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I've always heard hardcore lifters saying that resistance is not the same as weight. Bascially that 100lb of resistance is not equal to 100lbs of weight. Imagine a bowflex vs a cable machine.

I'd imagine that the resistance type of equipment might not offer 100lbs through the entire rep, possibly ramping up on a curve especially with a machine like bowflex.

Is there a difference and if so, what is each type good for? Keep in mind i'm not asking about bowflex or if I should get one, it's the only machine I can think of ATM.

Updating my question to be clear: When all is equal (machines or not), what is the difference between resistance (be it from a spring or tension) and actual weight (moving a heavy object)

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up vote 4 down vote accepted

Your question has two answers.

1) If everything really is equal, then resistance is precisely the same as weight. Force is force, whether it comes from mass being affected by gravity or from tension on a spring or from hydraulic pumps or from a ray gun.

2) What Yevgeniy's answer gets at is that it's ridiculous, within the context of strength training (or lifting of any kind, even bodybuilding) to suppose that "all else is equal".

The resistance of a machine exercise is force in a certain plane. In the case of Bowflex-type machines, the force may change along the path of the exercise. With free weights (barbells, kettlebells, dumbbells) the only things involved are the weight, gravity and how your body is structured (your anthropometry).

Let's use your example in the comments of a "thighmaster for the chest" versus free weights. As I understand it: The resistance of the spring would be least in the "open" position and greatest as you get near the "closed" position. If you used dumbbells (say, from a position on your back), the force (from gravity) would be equal throughout, but your body would be applying force in different directions across the movement (always "upward", but using different muscles since the weight moves across different angles in relation to your body), in addition to stabilizing the weight in three planes during the entire exercise.

If you're asking about when to use one versus the other, see this question.

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Using machines is vastly different than free weights for a number of reasons:

  • Machines typically move the weight over a fixed path. Free weights require you to balance the weight yourself. This means the same exercise with free weights engages more muscles, but even more importantly, it allows you to develop neuro-muscular coordination. This coordination means that the strength you develop from free weights transfers much better to real world situations.
  • The fixed motion of machines often does not allow for proper biomechanics. Everybody is a little different and you naturally make the appropriate adjustments to exercises when using free weights. These are typically not possible with machines, which leads to unnatural and sometimes dangerous movements. For example, check out the images below of a smith machine squat and a free weight squat. Because the smith machine only allows you to move straight up and down, most people end up leaning back against the bar, squatting behind their knees and rarely getting below parallel, which means the exercise almost exclusively uses your quads. The free weight squat, on the other hand, allows for a little curvature during the descent and results in the person squatting between the knees, going below parallel and engaging almost every single muscle in the body (quads, hamstrings, glutes, adductors, erectors, abs, obliques, etc). Smith machine squat Free weight squat
  • Machines are often focused around isolation exercises, where a single muscle/joint is used. For example, using solely the hamstrings when doing leg curls. These are unnatural - all normal uses of the hamstring (running, jumping, lifting objects, etc) always involve all the other muscles in the leg too - and also not as efficient for training. Although you can certainly do isolation exercises with free weights, you have far more options for compound exercises: squats, deadlifts, bench press, overhead press, cleans, snatches, rows, etc.
  • Machines simply can't provide for certain types of exercises/loads. For example, the olympic lifts - clean, jerk, snatch - are phenomenal for building power ("speed strength"). However, they require very rapid/explosive movements that most machines can't handle. Also, most machines (other than the smith machine, which is just a barbell anyway) can't provide enough resistance for the heavy lower body lifts. Most males can very quickly work up to a barbell squat of over 200lbs and deadlift of over 300lbs.
  • On top of all of that, machines differ greatly in what a certain amount of "resistance" means. For example, depending on the levels/angles/etc involved, 150lbs on one pull-down machine can be vastly different than 150lbs on another one. However, a 150lb man doing pull-ups is the same just about everywhere.
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Great info but except for the last part, does not answer my question at all. When all is equal (machines or not), what is the difference between resistance (be it from a spring or tension) and actual weight (moving a heavy object) – DustinDavis Mar 19 '11 at 16:53
@DustinDavis: apples and oranges. The whole point of my response was that the two are completely incomparable. The movements are different, the muscles involved are different, the ROM is different, and even the "units" used on different machines means different things. So in reality, no meaningful comparison can be made between doing "100lbs" on some machine and "100lbs" with free weights. – Yevgeniy Brikman Mar 19 '11 at 20:08
I see your point but let's use another example. Sometimes I use a device similar to a thigh master to tone my chest. If it provides 20lbs of resistance, how does that differ from me sitting on a bench doing butterflies with 2 10lbs dumbells? – DustinDavis Mar 19 '11 at 20:40
@DustinDavis I think @Yevgeniy's first two points cover this scenario. Just about any device produces resistance only over very specific lines of movement, which limits the range of motion and the extra stabilizing required. I know the original question was "when all is equal" but the problem is that all being equal isn't a realistic scenario. – Greg Mar 19 '11 at 21:14

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