This is quite possibly the most important single contributor to running success that almost no runner knows about. Recoil refers to the ability of your connective tissue (e.g., tendons, fascia) to store energy each time it’s stretched and then release that energy as your muscles contract, simultaneously shortening the connective tissue. The best example of this is your Achilles tendon, which is significantly stretched during every stride. Recoil provides up to 50 percent of the propulsive force for each running stride.
A split can mean two different things. First, it can refer to time recorded en route during a race, usually at evenly spaced junctures. For example, if you’re running a 5K, you might want to know your time at the first mile, which would be your “mile split.” Running “even splits” means you maintain the same pace for each split. A “negative split” means you picked up the pace over the final portion of the race.
The second way runners use “split” is when dividing a workout into parts. On distance runs, you might want to check your splits at each mile using a GPS watch. And during an interval workout, you’ll record a split for each repetition. Runners often target specific splits during repetition training as preparation for upcoming races, where they hope to hit the same split times on their way to the full race distance.