Ahhhh I see the distinction and where there is some confusion here. If you are shooting for 20 reps during your 15RM weight you wouldn't break up the 20 reps into sets of 5, not necessarily because of fiber recruitment (also recruitment is a CNS and metabloic issue not a tissue specific issue anyway), but because there wouldn't be any advantage to not inducing the metabolic pathways of ERK 1/2. Clustering is only a means of keeping TUT/TUL/VOLUME/ or whatever you want to call it, consistent throughout the entire cycle, taking that one variable out of the mix.
My clustering is a bit less complicated than most think, I simply aim for a rep count, if it takes me 1 set, great. If it takes 5, so be it, but I always stop short of true concentric failure.
Typically I hit at least the number of reps dictated, 15, 10, 5 in the first set (sometimes more) it isn't until the subsequent sets that I need to do more clusters to acheive my rep count. See what I'm saying.
So again I am not sure where there would anything different recruitment wise.
As far as recruitment, and someone correct me if am wrong here.
1. Above 80% 1RM all fiber types are recruited.
2. I think you might be a bit confused, or perhaps I am, on the importance of the IIb isoform.
Muscle fiber characteristics of competitive power lifters.
Fry AC, Webber JM, Weiss LW, Harber MP, Vaczi M, Pattison NA.
Human Performance Laboratories, The University of Memphis, Memphis, Tennessee 38152, USA.
afry@memphis.edu
To examine the skeletal muscle characteristics of power lifters, 5 competitive power lifters (PL; X +/- SE; age = 31.0 +/- 1.5 years, squat = 287.7 +/- 15.7 kg, bench press = 170.5 +/- 17.7 kg, and deadlift = 284.2 +/- 7.5 kg) and 5 untrained control subjects (CON; age = 27.3 +/- 3.3 years) served as subjects. Isokinetic squat force and power was greater (p < 0.05) for the PL at all bar velocities (0.20, 0.82, and 1.43 m;pd s(-1)), as was vertical jump height and estimated power. Muscle biopsies from the vastus lateralis m. revealed significant differences for percent fiber type
(PL, IIA = 45.5 +/- 1.6%, IIB = 1.3 +/- 0.8%; CON, IIA = 33.4 +/- 3.1%, IIB = 12.0 +/- 2.4%); percent fiber type area (PL, IIA = 51.8 +/- 1.6%, IIB = 1.3 +/- 0.8%; CON, IIA = 43.5 +/- 3.4%, IIB = 12.4 +/- 2.6%); and percent myosin heavy chain isoform (PL, IIa = 59.5 +/- 6.1%; CON, 46.5 +/- 2.5%). Muscle fiber characteristics were significantly correlated (r = +/- 0.61) with numerous strength and power measures for the PL. These data illustrate the muscle fiber characteristics necessary for the maximal force production requirements of power lifting.
Muscle fiber characteristics and performance correlates of male Olympic-style weightlifters.
Fry AC, Schilling BK, Staron RS, Hagerman FC, Hikida RS, Thrush JT.
Human Performance Laboratories, The University of Memphis, Tennessee 38152, USA.
afry@memphis.edu
Biopsies fro the vastus lateralis muscle of male weightlifters (WL; n=6; X +/- SE, age=27.0 +/- 2.1 years), and non-weight-trained men (CON; n=7; age=27.0 +/- 2.0 years) were compared for fiber types, myosin heavy chain (MHC) and titin content, and fiber type-specific capillary density. Differences (p<0.05) were observed for percent fiber types IIC (WL=0.4 +/- 0.2, CON=2.4 +/- 0.8); IIA (WL=50.5 +/- 3.2, CON=26.9 +/- 3.7); and IIB (WL=1.7 +/- 1.4, CON=21.0 +/- 5.3), as well as percent MHC IIa (WL=65.3 +/- 2.4, CON=52.1 +/- 4.2) and percent MHC IIB (WL=0.9 +/- 0.9; CON=18.2 +/- 6.1). All WL exhibited only the titin-1 isoform. Capillary density (caps.mm(-2)) for all fiber types combined was greater for the CON subjects (WL=192.7 +/- 17.3; CON=262.9 +/- 26.3), due primarily to a greater capillary density in the IIA fibers. Weightlifting performances and vertical jump power were correlated with type II fiber characteristics.
These results suggest that successful weightlifting performance is not dependent on IIB fibers, and that weightlifters exhibit large percentages of type IIA muscle fibers and MHC IIa isoform content.
Muscular adaptations in response to three different resistance-training regimens: specificity of repetition maximum training zones.
Campos GE, Luecke TJ, Wendeln HK, Toma K, Hagerman FC, Murray TF, Ragg KE, Ratamess NA, Kraemer WJ, Staron RS.
Department of Biomedical Sciences, College of Osteopathic Medicine, Ohio University, Irvine Hall, rm 430, Athens, OH 45701, USA.
Thirty-two untrained men [mean (SD) age 22.5 (5.8) years, height 178.3 (7.2) cm, body mass 77.8 (11.9) kg] participated in an 8-week progressive resistance-training program to investigate the "strength-endurance continuum". Subjects were divided into four groups: a low repetition group (Low Rep, n = 9) performing 3-5 repetitions maximum (RM) for four sets of each exercise with 3 min rest between sets and exercises, an intermediate repetition group (Int Rep, n = 11) performing 9-11 RM for three sets with 2 min rest, a high repetition group (High Rep, n = 7) performing 20-28 RM for two sets with 1 min rest, and a non-exercising control group (Con, n = 5). Three exercises (leg press, squat, and knee extension) were performed 2 days/week for the first 4 weeks and 3 days/week for the final 4 weeks. Maximal strength [one repetition maximum, 1RM), local muscular endurance (maximal number of repetitions performed with 60% of 1RM), and various cardiorespiratory parameters (e.g., maximum oxygen consumption, pulmonary ventilation, maximal aerobic power, time to exhaustion) were assessed at the beginning and end of the study. In addition, pre- and post-training muscle biopsy samples were analyzed for fiber-type composition, cross-sectional area, myosin heavy chain (MHC) content, and capillarization. Maximal strength improved significantly more for the Low Rep group compared to the other training groups, and the maximal number of repetitions at 60% 1RM improved the most for the High Rep group. In addition, maximal aerobic power and time to exhaustion significantly increased at the end of the study for only the High Rep group.
All three major fiber types (types I, IIA, and IIB) hypertrophied for the Low Rep and Int Rep groups, whereas no significant increases were demonstrated for either the High Rep or Con groups.
However, the percentage of type IIB fibers decreased, with a concomitant increase in IIAB fibers for all three resistance-trained groups. These fiber-type conversions were supported by a significant decrease in MHCIIb accompanied by a significant increase in MHCIIa. No significant changes in fiber-type composition were found in the control samples.
Lastly, as pointed out in the last study I posted. When training for hypertrophy any and all fiber types will hypertrophy to some degree. HST whether training traditionally or using cluster reps is training for hypertrophy so why even be concerned with fiber types. We should be concerned with the events that training with high reps or high load bring about, not what type is recruited when doing so.