Here's what will happen to your marathon time if you miss one or two weeks of training

missed training marathon study
How a gap in the training will impact your race

When training for a marathon, no build up is ever plain sailing. Whether it's injury, illness or life simply getting in the way, something will inevitably always happen which will see us missing a session here or there.

But what happens if you end up missing a full week of training, or even two or three weeks?

That's exactly what researchers at University College Dublin aimed to investigate in their new paper, published in Frontiers in Sports and Active Living.

Researchers looked at training data uploaded to Strava by 292,323 individual runners who completed 509,979 marathons during the period 2014–2017. The average runner in the study was between 38 and 40 years old, running 25 miles a week. The women had average marathon times of 4:24, while the men had average times of just under four hours.

The team identified 43,933 runners who had completed a marathon following a period of disrupted training (at least seven consecutive days missed during the 12 weeks prior to the race) and had also completed another marathon with no training disruptions.

They then calculated the performance cost of long training disruptions as the percentage difference between their disrupted and undisrupted marathon times.

The researchers also compared the frequency and cost of training disruptions according to the sex, age, and ability of runner, and whether the disruptions occurred early or late in training.

So, what did they find? Runners who missed seven to 13 days of training during a 12-week build up, ran 4.25% slower than when they had not experienced a training disruption of more than six days.

If runners missed 14-20 days of training, their marathon times increased by over 6%. And if they missed 21-27 days, their finish times increased by roughly 7.5%. At 28 days +, it was closer to 8%.

The results also showed a greater finish-time cost for males (5%) than females (3.5%), and for faster runners (5.4%) compared to slower runners (2.6%). Younger runners also endured a greater performance cost.

When the disruption in training happened also made a difference – when runners had a gap in training close to race day, they experienced a greater finish-time cost (5.2%) than similar disruptions occurring earlier in training (4.4%).

It's worth noting that over 50% of the runners experienced short training disruptions of up to, and including, six days, but longer disruptions were found to be increasingly less frequent among those who made it to race day.

While the research naturally has its limitations, such as the fact some runners may have, for some reason, failed to record all of their runs on Strava, it does provide a valuable insight into the importance of calibrating training and race-day expectations, if your marathon training hasn't gone exactly to plan.

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