If you are preparing for your first marathon, or you are an experienced runner, you will be familiar with the ‘long slow run’.

The term is used to describe a long distance run ran at a slower pace than other training runs and usually performed once a week. But just how slow should the ‘long slow run’ be?

Unlike other distances that runners train for, the marathon is unique in that any training plan will generally not prescribe running longer than the race distance, and the longest runs are normally in the region of 20 to 22 miles. If you compare this to training for a 5K race, you would want to train your body to run farther than the race distance itself, for example running some 8 mile runs.

In marathon training, running long runs of 16 miles or more causes a great deal of stress on your body and increases the risk of injury. A recovery period will be needed after each long run, especially if you are training for your first marathon, and usually, marathon training plans will aim to increase the distance of your long run no more than 10% per week.

Runners attempting their first marathon can worry they aren’t prepared mentally and physically to run the extra miles beyond the longest training run. The truth is there is no need to worry because runs of 20 to 22 miles as your longest training run prepares you to complete the marathon. So, the potential negative effects of injuries, wear and tear on your body by running longer than 22 miles, outweigh any mental or physical benefits, especially for that first marathon.

During marathon training or training at another distance, some runs should be at or close to your goal race pace, and some of your shorter runs should be faster. In good training plans, details on the distance and purpose of the training run will outline the appropriate pace.

The benefit of training at different paces is it maximises the use of different muscle fibres, targets different energy sources, reduces the risk of injury, and improves your overall base fitness.

Now back to the marathon ‘long slow run’ – as noted earlier the ‘long slow run’ should be at a slower pace than other training runs, and a distance over 16 miles is what we define as ‘long’.

By running your long runs at a slower pace, you reduce the stress on your body and the risk of injury. Running that bit slower also trains your body to target different energy sources, and in the case of a slower pace run, the body will rely more heavily on stored fat for fuel, thereby conserving your glycogen stored in your muscles.

In terms of how slow you should run your long runs, it depends on your current level of fitness, and the whether the terrain of the route is flat or hilly. An important thing to remember is the pace should be comfortable and conversational. If you are new to marathon training, a good rule of thumb is to slow down approximately one minute per mile less than a ‘standard’ run.

Also, listening to the body it is a great indicator, and if you run with a heart rate monitor, aim for about 70-75% of your maximum heart rate.

The ‘long slow run’ in marathon training is also the time to focus on your hydration and nutrition strategies for the marathon. Particularly in your first marathon, the training is about covering the miles rather than the pace, and after completing a couple of marathons, you can revisit your training plan and focus more on pace, aiming to do parts of your long runs closer to a goal marathon pace.