The idea of delayed hypertrophic supercompensation – the idea that your muscles can keep growing for several days after you complete a grueling block of training – is very contentious. A recent study provides us with the first evidence that it’s possible. However, there’s quite a bit more to the story.

This article is a review and breakdown of a recent study. The study reviewed is Delayed Myonuclear Addition, Myofiber Hypertrophy and Increases in Strength with High-Frequency Low-Load Blood Flow Restricted Training to Volitional Failure by Bjørnsen et al. (2018)

Key Points

This study had untrained subjects complete two blocks of high-frequency blood flow restriction training, with 10 days between blocks. Strength and muscle fiber cross-sectional area both appeared to follow a pattern of delayed supercompensation. Muscle fiber CSA decreased at first, and then increased until at least 10 days after the last session was completed. Maximal knee extension strength increased until at least 20 days after the last session was completed. Interestingly, muscle fiber CSA and whole muscle size followed different patterns of adaptation. Whole muscle size didn’t decrease initially, and it didn’t keep increasing after the training was completed.

I recently reviewed a study from Bjørnsen and colleagues with some interesting findings: Just two weeks of low-load training with blood flow restriction (BFR) caused really robust hypertrophy of type I fibers, providing the clearest evidence we have for fiber type-specific hypertrophy (2). The same group is back with another eye-catching study (1), potentially demonstrating delayed hypertrophic supercompensation for the first time. Delayed supercompensation is the idea that beneficial adaptations can keep occurring after a period of training is completed. It’s most often discussed in the context of overreaching: You train beyond your normal capacities for a time, but after several days of rest, you rapidly accrue beneficial adaptations. Most people think about delayed supercompensation from a performance perspective, and several theories of tapering and peaking are built around this idea. However, delayed hypertrophic supercompensation is much more controversial; the traditional view is that muscles stop growing when you stop training.

In this study, untrained subjects completed two five-day blocks of high-frequency, low-load training with blood flow restriction. The researchers measured maximal knee extension strength, muscle fiber cross-sectional area (CSA), and whole-muscle CSAs and thicknesses. While measures of whole muscle size increased quickly and potentially decreased a bit after the cessation of training (probably due to a reduction in swelling), muscle fiber CSAs and knee extension strength kept increasing long after the second block of training finished. The continued increase in fiber CSA and discordance between changes in fiber size and whole muscle size are very interesting and certainly worth a closer look.



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Purpose and Hypotheses

Purpose

The purpose of this study was to “investigate the effects of two blocks with high frequency blood flow restricted resistance exercise, separated by 10 days of rest, on fiber and whole muscle areas, myonuclear and satellite cell numbers and muscle strength, and the time courses of those changes.”

Hypotheses

In previous research (3), hypertrophy due to high-frequency BFR training plateaued after seven days of training. It was hypothesized that the 10-day rest period between training blocks would reset the subjects’ responsiveness to the anabolic stimuli so that they’d experience hypertrophy, increases in satellite cell number, and myonuclear accretion during both blocks of training.

Subjects and Methods

Subjects

16 recreationally active adults with no resistance training experience participated in this study. Three subjects dropped out over the course of the study, so 13 subjects were included in the final analyses. Further details about the subjects can be seen in Table 1.

Study Overview

The whole study took place over 46 days for each participant. One week before training began, the subjects underwent baseline testing, including assessments of quad muscle size and strength, a blood draw, and a muscle biopsy.

The training itself consisted of two blocks of high-frequency, low-load knee extensions with BFR. Each block lasted for five days. During the first three days of each block, the subjects trained once per day, and they trained twice per day during the last two days of each block (accomplishing seven workouts in five days). For all sessions, the subjects performed four sets of blood flow restricted unilateral knee extensions to failure with each leg, with 20% of 1RM and 30 seconds between sets. All four sets were completed on the right leg first, followed by four sets with the left leg. The pressure cuff used to achieve blood flow restriction (inflated to 90mmHg for women and 100mmHg for men) was left on between sets.

The subjects had a 10-day break between the two blocks of training, and follow-up measures were assessed at 3, 5, 10, and 20 days following the second training block. The authors assessed strength using 1RM knee extensions; they assessed hypertrophy with ultrasound scans, muscle biopsies, and MRIs; and they performed blood draws to measure blood markers of muscle damage (creatine kinase and myoglobin).

For a schematic of this study, see Figure 1.

Findings

Training loads didn’t change over the course of the study, but rep performance increased. The subjects completed 80 ± 14 reps per session during the first block, and 89 ± 13 reps per session during the second block.

Markers of muscle damage were significantly elevated during the first block of training, went back to baseline during the rest week, and then did not increase significantly above baseline during the second block of training. Soreness (assessed via a visual analog scale) peaked during the third day of the first block, whereas creatine kinase and myoglobin peaked on the last day of the first block of training.

Muscle fiber CSA significantly decreased at first. The decrease was larger in type II fibers (-15% during the rest period) than type I fibers (-6% during the first block of training). After the initial decrease in fiber CSA, fiber size increased throughout the rest of the study. It was back around baseline for both fiber types three days after the last training session and was elevated above baseline 10 days post-training (+19% for type I, and +11% for type II). The difference from baseline at 10 days post-training was significant for type I fibers (p=0.01), but not quite significant for type II fibers (p=0.09).

Hypertrophy estimates from ultrasound scans tell a very different story. Rectus femoris CSA and vastus lateralis thickness increased significantly above baseline by the end of the first block of training (+6.8% and +5.6%, respectively), trended back toward baseline measures during the 10-day rest period (down to 1.5% and 3.4% above baseline), increased significantly again by the end of the second training block (up to 7.9% and 6.9% above baseline), and stayed elevated above baseline (decreasing non-significantly to 7.0% and 5.7% above baseline) during the 10 days following the last training session. MRI scans were only taken at baseline and five days post-training, but rectus femoris CSA, vastus lateralis CSA, and total quadriceps CSA all significantly increased as well. However, the relative increases tended to be smaller than those seen with either the ultrasound scans or the biopsies (+6.2% for rectus femoris CSA, +2.4% for vastus lateralis CSA, and +1.2% for quadriceps CSA).

Much like fiber CSA, 1RM knee extension strength initially decreased slightly, though significantly (-4%), from baseline to the rest period. Strength did not significantly differ from baseline at 3 and 10 days post-training, but was significantly elevated 20 days post-training (+6%). However, the total swing in mean strength was very modest, from 65kg at baseline, to 63kg during the rest period, to 69kg 20 days post-training.

Satellite cells per muscle fiber increased quickly in both fiber types (by ~70% in type I fibers and ~50% in type II fibers by day four of the first block of training). That increase more or less leveled off for type I fibers (peaking at an increase of 96% three days post-training), but satellite cells per type II fiber increased progressively (peaking at an increase of 144% 10 days post-training).

In both fiber types, myonuclei per fiber didn’t increase between baseline and the rest week. However, myonuclei per fiber then increased following the second training block, peaking at 10 days post-training for both fiber types (+30% for type I fibers, and +31% for type II fibers). Interestingly, myonuclear domain tended to decrease in both fiber types.

Since this is a research review for strength athletes and coaches, I won’t belabor the cellular signaling markers, except to say that the pattern of gene expression looked to be most in favor of anabolism 10 days post-training.

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