Extra miles could prevent injury

Do the numbers to run further and injury-free

IF YOU GET INJURED, you must be running too much, right? Maybe not. Recently, sports scientists have been rethinking this belief. In some cases, hard training may act as a ‘vaccine’ against injuries by toughening up your body, so doing too little can be as risky as doing too much. That doesn’t mean you should crank up your mileage immediately. Instead, focus on the balance between how much you’re running now and how much running you’ve done over the past month. By tracking this ‘acute-to-chronic’ ratio, you guard against the twin perils of too much and too little.

CALCULATE THE RATIO

The acute-to-chronic training ratio compares your mileage for the last week with your average weekly mileage for the last four weeks. If you’ve run 50, 40, 50 and 60 miles in the past four weeks, your ratio is 60 (last week’s mileage) divided by 50 (average of last four weeks). That’s 1.2. Recent studies show injury risk climbs when this ratio exceeds 1.2, and increases significantly when it exceeds 1.5. This is a more sophisticated version of the old 10 per cent rule: if you increased your mileage by 10 per cent each week for four weeks, you would end up with a ‘safe’ acute-to-chronic ratio of 1.15. But by looking back for four weeks instead of one, the ratio protects you from overdoing it after periods of missed or reduced training, which leave you more vulnerable when you resume your routine.

CONSIDER INTENSITY

How much you run isn’t the only factor that affects injury risk – hard workouts take a greater toll on your body than easy runs do. You can account for this by calculating a training load ratio. After each run, rate the intensity of the session on a scale from one to 10. Then multiply that rating by the duration of the run in minutes to get a more comprehensive measure of training load. For example, a 40-minute run at an effort level of six would produce a training load score of 240. Now calculate your acute-to-chronic ratio but using weekly totals of training load instead of miles.

Some GPS watches and heart-rate monitors calculate a training score for each workout based on duration and average heart rate or speed instead of subjective effort. These are also good options for tracking acute-to-chronic ratio, if you stick to one measure for consistency.

PERSONALISE IT

You can think of a ratio of 1.2 as an amber light and 1.5 as a red light. But every runner is different, so what applies to the ‘average’ runner may not apply to you. This approach will be most valuable if you keep track of your changing ratios over several years while making note of injuries – not just major ones, but also minor pains. Eventually, you’ll discern patterns that tell you which ratios your body can tolerate and which ratios trigger problems.

The obvious time to be careful is when you’re pushing your mileage or intensity; keeping the ratio low will help you do it safely. But watch for patterns at the low end, too. You might find, for example, that whenever you let your mileage drop below 20 miles for two weeks in a row, your acute-to-chronic ratio spikes a few weeks later when you get back to normal training – and that you often get injured as a result. You can’t always avoid injuries, but by looking for patterns, you can at least avoid making the same mistake twice.