It's a form of circuit training that challenges both strength and cardiovascular systems. Complexes create a ton of metabolic stress and oxygen debt in a short period of time. Since you're using a moderate resistance, they also help to preserve lean muscle mass – an area where cardio falls short.

For a single complex, you'd perform 4-6 exercises in sequence, with minimal rest, using the same weight/resistance. For example, you'd do the entire complex with the same kettlebell, same dumbbell, etc. Typically, you wouldn't take your hands off the weight until the entire set is over.

For practical purposes, the weight remains the same throughout and, traditionally, so do the reps. But we'll address that in a minute.

Here's an example of a classic complex. Note the exercise order and the same number of reps being used throughout.

• Row x 4-6
• Clean x 4-6
• Front Squat x 4-6
• Military Press x 4-6
• Back Squat x 4-6
• Good Morning x 4-6

We can make this work even better. But first...

• Complexes put a very high demand on your anaerobic energy systems (both ATP-PC and glycolytic systems). Using these energy systems for repeated bouts is associated with growth hormone release and activating the biochemical pathways associated with fat loss.
• Complexes cause a ton of excessive post-exercise oxygen consumption (EPOC). Although not as large an "afterburn" effect as some might have you believe, around 30 minutes will cause a spike in your metabolic rate for up to 38 hours. Effects range from tens to hundreds of extra calories burned, even at rest.
• Complexes are a form of resistance training. That means stronger muscles, bones, and connective tissues. Traditional cardio just doesn't compare.
• Steady-state cardio can promote muscle breakdown, especially when in a calorie deficit. This is due to activation of certain biochemical processes (namely the AMPK pathway). Complexes, on the other hand, will have a muscle-sparing effect.

The biggest downfall of complexes? You're using the same weight throughout.

In the example above, imagine if you were to do each exercise without a time limit. You'd select a different weight for each exercise, right? You'd probably lift the most in the back squat and the least in the military press.

Being time efficient is important, but so is maximizing your workout productivity. With upgraded complexes, you'll be varying the reps based on each exercise and your ability. This helps to accommodate for the same resistance being used throughout and works to load each exercise more appropriately.

The second major upgrade is in the order of exercises. Unlike common weight circuits which lack purpose, complexes should have a specific structure that allows each exercise to be challenged. While the aforementioned complex does flow nicely and does have some purpose, it could flow just as nicely but pack an even bigger punch.

As an example, let's look at how mechanical drop-sets work. In short, with the same weight you'd start your set with your weakest exercise first. Once you reach near technical failure you'd then change to an easier variation, then switch to an even easier variation after that. Each change in variation represents a "drop," but instead of dropping weight you're manipulating the exercise and leverage factors to continue your set. It's horrible, but in a good way.

If you want to maximize both fat loss and muscle gain, metabolic complexes should be viewed in much the same way. Think of it as a "metabolic mechanical drop set" for your entire body.

Since this is a high metabolic stress technique, it's also wise to choose your exercise order carefully to avoid sloppy reps.

Let's cut right to the chase and look at some upgraded complexes, then we'll break down what's happening below.

Each of these will take you 15-20 minutes, maybe less.

You'll use the same weight throughout the complex, but your rep ranges for each exercise within each complex can vary. Just choose the right weight on the first exercises in the complex. That's a weight that allows you to get 10-12 reps.

With each exercise to follow, just stop a couple of reps short of failure. If you hit 6 reps with one exercise and 15 reps with another exercise, that's fine.

Note: The videos only show 4 reps of each exercise for demo purposes.

Single Dumbbell Complex

Select a weight you can do 10-12 dumbbell power snatches with. Do 3-4 rounds of the entire complex using the same weight.

• Hang Power Snatch, Each Side
• Dumbbell Row, Each Side
• Reverse Lunge, Each Side
• Push Press, Each Side

Two Dumbbell Complex

Select a weight you can do 10-12 hang power cleans with. Do 3-5 rounds.

