Mechanical overload might be the most important principle in strength training. It involves loading the target muscle to the point of fatigue, and ultimately, mechanical failure. When the target muscle hits the point when the force it produces no longer surpasses the force produced by the weight, we see an increase in microtrauma to the muscle tissue, which leads to a series of adaptations—all causing the athlete to grow bigger and stronger.
So, to a certain extent, more mechanical overload equals more size and strength.
Advanced Overload Techniques
Most overload techniques rely on overloading the eccentric portion of the lift—i.e., the lengthening of the target muscle—most often the downward phase of the rep—because this is the portion during which we simply resist the force of the weight rather than try to overcome it. The eccentric portion may also stimulate more muscular growth than the concentric portion, with the body adapting and requiring greater stimuli to elicit the same effects during subsequent bouts. I often communicate this to my clients by saying, "We build strength and power on the way up and size on the way down."
In this technique, the spotter(s) may assist the lifter a great deal through the concentric (often upward) portion of the rep, then leave the lifter to focus on resisting the force to his or her greatest ability on the way down. The primary job of the lifter during a set of negatives is to resist the weight as long as possible through the eccentric phase, while the spotters do most of the work through the concentric.
This technique can be performed in a manner similar to negatives, but with possibly a more thorough overload. The spotter presses or pulls in a direction opposite from the lifter, adding to the force the lifter is trying to overcome. For example, pressing down during a Bench Press or pulling up on a Lat Pull-Down. The lifter has to overcome the force added by the spotter along with the force of the weight.
This technique is interesting, because different movements have different sticking points that would normally limit a lifter's load. Using partner resistance, we can make the portion of the rep that might be easier much more difficult, leading to a more "thorough" rep.
Different angles around a joint require different amounts of torque to produce movement. For example, a Bicep Curl is most difficult at 90 degrees of flexion, requiring more force to move past this point than, say, 50 degrees of flexion. For this reason, we may be able to increase the load, move through a smaller range of motion, and further overload that particular range of motion.
For movements with such sticking points, I'd actually prefer to assist the lifter through the sticking point for the first few reps, then have him move into partial reps at the end of the set. I'd hate to think we'd cut the entire set short simply because the lifter couldn't overcome that one point.
I am a very big fan of eccentric time-under-tension (TUT). It has quite a few benefits: increasing the total work done during the set, which conditions the lifter to mentally engage for the the entirety of the set and makes the transition from eccentric resistance to concentric drive exponentially more difficult (and by extension, more productive). Adding a little extra eccentric TUT, especially to the techniques listed above, can create a huge stimulus, literally forcing the muscle to respond with increased motor recruitment and overall adaptations.
Use these techniques sparingly. Standard training guidelines recommend two to three days rest between fatiguing exercise sessions (per target muscle group). Adding advanced techniques may require additional rest. I normally reserve these techniques for pre-vacation sessions or to break out of a stagnant plateau. Simply moving to fatigue is a strong enough signal to spur adaptations in most athletes, if their programming is solid. But if you're looking for an extra workload or strategy to break a plateau, these may be valuable techniques. Just be sure to consider recovery variables like sleep, nutrition and time.
Neme Ide B1, Alessandro Soares Nunes L, Brenzikofer R, Macedo DV. (2013). "Time course of muscle damage and inflammatory responses to resistance training with eccentric overload in trained individuals." Mediators Inflamm. Epub 2013 Jan 22.
Fernandez-Gonzalo R1, Lundberg TR, Alvarez-Alvarez L, de Paz JA. (2014). "Muscle damage responses and adaptations to eccentric-overload resistance exercise in men and women." Eur J Appl Physiol. Epub 2014 Feb 12.
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