Why do we need to stretch our muscles? In the wild we wouldn’t have time to stretch before running from danger so shouldn’t our bodies be ready to move optimally whenever needed?

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Why do we need to stretch our muscles? In the wild we wouldn’t have time to stretch before running from danger so shouldn’t our bodies be ready to move optimally whenever needed?

In: Biology

We don’t and static stretching is highly discouraged.

What we do need to do is “warm up” the muscles. This entails some minor activity to increase blood flow to the area. This helps protect the muscles when in use.

If you stretch a “cold” muscle you’re more likely to cause tears and further injury.

It would be wasteful and difficult to keep a body at optimal for rapid motion all the time. This would be like keeping a car engine running all the time. It wears things out and wastes fuel.

Stretching and warming up is a way to protect yourself. In an emergency you can, of course, do stuff immediately – it comes with higher risk of injury which wouldn’t matter much if, for example you need to escape from a chasing lion. But if you’re exercising, there is no reason to risk injury.

Warm up before, stretch after.

Warming up serves as a low intensity precursor to high intensity movement. It allows muscles to be oxygenated and warmed so that fibres can be stretched. Animals often move for periods at a time at low activity, keeping them warmed up in case of high activity because the need to conserve calories.

Stretching precents muscle shortening due to training or strain. Animals often stretch after rest but because we train for performance, we need to stretch ao that we do not lose range of motion.

Not all of our physiology is figured out yet but stretching afterwards prevents issues such as spasm and tears wgile warming up promotes range of motion and performance.

Your question assumes that in the wild we would have the same “baseline” activity that our modern advancements has allowed us. We rely on transport to get us anywhere, where as in the wild we would have to walk for everything, even the fact that we turn a tap and water comes out has removed the need to go and fetch water. Some rural villages have a 25km walk everyday, just to get their daily water needs. In contrast we sit 8+ hours a day in an almost static position, we use tools to carry our loads, we have effectively reduced our bodies baseline ability and fitness level, which leaves us in a position that our muscles are just not used as much as they should be to allow for impromptu bursts of effort.

In short we are chronically unfit in comparison to how fit we would be with a lifestyle in the wild.

But that being said, on a biological level, our brains (in comparison to wild animals) consumes a massive portion of our daily energy requirements (I believe its something like 1/3), and because of that our bodies are constantly optimising its energy allocations. If something isn’t being used, and it is considered non-essential, the body starts reducing the resources it allocates to those non-essentials. This is why people who are bed ridden for extended amounts of time, develop muscle atrophy, because the muscles are not being used. This is obviously an extreme example, but essentially this is what our modern day life of sitting behind desks, and transportation has done to our muscles as we don’t demand much from them on a regular basis.

Stretching comes in and engages the muscles and makes sure that we are forcing the range of motion of the muscles as well as the nerves which is trying to counter the hours of inactivity. These stretches shouldnt be done cold, as that can lead to damage, but after some light activity we have increased the blood flow, and then proceed to stretch and warm up the muscles and nerves before putting full exertion on the muscles.

Stretching is effectively the hack we have found to counter the lack of physical activity our modern lifestyles have created.

Anyway, that’s as close to an eli5 answer I can think of…

Both warming up and stretching/cooling down are more important and necessary for us now because of the lack of exercise and general movement we have in comparison to our ancestral counterparts. Society has grown increasingly lazy and constantly opted for easier, more effortless options that require the least amount of energy and effort. As a result, it is harder for our bodies to “be ready to move optimally whenever needed.”

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Other’s have included good information; I’ll see if I can’t add a bit more for clarity. (disclaimer: not an expert at all but have casually done sports alongside more experts for a while)

Two things worth considering are 1: We are warm blooded animals, so our movement/muscle use helps provide useful warmth to our bodies. 2: Humans have a Lymphatic System, that mainly is used to flush trash out of our system, which has no pumping like blood; it requires us to move function properly.

Also, people recommend Dynamic Stretching before workouts, like lunges, limb rotations, etc. anything to get joints moving, not particularly pushing for end range of motion. Save the Static Stretches like Toe-Touch and Butterfly for after the workout (doing it before can increase injury risk!)

In the wild, we’d move a lot more; most anything would involve muscle movement along with walking/running/climbing, so we would naturally have this “warmed-up” status at all times. Because this movement was so standard, there wasn’t enough evolutionary pressure to develop a “always ready” status even without movement before.

Nowadays, we often have our workouts in a short time frame; we go from little movement to a lot of movement when we work in an office, then drive to a gym and doing an hour of High Intensity workout/swimming/running. Our survival evolution doesn’t support this fast switch, but by the time the fast switch became common, we didn’t exactly need to worry about being eaten by animals anymore.