• Hang Power Clean
• Strict Shoulder Press
• Bent-Over Row
• Front Squat
• Romanian Deadlift

Kettlebell Complex

Select a weight you can do 10-12 kettlebell clean & presses on each side with. Do 3-5 rounds.

• Clean & Press, Each Side
• Dead-Stop Row, Each Side
• Kickstand RDL, Each Side
• Goblet Squat

Barbell Complex

Select a weight you can do 10-12 hang high pulls with. Do 3-5 rounds.

• Hang High Pull
• Pendlay Row
• Front Reverse Lunge
• Romanian Deadlift
• Sumo Deadlift

1. When arranging exercises, Olympic lift variations should come first, if ever.

Exercises should be performed in a descending order from the most technically demanding to the least technically demanding (whenever possible). Ideally, try to place the most technical exercises towards the start where fatigue is lowest. The complexity will also depend on your abilities.

If you're going to use Olympic lift variations, these will go first due to their high complexity. That being said, you should still be picking versions of these with low relative complexity. High pulls and power variations are much safer when you're fatigued.

Placing every exercise in order of complexity isn't always possible, but try to start with the most complex exercise when you can.

2. Select the best exercises. Period.

During complexes there's no room for prissy isolation exercises, or those that look more at home in a circus. You want exercises that activate the most muscle tissue and force the most output. This will likely include some kind of squat, deadlift, row, and press.

3. When arranging exercises, start with your weaker lifts and end with your strongest.

Put some key lifts down on paper and arrange them in order of weakest to strongest. Ignore everything you know about structuring strength workouts.

Remember, to do these well it should feel a little like a mechanical drop set. There's no point starting with a heavy deadlift then trying to row with the same weight. It might go against typical strength programming rules, but flipping that order will ensure that the weight is set better for the rows before crushing it with the deadlifts. Your back will also thank you.

4. Use a non-competing exercise order whenever possible.

Non-competing exercises are those that don't rely on the same muscles. This allows one muscle group or pattern to work while a potential antagonist is resting.

Given that many complexes work multiple muscles at once, and Law 3 should take precedence, don't get too hung up on this. If possible, try to alternate a pushing exercise with a pulling exercise, a quadriceps-dominant exercise with a hip-dominant exercise, etc.

For example, there's no need to program a front squat and back squat in the same complex. You're better off leaving the second squat variation for another complex.

5. Select the weight based on your weakest lift.

This works alongside Law 3 to ensure you get the most out of each exercise.

Let's say you pick a weight you can bent-over row for 10 reps (your 10RM). Once you reach around 6-8 reps you'd then change to the next exercise where the same weight will allow you to complete even more reps.

If your first exercise is an Olympic lift variation, then you'll want to be using a lighter weight for these anyway. This helps maintain explosiveness.

6. Don't go too light and don't AMRAP!

Complexes should be relatively short. The entire draw is that they're brutal but brief.

Using somewhere near your 10-12 rep max of your first exercise will generally produce the best results as far as body composition goes. The weight is heavy enough to stimulate some hypertrophy and not take a lifetime to complete, while light enough to create a metabolic training effect.

Keep your form in check and never go to absolute failure with any exercise. Always have two good reps in reserve for each exercise for the duration of the complex.

7. Be flexible with rep ranges.

Set repetition ranges rather than specific repetition goals. There seems to be an unwritten rule in any circuit-type training that every exercise needs to be done for the same amount of reps.

Instead, set your first exercise to be in the vicinity of a 10-12RM, then simply hit a few reps short of failure with each exercise to follow. If you hit 6 reps with one and 15 reps with another, no problem. Not every exercise in the complex has to be 4-6 or 8-10 reps.

8. Test and try!

Rather than jumping straight into a metabolic complex, do a tester workout. Or at least do some warm-up sets. That way you can work out exactly what weight you need and set some target rep ranges.

Testing also allows you to see how it feels and if it flows as it should. While traditionally, complexes don't allow you to put down the weight until the end of each circuit, feel free to put it down for 10 seconds if it helps you reset and maintain better form.