Effects of β‐hydroxy‐β‐methylbutyrate (HMB) on Muscle IGF‐I and MGF mRNA Expression in Aged Female Rats during 10‐Week Resistance Training

Abstract

HMB intake during resistance training (RT) has been shown to improve muscle mass and function. Our purpose was to determine whether HMB intake would enhance RT‐induced improvements in muscular function and mitogenic responses in aged animals. Sixteen, 19‐month old, Sprague‐Dawley female rats were randomly divided into 3 groups: control (CON), HMB (0.46 g/kg/d) and non‐HMB. After CON was sacrificed as a baseline, the HMB and non‐HMB groups underwent intense ladder climbing exercise training every third day for 10 wks with weights attached to the tail. Maximum strength was assessed pre‐, mid‐ and post‐RT by measuring the maximum weight (g) the animal could climb to the top of ladder with one time. RT‐PCR was used to analyze IGF‐I and MGF mRNA expression in gastrocnemius and soleus muscles. There was a main time effect (+238%; pre 263±16 vs. post 890±28 g) and group × time effect (HMB +265% vs. non‐HMB +214%) for maximum strength (p<0.05). MGF mRNA expression increased in both HMB (+32%) and non‐HMB (+40%) after 10‐wk RT as reflected by the main group effect (p<0.05) with no between group differences. Although the main group effect for IGF‐I only approached significance (p=0.1), post hoc analysis revealed significant increases only in the HMB group (+33%, p<0.05). Our findings suggest that HMB intake during RT induces greater strength gains in aged individuals maybe by increasing muscle mitogenic responses (IGF‐I mRNA).