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How to safely increase mileage

Increasing your weekly mileage over a period of time lets you achieve those big goals, like running a marathon. But doing it incorrectly can lead to overuse injuries which will sideline your season.

If you want to achieve the next distance in your running, be it a 10K, marathon, or even an ultra, you need to do it safely. This is something I've struggled with; my ambitions are greater than my ability. In fact, I created Ready Planner so I could help others (and myself!) achieve their running goals safely.

There are a couple well known methods for doing this. Both involve slowly increasing weekly running mileage, also called running volume or base mileage. They are the 10% rule and the Acute to Chronic Ratio. You can calculate your mileage increase using either method with the running volume calculator.

10% Rule

The 10% rule says you can safely increase your weekly mileage at a constant rate of 10%.

If you are running 10 miles a week then the following week you can run 11 miles. I couldn't find any information on how this rule came to be, but many feel 10% is a safe percentage to go by.

Let's say you want to start training for a marathon and your current weekly average volume is 12 miles. Many training plans require you to have a base volume of 30 miles before you begin training for a marathon.

Using the calculator you would set the current mileage to 12 and the target to 30. Here is the results rounded to the nearest half mile:

Weeks of training to get to 30 miles a week using the 10% rule.
WeekMiles
January 2021
1: 1/18 - 1/2412
2: 1/25 - 1/3113
February 2021
3: 2/1 - 2/714.5
4: 2/8 - 2/1416
5: 2/15 - 2/2117.5
6: 2/22 - 2/2819.5
March 2021
7: 3/1 - 3/721.5
8: 3/8 - 3/1423.5
9: 3/15 - 3/2126
10: 3/22 - 3/2828.5
11: 3/29 - 4/431.5

With this method you would need 11 weeks of solid training before beginning marathon training. If the marathon training plan you picked is 12 weeks long you could conceivably run a marathon in June 2021.

The 10% rule doesn't factor in recovery time, it's a constant ramp up. The Acute to Chronic Ratio does factor in recovery time and is considered more sophisticated and an improvement over constant rates of increase.

Acute to Chronic Ratio

The Acute to Chronic Ratio involves periods of build up followed by recovery.

The ratio (more accurately called the Acute:chronic workload ratio) was created by Australian researchers in 2016. The ratio is determined by dividing an acute workload (this weeks training) by the chronic workload (typically the average of the last 3 weeks). The ratio should be between 0.8 and 1.5. The last week of the chronic workload, which is typically the third week, should be a recovery week. A recovery week should be a reduction in 20-30% of workload.

For example, a build up of 10% for 2 weeks followed by a recovery week consisting in a 25% reduction of volume is a ratio of 1.24. Using the calculator with the same average mileage and target we get the following results:

Weeks of training to get to 30 miles a week using the Acute to Chronic Ratio.
WeekMiles
January 2021
1: 1/18 - 1/2412
2: 1/25 - 1/3113
February 2021
3: 2/1 - 2/710
4: 2/8 - 2/1414.5
5: 2/15 - 2/2116
6: 2/22 - 2/2812
March 2021
7: 3/1 - 3/717.5
8: 3/8 - 3/1419.5
9: 3/15 - 3/2114.5
10: 3/22 - 3/2821.5
11: 3/29 - 4/423.5
April 2021
12: 4/5 - 4/1117.5
13: 4/12 - 4/1826
14: 4/19 - 4/2528.5
15: 4/26 - 5/221.5
May 2021
16: 5/3 - 5/931.5

With this method you could conceivably run a marathon in August 2021 using a 12 week training plan once you've reached the target running volume. It will take you longer, 16 weeks compared to 11, but is considered safer.


Whichever approach you choose try taking a structured approach by pairing the running volume calculator results in a Ready Planner. You'll be able to easy plan your next race with dated calendars, dated running logs, and more.

Which approach do you favor? Let us know in the comments.