Why Does the Slow, Long Run Make You Faster?

Kovács Ferenc Soma, national record-holder middle-distance runner

For most runners, regardless of age, gender, or fitness level, Saturday morning means one thing: the weekend long run.

For us runners, the long run is almost sacred. We are willing to leave a Friday night gathering early just to make sure we wake up rested for the following morning’s run. Our friends preparing for marathons, meanwhile, can become almost obsessive about planning their long-run routes and fueling strategies.

But why is a quality long run so important in a runner’s training plan?

That is exactly what we are going to explore in this article.

First of all, a long run is generally defined as the longest run within a training cycle. Some runners train in seven-day cycles, while others use longer or shorter cycles. The important point is that, for most runners, a long run falls somewhere between 10 and 40 kilometres and is usually scheduled either at the beginning or the end of the training cycle.

Alongside the steady run, it is one of the most valuable forms of training because it provides numerous physical and mental benefits.

A Denser Capillary Network

One of the most important adaptations caused by long-distance running is an increase in capillary density.

The capillary network is the finest, microscopic network of blood vessels in the circulatory system, connecting arteries and veins. Its primary role is gas exchange and the transport of nutrients to cells.

The organs and tissues most heavily involved in exercise — including the lungs, heart, and skeletal muscles — have particularly dense capillary networks.

In other words, the more extensive this network is around the muscles actively involved in running, the better their oxygen supply becomes. As a result, those muscles can work harder and more efficiently during exercise.

More Mitochondria

Long runs can also contribute to increasing the number of mitochondria.

Mitochondria are components of our cells often referred to as the powerhouses of the cell. For good reason: this is where biological oxidation takes place and where ATP (adenosine triphosphate), the cell’s primary source of energy, is produced.

A 2014 study investigated what types of training are most effective for increasing mitochondrial content and improving mitochondrial function.

David J. Bishop and his colleagues had cyclists complete 4–10 × 30-second sprint sessions. After four weeks, the participants showed increased mitochondrial activity. However, the total number of mitochondria remained unchanged.

Another research group prescribed two training sessions per day on three days per week. By the end of the experiment, mitochondrial content had increased by approximately 40%.

In simple terms, high-intensity training appears particularly effective at improving how efficiently mitochondria function, while increasing overall training volume can help increase the number of mitochondria themselves.

Better Running Economy

Thirdly, long runs can significantly improve running economy.

Just like in almost every other area of life, the more we do something, the better we tend to become at it.

Simply because we cover more kilometres during a long run than during many of our regular training sessions, we spend more time practising the movement of running itself. Over time, our running mechanics can become more efficient. Our push-off improves, and our stride length can gradually become better optimized.

This likely happens partly because the muscles of the lower body, together with the surrounding connective tissues, become stronger and more resilient.

Long runs also develop mental endurance. By the final stages of a long run, the mind has to deal with increasing muscular fatigue and gradually declining glycogen stores. Learning to continue despite that fatigue is itself an important form of training.

Long Runs Don’t Always Have to Be Easy

Depending on your fitness level and goals, long runs can also include specific training elements.

Although the vast majority of runners choose a steady, easy long run, competitive athletes — especially marathon runners — often incorporate intervals or faster sections into their long runs.

This forces the body to perform demanding work even after accumulating a significant amount of fatigue and kilometres.

Another commonly used variation is the hilly long run. In these sessions, runners deliberately challenge themselves across flat terrain, climbs, and descents while trying to maintain a consistent level of effort or pace.

These variations should, of course, be used strategically. Not every long run needs to become a hard workout.

Becoming Better at Using Fat for Fuel

Last but certainly not least, long runs improve the body’s ability to use fat as a source of energy.

At low and moderate intensities, the body uses both carbohydrates and fat for fuel. However, as we regularly complete long runs, the body can become increasingly efficient at accessing and utilizing its fat stores.

As a result, it can preserve the glycogen stored in the muscles and liver for longer.

This is particularly important in the half marathon, marathon, and ultradistance events, where glycogen stores are limited.

The longer we can preserve those carbohydrate stores, the lower the risk of hitting the famous “wall” near the end of a race — the point at which a sudden shortage of available energy can cause a dramatic decline in performance.

Using Data to Control Your Long Runs

Long runs also provide a huge amount of useful data that can help us determine whether we are actually training at the right intensity.

With a Polar running watch, we can monitor heart rate, average pace, elevation gain, and even how our heart rate changes as the run progresses.

Features such as Polar Training Load Pro and Recovery Pro can also help ensure that long runs provide enough training stimulus to promote improvement without unnecessarily compromising recovery.

Because even the best long run is not particularly valuable if it leaves you starting the following week’s training exhausted or overtrained.

References

Bishop DJ, Granata C, Eynon N. Can we optimise the exercise training prescription to maximise improvements in mitochondria function and content? Biochim Biophys Acta. 2014 Apr;1840(4):1266–75. doi: 10.1016/j.bbagen.2013.10.012. Epub 2013 Oct 12. PMID: 24128929.