Did they used the 10,000 steps a day idea where 2,000 steps approximately equals a mile but if the person is trained, they'd know that originally started out as a marketing slogan and stayed around. It took a bit but then I discovered a mathematical formula involved in helping the instructor determine when they've reached a mile. If you've every worked out in some sort of group exercise such as aerobics, the instructors always have music on. If it's a cool down, the music is slower, if its at the point of highest activity, the music is faster.
The background music inspires us to move faster or slower and it is the music that helps instructors calculate when they've incorporated enough movement into the session to reach a mile or more. The calculation begins with the number of beats per minute the music is set at. The slower the music the fewer beats per minute and the faster, the more beats per minute. It is the number of beats per minute that is the starting point to calculate miles per hour.
The beats per minute is either comes with the music if it is specifically designed to be used with an exercise routine or it can be found by counting the number of downbeats during one minute of music. The next step is to determine how long your stride or the distance between one step and another. An easy way to do this is to place a marker on the floor as your starting point, then walk or stride for 10 steps and mark where your foot is. Take a measuring tape and measure the distance between starting and finishing marks. The last step is to take this distance and divide it by 10 to determine the distance you cover in one step.
So now we are ready for the actual formula used to convert beats per minute into miles per hour.
(Beats per minute x stride length in feet x 60)/ 5280 feet
This means the instructor on the DVD used this formula to determine how far they might travel in one hour. Then using a bit more math, they'd figure out how long it takes them to cover one mile and you end up with the time it takes to complete the mile based on the pacing of the music. This is why they separate the warm-up and cool downs from the actual mile so the calculations can be done
Based on this, the miles done on the DVD's are based on the instructor's stride but I tend to look at time only when I record my daily exercise but it is still cool to see the math behind this. Let me know what you think, I'd love to hear. Have a great day.