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Resting long enough to maximize your training volume could be the key to success, i.e. strength and size gains.

If you have been following the various affords to ascribe differences in strength and, even more so, size-increases to a specific training variable, you will remember that the only promising parameters that appear to be supported by more than the literal "outlier study" are training load and volume.

Of these, the former is pretty much uncontested. The latter, however, is still questioned by a camp of inconvincible skep- tics, who simply ignore the fact that there's ample evidence that "[h]igher-volume, multiple-set protocols have consistent- ly proven superior over single set protocols with respect to increased muscle hypertrophy" (Schoenfeld. 2010).
What still isn't clear, though, is the role of other training parameters, such as the time you take to recover between multiple sets and exercises aka the "rest intervals". As Schoenfeld et al. point out in the introduction to their most recent study, "several studies have investigated the effects of varying rest interval length on muscular adaptations," (Schoenfeld. 2015) albeit with contradictory results: While Ahtiainen et al (2005) were unable to find a significant inter-group size or strength difference in well-trained subjects (6.6 +/- 2.8 years of continuous strength training) who rested 2 minutes compared to those who rested only 5 minute in response to their 21-week training intervention, Buresh et al (2005) reported more recently that significantly greater size increases of the arms and a trend for greater muscle hypertrophy in the legs in young, albeit untrained subjects who rested for 2.5 minutes instead of just one.

Figure 1: Previous studies found "conflicting" evidence. While Ahtiainen et al. found no effects of 2 vs. 5 minutes in trained, Buresh et al. found effects of 2 vs. 1 minutes rest in untrained subjects. With different subjects, different workouts and most importantly different rest times that were compared it is yet not exactly right to say that the studies contradict each other.

Now, obviously, the ostensible "contradiction" I alluded to in the previous paragraph does eventually not exist. With trained vs. untrained subjects, different workout protocols and most importantly different rest intervals (1 vs. 2 minutes and 2 vs. 5 minutes) the studies by Ahtiainen and Buresh cannot really contradict each other. The same must be said of an even more recent study by Villanueva et al. (2014) the surprising findings of which, i.e. "longer rest periods compromise the gains of older trainees", I've discussed last year, already.Eventually, however, this does not change that there is, as Schoenfeld et al. write that "a need for more research to provide greater clarity on the topic" (Schoenfeld. 2015). A "clarity" Schoenfeld et al. sought to find with a study that "used current rest interval recommendations for hypertrophy and strength of 1 versus 3 minutes, respectively, and employed validated measures to directly assess site-specific changes in muscle thickness" (ibid). In that, the researchers speculated that ...

"[c]onsistent with generally accepted guidelines on the topic (Willardson. 2006), we hypothesized that short rest intervals would produce greater increases in muscle growth and local muscle endurance while long rest intervals would result in superior strength increases" (Schoenfeld. 2015).

As you will know if you didn't miss the headline of this waredownloadsoft article, this hypothesis was only partly validated. The data in Figure 2 confirms that the subjects, "experienced lifters (defined as consistently lifting weights for a minimum of 6 months and a back squat / body weight ratio ≥ 1.0)" (Schoenfeld. 2015), gained significantly more strength, when they rested 3 versus just 1 minute between the 3 sets of their three weekly workouts (Figure 2 does also tell you that the strength endurance increases were identical in both groups).

Figure 2: Changes in markers of strength and strength endurance; * denotes significant pre- vs. post difference, # denotes significant inter-group difference (here in favor of long(er) rest periods | Schoenfeld. 2015).

What was Schoenfeld et al. did not find, however, were increased size gains in the short-rest period group whose 24 workouts that were performed on non-consecutive days over the course of the 8-week study period, were otherwise identical with those of the long-rest period group and comprised a total of 7 exercises for all major body parts, namely...

• three leg exercises, i.e. barbell back squats, plate-loaded leg presses, and plate-loaded leg extensions), 
• two exercises for the anterior torso muscles, i.e. flat barbell presses and seated barbell military presses, and 
• two exercises for the posterior torso muscles, i.e. wide-grip plate-loaded lateral pulldowns, and plate-loaded seated cable rows

This is a highly significant result even for you who is - according to an older waredownloadsoft Poll - probably training according to a split regimen, albeit most likely with very similar exercises. What may be different from the some, but obviously *smile* not your workout though, is that the supervision by members of the research team ensured that the subjects stuck to the prescribed cadence of 1 second for the concentric and "approximately 2 seconds" (ibid.) for the eccentric part of every the exercise. This as well as the imperative progression to higher weights, whence the prescribed number of 8-12 reps per set could be performed is unfortunately overlooked by many recreational trainees - with disappointing consequences in the form of inferior or even no size and strength gains, by the way... but I am digressing, let's rather take a look at the already mentioned, unexpectedly superior strength size gains in the long(er) rest interval group (Figure 3).

