Cluster Sets for Power, Mechanical Loading for Growth

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I saw a nice infographic (by Dr. Eddie Jo) on this article: Influence of a Cluster Set Configuration on the Adaptations to Short-Term Power Training. “The purpose of the present study was to investigate the effects of 2 different muscle power training set configurations (traditional vs. cluster) on the lower-body maximal force, velocity, and power capabilities. It was hypothesized that a power training period comprising cluster sets would lead to further short-term power performance improvements.”

Subjects: 19 male sport science students volunteered. Each were physically active yet had no prior systematic strength training background. “Body mass, height, and age at the start of the study were ± SD 76.6 ± 9.7 kg, 178.3 ± 6.3 cm and 23.6 ± 5.8 years, respectively.”

Methods: Randomized repeated measures design evaluated different protocols during a power-oriented resistance training mesocycle. Subjects began with an 8-week general preparatory period for initial strength adaptations. Following this, “…subjects performed 3 mesocycles (8 weeks) of progressive resistance training including 2 weeks of strength circuit training, 3 weeks of hypertrophy-oriented strength training, and 3 weeks of maximal strength training.” As seen below in figure 1A.

Before and after the cluster training (CT) and traditional training (TT) period, force-velocity relationships were determined with loads relative to body weight (25%, 50%, 75%) as well as maximum strength levels (1RM).

Procedures began with a 5 minutes general cycling warm-up, followed by mobility exercises and finally 3-4 unloaded countermovement jumps (CMJ). The following CMJs with the three previous defined loads performed in a smith machine, to a depth of 90° of knee flexion. 2 attempts were performed at each load, with 1-minute rest between each repetition. High speed cameras and force plates collected data such as GRFs, acceleration, velocity, peak force, and power. Training sessions were completed twice per week.

Results: “Compared with TT, greater improvements in peak power and velocity output were observed after CT. These results seem to support previous suggestions on the efficacy of CT at inducing short-term velocity and power adaptations after ballistic training.”

“…the CT group showed greater improvements in power output (9.7 vs. 2.7% in P25) and movement velocity (8.2 vs. 2.3% in V25) than the TT group although no clear differences were observed in the F-v profile. …Similarly, we observed greater power and velocity improvements after CT at low loading conditions, but no meaningful differences were detected at higher loading conditions.”

No significant changes were seen in maximum strength the TT or CT periods (+2.5 vs. +1.3%, respectively).

Takeaway: Coaches should consider CT protocols, possibly in a tapering period before competition due to the short-term adaptions facilitated.

“Our results suggest that a cluster set configuration may allow to achieve superior velocity and power performance adaptations at the specific training loading condition after short-term CMJ training.”

Previous literature has demonstrated that CT can lead to timelier “…phosphocreatine replenishment rates, lower acid lactic accumulation, and lower ratings of perceived exertion.”

Chris Beardsley consumes such a vast amount of literature, publishing new article summaries and infographics daily. I found this article on mechanical loading and muscle growth I found worth sharing.

It may be that reaching maximal motor recruitment is not as important for muscular hypertrophy as previously thought. There are now consistent findings that suggest mechanical loading, with some influence of metabolic stress, is more indicative of growth. Active mechanical loading is achieved by simply lifting weights. On the other hand, passive loading is done with static stretching. Both have shown increases in hypertrophy.

Motor units are comprised of an alpha motor neuron and all the muscle fibers which this neuron innervates. These can be categorized into two primary subgroups: low-threshold units and high-threshold units. Low-threshold units are typically composed of slow-twitch fibers used for fine motor control. High-threshold units use fast-twitch fibers for gross force production. The size principles states that low-threshold units are selected by the central nervous system initially, and if greater amounts of force are necessary, higher-threshold units will be stimulated.

Three keys for maximum recruitment:

  • Heavy loads (>80% 1RM)
  • Light loads until failure increase recruitment positively throughout the set
  • Light loads at high velocities (throws, plyometrics)

 The first two will show similar levels of hypertrophy over time, but why is this not true for high velocity training? The answer is lack of mechanical loading. At high velocities, high levels of recruitment are seen- but only small levels of load are placed on each fiber (since all fibers are contributing and failure is not an issue). Myofilaments are attaching and detaching at rapid rates, which shows less crossbridge interaction.

In summary, maximum mechanical loading is achieved maximal contractions at low velocities. As previously stated, this is done with heavy loads or high levels of fatigue.

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Thanks, 
AJ

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