Shorter Inter-Set Rest Periods Maximize Muscle Activation During Antagonist Super-Set Training - Downstream Effects on Strength and Size Gains Less Unambigous

You don't have to push and pull at the same time - don't worry!
You may have read Menno Henselmans', Brad J. Schoenfeld's review of the effects of inter-set rest periods on muscle and strength gains in the latest issue of Sports Medicine (Henselmans. 2019). In said paper, Henselmans and Schoenfeld conclude that the increase in the production of purportedly anabolic hormones in response to the reduction of rest-times to 1 min or less is, at best, weakly related to the long(er)-term study outcomes.

The reason I am repeating this previously cited conclusion is simple, I don't want you to overrate the increase muscular activation Marianna F. Mai and colleagues from the Federal University of Rio de Janeiro and the  Eastern Illinois University report in a soon-to-be-published paper in the Journal of Strength and Conditioning Research (Maia. 2014).
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In the corresponding randomized cross-over study the scientists randomly assigned their fifteen recreatinally trained male subjects subsequently to one out of the six resistance training modes outlined in Figure 1:
Figure 1: Summary for experimental protocol trials. TP = traditional protocol; PMR = paired sets with minimal
allowable rest; P30 = protocol with 30-second rest interval; P1 = protocol with 1-minute rest interval; P3 =
protocol with 3-minute rest interval; P5 = protocol with 5-minute rest interval (Maia. 2014)
The recovery period between the experimental protocols, which were executed on conventional resistance training machines, was between 48 and 72 hours. The number of repetitions performed and the EMG activity of vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles were recorded during the knee extension set in each protocol.

So, how exactly did the resistance training protocol look like?

Before all protocols, warm up sets for the knee flexion (KF) and knee extension (KE) exercises were performed for 10–15 repetitions with 50% of the 10RM load, and then a 2-minute interval was instituted before initiating each protocol. To verify the acute effect of rest interval between paired sets of agonist and antagonist muscles, 5 experimental protocols were applied as the following.
  • SuppVersity Suggested Read: "Want to Design a Killer Workout? Reduce the Rest Times and Burn 37% More Energy During Your Workout!" | more
    Traditional protocol: the subjects in this protocol performed a set of KE with 10RM loads until concentric failure;
  • PMR (antagonist paired sets = APS with minimal allowable rest interval): the subjects in this protocol performed a set of KF followed immediately by a set of KE. In addition, the time allowed for changing exercises (KF and KE) was fixed and controlled at 15 seconds.
  • P30: the subjects in this protocol performed a set of KF and after 30 seconds of rest performed a set of KE;
  • P1: the subjects performed a set of KF and after 1 minute of rest performed a set of KE;
  • P3: the subjects in this protocol performed a set of KF and after 3-minute rest performed a set of KE; 
  • P5: the subjects in this protocol performed a set of KF and after 5-minute rest performed a set of KE. 
During the resistance exercises (KF and KE), the 10RM loads were adopted, and the number of repetitions completed were recorded in each protocol. The EMG signal of the VL, VM, and RF was also recorded during the KE exercise.
Will this work for back and chest, as well? Due to the fact that the biomechanics are different, the outcome of antagonistic sets of say bent over row and bench presses will probably be very different. Still, studies by Robbins et al. (2009 & 2010a,b) suggest that push and pull training could produce superior results compared to regular push or pull workouts.
All subjects had previous RT experience (2.7 +/- 0.8 years), with a mean frequency of four 60-minute sessions per week, using 1- to 2-minute rest intervals between sets and exercises. Subjects were on their typical diet, not permitted to use nutritional supplementation, and did not consume anabolic steroids or any other anabolic agents known to enhance performance.
Figure 2: Number of repetitions completed in each protocol and RMS average of EMG amplitude for the muscles evaluated in each protocol; data expressed relative to group means (Maia. 2014)
As you can see there were two factors influencing the muscle activation: The inter-set rest periods and the execution of knee flexion (KF) and knee extension (KE) exercises shortly after each other.

Increases in activity and rep-max (volume) = growth triggers?

