Exercise scientists and the bodybuilding community are in agreement that to create the maximum muscle growth, the most effective training protocols place the muscle under tension for about 20–70 seconds. Although this exercise guideline will help develop large muscles, those muscles may not be as strong as they look. Weightlifters and powerlifters focus much of their training on developing the nervous system with low reps and heavy weights to recruit Type IIb muscle fibers, while bodybuilders focus primarily on recruiting Type IIa muscle fibers. For maximum development, bodybuilders should occasionally perform a strength-training cycle that focuses on the Type IIb fibers. In other words, train like a weightlifter.
This isn’t a new concept, as many of the best bodybuilders throughout the history of muscle building often practiced low-rep, heavy weightlifting. From a neuromuscular perspective, developing the Type IIb fibers involve performing brief but maximal voluntary contractions to improve the neural drive to the muscles. The result is activation of the highest-threshold motor units so as to make use of their greater strength and rate of force development. Near-maximal and maximal weights must be used. One of the best training methods to develop these fibers is called cluster training, which was popularized in the 1970s by U.S. weightlifting coach Carl Miller in his articles and weightlifting clinics.
A typical strength workout for the deadlift, for example, might involve performing three sets of your five-rep max (5RM), which translates into about 85% of what a trainee could perform for one rep. Cluster training, in contrast, would enable the trainee to perform the same number of total reps (15) but at a higher intensity. Cluster training does this by allowing 10–15 seconds of rest between reps. If you’ve found that you respond better to higher reps and are thus considered a slow-twitch trainee, it’s likely your rest time would be 10 seconds; if you respond better to lower reps and are thus a fast-twitch trainee, your rest time would be longer, say 15 seconds.
It’s important to use heavy weights in cluster training, usually about 92% of your 1RM. Because such training is quite challenging and advanced, it’s permissible to use 87% of your 1RM on initial cluster-training workouts. If you cannot use 87% of your 1RM and perform three sets at that weight, you don’t have sufficient conditioning to perform cluster training. Further, advanced trainees can do as many as five sets per exercise in a workout, but may need to start with three clusters for their first two training sessions due to the difficulty of this training method.
Again, using the same number of reps per set and total reps per workout, you should be able to use about 5% more weight compared to traditional relative-strength-training methods. Because cluster training is quite challenging and time consuming, you should generally reserve it for exercises that work a lot of major muscle groups, such as squats, deadlifts, military presses, and bench presses. If you use cluster training for Olympic-lifting exercises, you’ll need longer rest periods between sets, such as 30 seconds, due to the technical complexity of these movements.
Cluster training is an extremely demanding training method, so you should allow at least two days of rest between cluster training workouts for the same muscle group. As a general guideline, after performing six cluster training workouts for a specific exercise, you should switch to another training method to avoid overtraining. Because a bodybuilder’s focus should be on developing the Type IIa fibers, you shouldn’t perform cluster training more frequently than 2–3 times a year. Finally, consider that although champion weightlifters often display tremendous development in the quads, traps, and erector spinae, this development takes a long time to achieve. Russian weightlifter Dmitry Klokov has a tremendous physique, but it’s doubtful he could win a professional bodybuilding competition. - FLEX