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What now? Wait 3 minutes or off to the bench for an alternate set of bench presses or pulls ?

Traditional strength training with 80% of one-repetition maximum (1RM) utilizes 2- to 5-minute rest periods between sets. These long rest periods minimize decreases in volume and intensity, but result in long workouts. Performing upper-body exercises during lower-body rest intervals may decrease workout duration, but may affect workout performance.

The above is how Anthony B. Ciccone, Lee E. Brown, Jared W. Coburn, Andrew J. Galpin kick off their latest paper in the venerable Journal of Strength and Conditioning Research (Publish Ahead of Print).
The purpose of the corresponding study was to compare the effects of traditional to those of alternating whole body strength training on squat performance. To this ends, Ciccone et al. recruites 20 youn men, who had to perform two workouts:

• The traditional set workout (TS) consisted of four sets of squats at 80% of 1RM on a force plate with 3-minutes rest between sets. 
• The alternating set workout (AS) also consisted of four sets of squats at 80% of 1RM but with bench press, and bench pull exercises performed between squat sets 1, 2 & 3 with between-exercise rest of 50 seconds, resulting in approximately 3-minutes rest between squat sets. 

For both workouts, sets 1-3 were performed for four repetitions, while set four was performed to concentric failure. The total number of completed repetitions, the peak ground reaction force (GRF), peak power, (PP), and average power (AP) of every squat repetition were recorded and averaged for each set.

Figure 1: Maximal # of reps on last set and average power in the classic vs. alternating condition (Ciccone. 2014)

Interestingly, there was no significant interaction for GRF, PP, or AP. Only, the volume-equated AP was ca. 5% greater during the TS condition (989 ± 183) than the AS condition (937 ± 176). A more pronounced difference which was yet still within the margin of one standard deviation (in this case 2.2. reps) was observed for the fourth squat set to failure, where the TS condition resulted in 15% more reps to failure (7.5 ± 2.2) than the AS condition (6.5 ± 2.2). Reason enough for Ciccone et al. to suggest that:

1. Individuals who aim to optimize squat AP should refrain from performing more than three AS sets per exercise.
2. Those who aim to maximize squat repetitions to failure should refrain from performing upper body multi-joint exercises during squat rest intervals.

Certainly a sound advice, but in the end, we all live in a world where time is a precious gem and some people give a fuck about average power and the number of reps until they fail.
References:

• Ahtianen, 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.
• Ciccone AB, et al. "Effects of Traditional Versus Alternating Whole-body Strength Training on Squat Performance." J Strength Cond Res. (2014) Jun 17. Ahead of print.
• de Salles, Belmiro Freitas, et al. "Rest interval between sets in strength training." Sports Medicine 39.9 (2009): 765-777.

The study tested only leg exercises, but you can safely expect increased reps on other exercises, as well.

Citrulline? Yes thats the stuff the supplement industry claims to be a better version of arginine. A "super pump supplement", but not necessarily an ergogenic - in spite of the fact that corresponding evidence from rodent and human studies (Briand. 1992; Pérez-Guisado. 2010; Giannesini. 2011) existed years before the study at hand was published (Wax. 2014).

Benjamin Wax and his colleagues from the Mississippi State University and the Auburn University  investigated the effects of citrulline malate supplementation on lower-body resistance exercise performance, blood lactate, heart rate, and blood pressure.

Based on citrulline malate’s chemical composition and a review of the current literature Wax et al. hypothesized that citrulline malate supplementation would mitigate fatigue occurring to the working muscle; therefore, augmenting resistance training performance.
To test their hypothesis the researchers recruited 12 advanced resistance trained male subjects (85kg body weight; <12% body fat; 22.1 ± 1.4 years) and conducted a randomized, counterbalanced, double blind study.

The subjects were randomly assigned to placebo or citrulline malate (8 g; 60 minutes before the workout) groups and then performed repeated bouts of multiple lower body resistance exercise:

"Subjects warmed up on an upright stationary bike (Life Fitness, Brunswick Corporation, Lake Fores, IL) for five minutes, at 60 – 70 revolution/minute with a mass of 3 – 5 kg. Following this warm up, subjects performed two warm up sets (10 repetitions at 90.9 kg and 8 repetitions at 136.4 kg) on the leg press machine. Subjects rested three minutes between sets during the warm up and trial sets.

