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If Arnold did them you should do them, too - right? Curls and triceps extensions for bigger arms.  A recent study in subjects with at least two years of resistance training experience negates that: Neither size nor strength of the arms will benefit from isolation exercises. At least in trained athletes on an ABAB regimen w/ 4 workouts per week that's the case.

Some people say: "Squats, deadlifts and the bench! That's all you need to do." Others compile a longer list, but still believe that there's no need or even no room for single joint exercises like biceps curls or triceps extensions. Are they right? I mean, there's no debating about the time-efficacy of multi-joint only workout routines, but what about the "gains"? Will you compromise your strength and size gains on the altar of time efficacy?

A recent study from the Santa Cecilia University and other universities in Brazil tried to answer this and related questions in a group of  trained subjects: Their study evaluated the differential effects on alterations in upper body muscle strength and size of resistance training protocols involving only multi-joint (MG) or both multi-joint (MJ) and single-joined (SJ) exercises in a single workout session in trained men (França. 2015).
The participants were randomly assigned to one out of two groups: A combination group with both multi- and single joint exercise MJ+SJ (n = 10, 27.7 + 6.6 year) and a multi-joint only group MJ (n = 10, 29.4 + 4.6 years). To be included in the study, participants had to be currently practicing RT and have been continuously training for at least two years previous to the beginning of the study. Their programs had to involve both MJ and SJ exercises and had to be geared towards muscle hypertrophy. People with a history of anabolic steroid use were not accepted. Furthermore, all participants were instructed not change their nutritional habits or ingest ergogenic aids during the study. Minimum training attendance was set at 85% (all 20 volunteers complied).

"In order to increase ecological validity, RT [resistance training] program design and exercise choice were based on the common practices used in gyms and fitness centers by experienced trainees who desire to increase muscle strength and size. RT followed a linear periodization model with sequences of ordinary (two), shock (one) and restorative (one) microcyles as shown in Table 1" (de França. 2015).

During the ordinary microcycle, sets were performed to concentric failure - with one minute rest interval between sets. During the shock microcycle, each exercise was performed with the same load of the ordinary week, however, after failure, external assistance was given during the concentric phase to allow the performance of 2-5 additional repetitions, a method that's usually called forced repetitions (Ahtiainen. 2003).

Table 1: Periodization scheme used in the study (explanation follows | de França. 2015)

During the ordinary and shock microcycles,  the loads were reduced by ~10% from set to set to maintain the designated number of repetitions (Willardson. 2012). During the restorative microcycle, the loads were equivalent to 50% of the load used in the previous microcycle but the number of repetitions was kept at 10 and no load adjustment were necessary from set to set.

"Participants were instructed to take one second to perform the concentric and two seconds to perform the eccentric phase, whenever possible. Rest intervals were set at one minute between sets and two minutes between exercises" (de França. 2015).

Each session lasted approximately 35 and 50 minutes for MJ and MJ+SJ, respectively, and the subjects trained according to an A-B regimen that was performed twice a week for a total of four training days per week. In that, the lower limbs, low back and abdominal muscles were trained on Wednesdays and Saturdays through the same complementary training program for both groups.

Table 2: Overview of the RT programs | * denotes exercises done only in the MJ+SJ group (de França. 2015).

As show in Table 2, both groups performed the same MJ exercises, but the MJ+SJ groups also performed the exercises marked with asterisks. This means we are not comparing workouts with identical volume, but actually normal volume MJ only vs. high volume MJ + SJ workouts.
To assess the results of the program, the researchers did 1-RM tests (for strength) and measured the flexed arm circumference (FAC) and arm muscle circumference (AMC) before the training program and 5-7 days after the last training session (see red box to learn why this is important).

Figure 1: Pre-/post-changes in arm circumference and biceps + triceps strength (de Franca. 2015).

The results of these measurements or, more specifically, the mean changes between pre- and post-test are shown in Figure 1. As the scientists highlight in their paper, significant differences between pre- and post-tests (p<0.05) were found for all variables analyzed. Comparison between groups, however, did not show significant differences for any variable (p>0.05).
References:

• Ahtiainen, Juha P., et al. "Acute hormonal and neuromuscular responses and recovery to forced vs maximum repetitions multiple resistance exercises." International journal of sports medicine 24.6 (2003): 410-418.
• de França, Henrique Silvestre, et al. "The Effects Of Adding Single-Joint Exercises To A Multi-Joint Exercise Resistance Training Program On Upper Body Muscle Strength And Size In Trained Men." Applied Physiology, Nutrition, and Metabolism (2015): Ahead of print.
• Willardson, Jeffrey M., Roberto Simão, and Fabio E. Fontana. "The effect of load reductions on repetition performance for commonly performed multijoint resistance exercises." The Journal of Strength & Conditioning Research 26.11 (2012): 2939-2945.

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.