Concomitant Training: Cardio Before or After Weights? Cardio First Triggers 916% Increase in Growth Hormone. Plus: 7x Higher Testosterone & 3x Higher IGFBP-3 Peaks

Run first, lift second to end your workouts on an anabolic tune.

I know, judging the anabolic effects of exercise by the post-exercise testosterone, cortisol, growth hormone and IGFBP-3 response is controversial. On the other hand, Claudio Rosa and his colleagues from the University of Trás-os-Montes e Alto Douro are right, when they argue that "concurrent training (CT),  is  an  effective strategy to improve both cardiorespiratory and neuromuscular functions (26), as well to induce a high-energy expenditure (2, 21)" (Rosa. 2014) that comes with one significant disadvantage; a disadvantage scientists have labeled stimulus interference.

A reduction / reduced increase of testosterone and or IGF, of which Rosa et al. state that they are the "most important  anabolic  hormonal  indicators  associated  with  muscle  hypertrophy" would be one of the many potential reasons for said interference.
Accordingly, the aim of the Portuguese scientists was to investigate and compare the hormonal responses (testosterone, cortisol, growth hormone, and IGFBP-3) to different intra-session endurance and strength training order in concurrently trained men.

Figure 1: Anaerobic and aerobic performance markers of the study participants (Rosa. 2014).

As the data in Figure 1 goes to show you, the trainees were no absolute noobs. In addition, all participants had been physically active and had engaged in concomitant training at least 3 times a week, during the previous 12 months.

The protocol of the strength training sessions was designed in order to consider an appropriate and efficient manipulation of several training variables which have been associated in the literature with higher energy expenditure during and after the exercise(s), namely: multiple sets; exercises recruiting large-muscle mass; movement speed; number of repetitions ; the intensity and volume of the workload; resting time between sets ; and the execution order of the resistance exercises.If you feel hypo after the workouts, that's the way to go... well, at least if you want to maximize your growth hormone production. Hypoglycemia, which is characterized by low blood sugar levels, is after all a potent stimulus to secretion of growth hormone (Roth. 1963). Needless to say that your blood glucose levels will be lower if you do cardio first, if this is going to be more anabolic is a whole different question, though.The endurance training exercise was performed on a treadmill. The training included 32 minutes of intermittent exercise, with 2 minutes at a speed corresponding to a blood lactate concentration of 2 mmol/L, alternating with 1 minute at a speed corresponding to a blood lactate concentration of 4mmol • L/1 (compare the actual running velocities in Figure 1).

Suggested read: "Don't Want to Sacrifice Your Strength on the Altar of Cardio Training? Creatine Monohydrate to the Rescue! Differential Effects on HIIT / Steady State, Legs / Chest" | read more

"The strength training included three sets of 10 repetitions with 70% of 1RM for the following exercises: squat (SQ), bench press (BP), leg press (LP) and front lat pull down (FLPD). Moreover, subjects were also required to perform three sets of 30 repetitions of the abdominal crunch (AC) and lumbar extension (LE) exercise with their own body weight.All sets of an exercise were completed before changing exercise. The ST exercises always followed this order: SQ, BP, LP, AC, FLPD, and LE. A rest interval of 1 minute was maintained between sets. A metronome (Quartz, São Paulo, Brazil) was set used at a cadence of 40 beats per minute in order to establish a rate of 20 exercise repetitions per minute." (Rosa. 2014)

If you imagine the resulting training program which was performed either with the endurance (ES) or the strength (SE) component first, you will realize that the result (specifically SE) is not too far off the average concomitant training regimen of the Average Joes and Janes at your gym.

ES = Endurance first, to maximize testosterone and IGFB-3? 

If you take a look at the outcome values, you will realize that there were significant effects for the main effect of time in the testosterone (p = 0.017) and growth hormone concentrations (p < 0.001), as well as a significant interaction between exercise order groups and time in the IGFBP-3 levels (p = 0.022).

Figure 2: Changes (pre vs. post exercise; %) in testosterone, cortisol, IGFBP-3 & GH (Rosa. 2014)

There were no significant interaction or main effects in the cortisol concentration (p > 0.05) or effects due to the exercise order (p > 0.05). Still, the testosterone and IGFBP-3 concentrations significantly increased in the ES group after the exercise trainings (57.7 ± 35.1%,  p  = 0.013 and 17.0 ±
15.5%, p = 0.032, respectively), only. In the "endurance second" (SE) group  the IGFB-3 levels actually decreased.
Reference:

• Rosa C, Vilaça-Alves J, Fernandes HM, Saavedra FJ, Pinto RS, Machado Dos Reis V. "Order effects of combined strength and endurance training on testosterone, cortisol, growth hormone and IGFBP-3 in concurrent-trained men". J Strength Cond Res. (2014): Jul 15 Ahead of Print. 
• Roth, Jesse, et al. "Hypoglycemia: a potent stimulus to secretion of growth hormone." Science 140.3570 (1963): 987-988.