Next, 60% of each subject’s predetermined 1RM was loaded on the leg press machine and the subject completed as many repetitions as possible until failure occurred. This process was completed for 4 additional sets for a total of 5 sets on the leg press. Next, the subjects performed one warm upset (10 repetitions) on the hack squat machine at a mass of 40.9 kg. This warm up set was followed by 5 sets of 60% of their predetermined 1RM to failure. Finally, following one warm up set (10 repetitions at 36.4 kg) on the leg extension, subjects completed 5 sets of 60% of their 1RM to failure." (Wax. 2014)

The rest periods (recovery periods between sets of exercise), exercise order, and number of sets performed were the same for all subjects in this investigation, for sessions 2 and 3. Blood lactate, heart rate, systolic blood pressure, and diastolic blood pressure were determined pre and post exercise.
The exercise protocol resulted in sequential significant (p < 0.05) decrease in the number of repetitions in all three exercises. However, subjects in the citrulline malate group performed significantly (p < 0.05) higher number of repetitions during all three exercises compared to placebo group.

Figure 1: Wax et al. observed significant increases in maximal leg press, hack squat, and leg extension (not shown) repetitions in response to the ingestion of 8g of citrulline malate 60min before exercise (Wax. 2014)

Blood lactate and heart rate, on the other hand, were significantly increased (p < 0.05) post-exercise in both groups with no significant inter-group differences between citrulline malate and placebo (p > 0.05).
References:

• Briand, Joël, et al. "Use of a microbial model for the determination of drug effects on cell metabolism and energetics: Study of citrulline?malate." Biopharmaceutics & drug disposition 13.1 (1992): 1-22.
• Hickner, Robert C., et al. "L-citrulline reduces time to exhaustion and insulin response to a graded exercise test." Medicine and science in sports and exercise 38.4 (2006): 660-666.
• Giannesini, Benoît, et al. "Citrulline malate supplementation increases muscle efficiency in rat skeletal muscle." European journal of pharmacology 667.1 (2011): 100-104.
• Pérez-Guisado, Joaquín, and Philip M. Jakeman. "Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness." The Journal of Strength & Conditioning Research 24.5 (2010): 1215-1222.
• Verleye, M., et al. "Effects of citrulline malate on bacterial lipopolysaccharide induced endotoxemia in rats." Arzneimittelforschung 45.6 (1995): E712.
• Wax, Benjamin, et al. "Effects of Supplemental Citrulline Malate Ingestion During Repeated Bouts of Lower-body Exercise in Advanced Weight Lifters." The Journal of Strength & Conditioning Research (2014).

Original image from the publication.

As Meaghan E. Maddigan, Duane C. Button and David G. Behm from the Memorial University of Newfoundland rightly point out, "the back squat is a traditional resistance training exercise." (Maddigan. 2014).

The use of resisted sled exercises, on the other hand, is a relatively new phenomenon of which we dont even know yet how it compares to the classics.

Accordingly, Maddigan et al. set out to compare the muscle activation between squatting and sled pushing on the activity of leg and trunk muscles in ten healthy resistance-trained men in the context of a randomized crossover design study.
The study consisted of 2 preparation sessions and 2 testing sessions. Electromyographic (EMG) activity of the rectus femoris, biceps femoris, gastrocnemius, lower erector spinae, and the transversus abdominis/ internal obliques (TrA/IO) were monitored during a 20-step maximum push with the weighted sled apparatus and a 10 repetition maximum with a bilateral back squat.

All ten subjects were healthy resistance-trained men (age 24.6 years, mass 84.5 kg, height 178.3cm) who had at least 2 years of resistance training and squat experience and were also familiar with performing the sled exercises (however, the volume of squat experiences exceeded sled training volumes or training durations).

Figure 1: Average root mean square (RMS) EMG recorded in exercise phase 1, 2, and 3 (EMG signal was calculated over a 1-second segment of the concentric contraction phase of each step or repetition) from (A) rectus femoris, (B) biceps Femoris, (C) gastrocnemius, and (D) erector spinae during the concentric portion of the sled and squat exercises. Open circles represent the sled condition, whereas the filled squares represent the squat condition (Maddigan. 2014).

As you can see in Figure 1 there were nonsignificant trends for the rectus femoris ( p = 0.092: 8.6– 16.7%) and biceps femoris ( p = 0.09: 10.5–32.8%) to demonstrate higher activity with the sled and squat exercises, respectively. A result based on which you could conclude that

• squatting is better for the quads, while
• sled pushing is th better hamstring exercise

Maddigan et al. also observed main effects for condition with 61.2% greater gastrocnemius EMG with the sled exercise ( p = 0.01) and 74.5% greater erector spinae EMG activity with the squat (p = 0.002). For the transversus abdominis/ internal obliques, however, there were no significant differences between the exercises for the.
References:

• Maddigan, Meaghan E., Duane C. Button, and David G. Behm. "Lower-Limb and Trunk Muscle Activation With Back Squats and Weighted Sled Apparatus." Journal of strength and conditioning research/National Strength & Conditioning Association 28.12 (2014): 3346-3353.