Architectural, functional and molecular responses to concentric and eccentric loading in human skeletal muscle.
Level 2 - randomized trial
Individual controlled comparative intervention trial with an additional acute experimental cohort.
PubMed 24387247 · doi:10.1111/apha.12225
What was done
Twelve young males completed 10 weeks of either concentric (CON, n = 6) or eccentric (ECC, n = 6) resistance training. An additional 14 males were recruited to evaluate acute muscle fascicle behavior and molecular signaling from vastus lateralis (VL) biopsies taken 30 minutes after single CON or ECC exercise bouts. Vastus lateralis muscle volume was assessed by magnetic resonance imaging (MRI), muscle architecture (fascicle length [Lf] and pennation angle [PA]) by ultrasonography, and MAPK/AKT-mTOR and inflammatory signaling by immunoblotting.
What was found
Despite a ~1.2-fold greater absolute load in the ECC group, both groups had similar increases in muscle volume (+8% CON vs +6% ECC) and maximal voluntary isometric contraction (+9% CON vs +11% ECC). However, fascicle length increased more after ECC (+12% vs +5% CON), while pennation angle increased more after CON (+30% vs +5% ECC). Regional hypertrophy also differed, with ECC favoring distal VL growth (+8% ECC vs +2% CON) and CON favoring mid-belly growth (+11% CON vs +7% ECC). Acute MAPK activation (p38MAPK, ERK1/2, p90RSK) was specific to ECC, whereas neither mode changed AKT-mTOR or inflammatory signaling at 30 minutes post-exercise.
Why it matters
This study shows that concentric and eccentric resistance training elicit distinct structural and regional hypertrophy profiles, with eccentric loading specifically driving muscle fascicle lengthening and distal muscle growth.
Limits
The longitudinal sample size was very small (n = 6 per arm), limited to young males, and randomization was not described in the abstract. Acute molecular signaling was only evaluated at a single post-exercise time point (30 minutes).
Cited by
- supports Muscles develop regionally, with eccentric exercise promoting growth more in the distal portion and concentric exercise promoting growth more in the mid-portion.