Push – Pull?
One of the most common strategies for muscle grouping is known as “Push / Pull”. This is where the (so-called) “pushing muscles” are done on one day, and the (so-called) “pulling muscles” are done on a different day. I say “so-called” because all muscles actually pull. No muscles “push”. When they contract, they shorten – pulling the ends together – which then either flexes or extends a joint.

Still, the “pushing muscles” are known to be the Pecs and the Triceps. While the “pulling muscles” are thought to be the Back and the Biceps. (Note: Obviously “push” and “pull” were so named only because the weight being moved is getting farther away from the body, or closer to the body. Frankly, this is an absurd method of categorizing muscles. A muscle has no “idea” whether the weight it is moving is getting closer to the body or farther away from it.)

The rationale for this type of grouping is the belief that while the Pecs are working, the Triceps are assisting. So one “might as well” finish off the Triceps at that time. Similarly, when the Back muscles (Lats, middle Traps, Teres major, etc…) are working, the Biceps are assisting. So one “might as well” finish off the Biceps at that time. Yet, if one performs better Pectoral exercises, there would be little Triceps participation. And if one performs the better “back” exercises, there would be little Biceps participation.

So, this grouping rationale has already failed the first test. If one does experience considerable Triceps and Biceps fatigue, while doing their Pectoral and “Back” workouts, it’s safe to say that those workouts have other mechanical inefficiencies which should (ideally) be resolved, for maximum benefit to the Pecs and “Back”.

One would NOT feel much Biceps and Triceps fatigue during highly efficient Chest and Back workouts. Further, it would better to work the Biceps and the Triceps when they are fresh (on a different day) – not after they have been pre-fatigued by poorly executed Chest or Back exercises.

A More Sensible Approach for Muscle Combining
What makes more sense with body part grouping, is to combine opposing movements in the same workout. In other words, use “reciprocal innervation.” The fact that working an agonist muscles facilitates relaxation of the antagonist muscle – as the rationale for grouping those muscles in a given workout. Rather than working two muscles that may be working simultaneously (e.g., Chest and Triceps), it’s more sensible to work two muscles that do not work simultaneously (e.g., Chest and Back).

When the Pectorals work, the Back muscles are fully relaxing -and vice versa. This ensures that each muscle is fresh (recovered) each time you perform a set for that muscle. Here (below) are some of the “opposing muscles”, which would make for good muscle grouping in a given workout:

• 1 Chest / Back
• 2 Front Deltoids / Rear Deltoids
• 3 Biceps / Triceps
• 4 Quadriceps / Hamstrings
• 5 Abdominal / Lower Back
• 6 Forearm Flexor / Forearm Extensor
 (Note: Not all movements have, or require, an opposing exercise. For example, Calves (plantar flexion) does not automatically require that Tibialis anterior be worked; Glutes (hip extension) does not automatically require that Hip Flexors be worked; Medial Deltoids (lateral abduction) don’t really have an antagonist muscle – so a good strategy here is to alternate between right side and left side.)

Creating a Workout Structure
First, decide whether you want to divide your workouts into a two-way split, a three-way split, or a four-way split. Choosing between these three options assumes a person’s goal is ambitious enough to want more muscle gain than can be achieved with a single “full body workout” performed two or three times per week. This would be decided, in part, on how advanced – and how ambitious – a person is, as well as issues related to personal goals and time constraints.

My personal preference (which is “advanced”) is a four-way split program, which means doing four separate workouts with which to work the entire body. I like the four-way split because it allows me to complete each workout in a reasonable amount of time (approximately 1.5 hours), and yet still spend “enough” time (i.e., 6 to12 sets) on each muscle group. The next issue to consider is the frequency with which you would work each individual (physique) muscle. Ideally, a muscle should not be worked more frequently than three times per week, nor less frequently than one time per week.

There are roughly 15 muscle groups which “should” be worked. These include the following: Pectorals, Latissimus, “Upper Back” (middle Trapezius), Upper Trapezius, Medial Deltoids, Posterior Deltoids, Anterior Deltoids, Triceps, Biceps, Quadriceps, Hamstrings, Glutes, Calves, Abs and Obliques.

A person could also add a few more muscle groups, like – forearm flexors, forearm extensors, frontal neck, side neck, posterior neck, Tibialis anterior, Hip flexors, Erector spinae, shoulder rotators, etc. It depends on a person’s degree of ambition, and the amount of time they’re able to spend in the gym.

As a general guideline, I usually recommend that a person who only wants to workout three days per week, do a full-body workout, performing 3 sets per muscle group, per workout. That’s 45 total sets – assuming a person works all 15 basic physique muscles. In this case, a 90 minute workout would allow an average of 2 minutes per exercise, including recovery between sets.

A person who is willing to workout four times per week, could split their body parts into two groups (a 2-way split), and perform 5 or 6 sets per muscle group. This results in each muscle getting worked a little harder, but twice per week. A 3-way split (dividing the muscle groups into 3 separate workouts) can be used by a person who is able to workout 4 to 6 days per week. With this grouping, a person could do either do 5 or 6 sets per muscle group, and simply have a shorter workout… or he/she could do 8 to12 sets per muscle group.

