|Figure 1: Schematic illustration of the mTOR signaling cascade (Betz, Charles. Wikipedia)|
study and without any history of musculoskeletal disorders" perform 5 sets of 8 repetitions of an eccentric knee extension exercise at either a slow (20°·s–1; ES) or fast execution speed (210°·s–1; EF). After the workout, biopsies were taken from vastus lateralis at three timepoints: baseline (B), immediately after (T1), and 2 h after (T2). The results did not confirm the scientists' working hypothesis that execution velocity (and thus muscle tension) would have a direct influence on Akt, mTOR, and p70S6K expression in the trained muscles:
Akt, mTOR, and p70S6K total protein were similar between groups, and did not change postintervention. Further, Akt and p70S6K protein phosphorylation were higher at T2 than at B for ES and EF. MGF messenger RNA was similar between groups, and only significantly higher at T2 than at B in ES.So, with respect to the measured variables and in the confounding case of eccentric exercises, it does not matter whether you whack your reps out at maximum speed (assuming you still maintain adequate form) or try to slow the movement down deliberately. I guess this, aside from their (ab-)use certain "supplements", is why Coleman and Co. grew monstrous muscles despite training with the worst form you could probably think of.
Remember though, the results could be completely different for concentric exercises, like pressing movements or for equal times under tension, meaning 10x more repetitions in the EF group to make up for the total time difference. Results from previous studies, such as Farthing and Chilibeck (2003) and Shepstone et al., for example suggest that compared to slow training a faster (yet still controlled) exercise execution is linked to greater hypertrophy of the elbow flexor, in general, and the biceps' type IIa (+16%) and type IIx (+18%), in particular. I guess future studies will further elucidate the exact mechanisms and guess what: the SuppVersity is where you will read about them, first!