PHYSICS AND LIFTING: WORK
Basically, there are three physical concepts involved in lifting: the first is Force, the second is Work, the third is Power. You'll have seen all these words used in informal ways in articles about weight training -- but how about learning their rigorous meanings? In my previous article I spoke about force. You have to understand force first, before you can understand work or power.
Here:
For this article, I will look at work!
While we have a general everyday concept of what 'work' is and entails, in physics the meaning of work is very specifically defined. Work, in science, is force times distance. While force is merely how much of a push or a pull exists at any specific instant -- in lifting, how hard a muscle is contracting momentarily -- work gives a bigger kind of quantity.
If you for instance exert a force of ten Newton, in lifting something upward, the work you do depends on how far you lift that thing. If you lift it over a distance of twenty inches, you perform double the work you would if you lift it over a distance of only ten inches, and half as much work as you would in lifting it forty inches.
In science, we use metres and centimetres -- and metre is indeed about forty inches. We measure work in JOULES. One Joule of work is a force of one Newton exerted over a distance (in the direction of the force) or one metre.
When considering mechanical work, the only distance we take into consideration is the distance an object is moved in the direction of the force. So lifting an object, the work will depend only on how far upward it is lifted, since gravity works downward and the force we exert against works in the opposite direction, upward.
Moving a weight sideways doesn't involve any mechanical work unless there is a sidewards resistance against the motion.
This does bring up a point. While moving a weight sideways doesn't actually accomplish much mechanical work (there is actually a small amount of force necessary to move any object sideways, enough to overcome the resistance of its inertial to accelerate it into motion from a dead stop), there is indeed what is called 'metabolic' work involved.
Just holding an otherwise unsupported weight against gravity, for a period of time, requires a force from your muscles. And your muscles require energy for exerting force for any length of time. And energy is in a way equivalent to work.
Energy is the capacity for performing work, or a measure of the work expended. It is also measured in Joules.
There are various kinds of energy in science apart from the actual energy spent in moving a physical object. Any object that is in motion has 'energy of motion,' called kinetic energy, because its motion gives it the capacity for performing work on another object if it should hit it. One object bumping into another, causing it to move, has turned its own kinetic energy into work.
Electric energy exists in batteries and actually in any charged object, and can be turned into work in various ways, such as when an object of a positive electric charge attracts and is able to move an object of negative electric charge. Even in electric circuits, in which we can't even see anything moving, on a sub-microscopic scale the electric fields are actually moving many electrons, doing actual work on them. Through the phenomenon of magnetism, changing electric fields can set even large objects in motion.
Another kind of energy is gravitational potential energy. If you lift a weight against gravity, the work you do on that weight actually gives it energy. The higher you lift it from the ground, the more work it can do if and when you should drop it. For instance, some kinds of clocks use a weight that is allowed to slowly descend, having first been lifted up, in order to set and keep in motion the clock's gears and wheels; a pendulum clock also uses gravitational potential energy to keep the pendulum in motion, which in turn drives the clockwork.
Water that flows down from a higher to a lower position can perform work on turbines as it flows through them, generating electricity, also thanks to gravitational potential energy.
Chemical potential energy is stored in chemical bonds in certain substances at the molecular level. Explosives can rapidly increase this energy, but even the food we eat works through chemical potential energy, breaking the bonds so as to release this energy and turn it into motion.
During many processes, chemical and other energy can be turned into heat, which also is a kind of energy. Some heat energy can sometimes also be turned into motion, but energy is often lost as 'waste heat' with which we can do nothing useful. Waste heat is usually the final step in transforming energy from one form to another.
in the human body the heat produced by energy transformations does actually do some good, helping to maintain the body's temperature. Only when this heat is too much, we need to expend extra energy to reduce it by, for instance, sweating.
So, when you hold an unsupported weight stationary, you are not technically performing any work on it, but just to hold it demands force from your muscles; this must be fuelled by delivering energy from food to your muscles, and this energy is a work equivalent and actually involves work on the sub-microscopic scale. The longer you hold a weight, the more of this kind of work you do. This is called metabolic work, work done by your body's inner metabolism.
In practice, holding a weight for a certain amount of time would demand a bit less energy then lifting that weight upward for the same amount of time, but lowering a weight for the same amount of time would demand a bit less energy. Holding weights can be useful, especially if done at the points of maximal leverage -- for instance, holding a barbell at the midpoint of the barbell curl (forearms parallel to the ground). This is called an isometric movement/contraction. Generally, though, isometrics alone will not give the best results. They can be combined with more typical lifting and lowering.
Actual (or mechanical) work, and metabolic work, both make demands on your body's energy-providing systems, completely proportionately to how much work you perform. This work depends on the magnitude of the force and the distance over which it operates (for mechanical work), or the length of time for which it operates (for metabolic work).
Thus: the more work you do during a workout, the greater the impact on your body's energy systems. Your body's energy reserves get exhausted during any kind of physical exertion, and the more they are exhausted, the more time and input of new energy (through eating) is needed to replenish them again.
I hope you were astute enough to by now realize how the element of work comes into your weight training. Amount of work can be seen as what we call 'volume'. we know that doing a great many sets per workout constitutes a high volume -- a high quantity of work. But scientifically, the same goes for reps!
The more reps we do with a certain weight, the greater the quantity of work -- which means for the body essentially the same thing. So there's set volume, and rep volume, and both impact the body's energy systems. We should think of volume, as it affects the body, in terms of several factors:
the weights we lift;
the distance we lift them;
the duration of time for which we lift, hold, or lower them; and
the number of times we lift them --
for the entire workout.
We needn't sit and make exact sums. But it helps our understanding to think about these factors, even just roughly estimating them, for purposes of comparing different styles of working out.
