Increasing Metabolic Stress vs. Increasing Mechanical Strain
Increasing metabolic work is pretty easy. If you do a short bout of HIIT cardio with a full-body exerciser, you'll induce enough metabolic stress in your legs and back. If you do 15s after your normal set, you'll induce enough metabolic stress.
You also know that increasing metabolic work, partially by further activating the erk1/2 pathway, increases the muscle's metabolism, which increases mobilization of nutrients, increases glycogen and speeds protein uptake at a faster pace, improves recovery, etc. It stimulates sarcoplasmic hypertrophy and indirectly sarcomere hypertrophy.
But, the question remains: should you spend your extra time working on burn sets, or should you be trying to add another set of incline flies?
1) Extra metabolic work (esp. failure) can fry your neuromuscular junction and ECC system. This decreases the ability to excite the muscle to contract, but it also decreases your general ability to produce neural drive. However, most of us are good at managing this kind of fatigue now, and you can help things by replenishing glycogen and sleeping more. Moreover, this tends to be more skill-specific. Even if you fried out on dips, you can still manage on the incline press. If you did breathing squats, you can still muster enough to do leg extensions.
2) Extra mechanical strain, i.e. muscle damage by eccentric strain, decouples the ECC system quickly. The difference is that though you can muster the neural drive, you immediately find your muscle unresponsive. This transcends specific movements too. If you did negatives on flies, with little metabolic fatigue, than tried to do a normal bench, that bench will be suddenly very hard. To compensate, you would increase neural drive, which leads to step 1. Therefore, in my opinion, increasing strain -- though it will directly stimulate sarcomere hypertrophy -- has much higher risk for causing problems with progressive loading with 3x-a-week or higher frequency.
In a sense, it becomes an issue of descending risk. If you want to bring up a bodypart, you increase strain on it. Once you've designed your work to increase strain, you have to review your training experience and consider whether adding more strain (by adding more sets, increasing stretch, using a modality) will cause problems with completing the next workout. If you think this could be a problem, then you look at increasing metabolic work. Once you've done this, then you finally look at how many sets you want to add to all of your exercises to bring up the bottom line effect.
Range of motion, Concentric vs. Eccentric Contraction
There's sort of reciprocal relationship between Range of Motion and muscle. The more you increase stretch, the more amenable muscle becomes toward strain (and increasing the p38 signal.) But, the more you increase the contraction, the more a muscle becomes likely to fatigue. Two reasons figure into that: the force-production in an extremely contracted position signifiantly drops (though leverage factors can play a larger role in the actual strength strength), and decreases supply of oxygen to muscle.
Also, the concentric and eccentric portions of exercise work like a pump -- the lengthening of muscle pools blood in, the shortening of the muscle pumps it out. So, on a metabolic stress scale . . .
1) Contracted position > Stretched position
2) Concentric movement > Static > Eccentric
Essentially, you want to manipulate these two variables as best you can in order to generate metabolic stress from the set. Lengthening the period of concentric movement increases metabolic stress. Working from a more contracted position increases metabolic stress.
Rep cadence and TUL
Shortening and lengthening velocities (provided you're not going too slow that it's turning into static contractions) do not seriously factor into force production. However, they affect metabolic stress in basically two ways:
1) Vary the effective TUL ratio between concentric and eccentric. Practically speaking, we're talking about accumulation of metabolic stress vs. respite of same stress. The higher the concentric phase is relatively to eccentric, the higher net metabolic stress will be created for a given TUL. In effect, you want to delay the respite.
2) In the case of isolation exercises and any movements where the weak-link is at contraction (i.e. pulling movements), a slower rep speed of the concentric portion increases the rate of accumulation of fatigue. In fact,
slowing down as you complete your concentric rep, is the best way to go. The more contracted positions (specifically, in isolation and pulling movements) have significantly effect for metabolic fatigue. By slowing down or using a slow rep speed, you increase the effective time
at that moment spent at that rate. This, and not momentum, is the basis for why the 10/5 superslow cadence requires a significant drop in load in order to complete the same TUL as a normal set.
It should be noted, though, that pressing movements have leverage advantages that complicates the above situation. The effective load on muscle decreases as you approach lockout, thus the use of near-lockout (where the limbs are most contracted) can create something of a respite. Thus, there's a necessary balance between force-production of the movement and actual contracted position. Often the point in the movement where metabolic stress is highest will be somewhere in the middle, closer to the lockout than full-stretch. It's harder to locate for pressing movements.
In short, using slow rep cadences (without static contraction) with a very, very short eccentric period is ideal for increasing metabolic stress. That may be something like 10/1 or 4/1. Total range of motion will influence this.
Peak contraction exercises
Below is a list of POF peak-contraction exercises.
[b said:
Quote[/b] ]Quads: leg extensions
Hamstrings: leg curls
Calves: standing calf raises
Abs: full-range crunches
Chest: cable flyes or pec deck flyes
Lats: stiff-arm pulldowns or pullover machine
Midback: bent-arm bent-over rows
Delts: lateral raises
Biceps: concentration curls or double-biceps cable curls
Triceps: one-arm pushdowns or kickbacks
Most of them are pretty familiar. Generally, I think machine-assisted movements work much better than cables and free weights, because you want to get correct direction of resistance in the contracted position. A Nautilus biceps machne is going to work better than a concentration curl. A pec-dec or fly machine is going to work better than cable flies. A Cyber or Nautilus pullover produces an amazing amount of metabolic stress in the lats that would take twice as much volume with chins. (And note: I actually think the machine pullover is a better exercise for the lats than chins.)
Isolation movements are more efficient at generating metabolic stress than compound movements. You don't need a lot of time or glycogen to generate an incredible amount of metabolic stress. I also feel it's a much, much better alternative than using pressing movements. I personally feel that if you're doing a stretch-point exercise, you might as well add a matching machine-assisted movement. Since most people do specialization in their arms, it would make sense to throw in a triceps pushdown, biceps machine, and lateral raise to thoroughly burn the arms.
That being said, you don't want to pile on isolation movements just to fatigue your entire body. Specialization still applies. Therefore, you have to make the same judgement call between specialization and general bodypart coverage.
Progressive loading and absolute load
Of course, increasing the weight builds fatigue. But, it is not necessary in order to create sufficient metabolic stress for endurance adaptations, let alone create sufficient metabolic work. Progressive loading is designed to manipulate strain to beat RBE. Likewise, when working with isolation and pulling movements, you can and should use lighter loads than what you've been working with. Therefore, sets used to build metabolic stress DO NOT follow the HST rep scheme. Reps end by feel.
Okay, next time. Partials and pulses, drop sets, rest-pause, 21s, superslow, super-high fatiguing sets, and HIIT cardio.
cheers,
Jules