Figure 3: Changes in muscle thickness and corresponding effect sizes; * denotes significant pre- vs. post-changes, # denotes significant inter-group differences; overall it is obvious that there's a long(er) rest advantage (Schoenfeld. 2015).

As the single "#" in Figure 3 tells you, the inter-group differences and thus the advantage of the long(er) rest intervals was statistically significant only for the quads, though. If we also take into account the lack of statistically significant effects on the sleeve sizes (biceps and triceps) in the short rest interval group, as well as the obvious differences in effect sizes (Figure 3, right), there's yet little doubt that the hypothesis that shorter rest intervals yield greater size increases must be considered falsified - at least under the given experimental conditions (trained subjects, three full-body workouts per week, standard hypertrophy set and rep-ranges, etc.).
References:

• Ahtiainen, Juha P., et al. "Short vs. long rest period between the sets in hypertrophic resistance training: influence on muscle strength, size, and hormonal adaptations in trained men." The Journal of Strength & Conditioning Research 19.3 (2005): 572-582.
• Buresh, Robert, Kris Berg, and Jeffrey French. "The effect of resistive exercise rest interval on hormonal response, strength, and hypertrophy with training." The Journal of Strength & Conditioning Research 23.1 (2009): 62-71.
• Henselmans, Menno, and Brad J. Schoenfeld. "The Effect of Inter-Set Rest Intervals on Resistance Exercise-Induced Muscle Hypertrophy." Sports Medicine 44.12 (2014): 1635-1643.
• Schoenfeld, Brad J. "The mechanisms of muscle hypertrophy and their application to resistance training." The Journal of Strength & Conditioning Research 24.10 (2010): 2857-2872.
• Schoenfeld, et al. "Longer inter-set rest periods enhance muscle strength and hypertrophy in resistance trained men." Journal of Strength and Conditioning Research (2015): Publish Ahead of Print.
• Villanueva, Matthew G., Christianne Joy Lane, and E. Todd Schroeder. "Short rest interval lengths between sets optimally enhance body composition and performance with 8 weeks of strength resistance training in older men." European journal of applied physiology (2014): 1-14.
• Willardson, Jeffrey M. "A brief review: factors affecting the length of the rest interval between resistance exercise sets." The Journal of Strength & Conditioning Research 20.4 (2006): 978-984.

This is what science looks like... Well, at least in the Hiscock study, where the subjects, 10 young men with at leas 12 months of training experience did regular and hammer dumbbell curls on the preacher bench - (photo | Hiscock. 2015).

In today's waredownloadsoft feature article, I am going to address not one, but two potentially highly relevant articles from the Journal of Strength and Conditioning Research (Looney. 2015) and the European Journal of Sport Science (Hiscock. 2015). What makes these papers interesting is the fact that both investigated the effect of commonly prescribed remedies to "bust a plateau" by providing novel growth triggers: (a) Training to failure and (b) modifying rep schemes and whether you fail or don't fail on every set.

If you believe in what you can read in many articles on strength training, both, training to failure and decreasing rest times / drop sets should significantly increase the muscle activity and thus - this is the most important thing - the number of motor units that are recruited during the exercises.
But is this actually true? I mean, is there a link between EMG activity, the number of motor units that are firing and the way you train? I guess, it would be wise to take a brief look at the pertinent research before we get to design and results of the individual studies. So, what do we have? As Looney et al. point out, motor unit activity can be measured through electromyography (EMG) which is commonly considered to reflect the neural drive to the muscle. Since the electrical impulse should be proportional to the number of motor units that are firing and in view of the fact that the latter determines the acute force output, it should be obvious that increasing force demands result in higher EMG amplitude due to the greater recruitment of motor units and faster firing rates necessary to increase the contractile force.

