By enveloping your lower body in a bubble of pressurized air, these machines bear part of your weight. The result: You can go farther with less impact. Run between 85 and 95 percent of your true weight to keep the training stimulus close to normal.
With reduced weight, you'll run with higher turnover. Try a tempo workout of 5 x 5:00 at half marathon pace with one minute of easy jogging to recover.
There's still value in the old standby: pool running.
Wear a flotation belt so that you can focus on good form instead of not drowning, and use a heart rate monitor to gauge effort.
Olympic bronze medalist Brian Diemer, now a running coach at Calvin College, used this killer pool-running workout before the 1992 Olympic Trials:
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