Q: Are negative reps really superior when it comes to building mass?

A: Negative, or eccentric-contraction, exercise involves the controlled lowering of a weight to the starting position. Raising the weight is called a concentric contraction. Most bodybuilding trainers advise that you take about two seconds to raise a weight during each repetition, followed by another four seconds to lower it for negative emphasis.

Negative-only repetitions was a style of training advocated about 10 years ago but never accepted by most bodybuilders. It required you use weights that were far heavier than you could use concentrically. It never really caught on because of the nuisance of needing one to three training partners to help you raise the heavy weight, then spot you as you lowered it.

This technique was based on research showing that most of the strength and size gains accrued from weight training occur during the negative portion of a rep. So does most of the muscular soreness you feel after an intense training session or after you try an exercise you're not used to.

The explanation given was that when you lower a weight, you use fewer muscle fibers, but those fibers work harder to control the weight. As a result, more damage occurs in those fibers. The body then repairs those fibers, making them thicker as an accommodation to the higher load imposed by negatives. This translates into increased muscular strength and size.

The extreme damage to fibers during negative training came with a cost, however: the need for increased recuperation. When many bodybuilders became aware of this extra fiber damage and consequent needed rest time, they reduced the number of times they trained a muscle group each week.

Thus, instead of working their bodyparts three times a week, they dropped it to twice or even once a week. While most bodybuilders didn't know why they needed the extra rest, they instinctively sensed how much rest they needed because of rates of muscle growth and strength gains.

Further studies finally uncovered exactly why eccentric exercise exacts this muscle damage toll. The extensive damage incurred during negative reps apparently inhibits glycogen synthesis in muscle after exercise. Glycogen, a complex carbohydrate stored in muscle, is not only the primary fuel for weighttraining but is also needed for muscle repair.

This explained why negative exercise demands extra rest. Unless the muscle has repaired itself, you can rapidly fall into an overtrained state if you attempt to train that muscle before the repair-and-compensation process is complete. The remaining question was, What causes this diminished glycogen synthesis after negative training?

Danish scientists had subjects perform negative-accentuated one-legged exercise, then measured a number of intracellular mechanisms involved in glycogen synthesis. They found that negative exercise apparently inhibits an intracellular protein called GLUT 4, which transports sugar, or glucose, into the cell. If this activity is inhibited, glycogen synthesis slows because less glucose is available.

After two days or so the muscle GLUT 4 level returns to normal, and glycogen resynthesis begins again. In another study the same researchers discovered a possible antidote to the problem. Using isolated muscle cells, they found that vanadate, which is similar to vanadyl sulfate, increased and preserved the function of GLUT 4 in muscle. This may overcome the deficit incurred by negative training. It also partially explains the often-noticed increased carbohydrate utilization after athletes take supplemental vanadyl sulfate.

In addition, a study reported in a 2003 issue of Medicine and Science in Sports and Exercise seriously questions the assumed superiority of negative exercise for producing increased muscle size and strength. This new study compared concentric and eccentric contractions at equal power levels, but contrary to past studies, the researchers found that muscles work harder during the raising of the weight, the concentric part of the rep, rather than during the lowering.

Earlier studies verified that negative reps involve a smaller percentage of muscle fibers compared to concentric, but it was assumed that since these fewer fibers have to bear an equal load, more stress is placed on them and they work harder. Not so, this new study asserts.

The study involved exercising the front-thigh muscles, again using equal-power negative and positive contractions. The results showed greater muscular growth and strength after subjects performed the concentric, or positive, reps, although the scientists still aren't sure why this occurred. Other studies note an increased oxygen intake during concentric work, and frog muscle studies found that eccentric exercise uses only one-thirteenth the amount of ATP as concentric work.

All of this doesn't negate the importance of negative reps (pardon the pun). It doesn't mean you no longer have to control a weight on the way down, but it does point to the fact that both types of contractions (concentric and eccentric) are equally important. Significantly, the idea that you should do only negative exercise as a means of inducing gains in muscle size and strength now belongs in the pile of similarly authoritative but misguided pronouncements, such as "The Earth is flat."