMB compared to PL. The effect of HMB on FA in all muscles measured were unclear compared with the effect of PL. In addition, HMB ingestion resulted in a likely increase in ADC in the vastus lateralis only (86% likelihood) compared to PL. Other comparisons between HMB and PL for ADC were also unclear. In summary, short term HMB ingestion prior to intense military training appeared to provide some benefit for maintaining muscle volume but appeared to have only minimal influence on DTI responses.Support or Funding InformationMetabolic Technologies Inc.