Consistent with previous studies by Baker et al. (2005), Balsamo et al. (2012), Burke et al. (1999), Joean et al- (2001) and Roy et al. (1990), the repetition performance increased in response to the antagonist preactivation. This effect was albeit only evident, when the timespan between knee flexion and extension, i.e. the inter-set rest was below 3 minutes.
"Collectively, greater KE repetitions were demonstrated during the PMR, P30, and P1 protocols vs. the TP, P3, and P5 protocols. These data suggested that limited or minimal rest between APS provides the optimal window to enhance repetition performance and muscle activation for the agonist musculature. The longer rest intervals in this study (e.g., P3 and P5) seemed to negate the potentiation effects demonstrated in repetition performance and muscle activation." (Maia. 2014)
As Mia et al. point out, the significantly greater muscle activation observed in the RF and VM muscles for the PMR and P30 protocols might be associated with the increased number of repetitions
completed for these conditions.

Similar results have been generated by Roy et al. (25) who suggested that the preactivation characteristic of APS training has a positive effect on agonist muscles because of the facilitatory stimulation of Golgi tendon organs of knee flexor muscles and muscle spindles of extensor
So, shall I train like this? In the absence of data on the chronic effects of the different exercise modalities it is difficult to answer this justifiable question.

Supersets are also among Adelfo Cerame Jr's favorite training techniques | learn more about his "Fave Five", here at the SuppVersity.
The authors of the study at hand are unquestionably right, when they say that "[e]xercise models performed using a reciprocal antagonist/agonist protocol, as in this study, might be less time consuming and could be useful in clinical practice as well as sports performance training." (Mia. 2014).

Next to the increased time efficacy, there may be benefits related to the increase in muscle activation of which you should remember that it is restricted to the 2nd exercise in the superset. In other words, if you decide to copy the protocol in the study at hand, you should be aware that your quads, not your ham strings will benefit. Whether this is also going to result in increased strength and size gains, however, is - as mentioned in the context of rest times in general at the beginning of this article, questionable. In view of the fact that the knee flexions increased not just the muscle activation, but the number of reps, as well, I wouldn't be surprised if the consequent increase in training stimulus would pay off over time | Comment on Facebook!
  • Baker, Daniel, and Robert U. Newton. "Acute effect on power output of alternating an agonist and antagonist muscle exercise during complex training." The Journal of Strength & Conditioning Research 19.1 (2005): 202-205.
  • Balsamo, Sandor, et al. "Exercise order affects the total training volume and the ratings of perceived exertion in response to a super-set resistance training session." International journal of general medicine 5 (2012): 123.
  • Burke, Darren G., Thomas W. Pelham, and LAURENCE E. HOLT. "The influence of varied resistance and speed of concentric antagonistic contractions on subsequent concentric agonistic efforts." The Journal of Strength & Conditioning Research 13.3 (1999): 193-197.
  • Henselmans, Menno, and Brad J. Schoenfeld. "The Effect of Inter-Set Rest Intervals on Resistance Exercise-Induced Muscle Hypertrophy." Sports Medicine (2014): 1-9. 
  • Jeon, HS, Trimble, MH, Brunt, D, and Robinson, ME. "Facilitation of quadriceps activation following a concentrically controlled knee flexion movement: the influence of transition rate." J Orthop Sports Phys Ther 31 (2001): 122–129.
  • Maia Marianna F. et al. "Effects of Different Rest Intervals Between Antogonist Paired Sets on Repetition Performance and Muscle Activation." Journal of Strength and Conditioning 28, 9 (2014): 2529-2535.
  • Robbins, Daniel W., et al. "Effects of agonist–antagonist complex resistance training on upper body strength and power development." Journal of sports sciences 27.14 (2009): 1617-1625.
  • Robbins, Daniel W., et al. "The effect of a complex agonist and antagonist resistance training protocol on volume load, power output, electromyographic responses, and efficiency." The Journal of Strength & Conditioning Research 24.7 (2010a): 1782-1789.
  • Robbins, Daniel W., Warren B. Young, and David G. Behm. "The effect of an upper-body agonist-antagonist resistance training protocol on volume load and efficiency." The Journal of Strength & Conditioning Research 24.10 (2010b): 2632-2640.
  • Roy, M-A., et al. "Proprioceptive facilitation of muscle tension during unilateral and bilateral knee extension." International journal of sports medicine 11.04 (1990): 289-292.
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