Figure 1: Previous studies show that the motor unit recruited (or at least it's indicator, the mean EMG values) increases over the duration of sustained or repeated muscle actions at a constant force level (Masuda. 1999 - l; Mottram. 2005 - r)

Unfortunately, more does not necessarily help more. If you take a closer look at the existing research you have to realize you cannot stretch this proven increase of the EMG amplitude (Carpentier. 2001; Fuglevand. 1993; Lind. 1979; Masuda. 1999; Mottram. 2005; Petrofsky. 1982) infinitely. Over prolonged exercise / contraction times, the initially increasing firing rates will eventually decrease. That this is the case is interpreted by many scientists as evidence of the the fact that the initial rise in EMG amplitude is just a compensatory mechanism for sustaining contractile force as fatigue accumulates (when the individual fibers fatigue, more are recruited to sustain the same force). This hypothesis appears to be confirmed by numerous investigations that have demonstrated that EMG amplitude increases during dynamic exercise as the extent of the effort, or number of repetitions performed, increases (Hasani. 2006; Spreuwenberg. 2006; etc.).
This is where the "train to failure to maximize motor unit recruitment"-theory comes from. After all, this observation indicates that usually inactive motor units are going to fire only during prolonged training at high intensities (best to failure). As usual, though, there are problems with this theory:

"While the increase in EMG amplitude observed during repeated muscle actions has been explained by increased central drive necessary to sustain force as fatigue accumulates, it is inconclusive whether fatigue derived from earlier performed exercise induces greater EMG amplitude during subsequent exercise. Previous studies have shown EMG amplitude diminishes after strenuous resistance exercise protocols. In contrast, Smilios et al. demonstrated progressive increases in EMG amplitude over a series of 20-repetition sets with gradually decreasing resistance interspaced with 2-minute rest periods. Further uncertainly exists pertaining to consecutive maximal effort sets with progressively lighter resistance performed without allotted rest periods. This frequently incorporated training technique, commonly known as a “drop set”, has remained relatively uninvestigated" (Looney. 2015).

Needless to say that we all expect that lighter weights can stimulate greater motor unit recruitment, if you use them in dropsets, but as Looney et al. say, the science that would conclusively confirm that is simply not there (yet). The goals of Looney's study were thus as follows:

• Firstly, confirm / refute the assumption that EMG amplitude would be significantly greater in light resistance exercise (50% 1RM) performed in rested conditions to a maximal number of repetitions than to a submaximal number of repetitions. 
• Secondly, assess whether the EMG amplitude would be significantly lower in maximal repetition sets performed in rested conditions with 50% 1RM resistance than with heavy resistance (90% 1RM). 
• Thirdly, test whether the EMG amplitude would be greater in maximal repetition 50% 1RM resistance sets performed in pre-fatigued conditions (no prior rest period) than in rested conditions. 

As the authors rightly point out, the "findings of this investigation would provide critical information on understanding the changes in neuromuscular physiology during dynamic exercise related to variable levels of target repetitions, resistance, and fatigue" (Looney. 2015) and may thus be of great value to scientists (initially, because the would have to still check the practical consequences of any increases in motor recruitment) and coaches + athletes (later). What the Hiscock study in which the researchers evaluated the rate of perceived exertion (RPE) and its correlation with muscle activation and lactate levels can add to the table is information on the effect of another parameter: Different rest times.
In order to avoid any confusion, though, let's initially look at the Looney study in isolation. In said study ten resistance trained men (age, 23±3 yr; height, 187±7 cm; body mass, 91.5±6.9 kg; squat 1RM, 141±28 kg) had EMG electrodes attached to their vastus lateralis and vastus medialis muscles on two occasions:

• A drop set day, on which he subjects performed three consecutive maximal repetition sets at 90%, 70%, and 50% 1RM to failure with no rest periods in between. 
• A single set day, on which the subjects performed a maximal repetition set at 50% 1RM to failure (no "dropping" involved). 

The analysis of the EMG data yielded overall unambiguous results: The maximal repetition sets to failure at 50% and 70% 1RM resulted in higher peak EMG amplitude than during submaximal repetition sets with the same resistance. In view of the fact that the peak EMG amplitude was significantly (P ≤ 0.05) greater in the maximal 90% 1RM set than on any of the other sets the subjects performed, the classic drop set with 90%, 70% and 50% 1RM should thus still have an edge over any regular "low intensity + high rep to failure" single set training. The question remains, however, whether it will also have the edge over conventional training?

