Explosive Reps May Pay Off - At Least on the Bench: Fast Reps = Higher Muscle Activity, Higher Volume... Gains?

Explosive training can, but it does not have to involve medicine balls and plyometric exercises. You can also do the regular bench press as fast as possible and will - as the study at hand says - achieve higher levels of muscle activity and an increase in rep volume.

You will probably have heard the acronyms EMG = electromyography and TUT = time under tension before, but did you know how they go together? The simple assumption that a higher time under tension would yield greater EMG values and thus higher muscle activations is - as a recent study confirmed, once more - as far from being correct as it is from being logical.

Think of it: It's simple physics. The force you apply is the product of the mass you move and the acceleration you exert on that mass. It's F = m · a - Force equals mass times acceleration. If you go slow to achieve a maximal time under tension, the acceleration will be low and so will be the force. Since my friends from the exercise physiological department tell me that F ~ EMG, meaning there's a in parts proportional increase in muscle activity when the force you applied increases, it should be obvious why the previously phrased hypothesis that "a higher time under tension would yield greater EMG" cannot be correct.
Unfortunately, things are not as simple as they may seem. After all, the activation patterns are reversed on the way down. Whut? Yes, they are. The slower you lower the weight (almost) onto your chest, the higher the negative acceleration you apply, ... and you know what that mean, right? YES! The greater the force.

So under physically ideal (no one says that this must be physiologically ideal, at this point!) conditions, you'd be exploding on your way up and going super-slow on your way down.

Unfortunately, this is not what any of the thirteen males, all of whom were familiar with the bench press exercise, did in the BA study by Gustav Mårtensson (2015 | still great work for a bachelor's thesis, by the way). What they did was to perform the bench press at their individual 6 RM with a tempo of either

• 4 second per total repetitions, 6 second per total repetitions, or
• each repetition intentionally performed as fast as possible (as Lawrence rightly points on on Facebook, that's not going to look much faster than normal speed with a 6-RM weight)

The subjects had been instructed to to perform the exercise to fatigue. So, next to the muscle activity which was recorded by the means of surface electromyography (EMG) on the pectoralis major and
deltoideus anterior, Mårtensson also counted the number of repetitions his subjects performed and recoreded the total time under tension for each test in seconds.

Figure 1: Normalized (rel. to maximal voluntary contractinos) EMG values (Mårtensson. 2015) - p < 0.05 for pecs, only.

To make sense of the (otherwise arbitrary) EMG values, Mårtensson had recorded a set of reference values using MVIC (Maximum voluntary isometric contraction) tests, beforehand. To put the data from the actual trial into perspective, the only thing he'd had to do was to express the newly recorded EMG data relative to these maxima - a procedure that yielded the results in Figure 1.
As you can see, the results are not exactly as expected: YES, the fast tempo produces the highest, the low tempo the lowest muscle activation.  However, the authors found that "the difference was only statistically significant for pectoralis major" (Mårtensson. 2015) - a result that makes it difficult to tell whether "going fast will actually pay off".

Figure 2: Number of reps (indiv., left) + average (right) during the three BP conditions (Mårtensson. 2015)

The reason I still decided to put the line "explosive reps may pay off" into the headline is that the non-significantly enhanced muscle activity went hand in hand with a significantly increased rep-volume of 7.9 ± 3 reps in the fast vs. 6.0 ± 1 and 3.7 ± 1 reps in the medium and slow rep groups. In view of the fact that the same weight was used this would mean that the total volume was increased and the training stimulus should have been increased, as well - usually, that's reason enough, to assume that the outcome in terms of strength and size gains may benefit, no?
References:

• Caserotti, Paolo, et al. "Explosive heavy‐resistance training in old and very old adults: changes in rapid muscle force, strength and power." Scandinavian journal of medicine & science in sports 18.6 (2008): 773-782.
• Jenkins ND1, Housh TJ, Bergstrom HC, Cochrane KC, Hill EC, Smith CM, Johnson GO, Schmidt RJ, Cramer JT. "Muscle activation during three sets to failure at 80 vs. 30 % 1RM resistance exercise." Eur J Appl Physiol. 2015 Jul 10. [Epub ahead of print]
• Mårtensson, Gustav. "The effect of lifting speed on factors related to resistance training: A study on muscle activity, amount of repetitions performed, and time under tension during bench press in young males." (2015).
• McGuigan, Michael R., et al. "Effect of explosive resistance training on titin and myosin heavy chain isoforms in trained subjects." The Journal of Strength & Conditioning Research 17.4 (2003): 645-651.
• Newton, Robert U., and William J. Kraemer. "Developing Explosive Muscular Power: Implications for a Mixed Methods Training Strategy." Strength & Conditioning Journal 16.5 (1994): 20-31.
• Paavolainen, Leena, et al. "Explosive-strength training improves 5-km running time by improving running economy and muscle power." Journal of applied physiology 86.5 (1999): 1527-1533.
• Sakamoto, Akihiro, and Peter J. Sinclair. "Effect of movement velocity on the relationship between training load and the number of repetitions of bench press." The Journal of Strength & Conditioning Research 20.3 (2006): 523-527.
• Sakamoto, Akihiro, and Peter James Sinclair. "Muscle activations under varying lifting speeds and intensities during bench press." European journal of applied physiology 112.3 (2012): 1015-1025.
• Santos, Eduardo JAM, and Manuel AAS Janeira. "Effects of complex training on explosive strength in adolescent male basketball players." The Journal of Strength & Conditioning Research 22.3 (2008): 903-909.