As other mentioned, it’s often recommended to do these dynamic stretches or go for a walk when at a desk for long periods of time. It helps assist the Lymphatic System, and not using your muscles for 8 hour periods can be quite detrimental to your health.

Just adding to address the part of the question ‘we wouldn’t have time to stretch before running from danger’.

We have the fight or flight response to deal with these situations. These days it’s more of a redundant response, but originally the fight or flight response was designed to help humans deal with danger from predators etc.

When the Fight/Flight response is triggered:
1. Pupils dilate to let more light into the eye and enhance vision.
2. Heart rate and breathing rate increases, to prepare the body for the physical exertion of fighting or fleeing danger, by increasing blood flow and oxygen levels.
3. Blood is diverted away from the skin surface and towards the brain and muscles (often making us pale, or alternating between flushed and pale) to prepare for physically escaping danger and fast thinking.
4. Muscles become tense as they prime for action, which results in shaking/trembling.

These are mostly things that warming up prior to exercise will also achieve. The fight or flight response is a cheat code that enables us to replace a chill 10-minute warm-up with a split second magic trick that primes us for life-saving physical exertion, with some added bonuses that help us to see more clearly and think faster (if you’ve ever been involved in an incident where everything happened really fast, but in your mind, it seemed like time slowed down, this is because of the effect of fight or flight response on the brain, time didn’t slow down, your brain sped up and you were able to take in and process far more information than normal). Warming up is like manually activating the fight or flight response, it prepares the body for physical exertion, it just doesn’t come with the super brain-enhancing goodness.

As others have pointed out, stretching, or at least static stretching like many of us older folk were taught to do in PE classes, is not recommended before, only after exercise. Preparation for exercise requires us to increase our blood flow and oxygen levels, so that oxygenated blood is flowing through all our muscles, waking them up. Our bodies are super-efficient, so when we are not using muscles, we only send the muscle the minimum supplies it needs and send the resources elsewhere to do more important things, which is why some heart rate increasing exercise and dynamic stretching helps before exercise – it wakes up those muscles and gets the blood flowing to them efficiently before use.

Static stretching – stretching to the max range of motion and holding for a period of time, helps us increase flexibility/range of motion and in the long term may help keep our muscles and joints healthier. Because you are stretching muscles to the limit of their range of motion, static stretches should only be done when the body is fully warmed up and the muscles have been engaged. Don’t do static stretches when you are cold – you will likely do more harm than good and you certainly won’t get any benefit as you won’t be able to extend to your full range of motion when the muscle is cold. Static stretching isn’t a necessary part of a work out unless you’d like to maintain or increase your muscles range of motion. (For example, when I did dance, I did static stretches to work on things like the splits. When I did weightlifting, I did a lot of static stretching that worked on hip, knee and ankle mobility to increase the depth/stability of my squats).

Dynamic stretching – using your muscles within their normal range of motion repeatedly. Walking lunges, jumping jacks, burpees, walking, jogging, skipping, rowing etc. Building intensity up, getting the muscles moving gently, pushing blood and oxygen around the body. Helps to prepare and equip the muscles for exertion. Warming up and down using aerobic activity and dynamic stretching is a 100% necessary part of a work-out, this is what helps to prevent/reduce injury, as well as having other benefits such as increasing performance and stamina.

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If you try to bend a plastic ruler as far as it will go it will usually snap, this is like static stretching a cold muscle.

But if you do lots of smaller bends first, the plastic warms up, becomes more pliable and you’ll be able to bend the ruler further without snapping it. This is like dynamic stretching.

I guess aerobic warm-ups would be like heating the plastic ruler gently with a hairdryer before trying to bend it at all and fight or flight would be like adding a chemical to the plastic that temporarily makes it more flexible without any preparation.

This is interesting from ‘Survival of the Fittest’ by Mike Stroud:

> When you first start running, leg muscles are at only 37°C, or even a degree or so less on a cold winter’s day. Yet it is at 38°C that they work best. Of course, once you start running, you generate a lot of spare heat and the muscle temperatures rise, but this can take a couple of miles, even on a warm day, and through that distance you will not feel it. The reason for muscles working better when warmer is that their enzymes are set up to operate at the 38°C level, which is an interesting evolutionary choice. If we had evolved to be sprinters in temperate climes, we would have been better off if our muscles worked best at 37°C or even slightly cooler so that they were ready for action at any time. The fact that it takes a considerable distance to bring them up to operating temperature supports the view that our origins were warmer and our usual needs were for endurance rather than speed.