After my recent post on the relationship of tempo to work and time under tension, I thought I’d take a look at the role of slow eccentric actions in hypertrophy training. In my research into tempo recommendations being offered around the net, the most common was to use slow eccentric tempos to maximize muscle growth. Despite the prevalence of this recommendation, more often than not it was offered up without any citations to support it.

There’s no question that controlling the eccentric portion of the lift is important for technique, but does exaggerating the eccentric phase by slowing the movement really confer a hypertrophic advantage? Sure, nobody likes having a few cracked ribs after a set of bench presses, and I’m sure most of you don’t opt for careless eccentrics, but is there any hypertrophic value in prolonging the eccentric phase?

Eccentric overload: Are weight and time synonymous?

The popularity of eccentric training arose primarily from research indicating that eccentric training may produce greater hypertrophy than training with concentric contractions alone (26), and that eccentric overload may be superior to equivalent eccentric and concentric training (22). The literature is full of examples of the superiority of isokinetic (3, 4, 8, 10, 12, 28) and isotonic (5, 7, 11, 30) eccentric actions for strength and hypertrophy as compared to concentric contractions, however exceptions do exist (1, 2, 13, 15, 18, 21, 25)}. When put on a “level playing field” by work (18) or power (15) matching eccentric actions to the concentric phase, the strength and hypertrophy advantage of eccentric training seems to disappear. Despite some ambiguity in the results, a recent meta analysis has ruled a slight advantage in favour of eccentric actions for hypertrophy (26).

There is no confirmed, unifying mechanism into the potential hypertrophic superiority of the eccentric action. What does exist centres around differing fibre-type recruitment strategies between eccentric and concentric contraction, how this may produce more muscle damage (14), and how that may (or may not) promote greater hypertrophy (27). It is generally thought that eccentric actions result in a reversal of the size principle, preferentially recruiting type II fibres before type I fibres (16, 17, 19, 20). This results in fewer active fibres during an eccentric action and non-uniform force distribution within the muscle (16). Given the reduction in active fibres as compared to a concentric contraction, muscle damage is greater following eccentric-only actions versus concentric contractions alone (14, 16), and is greater following high rather than slow velocity eccentric actions (29). While data is mixed on whether muscle damage is essential for hypertrophy (27), the fact we have data that eccentrics produce greater hypertrophy and strength gains than concentric contractions alone (3-5, 7, 8, 10-12, 28, 30), may make any mechanistic speculation more of an academic endeavor anyway.

Somewhere along the way we equated the fact that we can use heavier loads eccentrically (9), the heightened effects of overloaded eccentrics (22), and the superiority of eccentric actions for strength and growth (3-5, 7, 8, 10-12, 28, 30) with the use of slower eccentric tempos. From a practical standpoint I can see how this evolution occurred, trying to overload the eccentric relative to the concentric portion of the rep is difficult to perform in the gym. Naturally then, since we can’t all have dedicated training partners there to hoist the bar off of us for the concentric phase, it only seems logical to emphasize eccentric time-under-tension by slowing eccentric velocities. Or perhaps the argument is even more simplistic than that, if eccentrics are good, why not spend more time in that phase of the lift?

Despite my recent posts on the indifference of training intensity and tempo as long as substantial fatigue is induced, I’m not convinced that the two conditions (heavy vs slow eccentrics) are equivalent in this case. The question is, do slow eccentric actions promote greater muscle growth?

Greater hypertrophy with fast eccentric tempos

Two isokinetic training studies have demonstrated the relative superiority of fast eccentric actions for strength and muscle mass development. Farthing and Chilibeck (4) investigated the effects of contraction mode (concentric vs eccentric) and velocity (30 degrees per second, slow; 180 degrees per second, fast) on muscle growth and strength. The groups performed 8 weeks of eccentric training randomized to fast or slow training, then a five week washout, followed by another 8 week period of concentric training randomized to fast or slow training (fast groups performed fast eccentric, followed by fast concentric and vice versa for slow). The unlucky subjects were randomized to a control condition, who remained sedentary over the training period to account for the potential effects of time throughout the experiment.

Following both training periods the authors found that, as far as strength was concerned, fast eccentric actions were superior. This pattern was more or less replicated for muscle thickness (hypertrophy), as fast eccentrics outgrew both concentric velocities, but was not statistically different from slow eccentrics (13% vs 7.8%). We could argue it was a limitation of their experimental design, or that they simply lacked power, however in either case this would suggest that purposely reducing eccentric velocity provides no additional hypertrophic benefit, as is often recommended.