This latter option would allow more intensity (“volume”) to be used. A 4-way split is useful if a person is doing more body parts than the 15 basic muscles mentioned above, or who wants a shorter workout. However, this option would ideally require a minimum of five or six workout days per week – in order to get enough frequency of workouts per muscle group. The four workouts would simply be rotated around the five or six days of the week selected as “exercise days”.

Here’s the typical workout structure I use:
• Day One: Chest & Back (Pecs, Lats and middle Traps)
• Day Two: Shoulders (Deltoids – Medial, Posterior, Anterior – plus upper  Trapezius and Infraspinatus / external shoulder rotator)
• Day Three: Arms, Forearms & Abs (Biceps, Triceps, Forearm Flexors, Forearm Extensors, Rectus abdominis and Obliques)
• Day Four: Legs (Quadriceps, Hamstrings, Glutes / Adductors, Calves & Hip Flexors)

Here’s is one way this could be scheduled, but several other variations could be created:

This particular workout schedule would allow you to work each muscle group three times every two weeks – or one time every 4 or 5 days.

Intensity, Recovery & Adaptation
A discussion on “how to structure one’s workout” would be remiss if the issues of intensity and recovery were ignored. However, as mentioned before, this book is primarily intended as a bio-mechanics guide. Muscle physiology is another subject altogether, and a complex one at that. Nevertheless, we can review some basic points. In general, a muscle needs a least two or three days of recovery after a workout – assuming a moderately high level of workout intensity is used. If one trains at higher levels of intensity, four or five may be required before that muscle can be worked again. The time between workouts for a given muscle is considered the “recovery” phase.

After the recovery phase, we transition into the “supercompensation” phase. This is where the muscle is adapting to the stimulus from the previous workout, with a slightly higher performance capacity – “preparing” itself for the next such encounter. Ideally, one should work a muscle again while at the peak of the “supercompensation” phase. This is important, because this phase begins its decline after the peak. If one waits until this phase has ended (see chart above), one returns to the baseline – almost as if no workout had occurred.

Working a muscle again, while it is at the peak of the “supercompensation” phase, will push it up to a higher level of strength / growth. This is how “muscle accumulation” (growth) occurs. It builds on previous “highs” – like adding small amounts of sand to a pile, which eventually becomes a “hill.” This is why infrequent workouts (done after the “supercompensation” phase has passed), is like starting over again at the baseline each time.

Conversely, if the next workout (for that particular muscle) occurs too soon after the previous workout, “over-training” occurs. “Too soon” would be before the recovery phase is complete; the muscle would not have had the chance to experience even then earliest part of supercompensation. When this happens, progress (muscle growth) for that muscle, would be impeded – or possibly even reversed.

Of course, the issue of exercise intensity factors in here. Using less workout intensity theoretically warrants less recovery time, and using more workout intensity theoretically warrants more recovery time – but only up to a point. There is such a thing as an “ideal intensity” for optimal results (green line, below). Ideally, it should not be too low nor too high.

The belief (by some) that annihilating a muscle during a workout (leaving it absolutely limp with fatigue) will lead to maximum muscle gains, is not correct. Recovery time is not the absolute equalizer of the intensity level used. One cannot make up for insufficient workout intensity, simply by taking less time between workouts. Also, one cannot make up for excessive workout intensity, simply by taking an extra day or two of rest, between workouts.

Too much exercise intensity results in muscle damage, from which one cannot easily recover. Yes – as we progress, our tolerance increases, and higher intensity is possible. But there is always a point of “too much.” The most extreme form of muscle damage caused by overly intense exercise is called “Exertional Rhabdomyolysis”. When this occurs, the muscle severely breaks down. Its byproducts (which enter into the bloodstream) are harmful to the kidneys – possibly leading to kidney failure.

Of course, this degree of “over-training” is extremely rare, especially in advanced athletes who are already highly trained. But it can still occur, even in advanced athletes. There are several stages of over-training that occur before the onset of Exertional Rhabdomyolysis. In other words, one does not need to get to the extreme point, before overly-intense efforts have become counterproductive.

The “right amount” of workout intensity is required, and this varies from person to person, based on a number of factors. These include one’s individual health, enough sleep, sufficient caloric intake, adequate endocrine production, other daily activities (calorie demands) – and one’s current level of strength / endurance. Each person should experiment to find their own optimal level of workout intensity, and then balance that with exercise frequency.

Conclusion
Reciprocal Innervation is part of the amazing natural design of the human body. Understanding the role it plays in Resistance Exercise allows a person opportunities to optimize muscle hypertrophy. However, it can also interfere with efficient workouts, if one is unaware that they are causing a “relaxation synapse” to be sent to their target muscle, due to a less-than-ideal exercise. Reciprocal Innervation can (and should) play an important role in exercise selection, exercise productivity, exercise comfort and exercise program design (muscle grouping).

Virtually any kind of body part combining will produce results (muscle growth), including conventional “Push/Pull”. I am not suggesting the using “Reciprocal Innervation” to organize one’s muscle groups into separate workouts is the “right way”, and all others are the “wrong way”. However, I do believe it’s a better way. It makes good sense to set up one’s workout plan in a way that creates as little “conflict of interest” as possible. It is advantageous to work a muscle group without it having any pre-exhaustion from a previous exercise. Using “Reciprocal Innervation” allows us to do that.