A comparison of fiber specific and whole muscle homogenate markers of muscle activation following HIT and END exercise

Abstract

Muscle activation following a bout of high‐intensity interval training (HIT) and endurance exercise (END) was examined in recreationally active men (n=6; age, 19.3±1.4 yrs; VO2peak, 51.9±5.1 ml/min/kg; WRpeak, 264.1±41.6 W). Muscle biopsies were obtained at rest and immediately following a bout of HIT (8 20s intervals, separated by 10s rest, at 170% WRpeak; 481.4±60.1 W) and END (30min of steady state cycling at 65% of WRpeak; 173.7±29.8 W). Bouts were performed a minimum of 1 week apart in random order. MHC expression was identified via immunofluorescent staining while glycogen content was determined via PAS staining. Changes in phosphorylated AMPK (p‐AMPK) and mTOR (p‐mTOR) were determined in whole muscle homogenates via western blotting. Changes in glycogen content were only examined in type I and IIA fibers as only 8 and 16 of 24 samples contained IIX and IIAX fibers, respectively. Significant (p<0.05) glycogen depletion was observed in both type I (HIT −55% END −42%) and IIA (HIT −49%; END −72%) fibers following both protocols but was greater (p<0.05) in type IIA fibers following END than HIT. Interestingly, whole muscle markers of activation, p‐AMPK and p‐mTOR were only elevated (p<0.01) following END (HIT: p‐AMPK, p=0.34; p‐mTOR, p=0.50). These data suggest that use of p‐AMPK and p‐mTOR as markers of whole muscle activation may not be appropriate following HIT. This research was supported by NSERC.