Early structural XXXX and @entity20962 -derived protein metabolic responses to eccentric and concentric loading in human skeletal muscle.

@entity1184 @entity1131 @entity20962 @entity2768 @entity5707 @entity121
We recently reported that the greatest distinguishing feature between eccentric (ECC) and concentric (CON) muscle loading lays in architectural adaptations: ECC favors increases in fascicle length (Lf), associated with distal @entity121 ( @entity121 ) @entity1184 , and CON increases in pennation angle (PA). Here, we explored the interactions between structural and morphological @entity5707 , assessed by ultrasound and dual x-ray absorptiometry (DXA), and long-term muscle protein synthesis (MPS), evaluated by @entity20962 ( @entity2768 ) tracing technique. Ten young males (23      4  years) performed unilateral resistance exercise training (RET) three times/week for 4  weeks; thus, one-leg trained concentrically while the contralateral performed ECC exercise only at 80% of either CON or ECC one repetition maximum (1RM). Subjects consumed an initial bolus of @entity2768 (150  mL), while a 25-mL dose was thereafter provided every 8 days. Muscle biopsies from @entity121 (MTJ) were collected at 0 and 4-weeks. MPS was then quantified via GC-pyrolysis-IRMS over the 4-week training period. Expectedly, ECC and CON RET resulted in similar increases in @entity121 @entity121 ( @entity121 ) (7.5% vs. 8.4%, respectively) and thigh lean mass (DXA) (2.3% vs. 3%, respectively), albeit through distinct @entity5707 : Lf increasing more after ECC (5%) versus CON (2%) and PA increasing after CON (7% vs. 3%). MPS did not differ between contractile modes or biopsy sites (MID-ECC: 1.42 vs. MID-CON: 1.4%  day(-1); MTJ-ECC: 1.38 vs. MTJ-CON: 1.39%  day(-1)). Muscle thickness at MID site increased similarly following ECC and CON RET, reflecting a tendency for a contractile mode-independent correlation between MPS and @entity121 (P  =  0.07; R(2)  =  0.18). We conclude that, unlike @entity121 , distinct structural @entity5707 responses to ECC or CON are not reflected in MPS; the molecular mechanisms of distinct @entity1131 , and/or the role of protein breakdown in mediating these responses remain to be defined.
