Why Does Exercise Make Us Stronger? It Starts With Tiny Tears.

It’s not a simple chemical reaction but a sequence of biochemical processes occurring within the body.

Not everyone enjoys the idea of working out. While many of us take part in sports to keep fit, others have to drag themselves to the gym simply to stay active.

As I’ve become busier over the years, I find it increasingly difficult to get my body moving while my brain is constantly occupied with deadlines, meetings and the seemingly endless stream of work that demands my attention.

Even when we do overcome that inertia and make it to the gym or join our friends for an intense game of sport, another challenge awaits us the following day. We wake up with aching muscles that protest every movement. And we feel it as completely normal.

Perhaps it’s also a subtle reminder that I’m no longer in my twenties.

This familiar ache is known as Delayed Onset Muscle Soreness (DOMS). It usually appears between 12 and 48 hours after an unfamiliar or particularly strenuous workout and can linger for several days.

But why does it happen? Exercise is supposed to make us healthier and stronger - then why does it leave us feeling sore?

Surprisingly, the answer lies in a fascinating combination of materials science, immunology and biochemistry. Our muscles become stronger not despite being damaged, but because our bodies know how to repair that damage.

This article may provide a little more insight into muscle soreness:

Exercise-induced muscle damage is frequently reported in healthy adolescents and adults following habitual and/or strenuous exercise, such as in military training, weight lifting, long distance running and in particular following short exercises that involve intense eccentric contractions. In contrast, exercise-induced muscle damage occurs very rarely following swimming.

Lifting weights, long-distance running, and “following short exercises that involve intense eccentric contractions” (otherwise known as high-intensity interval training, or HIIT) can contribute to exercise-induced muscle damage.

Imagine repeatedly pulling on a thick climbing rope. One hard pull is unlikely to snap it, but individual fibres inside the rope may begin to fray.

The rope still functions perfectly well because the vast majority of the fibres within the rope remain intact. If the damaged fibres are repaired and reinforced before the rope handles the next heavy load, it can still continue maintaining that kind of heavy load for years.

Our muscles behave in much the same way.

Lowering a dumbbell during a bicep curl often causes more soreness than lifting it. During this lowering phase, the muscle is trying to contract while simultaneously being stretched by the weight. This places greater mechanical stress on individual muscle fibres, increasing the likelihood of microscopic damage.

This microscopic damage to our muscles is not a sign that exercise has failed, but the damage is actually one of the main reasons why exercise works in strengthening our bodies.

From an engineering perspective, materials often become stronger after damaged components are repaired or replaced with better ones.

Likewise, our muscles do not simply restore the damaged fibres back to their original state. During recovery, the body synthesises new proteins and reinforces the muscle fibres so that they are better able to cope with similar mechanical loads in the future.

This phenomenon is known as adaptation. The soreness that we experience is therefore not simply the consequence of muscle damage, but also evidence that the body has begun the process of rebuilding itself stronger than before.

Like any construction project, rebuilding requires both raw materials and time.

Proteins from our diet provide the amino acids needed to synthesise new muscle proteins. Vitamin C plays an important role in collagen synthesis, helping to maintain the connective tissues that support our muscles, tendons and joints. Adequate sleep allows the body to devote energy towards tissue repair, while regular exercise provides the stimulus that initiates this entire cycle of damage and recovery.

Readers who have followed the past few weeks may recognise a familiar pattern. Whether we are discussing osteoporosis, hip fractures, wound healing or delayed onset muscle soreness, the same engineering principle repeatedly appears: our bodies are constantly balancing damage against repair.

Exercise temporarily shifts that balance towards damage by creating microscopic tears within muscle fibres. During recovery, however, nutrition, rest and the body’s own repair systems work together to reverse that damage and build stronger tissue.

The next time your muscles ache after a workout, remember that the soreness is not simply a reminder that you exercised yesterday, but it is a good reminder that your body has already begun preparing itself for tomorrow’s challenges.

After all, when we go to the gym and start a new exercise routine, the soreness can be felt very intensely the next day. However, as we acclimatise to the routine, we see ourselves eventually lifting heavier weights and getting into better shape.

Recovery Is a Construction Project

Creating microscopic tears within our muscles is only half the story. The real benefits of exercise occur after we leave the gym, when our bodies begin repairing the damaged tissue.

Muscle recovery functions similar to the renovation of an old building. Before a wall can be rebuilt, damaged materials first have to be removed. Only then can fresh concrete, steel and bricks be added to construct a stronger structure.

Our muscles follow a remarkably similar process.

Following the workout, macrophages and other immune cells migrate to the damaged muscle fibres to remove injured cellular components. This initial inflammatory response is a necessary part of healing, despite being responsible for much of the soreness that we experience during DOMS.

Once the damaged tissue has been cleared away, the rebuilding phase begins. Muscle stem cells, known as satellite cells, become activated and fuse with existing muscle fibres, allowing new muscle proteins to be synthesised. Over the following days, these repaired muscle fibres become slightly larger than previously and are better able to withstand future mechanical loading. This adaptation is one of the reasons why regular resistance training gradually makes us stronger.

Like every construction project, however, rebuilding requires raw materials.

Dietary protein supplies the amino acids needed to synthesise new contractile proteins within muscle fibres. Vitamin C is required for collagen synthesis, helping to maintain the connective tissues that support our muscles, tendons and ligaments. Vitamins and minerals act as essential cofactors for many of the biochemical reactions involved in tissue repair, while adequate sleep provides the body with the opportunity to prioritise recovery over physical activity.

Readers who have been following this series may notice that many of these nutrients have appeared before. The discussion 2 weeks ago on bone health and hip fractures highlighted calcium, collagen, vitamin D and protein. This is hardly a coincidence.

Our bodies do not repair bones, muscles, skin and joints using completely different biochemical pathways. Instead, many of the same nutrients are repeatedly called upon to support collagen synthesis, cellular energy production, tissue remodelling and protection against oxidative stress.

If you missed the previous discussion on the chemistry and materials science behind bone health and hip fractures, feel free to check it out below:

Good nutrition therefore supports not just one organ or one disease, but the healthy functioning of the body as a whole!

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