# Reply To: 400 free set recovery question

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#2235

The formula below helps me to plan interval training and predict race times. Keep in mind the formula below might not accurate for all distances.

In order to plan USRPT interval training you have to take start and turns into account. Let’s say you train for 100m free and plan 25m intervals.
Your swimmer can hold 20s for 20x25m. To make a race prediction based on interval times you would do 4*20s = 80s.
In a 100m short course race are 3 turns hence a better calculation would be 4*20s + 3*1.2s = 83.6s.
The start gives an extra boost which should be considered as well so the final calculation looks like 4*20s + 3*1.2s – 1.7s = 81.9s.
Second example if your swimmer trains 50m intervals and can hold 40s then 2 turns are already included in the interval and
you have to add 1 turn only to your 100m race prediction: 2*40s + 1.2s – 1.7s = 81.9s
1.2s for turn and 1.7s for freestyle start might be different for your swimmer. For backstroke I calculate 1.0s for start but again it’s an individual value.

In your case 400m/50m interval = 8*33.5s + 7*1.2s – 1.7s = 274.7s (4:34.7)

If you train in a 25m pool but plan for 50m pool I found in the internet the conversion rate 1.035.
So if you want to know how fast would your swimmer swim 100F in a 50m pool then calculate 81.9 * 1.035 = 84.7

In your case 274.7 * 1.035 = 284.3s (4:44,3)