The Physics Of Weight Lifting

This is the first of a series of articles that will look to the science of physics to help us make our training more effective. In this article we will look at the simple law of gravity and how this effects lifting weights. Gravity is defined as – The natural force that causes objects to be pulled towards the center of the earth, it causes objects to have weight.Part I – Gravity

Because the earth is round, no matter where you are on it the center is always straight down. Thus, in order to have continuous tension on our muscles while training we must make sure the actual resistance we use travels a path that is straight up and straight down. an example of this is the military press, the weight is pushed against the force of gravity in a straight line up until the arms are locked over your head, then it is lowered slowly resisting gravity, in a straight line to about shoulder level.

In all of the big basic exercises (deadlifts, squats, bench press, military press, rows, etc.) the bar always travels straight up and straight down, this keeps the muscles being worked under a constant load. The basic exercises produce the best results because they stimulate growth in more then one muscle at a time, but we also now know that they provide continuous tension in the muscles involved – this is the secondary reason why they are so productive.

There are a group of exercises called isolation exercises these tend to work only one muscle or muscle group at a time, these exercises are not very efficient at producing overall body mass as the basic exercises. The reason for this is they don’t stimulate growth in many muscles at once, but also secondarily because most of them don’t provide continuous loading of the muscles.

In most isolation exercises the bar travels in arcs where only the middle of the movement approximates a pull against gravity. Take the barbell curl for example, The bar is lifted from the upper thighs in a circular path towards the chin, at the beginning of the movement the bar is traveling more horizontally then vertically, it is only when the bar is in the middle position that you are pulling it upwards against gravity, then as you move into the top position of the movement you are once again moving the bar in an almost completely horizontal direction. This is why curls tend to be easy at the beginning, hard in the middle and the easy again at the end.

Other examples of this type of exercise are, lateral raises, flys, tricep extensions, pullovers, etc.. Any exercise preformed with a barbell in which the resistance doesn’t travel straight up and down, will cause a loss of continuous load on your muscles. As a side note, preacher curls done with a barbell are even less effective because it make almost the whole movement horizontal, the only benefit is the elimination of cheating by benefit the upper arms from moving.

Ok, so how do we use this data to make our training more productive? We make sure that we have continuous tension on our working muscles by making sure that the resistance we are using is traveling straight up and down. There are many machines that use pulleys to lift a weight stack up and down against gravity even though you may be moving in a circular motion, if you workout in a gym where these are available – make use of them.

But even if you train in a home gym you can still use these principles to build more muscle. Let’s take bicep work for example, do some close grip pull-ups with the palms toward your face, this strongly works the biceps and the resistance (your own body and any extra weight you add) is moving straight up and down, it also give you the added benefit of peak contraction at the top of movement. Or instead of regular barbell curls try body drag curls, take a shoulder-width grip and start from the regular curl position drag the barbell against your body up to your throat while keeping your elbows back.

For your triceps, nothing beats dips with extra weight added by mean of a belt you can hang plates on to. For deltoids, notice that the shoulder joints do the exact same motion when doing military presses as doing lateral raises, so you don’t even need to really do the lat. raises it’s just more of the same.

You may ask “But what if i want to do some pre-exhaustion, I would have to do some lateral raises then, wouldn’t I?”. No, you don’t Try this instead – do a set of upright rows immediately followed by a set of military presses. It works this way, the upright rows fatigue the biceps and shoulders but leave the triceps fresh, now on the presses the strong triceps push the already fatigued shoulders even harder really making them grow. This is what I call the pull/push method of pre-exhaust, it can also be used for other muscles of the torso.

In conclusion, there are many ways to make gravity work for you in weight training, now that you know the theory of this article you may come up with some new and interesting exercises or exercise combinations.

Part II – Friction

In Part II of this series we’ll look at friction and how it can affect our training. Friction is defined as – (1) A rubbing of one object or substance against another. (2) The resistance to motion of moving surfaces that touch.When working with machines friction can become a problem, you have the situation of weight on the machine plus friction making it feel much heavier than the weight stack says it is. This can wreck your progression, let’s say you’re going along on lat pulldowns, last workout you made over 10 reps, you add 5 lbs and start to pull and nothing happens, a big yank gets the weight moving and you have to use excessive momentum to keep it moving, all this cheating still only gets you 4 reps. You wonder “what’s wrong?”, friction that’s what.

Each time you use a machine, you should inspect in for any loose nuts and bolts, frayed cables, stuck pulleys or any broken plates on the weight stack. Any of these can cause you problems with friction. Also you should regularly keep machines oiled and otherwise well maintained.

There is another kind of friction I’d like to talk about, and that is the friction within your own body, yes, of course your body has it’s own friction, and this gives us 3 levels of strength:

1.) Positive strength – contracting your muscles to lift or pull a weight, during this phase you are working against your own bodies friction.

2.) Holding strength – contracting your muscles to Keep a weight in one position, you are aided by your bodies friction here and can thus hold 20% more then you can lift.