Starting to think about the weight and the distance we lift it, we can understand why certain exercises are so demanding. Squats, for instance, if done to parallel or below, not only involve a very heavy weight, but also a considerable range of motion -- the distance over which the weight is lifted. And this by our scientific definition means a lot of work.
Deadlifts have a comparable range of motion.
Bench presses typically move a much shorter distance, and (unless you neglect your lower body) involve a lighter weight also. Consequently, bench presses are much less demanding on your body's energy systems.
Overhead presses, if done with a grip not much beyond shoulder width, move the bar through a bigger range of motion and thus, though usually done with less weight, are comparable in demandingness with bench presses.
Rows, pulldowns/chins, and dips are also all comparable.
Curls have a fair range of motion, but cannot be strictly done with heavy weights, and thus aren't as much work. Even with heavy weights and done intensively, they will not 'wipe you out' as much as those exercises where the weight moves through a greater range.
You can understand that: there simply is not that much work done over such a short range, and consequently there's not that much demanded from your body's energy systems.
Actually the ultimate in 'work' would be the Olympic lifts and their variants. An expert lifter uses very heavy weights for these lifts, and also moves them over a very great range of motion. Both the snatch and the clean & jerk start with the weight on the ground, and end with the weight at arm's length overhead. This range of motion is FAR greater even than in squats or deadlifts. Consequently, a single rep with a heavy weight in one of these lifts is a very large amount of work.
Pondering the above some more; those exercises that involve the most work are the most demanding and as we know in our abbreviated training philosophy, are also the ones to focus on -- they give us the 'most bang for out buck.' The Olympic lifts, however, are technically demanding and somewhat risky and not much recommended for typical trainees. And they're certainly not essential: squats, deadlifts, bench presses, dips, chins and the rest we know from experience will work just fine. But, thinking about how demanding they are, and comparing them with the other stalwart exercises, Olympic moves might indeed be worth including -- or perhaps somewhat 'easier' related lifts such as power cleans, power snatches, and high pulls.
We'll speak more of them once we get to the article dealing with power.
Understanding that the movements that involve a large weight and range of motion per rep are the most demanding ones, should lead us to another insight: that work IS indeed part of what makes an exercise -- and consequently also an exercise regimen -- productive. While force just tests the momentary intensity of contraction of muscles, work means having them contract over a period of time or repeatedly.
Force tests the muscle fibers, work tests the systems delivering energy to the muscle fibers. But in practice these are never isolated: even for the briefest contraction, a muscle fiber needs to have energy supplied to it. So, we are always involving the body's energy systems when we lift.
There are a few different such energy systems, from anaerobic to aerobic, and I'm not going to go into them much here (I'll have to do more research about them, and it will constitute a whole new big topic), but we know that for size and strength we focus more on the short term, anaerobic energy systems. Even so, those systems do indeed provide energy and enable muscle to work. Typical weight training sets may last from a few seconds to a minute or two. Singles, doubles or triples need muscles to be energized for just a second or two, high rep or slow rep sets need sustained energy for many seconds.
Pondering the work performed during lifting, it can be interesting to multiply weights and reps together for an exercise to get a rough number for 'set volume' . . . let's call it the work score. Let's look at the bench press . . .
Say you have 100 kg on the bar. If you can do only one rep with that, just give it a work score of 100 x 1 = 100. That is a 'set' consisting of just one rep -- we're going to compare that with sets done with more reps. You don't need to convert to Newtons or do any measuring of the range of motion to get Joules; we're just going to compare bench presses with bench presses.
Now, typically if you can bench press 100 kg once, you'll be able to bench press 75 kg from six to ten times. If you're a good 'repper' and can do 10 reps with 75 kg, give it a work score of 75 x 10 = 750. You can get a work score seven and a half times higher for a 'set' if you do that set with 75% of your one rep max! (In this example different people will get different work scores in real life, depending how good they are at repping). And if you reduce the weight to 50 kg, you might get 20 or 30 reps. That will give you a work score of 1,000 to 1,500, ten to fifteen times that of a single rep. Now, this is for a trainee that is a good repper. A trainee that is worse at doing reps will get a lower work score. Say such a tranee, with a 100 kg single, can only do 10 reps with 50 kg. That still gives him a work score of 500, five times as much as his top single. For any exercise, by reducing weight, you can always get so many more reps that your work score will go up markedly.
But that doesn't mean we should do very, very high reps with very low weights! Work DOES feature into how productive an exercise is, but only up to a limit. When very high reps are done with very low weights, the work is indeed high, but the lighter loads involved will no longer stimulate as much of a strength gain. This can still be stimulating, as Dr. Ken Leistner used to prove by making his trainees do sets of 100 reps or more in the squat, leg press or deadlift. But those were still done with challenging weights and also tended a bit to the 'rest pause' with interruptions throughout the set so that the body can recharge some of the systems that deliver energy over the shorter term. Again the recommendation of most of the time doing 5-12 reps per upper body exercise, and 8-20 for squats, deadlifts and leg presses, will keep us in a sensible work zone.
As for reps, so for sets. Every additional set counts as 'more work' and thus more stimulus. Resting in between sets allows the energy systems to be partially replenished, letting us do more work while staying in the anaerobic zone. But again, this soon becomes counterproductive, in this case because we end up overstepping our ability to recuperate in a conventional time.
More work is positive by stimulating a greater response, but negative by demanding a longer period of recuperation.
Following the general recommendations for abbreviated training, and doing a little bit of experimentation on yourself, should get you close enough to your sweet spot: doing enough work to give you a serious stimulus from your workout, yet not so much that you need an inordinately long period to recover from it.
In the third article, we will look at power -- another word much misused,j but with a very precise, clear and illuminating meaning in the world of science.
Enjoy Your Lifting!
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