Everyone has heard of age old bodybuilding maxims like, "You don't grow when you train, you grow when you rest". Or, "If you under-train your progress will be slow, but if you over-train your progress will be zero." The popular explanation for the importance of recovery is that if you train too frequently you simply don't give your muscles enough time to recover. While this is true in a sense, the ability of individual muscle fibers to recover is not really all that limiting when it comes to what most people call recovery. This is particularly true if you train with body-part splits like most bodybuilders do. To illustrate the relative unimportance of muscular recovery, a marathon runner will go out and routinely run 10 miles every day. Competitive swimmers will routinely swim 2 or more hours per day. A pre-contest bodybuilder will often perform 45 minutes of cardio 6 days per week. When you think about it, that is loads of volume on individual muscles.

You'd think there'd be a lot of fatigue induced in your muscles after executing 4500 + consecutive stride reps for 45 minutes straight on a treadmill, stairclimber, or elliptical. Yet why is it that people can do cardio everyday without any problems, but only 30 reps or so of moderately heavy weight training for a given body-part can take a week to recover from? Well, one of the main reasons is that intense training like bodybuilding strongly involves the nervous system. A lot of bodybuilders do pay significant attention to recovery, but I believe most could stand to give more attention to the nervous system and its influence on recovery.

What is the Nervous System?

I'm not going to get into a big scientific rant on the various aspects of the nervous system and what they do. Really all you need to know is that the central nervous system includes your brain and spinal cord and connects to your muscles through the peripheral nervous system. Thus, the central nervous system controls your muscles. When you contract a muscle, a message goes down your brain and spinal cord where it eventually connects to the individual muscle motor units through something called a neuromuscular junction. The muscle receives your message telling it to contract, fires, and tension is generated. It's really that simple.

Neural Fatigue

It should come as no surprise that the nervous system can fatigue. That fatigue is paramount from a training standpoint. With neural fatigue, you can drain both the central nervous system, (the ‘brain’ - the cerebral cortex, cerebellum etc.), or the local nerves (neuromuscular junctions), that join the nervous system and the muscle together. Central fatigue appears to mainly be mediated by the effect of various stressors (including training) on neurotransmitters and hormones like dopamine, serotonin, epinephrine, and cortisol in the brain. Really, any type of stress can affect central nervous system recovery including undersleeping, partying and stimulant usage.

When the central nervous system is fatigued, the strength and functionality of all major muscle groups will be negatively affected, due to the fact that the battery that fires the muscles is drained. Not only will you have a tendency to feel a bit run down, but the control, function and strength of all your muscles becomes compromised. With excessive central fatigue, strength gains are hard to come by, which is one reason why powerlifters tend to train with less volume than bodybuilders, yet tend to gain more strength. Get too much central nervous system fatigue and you become over-reached and/or over-trained.

Think of the central nervous system as the central powerplant to a city. It’s a limited pool of energy. If the city gets too big and puts too much strain on a particular powerplant, the power goes out. Fatigue in the central nervous system explains the old, “throw a rock in the pool” effect of whole body movements. This is why you can do a hardcore leg workout today, come in the gym tomorrow, and find that the strength on your bench press is negatively affected. The fatigue in your bench press doesn't come from muscular fatigue, but through neural fatigue.

Local Neural Fatigue

In contrast to central nervous system fatigue, which affects the whole body, when the local nerves that join the nervous system and muscle together are drained, the strength and functionality of a given muscle group will be affected. So, if you do 10 sets of forearms today you could come back in the gym tomorrow and wouldn't find the strength of your quads, chest or hamstrings to be negatively affected. However, you probably wouldn't be able to lift the same weight in forearms tomorrow that you did today.

Now, why can a session of deadlifts and squats today have a negative effect on your bench press tomorrow, but forearms today not cause any fatigue in opposing muscle groups? Because deadlifts involve so many more muscles and require a much greater output by your CENTRAL POWER PLANT.

The reason cardio and other low intensity activities can be performed every day, even with significant muscular involvement, is because these activities don't create much central or local neural drain. On the other hand, activities like high intensity cardio and sprints are more like weight training as far as the way they impact the nervous system, thus tend to require more recovery time.
Calculating Central Fatigue

Central fatigue from weight training can be calculated by looking at the following factors:

1. Intensiveness level (psychological effort)
2. Magnitude of muscular activation (size and number of muscles activated)
3. Micro-trauma of a given stimulus (total protein breakdown in a workout)

Any of those things can affect central fatigue. From a psychological effort standpoint, this refers to motivation. Stimulant users get hardcore CNS type crashes when they come off a high. Training with extremely high levels of psychological intensity and motivation (getting slapped in the face to gear up for a heavy set) can create many of the same negative after-effects including sensitivity to light, muscle aches, pains, chronic fatigue, and lack of strength. All of these are due to CNS drain. This explains why just a single highly motivated PR type performance in something like a deadlift can leave you temporarily wired for a few hours, yet somewhat fatigued for the next week. Lifting with an extreme amount of intensiveness can allow you to lift more weight, but also prolongs recovery time, which is one reason why HIT devotees rest so long between workouts.

The number of muscles activated is fairly self-explanatory from a central fatigue standpoint. A leg workout is obviously going to be inherently more demanding than an arm workout.

As for micro-trauma, your body releases inflammatory cytokines (chemical messengers) in response to the muscle damage induced by your training. These inflammatory messengers go about the body and dock on receptors in your CNS, thus negatively affecting neural recovery. Some illnesses like chronic fatigue syndrome and fibromyalgia carry out their effects on mental state (depression, lack of energy, fatigue), through this same inflammatory process. This is why you're likely to feel drained through your entire body anytime you create a great degree of micro-trauma in a given body-part – particularly a large body-part. The amount of micro-trauma induced in a training session will be correlated with the volume of the eccentric contractions.

