by Steve Holman and Jonathan Lawson Iron Man Magazine
End-of-set X-Rep partials have evolved since we first began using them. In the beginning, in The Ultimate Mass Workout e-book programs, we did end-of-set X-Rep partials at an exercise’s Positions-of-Flexion classification point.
For example, on midrange moves—like pulldowns for lats and bench presses for chest—when we reached full-range exhaustion, we would do X-Rep pulses in the middle of the stroke to extend the set. For stretch moves—like incline curls for biceps and flyes for chest—we did X Reps in the full-stretch position. Contracted moves like cable crossovers for chest and concentration curls for biceps got X Reps at the flexed, or contracted, position.
As we did more research, however, we found that the best spot for maximum fiber recruitment on the stroke of any exercise is just short of the fully stretched position—such as from a few inches off the chest up to just below the halfway point on bench presses or incline presses. That’s about an eight-inch partial. Here’s a quote from respected researchers Steven J. Fleck, Ph.D., and William J. Kraemer, Ph.D., on the subject:
“There is an optimal length at which muscle fibers generate their maximal force…. At the optimal length there is potential for maximal crossbridge interaction and thus maximal force. [Past] this optimal length, less tension is developed during an activation because with excessive shortening there is an overlap of actin filaments so that the actin filaments interfere with each other’s ability to contact the myosin crossbridges. Less crossbridge contact with the active sites on the actin results in a smaller potential to develop tension.”
In other words, in the peak-contracted position, like the top of a concentration curl or leg extension, the fibers are very bunched up, so much so that they can’t produce as much tension as when the muscle is in a more lengthened state. You see that when you fail on concentration curls—you can still pull the weight through the bottom of the stroke but not the top. That’s because the bottom is where the biceps fibers best generate force.
Since the tension and force connection is a key hypertrophic trigger, that means X Reps produce the most fiber activation when the muscle is almost fully stretched—but not quite. At a full stretch on many exercises the nervous system begins to shut down to prevent injury.
So at the end of a set of chins, when you can’t get any more full reps, you lower to a point just short of the full arms-extended position and then pull up about eight inches. That’s the ideal X range.
As we said, the research shows that the semistretch position on the stroke of any exercise is the ideal X Spot; for example, near the bottom of a concentration curl, leg extension, incline press, bench press, row or squat—although with free-bar squats a leverage shift makes it almost impossible to do end-of-set X Reps near the bottom. You can do X Reps near the bottom of Smith-machine squats and hack squats, however. It’s good to have a spotter standing by, even though they are machine exercises.
There’s even research that shows that doing isometric, or static, holds in the semistretch position is more effective for stimulating size and strength increases than isometric contractions done at any other place on the stroke. That shows the semi-stretch position’s hypertrophic superiority. Other studies have shown that immobilizing a joint where a muscle is elongated can actually increase muscle sarcomeres, while immobilizing the joint with the muscle shortened decreases sarcomeres. [Eur J Appl Phys. 97:643-663. 2006.]
Now, all of the above doesn’t mean you can’t do end-of-set X Reps at the top of leg extensions or the flexed spot of any other contracted-position exercise in Positions-of-Flexion mass training. We incorporate that in X Fade. Here’s the X-Fade drill. At full-range exhaustion you first do X Reps in the contracted position—the target muscle’s flexed spot—and end with more X Reps in the semi-stretch position. That’s a great change for more muscle gains, a good variation for more mass creation.
—Steve Holman and Jonathan Lawson