Chris Beardsley response to the question: ‘Would you say the eccentric phase can produce more hypertrophy than the concentric phase, since you can use a heavier load?’
‘Talking about eccentric only vs. concentric only training, that is actually a lot harder to answer than it sounds, for a couple of reasons.
Firstly, it is true that the long-term research shows that eccentric only training probably does cause more hypertrophy than concentric only training. However, when you segment studies (1) type of load (i.e. isokinetic vs. constant load) and (2) training status (i.e. trained vs. untrained), the picture is much less clear. As far as I can tell, it probably does produce greater hypertrophy in untrained people, and when using isokinetic loads (which nobody does). In trained people using constant loads (which is all of us, really), I am not so certain.
Secondly, we have to be a bit cautious about what we mean by hypertrophy. Eccentric training tends to increase muscle fascicle lengths by more, while concentric training tends to increase cross-sectional area and pennation angle to a greater extent. Both approaches increase muscle volume, but might produce different changes in cross-sectional area or regional hypertrophy, depending on what your measurement is. This might contribute somewhat to the confusing results in the literature.
In practice, I think accentuated eccentric training (where you train normally using both concentric and eccentric phases, but increase the load on each eccentric phase) is probably the best option. If that is not logistically possible, then slowing down the eccentric phase is the next best thing. It will probably give similar results for size, but IMO it is probably not quite as effective for strength. Having said that, if hammering the eccentric makes you so sore that you can’t train as often, then it is probably not such a good idea. I think we have to take these things in the round.’
Link to his great FB page: https://www.facebook.com/StrengthandConditioningResearch/?fref=nf