Data from Shepstone et al (29) clarifies the ambiguity of eccentric tempo, at least when trained with isokinetics. The participants were randomized to either fast (3.66 radians per second) or slow (0.35 rads/second) eccentric actions, performed in a progressive program over eight weeks. At the end of training, fast eccentrics were superior to slow, increasing strength across the range of concentric and eccentric velocities more so than in slow training. Whole muscle growth was increased in both conditions, however there was a trend (nsd, p=0.06 on the ANOVA) for increased growth in the fast eccentric group. Fibre-type specific growth found a similar effect on type I fibres between conditions, however growth of type IIa and IIx fibres was greater with fast eccentric actions.

Cumulatively, these two studies favour fast eccentric actions for the development of both muscle strength and hypertrophy over both concentric contractions alone and slow-eccentric actions. While such a response may be due to the fact that fast eccentric actions promote greater torque production and muscle damage than slow (29) (data from (23) disputes part of this) that may promote elevated hypertrophy (27), more experiments are required to clarify such relationships. We also cannot rule out that these results are dependent on use of isokinetic training, and as such may not translate to what most of us actually do in the gym.

The effects of altering eccentric and concentric time under tension with isotonic resistance

In researching this article, I’ve realized that despite the wealth of data on eccentric actions, there is very little regarding the use of tempo under isotonic (or dynamic, constant, external resistance if you’re paid by the syllable) conditions, or simply put, stuff we’d actually pick up in the gym. I did however, stumble across an interesting study from Gillies et al (6) that gets to the meat of the problem. The authors compared differing eccentric and concentric tempos but with total time under tension matched between conditions, answering our question of whether we should focus on eccentric or concentric time under tension when pursuing more muscle mass.

Participants were randomized to perform either the long concentric (2/1/6 tempo) or long eccentric (6/1/2 tempo) for a primarily lower body program performed three times per week over nine weeks. At the completion of training, strength was increased regardless of training condition, however muscle growth was not equivalent. Type I fibres were increased similarly in both groups, while only the long concentric training group had increased type IIa fibre cross sectional area. In addition, urinary cortisol was elevated in the long concentric group, a point the authors theorize to be linked to the greater metabolic stress associated with a longer concentric contraction.

This fibre-type data is interesting in the context of the reversal of the size principle (16, 19, 20), as I would have anticipated greater type II growth with the eccentric group more than the concentric. We cannot rule out the possibility that dramatically slow eccentric actions could have an impact on the previously documented neuromuscular properties of eccentric actions. This data does agree with the isokinetic work of Shepstone et al (29), that indicated equivalent type I fibre growth between slow and fast isokinetic contractions, but varies from Hortobagyi et al (12) who found 10x greater type II fibre growth with eccentric than concentric contractions. This indicates we may not achieve similar effects between isokinetic and isotonic studies, but cumulatively these studies indicate that using slow eccentric velocities to prolong time-under-tension may not be the hypertrophy holy grail we’ve made them out to be.

There’s always a limitation regardless of the study, or something that stands in the way of the overall applicability of how a research study applies to those of us who actually train. Oversimplified, machine-based programs is often one, sedentary, untrained participants is definitely another, but in this case, it would have been nice to have an additional training group that trained at a tempo more representative to how many of us actually train. This would give a clear picture of the effect of prolonging the eccentric or concentric phase relative to a standard tempo, and more specifically address the questions I’ve raised in this article. I can count on one hand the number of times I’ve seen anyone in a gym perform something resembling a 2/1/6 or 6/1/2 tempo, and while I know many of you out there do experiment with tempos, I’d argue that in most cases a 1/0/1 tempo would be a generous description.

Don’t lower it slow to grow!

While tempo may ultimately be irrelevant for pure hypertrophic adaptations when training to failure, these studies suggest that there isn’t a hypertrophic benefit from exaggerating the eccentric phase with slow velocities. We could use another study or two in the area, however the existing literature supports that, even though eccentric overload may promote greater gains (22), extending eccentric time-under-tension with slow velocity eccentrics may not be similarly advantageous (4, 24, 29).

That being said, while I personally don’t prefer slow eccentrics (although I’d do them in a second if it meant more muscle mass), I do know that many of you have experimented with them in your own training. Take to the comments below to let me know what you’ve experimented with, what you felt worked or didn’t, and last but not least, why.