3.) Negative strength – lengthening your muscles to lower a weight, you are also aided in phase by friction and it has been found that most trainees can lower 40% more then they can lift.

This would mean that if your max on the bench press was 200lbs, that you could hold 240lbs and lower 280 lbs. Research done by Nautilus in the 1970’s showed that any increase in positive or negative strength would result in an increase in the other, of course, skill is also a factor.

Now all this is very interesting. But, can it help us to build larger and stronger muscles? Yes, it can, let’s take a look at some of the techniques that can come from this.

If your lowering strength is 40% more then your lifting strength, but you use the same weight for both then you will not be really be taxing your negative strength. We must find a way to make the negative harder, there are many ways to do this. One way is to do some of your exercises on Life Circuit machines they automatically make the negative 40% heavier then the positive, while these machines are good I feel they can be improved on due to a perceived lack of resistance during the change from positive to negative and then back again. Another way would be for your training partner to grab the bar and push down what he approximates to be 40% of what your lifting, have him do this on each negative of the set. And for safety have him have a good hold on the bar while doing this and make sure he’s ready to stop pushing and Start pulling, in case you for some reason lose control of the weight. You can also try it this way, (use only a universal type machine for this, because you couldn’t balance a barbell for this technique.) take a weight that’s about 50% of what you usually use lift it with both arms and then lower it with your right arm only, lift it again with both arms and now lower it with your left arm only, continue to alternate the lowering arm till you make you target reps or until you can no longer lift the weight with both arms.

Other techniques would involve training the holding and lowering phases totally separate from the lifting phase. When doing this you would need at least two very strong training partners to lift the weight for you while you try to hold it in place as long as you can (a good position would be the sticking point for that particular lift), or you have them lift in up and then you lower it slowly and under control and they lift it again and then you lower it again, repeat for you target reps or till you can keep the bar moving slowly and controlled. Again for safety your training partners should keep their hands on the bar and be ready to take the weight if you should lose control. You would also want to work gradually up to the really heavy poundages.

These techniques will raise the intensity of you workouts and can lead to overtraining if used too often, but if used properly can help you reach new levels of size and strength.

Part III – Mechanical Advantage

Here in the third part of this series we will examine mechanical advantage and how this effects weight training and how it can be used to our advantage to get better/faster results.

Mechanical Advantage – is the ratio of the force exerted by a machine to the force applied to a machine.

Our muscles contract to exert force and our skeletal structures (made up of simple machines – hinges, ball and sockets, etc..) transfer that force into motion. But the force exerted by our muscles (input) is not equal to the force we can use to move our bodies or lift other objects (output). let’s look at some of the factors that cause this increase in force output, first would be bone length and muscle attachment points. Generally shorter bone lengths are better for strength output then longer bones, also attachments further down the bone being moved would give better leverage and therefore the ability to lift more.

The above two factors explain why a smaller man may lift more then a bigger man, but there is nothing we can do about the length of our bones or the placement of our muscle attachments. There is another factor that we can use in our training and that is that even taking into consideration the information from Part 1 of this series (Gravity), due to the change in mechanical advantage during a full range of motion all exercises have a harder part and an easier part. Different movements have different strength curves, but usually the closer you get to full contraction the stronger you are.

All this just serves to show that when lifting fixed resistance over a full range of motion you are limited by the range of least mechanical advantage, in other words – The Sticking Point. If you are only lifting as much as you can handle in your weakest position you are not overloading your muscles to your fullest ability.

There are a few ways to overcome this – (1) Partial Movements and (2) Variable Resistance.

(1.) Partial Movements, these are also called 1/4 reps or lockouts. With this method you need some adjustable squat stands or a power rack, set the barbell so you only do the top part of the movement. For example, the top 6 to 8 inches of the squat, this is when you’re in your strongest position to lift some really heavy poundages. The benefits to this type of training are both physical and mental, on the physical side you will be forcing you muscles to lift heavier weights thus increasing their strength (most trainees find that they are much stronger, when they return to full movements after a cycle of partials), on the mental side you get over a fear of handling really heavy weights and feel like “I can lift this, I’ve lifted even more then this before”.

You can do partials on overhead presses, bench press, deadlift, curls, etc., you will be able to handle a lot of weight with this technique, but to avoid the chance of injury work up to it gradually, so that your muscles, tendons and ligaments get used to the big poundages.

(2.) Variable Resistance, this is done over a full range of motion and requires some method of increasing the resistance as your strength increases due to more mechanical advantage as you get closer to the fully contracted position. Nautilus was the first to put out machines that provided variable resistance and since then many manufacturers of exercise machines have also built this factor into their machines. But not everyone trains in a big commercial gym and even some that do prefer to train with free-weights, well there are some very simple ways to create an increasing resistance.