Figure 2: Very general summary of the research interests and designs of the two studies discussed in today's waredownloadsoft article by Looney et al. (2015) and Hiscock et al. (2015)

We will get back to that question in the bottom line. In the mean time, let's briefly take a look at another, quite surprising result, one that will also lead us to the results of the previously mentioned study by Hiscock et al. (2015): The lack of association between the ratings of perceived exertion (CR-10). In contrast to what most of you certainly expected, the fatigue levels did not differ over the intensity range of loads and did not reflect the degree motor unit recruitment in any way (see Figure 3). You as an individual without the necessary technical equipment are thus probably unable to tell hor many motor units you've actually recruitment in a workout; and - even more importantly - the mere fact that you have to crawl instead of walk out of the gym is not a sign of a productive workout.

Figure 4: Mean number of repetitions (left, top), rate of perceived exertion (RPE | left, bottom), and peak EMG amplitude as a measure of motor recruitment (Looney. 2015).

You don't want to believe that? Well, bad luck for you: This result appears to be confirmed by Hiscock's study, in which 10 recreationally trained (>12 months of previous resistance training) did DB Curls and DB Hammer Curls on the preacher bench for three sets with their preferred arm at a constant load of 70% of their individual 1-RM over 4 trials:

1. 3 sets × 8 repetitions × 120 s recovery between sets; 
2. 3 sets × 8 repetitions × 240 s recovery; 
3. 3 sets × maximum number of repetitions (MNR) × 120 s recovery; 
4. 3 sets × MNR × 240 s recovery.

After each of the exercises the participants rated their overall and active arm muscle rate of perceived exertion (RPE-O and RPE-AM) and the data was correlated with the biceps brachii and brachioradialis muscle EMG activity during each set for each trial.

Figure 5: Despite sign. higher volumes (see boxes) and a 100% increase in rate of perceived local muscular exertion there was no significant increase in muscle activity with lifting 70% of the 1RM for 8 vs. to failure (Hiscock. 2015).

Just like in the Looney study, the measured rates of perceived exertion in the Hiscock study had did not correlate with with either the muscle activation or the lactate accumulation in the biceps. Rather than that, it appears as if the subjects' bicepses didn't even care about rep schemes and failure. While the RPE increased significantly, when the subjects trained to failure, the mean and peak EMG activity levels in Figure 5 are more or less identical for all rep x intensity (+/- failure) schemes.
References:

• Carpentier, Alain, Jacques Duchateau, and Karl Hainaut. "Motor unit behaviour and contractile changes during fatigue in the human first dorsal interosseus." The Journal of physiology 534.3 (2001): 903-912.
• Fuglevand, A. J., et al. "Impairment of neuromuscular propagation during human fatiguing contractions at submaximal forces." The Journal of physiology 460.1 (1993): 549-572.
• Gibson, A. St Clair, E. J. Schabort, and T. D. Noakes. "Reduced neuromuscular activity and force generation during prolonged cycling." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 281.1 (2001): R187-R196.
• Hassani, A., et al. "Agonist and antagonist muscle activation during maximal and submaximal isokinetic fatigue tests of the knee extensors." Journal of Electromyography and Kinesiology 16.6 (2006): 661-668.
• Hiscock, Daniel J., et al. "Muscle activation, blood lactate, and perceived exertion responses to changing resistance training programming variables." European Journal of Sport Science ahead-of-print (2015): 1-9.
• Lind, Alexander R., and Jerrold S. Petrofsky. "Amplitude of the surface electromyogram during fatiguing isometric contractions." Muscle & nerve 2.4 (1979): 257-264.
• Looney, David P., et al. "Electromyographical and Perceptual Responses to Different Resistance Intensities in a Squat Protocol: Does Performing Sets to Failure With Light Loads Recruit More Motor Units?." The Journal of Strength & Conditioning Research (2015).
• Masuda, Kazumi, et al. "Changes in surface EMG parameters during static and dynamic fatiguing contractions." Journal of Electromyography and Kinesiology 9.1 (1999): 39-46.
• McMahon, Gerard E., et al. "Impact of range of motion during ecologically valid resistance training protocols on muscle size, subcutaneous fat, and strength." The Journal of Strength & Conditioning Research 28.1 (2014): 245-255.
• Mottram, Carol J., et al. "Motor-unit activity differs with load type during a fatiguing contraction." Journal of neurophysiology 93.3 (2005): 1381-1392.
• Petrofsky, Jerrold Scott, et al. "Evaluation of the amplitude and frequency components of the surface EMG as an index of muscle fatigue." Ergonomics 25.3 (1982): 213-223.
• Smilios, Ilias, Keijo Häkkinen, and Savvas P. Tokmakidis. "Power output and electromyographic activity during and after a moderate load muscular endurance session." The Journal of Strength & Conditioning Research 24.8 (2010): 2122-2131.
• Spreuwenberg, Luuk PB, et al. "Influence of exercise order in a resistance-training exercise session." The Journal of Strength & Conditioning Research 20.1 (2006): 141-144.

