LSAT 147, Section 2, RC Passage 1, Muscle Memory

Paragraph Summaries

Passage A

1. Muscle Memory is confusing. Most bodybuilders have found that when they take time off, they gain muscle size easier when they restart, even from the same starting point. Yet science has hardly discussed this.
2. Maybe it’s neurons. During straining, only a portion of neurons will fire. With strength gains, a larger percent of neurons will fire and activate muscles. When you restart, it may be that a larger portion of neurons are ready to fire, and thus you can use a larger percent of your total muscle than you could before training.
3. It could be psychological. When you start, you don’t know your limits, and so you increase slowly. With practice, you know what you can do and so you add weight more quickly when you restart.

Passage B

1. Scientists think they know why it’s easier for people who once had muscle to regain muscle quickly.
2. Muscle cells are large, and need much protein. In order to do make a lot of protein, muscle cells need more than one nucleus. When muscles grow, they merge with nearby stem cells, and get even more nuclei. Researchers used to think these nuclei died when muscles shrank.
3. A recent study in mice showed that muscles keep their extra nuclei even when the muscles shrink from disuse.

Analysis

First, it’s worth clarifying what the passage is talking about. Let’s say you start weight training, and bench press 100 pounds. Then it takes you four weeks to reach 150 pounds.

The articles are talking about a situation where you stop training, and your bench press weakens back down to 100 pounds. How long will it take you to get to 150 again?

The articles are saying it will take less time, perhaps 2-3 weeks. That “muscle memory”, which lets you regain strength faster, is what each author tries to explain.

The first author is more uncertain than the second. They put forward two different situations. Either:

1. Your muscles remember how to use more nerves to recruit more muscles. 
2. Or, it’s all in your head, and you can lift faster because you have more understanding of your abilities.

The second explanation is pretty weak. “All in your head” is rarely a good explanation. Also, the article suggests new lifters are cautious (lines 31-32), but they gave no evidence for this. If you’ve ever weightlifted, you’ll know that new lifters are sometimes likely to overestimate their skills and add too much weight.

Recruiting Muscle Fiber

What does the author mean by recruiting muscle fibers? Well, say you have 100 muscle fibers, controlled by 100 neurons. When you first start lifting, you might only use 20 neurons on a bench press. As you get experienced, you might be able to use 40 neurons on the same lift.

(This is why they say weightlifting is intense for the central nervous system. It has to coordinate many neurons in intense exertion)

Now, the underlying muscle fibers also grow stronger with weight training. So, let’s say at the start, each muscle fibre can lift 2 units of weight. Then, with training, they are able to lift 3 units of weight. (The units are meaningless, this is just for sake of comparison.)

So:

• At the start, you have 20 neurons, controlling 20 muscle fibres which can lift 2 units of weight each. So you have 40 power.
• With training, you have 40 neurons, and the fibers can lift 3 units of weight each. So you have 120 power.
• Once you detrain, your fiber goes back to only lifting 2 units of weight. But, you still have 40 neurons you can use for the lift – these don’t go away. So, you can lift 80 units of weight, even thought your muscle is no stronger than when you first started.

Hopefully this clears up muscle fiber recruitment. Note that from lines 19-28, passage A is merely speculating. This isn’t certain science, it’s just a hypothesis. The phrase “It could be” is your clue that this is mere speculation (line 19).

Passage B

The author of passage B is much more certain. They offer a clear explanation for increased strength gain following detraining. Basically, muscle cells use nuclei to make protein. When muscles grow, they add nuclei from nearby stem cells. It seems that, in mice, when muscles shrink they keep these extra nuclei. So, the muscles are able to produce more protein from the getgo even after the muscle has atrophied.

Several of the questions focus on passage B. Compared to passage A, passage B is:

• More sure of its answer
• More focussed on recent science. Passage A tended to speculate more.

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