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Here are some examples of various workouts and their impact on the CNS:

• Low microtrauma + low motivation + medium muscle activation = Small drain. (low to medium intensity conditioning and cardio workouts)
• Low microtrauma + very high motivation + high muscle activation = Potentially high drain (maximal deadlift or squat single)
• High microtrauma + medium motivation + high muscle activation = High drain (standard bodybuilding leg workout)
• High microtrauma + low motivation + low muscle activation = Low drain (bodybuilding arm workout)
• Medium microtrauma + medium motivation + medium muscle activation = moderate to high drain (standard chest and back type upper body workout)
• Low microtrauma + low motivation + low activation = low drain (Abdominal, calf, and forearm training)

Basically, activities that could generally be considered high-intensity or highly draining activities would be the following:

1. Strength work (anything above 80% of 1rm for lower body and "whole body" movements such as deadlifts, squats etc.)
2. Lower body hypertrophy work (8-12 reps to failure
3. Maximum effort speed work with full recovery between reps
4. Maximum effort plyometric work (e.g. depth jumps)
5. Maximum effort agility and deceleration work will full recovery between reps
6. Maximum effort conditioning work (ie. Timed max effort intervals)
7. Combat sports - sparring and heavy bag
8. Any activity performed with heightened and competitive emotional intensity (competitions)
9. Any activity performed under the influence of artificial stimulants
(ephedrine, various energizing supplements)

Activities that could generally be considered low-intensity activities would be the following:

1. 1. Aerobic work
2. Sub-maximal conditioning work
3. Dynamic warm-ups and form running drills
4. Upper body isolation bodybuilding work (curls, triceps)
5. Sub-maximal speed work with full recoveries (runs less than 80% top speed)
6. Easy plyometric work (basic unilateral and bilateral hops etc.)
7. Footwork drills (agility ladders and dot drills)
8. Jump rope
9. Combat sports kata, mitt work, or shadowboxing

These activities tend not to induce much neural fatigue and can be repeated on a daily basis if desired.

The significance of all of this is anything that creates low strain won’t require much, if any, recovery time and won’t affect the body much from a systemic perspective. Anything that creates high strain will create at least a certain degree of whole body fatigue that will last around 48 hours. Standard upper body bodybuilding workouts and high intensity cardio would fall about right in the middle. They wouldn’t really be high intensity, yet wouldn’t be low intensity either. Anything that creates moderate strain will be variable as far as how it affects systemic recovery. You might be able to tolerate a moderate stimulus every day, but you might not.

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Recovering from CNS Drain

How do you recover once you've induced a good amount of central nervous system fatigue? Well, unfortunately, there are only really 2 things you can do. Give your body time and sleep!** One principle that has been around in the sports training world since probably the 1950's is that when the CNS is drained through high intensity effort, you should allow about 48 hours for it to recover. Any other intense activities you do within that 48 hr. time span will be negatively affected and possibly create more CNS drain then the body can comfortably deal with. Thus, from a nervous system standpoint, it’s really NOT a good idea to perform a hardcore leg workout today, come back tomorrow and do chest, come back the next day and do shoulders and arms, and so forth. Even though you’re working opposing muscle groups, you’re still stimulating the CNS to at least a moderate degree each and every day, and never really allowing complete central recovery.

** Some supplements like magnesium at 300 mg per day may also help with recovery from neural fatigue.

Many in the sports training world will place all highly intense activities together on the same days with 48 hours rest between ‘intense’ activities. Thus, instead of evenly distributing the workload throughout the week, many track and field athletes will place high intensity activities like weights, intense sprints, and plyometrics on Monday, Wednesday, and Friday, with low intensity activities (conditioning) on Tuesday, Thursday, and Saturday. Even though there is substantially more volume on hard days, this allows for better recovery of the nervous system between demanding workouts.

A bodybuilder can take advantage of the same methodology. Thus, instead of training on a split like this:

[b]Day 1[/b]: Chest and cardio
[b]Day 2[/b]: Hamstrings
[b]Day 3[/b]: Back and cardio
[b]Day 4[/b]: Quads
[b]Day 5[/b]: Shoulders, Arms and cardio
[b]Day 6[/b]: off
[b]Day 7[/b]: Start over with day 1

A bodybuilder would be better off from a recovery and strength perspective to train on a split like this:

[b]Day 1[/b]:
AM: Chest
PM: Hamstrings
[b]Day 2[/b]: off/forearms, calves, abs, cardio
[b]Day 3[/b]:
AM: Back
PM: Quads
[b]Day 4[/b]: off/forearms, calves, abs, cardio
[b]Day 5[/b]:
AM: Shoulders
PM: Arms
[b]Day 6[/b]: off/forearms, calves, abs, cardio

This split would serve the bodybuilder better because he'd have a full 48 hours between demanding sessions.

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Local Neural Fatigue and Recovery

Now let's talk about local neuromuscular recovery. This is referring to recovery from the fatigue induced in the neuromuscular junctions, which join the nervous system and muscular system together. You’ve probably heard the old 96-hour rule, which says a muscle should be given 4 full days rest after an intense training session because it takes that long for it to return to full strength. This is true. If you go in the gym today and knock out 5 heavy sets of bench presses to failure**, you'd probably have to wait at least 4 days before you'd be capable of repeating and/or beating what you did in that workout. Does that mean it really takes your muscles that long to recover? No, in reality, your muscles would be ready to go in about 48 hours or less, depending upon how fast they could resynthesize muscle glycogen. But it would take the neuromuscular junction that joins your muscle and your nervous system together about that long (4 days) to fully recover so that you could produce a maximal contraction.

**Stopping each set a couple of reps shy of failure allows for quicker recovery between workouts.