Single-legged leg presses that make both legs stronger are only one of many topics, today.

Time for an update on the latest resistance training research - just the interesting stuff, obviously ;-) What exactly? Well, let's see: We'll take a look at how long rest periods sustain the exercise induced. Then, we'll dive right into a placebo-controlled study on blood flow restriction as a means of preconditioning before resistance training, only to top things off with a study that found that training your dominant leg will also increase the leg press strength of the untrained, non-dominant limb.

Ah, and since there was some space left in the bottom line, we will acknowledge that AM vs. PM training have identical effects on power, force and hormonal response in young men and pretend to be surprised that a three-set upper-body workout is much more energetically demanding than its one-set analog. All in all, a very balanced update on the latest resistance training research, I'd say.

• Long rest periods prolong testosterone response to bench press exercise -- From various previous waredownloadsoft articles you know that resistance training triggers an acute increase in testosterone. That this increase may depend on the rest between sets, though, is news. News from a recent article in the Journal of Strength and Conditioning Research.
  
  The purpose of the study was to examine the influence of rest period duration (1 vs. 3-minute between sets) on acute hormone responses to a high intensity and equal volume bench press workout (5x3 sets at 85% of the 1RM, to be specific).
  

  Figure 1: Mean (left) and individual (right) free testosterone levels before and after performing bench presses with 1 min or 3 min rest (Scudese. 2015).

  To this ends, Scudese et al. (2015) recruited ten resistance trained men (25.2 +/- 5.6 years; 78.2 +/- 5.7 kg; 176.7 +/- 5.4 cm; bench press relative strength: 1.3 +/- 0.1 kg/kg of body mass) and had them perform two bench press workouts separated by one week. Each workout consisted of 5 sets of 3 repetitions performed at 85% of 1-repetition maximum, with either 1 or 3-minute rest between sets. The rates of perceived exertion and serum levels of growth hormone (GH), cortisol, free and total testosterone were sampled at three different timepoints right (PRE), right after (T0) before, 15 (T15) and 30 (T30) minutes after. The results were as follows:
  • For total testosterone, both rest lengths enhanced all post-exercise verifications (T0, T15 and T30) compared to PRE, with 1-minute showing decreases on T15 and T30 compared to T0.
  • For free testosterone, both 1 and 3-minute rest protocols triggered augmentations on distinct post-exercise moments (T0 and T15 for 1-minute; T15 and T30 for 3-minute) compared to PRE.
  • Since the the cortisol values did not change throughout any post-exercise verification for either rests, the total testosterone/cortisol ratio was significantly elevated for both rests in all post-exercise moments compared to PRE.
    The growth hormone values did not change for both rest lengths.
  Now, that's exciting, right? The free testosterone levels kept increasing... well, not exactly. If you look at the data in Figure 1 right, you will notice interpersonal differences that suggest that the elevation would not have lasted for much more than those 15 extra-minutes .
  
  What's of significantly greater importance for the interpretation of the study results is yet a study by West et al. (2012) who observed that the testosterone response (both free and total) to resistance training is not associated with either strength or size gains. So what? It is very likely that the results of the study at hand are of zero practical relevance for your gains (strength- and sizewise, as West's study indicates).
• Blood flow restriction before strength training? It works - just as well as placebo! -- You will probably remember my recent article about the benefits of using blood flow restricting cuffs before a sprint workout, right (click here if not)? With the publication of the results of Moacir et al.'s (2015) latest study, we do now know that similar benefits will be seen with subsequent resistance training, too.