Before he released the first Nautilus machines, Arthur Jones experimented with chains to regulate resistance. It works this way, you attach some long sections of heavy chains to the bar or weight stack and as the chains are lifted off the floor they add more resistance. You can also use small plates tied every six inches to some long pieces of strong cord or rope, you can even tie some slightly larger plates near the end of the rope so that at the point just before full contraction/lock-out you are really pushing a lot of weight. Work with this a while to get the right amount of increasing weight, when you get it right the weight should feel consistent all the way through the movement, you will have to make some extra adjustments after using this method for a while because of the previously under worked areas of your strength curve will gain more then the area near the sticking point.

These methods force you to lift more weight and you will get bigger and stronger because of them.

Part IV – Work

In Part IV of this series we’ll look at the formula for work and how we can use it to monitor our training. The formula for work is: Force X Distance.

When we workout we use a certain amount of muscular force to lift a weight across a certain distance, the work done is measured in Foot/Pounds. If we kept track of the work we do each workout it will tell us much about our progress and also how we should proceed with our training. You can measure the work done each workout in the following way:

1.) Take an empty bar and do the full range motion for each exercise you are currently doing in your workout, have your training partner measure the distance (e.g., how far is it from the bar being on your chest to it being at full extension for the bench press, how far is it from the bar being on the ground to when you are standing up with it on the deadlift, etc.) and write down all these measurements. When there is an exercise that the movement is in an arc, like curls, you will have to find a way to measure the distance of the arc, you might want to take some chalk and do the motion against a wall and then measure the arc of the line you drew, or some other bright idea on measuring the distance of an exercise that travels in an arc.

2.) Now the next time you workout you can figure the amount of work done (called workload), just take the reps done on your first set and times it by the distance (this would be twice the distance of the distance you measured, since one rep is both down and up), for example, if one rep down and up on the squat is 7 feet and you did 10 reps that would be 70 feet. Now take the weight lifted and times it by the distance, for example if you squatted 265 lbs: 265 lbs X 70 ft = 18,550 ft/lbs.

3.) Take every set of the workout and used the same formula (F X D) and you will know the workload for each set add the workloads of all the sets and you will have the total workload of that one training session.

Now when you keep track of your workload each workout in this way you can see that as you get stronger your workload increases, you will also see that you can monitor how much workload you can handle each week before overtraining sets in. Just watch yourself for signs of overtraining and see where you workload is at.

You can increase or decrease your workload as you feel is necessary, and you can see that not all sets are created equal – a set of curls is much less work then a set of squats or deadlifts. You can also vary the workload from workout to workout, may alternating heavier with lighter sessions.

Keeping track of your workload will give you a much insight and the ability to predict things in your training, experiment with it and you will learn much more about how useful it is. In the part 5 I’ll expand a bit on this formula.

Part V – Power

In our final installment of this series we’ll look at the formula for power and how to use it to make training more productive. The formula for power is: Force X Distance -:- Time. And is measured in foot-pounds/second.In the last issue we talked about work and how to calculate your workload for each workout, the first part of the formula for power is the same (Force X Distance), now we add the factor of time.

Now, for the purposes of muscle building we don’t mean increasing lifting speed, this just allows momentum to do the work and not the muscles. All exercises should be preformed slowly and deliberately.

As you will see when we talk about power, we are talking about training intensity. Let’s look how we can increase our workout power (intensity):

1.) Use a full range of motion, for example let’s say your full range of motion on the bench press is 2 1/2 feet, that means1 rep (up and down) is 5 feet. And let’s say each rep takes 6 seconds (2 up and 4 down), if you use 250 lbs for 8 reps the power would be – 250 lbs X 40 ft -:- 48 sec = 208.3 ft-lbs/sec.

Now let’s say you cut 3 inches off the range of motion by not bringing the bar all the way down to your chest, this takes 1/2 foot off of each rep. So, if all other factors are the same, the above set now looks like this – 250lbs X 36 ft -:- 48 sec = 187.5 ft-lb/sec. With less range of motion power goes down.

2.) Increase the weight you lift, for example, on our full motion bench press (250 lbs X 40 ft -:- 48 sec = 208.3 ft-lbs/sec) if next workout 5 lbs is added , it then looks like this – 255 lbs X 40 ft -:- 48 sec = 212.5 ft-lbs/sec. Lifting more weight increases Power.

3.) Decrease time between sets, for example, 3 sets of bench using 250 lbs for 8 reps has the workload of – 250 lbs X 40 ft = 10, 000 ft-lbs. If these 3 sets are done in 10 mins (600 sec) the power is – 10,000 ft-lbs -:- 600 sec = 16.7 ft-lbs/sec.

If by decreasing rest time those same 3 sets are done in 6 mins (360 sec) then the power is – 10, 000 ft-lbs -:- 360 sec = 27.8 ft-lbs/sec.

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About The Author:
Paul Becker is a natural (steroid free for life) bodybuilder and fitness consultant.For more information on Bodybuilding and Bodybuilding Supplements visit his website at