מהירות התנועה בשלבים השונים

[Eli]

חיפשתי באינטרנט על מהירות התנועה האופטימלית לשלבים השונים של התנועה (קונצנטרי, אקסצנטרי).
מצאתי מאמר של פרדריק הטפילד (Dr. Squat), מסביר די טוב:

There is a false polemic raging in the world of Irondom whether fast or slow movements are best. I will address this issue, and give you some solid, scientific guidelines regarding how fast you should move the weights while training. You will see that the controversy exists only among those with limited background in the science underpinning various forms of training

It is not appropriate to dichotomize the speed with which you move a weight as either fast or slow. The simple truth is that the speed with which you move a weight often varies from almost no movement at all (in fact, no movement is the essence of isometric training) to explosively fast movement speed. This applies to both concentric and eccentric movements as well as to heavy and not-so-heavy weights.

Your movement speed during any exercise should be predicated on several important factors. Here are the more important ones that come to mind:


· Immediate training objectives (limit strength, speed-strength, muscle mass increase, etc.)

· Long-term training objectives (bodybuilding, sports, fitness, etc.);

· Predominant muscle fiber type (mostly red, mostly white or equal ratio of both);

· Position in training cycle (just beginning, middle or pre-competition);

· Injury history and injury proneness (e.g., age may play a part);

· Available equipment; and, most of all;

· the percentage of your maximum (1RM) that you're training with.


Let's get the eccentric movement debate out of the way first, as it's the easiest to explain.

When you lower a weight, you are allowing the weight (gravity) to become the dominant force. This can be done in two ways: 1) by willfully turning off some of the motor units that you used to lift the weight in the first place, or 2) by using a weight that is so heavy that concentric contraction of your muscles cannot overcome the gravitational force of the weight. You let the weight fall very rapidly (but under control) when you want to minimize the amount of microtrauma inflicted to the muscle cells. Conversely, letting the weight down slowly increases the extent of microtrauma taking place inside your muscles. There is an appropriate time and place for both, a point that deserves an article of its own. For now, though, remember that 1) microtrauma is essential for maximizing muscle growth, and 2) while recovering and supercompensating from mircotrauma, it's necessary to train sans eccentric stress in between heavy eccentric workouts to avoid detraining.

Now, let's attack the concentric speed issue. We must set some definitional ground rules in order to understand the dynamics of this issue. I believe that the false polemic stems, in large part, from some well-meaning lifters not fully understanding simple concepts in physics. Here are some simplified (but easily understood) rules:


· Mass -- the amount of matter a body contains (expressed in pounds or kilograms of iron for the purposes of this discussion)

· Velocity - The rate of movement (how fast you are moving a weight at any point in an exercise movement)

· Acceleration -- velocity divided by time (changes in velocity during the time it takes to perform an exercise movement)

· Force -- mass times acceleration (For any given amount of weight, decreased velocity means less force is being applied, and increased velocity means more force is being applied)

· Momentum -- mass times velocity (the heavier the weight gets the slower you can move it, and eventually momentum drops to near zero)

· Inertia -- the tendency for the velocity of a mass to remain constant in the absence of external forces (The heavier the weight and/or the slower the movement, the less the inertia. When velocity equals zero, inertia is at its lowest point. In resistance training utilizing air pressure as the source of resistance, there is little or no appreciable inertia.)


In the light of these (admittedly oversimplified) definitions, let's take a look at another well known definition. Power equals force times distance per unit of time. Assuming that you're moving the weight as fast as you possibly can, if the mass is low, the time it takes to complete the movement is also low. And if mass is high time will also be high.

In the case of lighter weights being used, the time is so low that you never have enough time to activate sufficient motor units to achieve an optimal training effect. It takes around three quarters of a second to achieve maximum muscle contraction, and this is not possible to do when the weights are light. Additionally, the velocity of movement is so high that momentum creates a dangerous element in your training. The weight is being moved so fast that inertial forces at the end points of the exercise (where changes in velocity are greatest) can tear tissue far more easily. It's the abruptness of force changes that do the damage.