  The study at hand should make you question the results of the previously discussed study which did not have a placebo group | learn more

  "Thirteen men participated in a randomized crossover design that involved 3 separate sessions (ischemic preconditioning, placebo and control). A 12-RM load for the leg extension exercise was assessed through test and retest sessions prior to the first experimental session. The IPC session consisted of 4 cycles of 5 minutes occlusion at 220 mmHg of pressure alternated with 5 minutes of reperfusion at 0 mmHg for a total of 40 minutes. The PLACEBO session consisted of 4 cycles of 5 minutes of cuff administration at 20 mmHg of pressure alternated with 5 minutes of pseudo-reperfusion at 0 mmHg for a total of 40 minutes. 

  The occlusion and reperfusion phases were conducted alternately between the thighs, with subjects remaining seated. No ischemic pressure was applied during the control (CON) session and subjects sat passively for 40 minutes. Eight minutes following IPC, PLACEBO or CON, subjects performed three repetition maximum sets of the leg extension (2min rest between sets) with the pre-determined 12-RM load. Four minutes following the third set for each condition, blood lactate was assessed" (Moacir. 2015)

  When the researchers analyzed the results, they found that for the first set, the number of repetitions significantly increased for both the IPC (13.08 +/- 2.11; p = 0.0036) and PLACEBO (13.15 +/- 0.88; p = 0.0016) conditions, but not the CON (11.88 +/- 1.07; p > 0.99) condition.
  

  Figure 2: Significant increases in the number of reps (left) were observed for both the placebo and IPC group. The fatique index (right) did not differ between treatments, but the large inter-individual variety in the IPC group clearly suggests that BFR as a means of preconditioning ain't for everyone (Moacir. 2015).

  Similarly, the IPC and PLACEBO conditions resulted in significantly greater repetitions versus the CON condition on the 1st set (p=0.015; p=0.007) and 2nd set (p=0.011; p=0.019), but not the 3rd set (p=0.68; p>0.99). No significant difference (p=0.465) was found in the fatigue index and lactate concentration between conditions.
  
  As the researchers point out, their results "indicate that IPC and PLACEBO ischemic preconditioning may have small beneficial effects on repetition performance over a CON condition" (Moacir. 2015). It is thus not completely logical that they suggest "that ischemic pre-conditioning might be practiced gradually to assess tolerance and potential enhancements to exercise performance" (ibid.). What? Oh, you think your clients would notice that their blood flow is not actually impaired and the placebo effect would be lost? Right, now I understand why you should keep using it. Unfortunately that does not exclude that it is still a placebo effect which seems not unlikely in view of the larg(er) inter-individual differences in the IPC vs. any other group. Further studies are necessary... obviously!
• Train your right leg, and your left leg will become stronger, too - on leg presses, at least -- What sounds like a joke (or magic) is actually science. Science that is going to be presented in an article in a future edition of the Journal of Strength and Conditioning Research; and more precisely from a study that assessed the cross education of strength and changes in the underlying mechanisms (muscle size, activation, and hormonal response) following a 4-week unilateral resistance training (URT) program.
  
  In said study by Beyer et al. (2015), a group of nine untrained men completed a 4-week URT program on the dominant leg (DOM), while cross education was measured in the non-dominant leg (NON); and were compared to a control group (n=8, CON).

  "Unilateral isometric force (PKF), leg press (LP) and leg extension (LE) strength, muscle size (via ultrasonography) and activation (via electromyography) of the rectus femoris and vastus lateralis, and the hormonal response (testosterone, growth hormone, insulin, and insulin-like growth factor-1) were tested pre- and post-training" (Beyer. 2015).

  In all strength and size related measures, the trained group improved significantly better than CON. Significant group x time effects for PKF, LP, LE, and muscle size were observed only in the dominant leg (DOM), the non-dominant (NON = untrained leg), on the other hand, the scientist observed not just a trend, but rather an actual and statistically significant increase in leg press strength.
  

  Figure 3: Relative leg press and leg extension strength relative to body weight; the values above the post-bars indicate the relative difference between post and pre-test (2015).

  Whether that's related to the acute hormonal response to URT, the scientists observed, is more than questionable, after all the strength increase in the non-dominant leg didn't just occur in the absence of "detectable changes in muscle size, activation (EMG), or the acute hormonal response" it did also occur only during leg presses - if it was the result of any of the aforementioned factors one would expect to see at least something like a trend for leg extensions, as well.
  
  Against that background it should also be clear that you must not neglect one leg or arm when you train in the definitely false hope it would grow and the almost certainly false hope it would get stronger as you train your "favorite" limb.