Longitudinal hypertrophic and transcriptional responses to high-load eccentric-concentric vs concentric training in...

High-load eccentric training reputedly produces greater muscle hypertrophy than concentric training, possibly due to greater loading and/or inflammation. We quantified the temporal impact of combined maximal concentric-eccentric training vs maximal concentric training on muscle cross-sectional area (CSA), volume, and targeted mRNA expression (93 transcripts). Eight recreationally active males (24 ± 5 years, BMI 23.5 ± 2.5 kg/m² ) performed 3 x 30 maximal eccentric isokinetic knee extensions and 2 x 30 maximal concentric knee extensions in dominant limb (ECC + CON) and 5 x 30 maximal concentric contractions (CON) in the non-dominant limb for 12 weeks (all 90°/s, 3x/wk). Quadriceps muscle CSA and volume were measured at baseline, 28 days (d), and 84 d in both limbs (3T MRI). Resting vastus lateralis biopsies were obtained from both limbs at baseline, 24 hours (h), 7, 28, and 84 d for mRNA abundance measurements (RT-PCR microfluidic cards). Work output was greater throughout training in ECC + CON vs CON (20.8 ± 9.7%, P < .001). Muscle CSA increased from baseline in both limbs at 28 d (CON 4.3 ± 2.6%, ECC + CON 4.0 ± 1.9%, both P < .001) and 84d (CON 3.9 ± 2.3%, ECC + CON 4.0 ± 3.1%, both P < .001), and muscle volume and isometric strength at 84 d (CON 44.8 ± 40.0%, P < .001; ECC + CON 36.9 ± 40.0%, P < .01), but no between-limb differences existed in any parameter. Ingenuity Pathway Analysis identified several cellular functions associated with regulation of muscle mass and metabolism as altered by both modalities at 24 h and 7 d, but particularly with ECC + CON. However, mRNA responses waned thereafter, regardless of modality. Initial muscle mRNA responses to training did not reflect chronic training-induced hypertrophy. Moreover, ECC + CON did not produce greater hypertrophy than CON, despite greater loading throughout and a differential mRNA response during the initial training week.