On the flip side of the coin, if the weight is so heavy that only one or two reps can be accomplished, the time your muscles spend under maximum tension before fatigue stops you is so low that it is impossible to achieve an optimal training effect. You should be able to spend a total of 30-60 seconds over your body part workout with your working muscle(s) straining at their maximum ability. On the other hand, since momentum is minimal at these slow speeds, the chances of injury stemming from velocity are lessened. However, the chance of injury stemming from having to bear the mass is also slightly greater.

So, this discussion on power adds up to the fact that your movement speed is indeed important, but the percentage of max (the mass) being used is also quite critical. It should not be too light or too heavy. Somewhere between 50-55 percent and 80-85 percent is the range within which power output is optimized. There are two reasons for this. First, it's a relatively safe range since neither excessive mass (lifting a weight that's too heavy for optimal time under tension) nor overly rapid velocity changes (typically associated with using lighter weights) threaten tissue integrity as much. Secondly, it is the range within which it's possible to place your muscles under maximum tension. Then, it's a simple problem of repeating the movement for several sets of reps until 30-60 seconds of time under maximum tension is achieved.

Those who claim that "super slow" movements are best typically cite three reasons for their belief. They believe that slow movements are safer (they are), and also because you can increase your time under tension (you can). Their thinking is nonetheless erroneous. Moving weights as fast as possible is completely safe, provided you take care in ensuring that the velocity changes at the ends of the movement are controlled as opposed to abrupt (that's something even a monkey can learn on the first try). And, the tension produced by purposefully lifting a weight slowly is almost assuredly sub-maximum, therefore providing sub-optimal overload.

The superslow proponents have also clung to the belief that lifting a weight fast means that the weight is moving on its own from previously applied force, thereby "robbing" you of any training effect. Nonsense! This is only possible when the weight is so light that its possible to propel the bar as you might propel a shot put. Or a bullet from a gun. Anyone training with weights that light isn't weight training! They're playing! The one exception to this involves "cheating" a weight past a sticking point. This is appropriate, so long as you recognize that the "cheated" portion of the movement cannot contribute to overload. The rest of the movement certainly does, however, and that's never bad.

[Eli]

Here's the bottom line. Lifting a weight that's above 55-60 percent of your 1RM as fast as possible is almost assuredly going to produce maximum tension, and therefore optimum overload. Conversely, lifting a weight that's below 55-60 percent of max will yield submaximum overload and therefore submaximum results in increasing strength. I defy ANYONE to lift more than 85 percent of their max purposefully slowly for a reasonable number of reps! It can't be done! Fatigue will invariably set in so quickly that you'll never manage to get in the requisite number of reps to provide optimal time under maximum tension.

A side issue that proponents of superslow training love to bring up is the practice of the Olympic lifting movements. Snatching and cleaning involve abrupt velocity changes. So, why is it that Olympic lifters suffer far fewer injuries than do other athletes? First the sudden application of abrupt force takes place after the weight is moving off the floor (i.e., at near knee height). This is not dangerous. The end points of these two lifts require perfect timing such that the weight is "caught" as momentum slows and velocity is at near zero. Again, not dangerous. Impact, as experienced in tackling, hitting, being hit and falling to the ground involved massive impact, far beyond what Olympic lifters experience.

So, almost every bit of solid scientific research shows that faster movements produce better results in lifting. This being true, when does it pay to do slow movements? Of course, when training aged clients, you have to be prudent and avoid taking them to any sort of ballistic or explosive realm of lifting. Also, rehab (clinical) situations certainly often require slow movements. And constant tension (it doesn't have to be maximum tension) has been shown to improve local muscular endurance better than do fast movements. The mechanisms of improved local muscular endurance are increased enzyme concentrations within the muscle cells, mitochondrial proliferation and capillarization. These all contribute to improved mass to a measurable degree, and are therefore worthy of inclusion in one's training regimen at least once or twice yearly. Eight weeks of such slow training appears optimal, however.

מי שרוצה את השורה התחתונה - פסקה אחרונה.